Superelectrophiles and Their...

SUPERELECTROPHILESAND THEIR CHEMISTRY

GEORGE A OLAH

DOUGLAS A KLUMPP

WILEY-INTERSCIENCE

A John Wiley amp Sons Inc Publication

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GEORGE A OLAH

DOUGLAS A KLUMPP

WILEY-INTERSCIENCE


Copyright copy 2008 by John Wiley amp Sons Inc All rights reserved

Published by John Wiley amp Sons Inc Hoboken New JerseyPublished simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data

I Olah George A (George Andrew) 1927- II Klumpp Douglas A 1964-Superelectrophiles and their chemistry by George A Olah and Douglas A Klumpp

p cmIncludes indexISBN 978-0-470-04961-7 (cloth)

1 Superelectrophiles 2 Chemical afTHORNnity 3 OrganiccompoundsSynthesis I Klumpp Douglas A II Title

QD27135E54043 2007547prime2dc22

2007019597

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

CONTENTS

Preface vii

1 General Aspects 1

2 Study of Superelectrophiles 17

3 Generating Superelectrophiles 81

4 Gitonic Geminal Superelectrophiles 105

5 Gitonic Vicinal Superelectrophiles 125

6 Gitonic 13-Superelectrophiles 187

7 Distonic Superelectrophiles 231

8 SigniTHORNcance and Outlook 283

Index 287

v

PREFACE

Our book is about the emerging THORNeld of Superelectrophiles and TheirReactions It deals THORNrst with the differentiation of usual electrophiles fromsuperelectrophiles which show substantially increased reactivity Waysto increase electrophilic strength the classiTHORNcation into gitionic vicinaland distonic superelectrophiles as well as the differentiation of superelec-trophilic solvation from involvement of de facto dicationic doubly electrondeTHORNcient intermediates are discussed Methods of study including sub-stituent and solvent effects as well as the role of electrophilic solvation inchemical reactions as studied by kinetic investigations spectroscopic andgas-phase studies and theoretical calculations are subsequently reviewedSubsequently studied superelectrophilic systems and their reactions arediscussed with speciTHORNc emphasis on involved gitionic vicinal and distonicsuperelectrophiles A brief consideration of the signiTHORNcance of superelec-trophilic chemistry and its future outlook concludes this book

Results of substantial experimental and theoretical work of the THORNeldaccumulated in recent years warrant a comprehensive review and discus-sion This should be of general use to chemists not only with academic andresearch THORNelds interest but also to advanced students Because of relevanceto potential signiTHORNcant practical applications (including the pharmaceuticaland petrochemical THORNelds) industrial chemists should also beneTHORNt from it

vii

viii PREFACE

We believe that continuing work will result in much further progress andpractical applications If our book will be of help toward this endeavorour goal will be achieved

George A OlahDouglas A Klumpp

1GENERAL ASPECTS

Electrophiles (ie electron-deTHORNcient species) are of fundamental impor-tance to chemistry The concept of nucleophiles (lit nucleus seeking)and electrophiles (lit electron seeking) was suggested by Ingold follow-ing similar views implied by Lapworths description of anionoid andcationoid reagents Robinsons concepts and Lewiss theory of bases(electron donors) and acids (electron acceptors)1

The realization of carbon electrophiles or carbocations dates back to1901 with the reports of the ionization of triphenylmethyl alcohol in con-centrated sulfuric acid and triphenylmethyl chloride with aluminum andtin chlorides1b2 These reactions gave deeply colored solutions whichare now attributed to the formation of the π -conjugatively delocalizedtriphenylmethyl cation In later studies by Meerwein Ingold HughesWhitmore Roberts Winstein Schleyer and others using kinetic stere-ochemical and varied experimental methods carbocation electrophileswere recognized as intermediates in reactions It was Olah who discov-ered in the early 1960s methods to prepare and study long-lived persistentcarbocations for which he received the Nobel Prize in 1994 The topicwas well reviewed and there is no need for further discussion here3 Varieddiverse electrophilic reagents functionalities and intermediates have beenfurther studied in detail3 They were reviewed in preceding monographswhich are referred to for the interested reader3bd With the advance of our

Superelectrophiles and Their Chemistry by George A Olah and Douglas A KlumppCopyright 2008 John Wiley amp Sons Inc

1

copy

2 GENERAL ASPECTS

structural and mechanistic understanding it became clear that electrophilicreactivity is an important driving force in many chemical reactions

Extensive efforts have been made to characterize nucleophile and elec-trophile strengths Hammett THORNrst correlated4a the acidities of substitutedbenzoic acids (1)

OH

OX

1

with the structures of the substituent groups and set up his equation aslog k ko = σp (where ko is the rate or equilibrium constant for X=Hk is the rate or equilibrium constant for the substituted benzoic acidp is a constant for the given reaction and σ (Hammets constant) is thevalue characteristic for the substituent)4 In their linear free-energy studiesSwain and Scott characterized nucleophiles and electrophiles in kineticexperiments by comparing reaction rates according to the equation 1

log kxkH2O = snx (1)

where s is the parameter characteristic for the electrophile and nx isthe parameter characteristic for the nucleophile5 More recently Mayrand co-workers have conducted extensive kinetic studies in estimatingthe electrophilicities and nucleophilicities of a wide variety of reactants(Figure 1)6 Using equation 2

log k(20C) = s(N + E) (2)

the rate constants k for nucleophile-electrophile reactions may be cal-culated from three parameters (N the nucleophilicity parameter E theelectrophilicity parameter and s the nucleophile-dependent slope param-eter) By analyzing pseudo-THORNrst order rate constants with various types ofnucleophiles the electrophilicities of many cationic and neutral specieshave been established These electrophiles include dithiocarbenium ionsiminium ions cationic organometallic complexes (such as propargylcations with cobalt carbonyl stabilization cationic palladium complexesand others) and quinone methides When experimentally observed rateconstants k are compared with those values of k predicted from the threeparameter equation (eq 2) they are generally accurate to within a factor of10 to 100 excluding reactions with bulky reagents or multi-centered reac-tions (like SN2) Moreover the three-parameter equation may be used to

GENERAL ASPECTS 3

MeO

CO2Me

CO2Me

Me2N

CN

CN

(OC)3Fe

MeOOMe

minus25

minus20

minus15

minus10

minus5

0

5

10

N O

tBu

tBu

E

252015minus10 minus5 0 5 10

Me MeO

Me

Me

Me NO2

OSiMe3N

O

O

OSiMe3MeMe

N

k = 1 Lbullmolminus1bullsminus1

Diffusion-controlledreactionskcalcd gt 1010 Lbullmolminus1bullsminus1

No reactions at 20degCkcalcd lt 10minus6 Lbullmolminus1bullsminus1

Me3C+

+

+

+

+

minusminus

Figure 1 Estimated reaction rates k calcd using nucleophilicity parameter N and elec-trophilicity parameter E

describe numerous types of reactions involving electrophiles in such reac-tions as Michael additions Mannich aminoalkylations palladium-cataly-zed allylations Freidel-Crafts alkylations and others

In addition to the linear free energy studies discussed there have beenmany attempts to estimate the thermodynamic stabilities of electrophilicspecies such as carbocations7 The pKR+ values for carbocations revealtrends in relative stability and is deTHORNned as according to the equilibriumestablished between the carbinol

pKR+ = log([R+]ROH]) + H+

and carbocation in acidic solution The pKR+ value for triphenylmethylcation is minus663 and that of the tri(p-nitrophenyl)methyl cation is minus1627which is consistent with the resonance destabilization of the cationic centerby the nitrophenyl substituents Gas-phase ionization techniques have alsobeen used to provide thermodynamic data for a variety of electrophiles8

4 GENERAL ASPECTS

It has been recognized that electrophiles must have sufTHORNciently highreactivity in order to react with weak nucleophiles This concept of elec-trophilic reactivity is well demonstrated in the carbonyl chemistry of alde-hydes and ketones The carbonyl group is a reactive electrophilic centerwhen encountering strong nucleophiles like Grignard and organolithiumreagents (eq 3) The rapidly formed alkoxide product is thermodynami-cally heavily favored With weaker nucleophiles like water or alcoholsreaction rates are considerably slower and the equilibria often favor thestarting carbonyl compounds However protonation or complexation ofa carbonyl group increases its electrophilic reactivity and weaker nucle-ophiles may then react with the resulting carboxonium ion (eq 4)

H3CC

CH3

O

CH3Li +CH3

C CH3

OLi

H3C

dminus

d+ (3)

H3CC

CH3

O

CH3OH +

CH3

C OCH3

OH

H3C

H+

+ (4)

Examples of acid-catalyzed carbonyl chemistry are abundant in syntheticorganic chemistry biochemistry industrial processes (such as in the syn-thesis of malachite green eq 5) and in polymer chemistry (such as in thesynthesis of bisphenols of derived epoxy and polycarbonate resins eq 6)9

PhCHO+2

N(CH3)2

N(CH3)2

N(CH3)2

HCl

H

leucomalachitegreen

(5)

OH2

H3C+ C

CH3

O H2SO4

H3C CH3

OHHO

epoxy andpolycarbonateresins

bisphenol A(6)

Without protonation of the carbonyl group weak nucleophiles (NN -dime-thylaniline and phenol) would only react slowly or not at all with the car-bonyl groups Similarly complexation with Lewis acids can enhance theelectrophilic reactivities of carbonyl compounds This occurs by decreas-ing participation (using Winsteins concept) of the neighboring oxygen

GENERAL ASPECTS 5

into the developing carbocationic center and thus increasing the polarizedcharacter of the (complexed) carbonyl group and lowering the energy ofthe LUMO (as described by the frontier molecular orbital theory) It hasalso been shown that substitution by electron withdrawing groups can sig-niTHORNcantly increase the electrophilic reactivity of carbonyl groups and theirrelated protonated carboxonium ions Whereas protonated acetophenone(2) is unreactive towards benzene (a weak π -nucleophile) the carboxo-nium ion from 222-triszliguoroacetophenone reacts to give the condensationproduct in high yield (eqs 78)10

O

CH3

CF3SO3H

C6H6

unreactive tobenzene

2

OH

CH3

+

(7)

O

CF3

CF3SO3H

C6H6

OH

CF3 F3C

C6H5

C6H5

C6H5minusH2O

3

C6H6 C6H6

+

(8)

The electron withdrawing inductive effects of the szliguorine substituentsrender the carboxonium ion 3 more electrophilic than carboxonium ion 2and consequently it reacts with benzene Thus the electrophilic reactivityof the carbonyl group can be greatly enhanced by Broslashnsted or Lewis acidsolvation and by substitution with electron withdrawing groups

Although increased electrophilicity can lead to reactions with weaknucleophiles highly electrophilic cations can exist as stable long-livedspecies in solutions of low nucleophilicity11 Superacidic media are espe-cially well suited for studies of such highly electrophilic species Super-acids and their chemistry a topic extensively reviewed in a previousmonograph11 have enabled the preparation and study of varied long-livedcationic electrophiles such as carbocations acyl and carboxonium cationsand varied onium ions such as oxonium sulfonium halonium nitroniumand azonium ions3d Whereas these electrophilic species react instan-taneously with many common electron donor solvents the superacidicmedia is essentially an environment of very low nucleophilicity Forexample efTHORNcient routes to carbocation electrophiles include the ioniza-tion of alkyl szliguorides in SbF5 and the ionization of alcohols in magicacid FSO3H-SbF5 (eqs 910)1213

6 GENERAL ASPECTS

H3CC

CH3 +minus

F CH3SbF5

H3CC

CH3

CH3

SbF6(9)

CH3

OH FSO3H-SbF5CH3

+

minus[FSO3-(SbF5)n]

(10)

In the superacids the resulting counterions are weak nucleophiles SbF6minus

or [SbF6minus(SbF5)n]minus [FSO3-(SbF5)n]minus etc

Gillespie proposed the widely accepted deTHORNnition of superacids as thosebeing stronger than 100 H2SO4 for Broslashnsted acids (ie H0 le minus12)11

Similarly according to Olah Lewis acids stronger than anhydrous AlCl3are considered superacidic Broslashnsted superacids span the logarithmic Ham-mett acidity scale from H0 minus12 for anhydrous H2SO4 to minus27 for FSO3H-SbF5 (91) and ca minus30 for HF-SbF5(11) (Figure 2) The isolated (naked)proton is unobtainable in solution chemistry but by comparing gas phasedata with superacid solution chemistry its acidity has been estimated to bein the minus50 to minus60 H0 range Superacids can react with weak base-sites likethe n-electrons of carbonyl and other groups the π -electrons of unsaturatedgroups (alkenes alkynes and arenes) and even with σ -electrons of alkanesNot only carbocationic but also other varied reactive electrophiles can begenerated as long-lived species in the superacids and these electrophiles canoften be studied directly by spectroscopicmethods They can also participatein many superacid-catalyzed reactions

H2SO4

SO3(50)

HSO3FSbF5

(50)

Magic Acid(90)

CF3SO3HSbF5

(10)

HF (7)BF3

HFSbF5

(2)(50)

10 15 20 25 30

10 15 20 25 30(minusH0)

(minusH0)

Figure 2 Acidity ranges for several common superacids The solid bars are measuredusing indicators while the broken bar is estimated by kinetics measurements in () molLewis acid

GENERAL ASPECTS 7

With respect to electrophiles and electron-deTHORNcient varied species therehave been suggestions of non-coordinating solvents and non-coordi-nating anions Of course by deTHORNnition anions are electron donors Inorder to prepare highly electron-deTHORNcient species such as trialkylsilylcations claims were made for the use of non-nucleophilic or non-coordi-nating anions14 Even more surprisingly some of these reactive ions havebeen prepared from toluene solution referred to as a non-nucleophilicsolvent14 It should be mentioned that the myth of non-coordinatinganions was discussed as early as 1973 by Rosenthal who concluded thatit is clear that the notion of the non-coordinating anion should be putto rest alongside the notion of non-coordinating solvent15 Olah et alsubsequently discussed this point critically As a result the terms leastcoordinating and more correctly weakly coordinating anions weresubstituted

Much effort has been made recently to THORNnd new weakly coordinatinganions as counter ions for strong electrophiles and acids16 Like the con-jugate bases of superacids these weakly coordinating anions are generallycharacterized by the anionic charge being delocalized over the entirety oflarge anions with no individual atom bearing a substantial part of thecharge Many of the most useful weakly coordinating anions have hydro-gen and szliguorine atoms on their periphery thus avoiding the presence ofstrongly Lewis basic-sites Among the most common low or weakly coor-dinating anions are borate anions such as Meerweins BF4

minus (which is ofcourse the conjugate base of the important superacid HF-BF3) WittigsB(C6H5)4minus and the more recent B(C6F5)4minus and [B(OTeF5)4]minus as wellas Olahs SbF6

minus or SbF6minus-(SbF5)n The weakly coordinating borates

are of particular practical importance to the activity of the electrophilicone-component Ziegler-Natta oleTHORNn polymerization catalysts17 Thesecationic metallocene catalysts have been shown to have high activities aspolymerization catalysts due in large part to their electrophilic metal cen-ter and weakly coordinating anions It has been shown that for a given typeof catalytic site the more weakly coordinating anions result in more activepolymerization catalysts Another class of less coordinating anions areReeds 1-carba-closo-dodecaborate monoanions (CB11H12

minus and relatedhalogenated analogs) In addition to being used as counter ions in activecationic polymerization catalysts these anions have also been shown to beuseful in the preparation of salts of varied electrophilic cations18 Theseinclude four-coordinate Fe(III)porphyrins crystalline salts of carbocations(eq 11) a weakly coordinated highly crowded stannyl cation (eq 12) andhighly stabilized silicenium cations (eq 13) and other salts despite thehigh electrophilic reactivities of the cations Reactive electrophilic salts

8 GENERAL ASPECTS

CH3[CHB11(CH3)5Br6]++

CH2Cl2minus30degC

minusCH4

[CHB11(CH3)5Br6]minus(11)

Sn Snn-Bu

n-Bun-Bu

n-Bun-Bu

n-Bu+

+2 CB11(CH3)12 bull Sn

[CB11(CH3)12]minus

(12)

ArSi

ArAr

Ar = mesityl

+ (CH3CH2)3Si[CHB11(CH3)5Br6]minus(CH3CH2)3SiCH2CH=CH2

ArSi

Ar

Ar

[CHB11(CH3)5Br6]

+

minus

(13)

PhC

CH3

+ minusO

(CH3CH2)3SiH

(C6H5)3C B(C6F5)4

minus78degC

PhC

CH3

OSi(CH2CH3)3

B(C6F5)4

(C6H5)3CH

4

+

minus+ (14)

such as the silylated carboxonium ion (4 eq 14) and the tris-mesitylsilicenium ion have been prepared as tetra(pentaszliguorophenyl)borate saltsRecent reviews have been published on weakly coordinating anions espe-cially with respect to polymerization catalysts1617

Although monocationic carbon electrophiles have been involved inchemical reactions for many years multiply charged organic electrophiles(dications trications etc) have only been studied recently19 It was thehigh reactivity of dicationic vicinal and geminal electrophiles that led tothe concept of superelectrophilic activation as proposed by Olah in the1970s20 In 1973 Brouwer and Kiffen reported the results of superacid-catalyzed reactions between protonated aldehydes and ketones (carboxo-nium ions) and alkanes as well as the reactions of the acetyl cation withalkanes (Scheme 1)21 In solutions of HFSbF5 or HFBF3 reactionproducts are formed that are consistent with hydride transfer between theacetyl cation (generated in situ from acetic acid) and isobutane Earlierstudies by Olah and co-workers showed however that acetyl salts likeacetyl hexaszliguoroantimonate do not abstract hydride from alkanes in apro-tic solvents (SO2 SO2ClF or CH2Cl2) In order to explain the enhancedreactive of the acetyl cation in superacid Olah proposed the formation ofa protosolvated superelectrophilic intermediate (5)20 Despite the fact thatthe acetyl cation has a positive charge it has nonbonding oxygen elec-tron pairs which are capable of interacting with the superacidic mediaIn the limiting case the hydrogen-bonded species (7) can lead toward theformation of the highly electrophilic doubly electron deTHORNcient dicationic

GENERAL ASPECTS 9

CO

H3C OHC

CH3

CH3CH3HC

O

CH3

H+

COH

CH3

CCH3

CH3CH3H

COH

H3CC

H3C

CH3

CH3H

NO REACTION

ISOBUTANE

HFBF3CO

CH3

5

COH

H3CC

CH3

CH3CH3

H

2+

6

Increasing Reactivity

CO

CH3

CO

CH3

CO

CH3

H Ad+

COH

CH3

57

+

+

+

+

+

+

+

+ +

+

+

Scheme 1 Protosolvation of the acetyl cation and its reaction with isobutane

species 5 It is the superelectrophilic intermediate (5 or 7) that is capableof reacting with the CH bond of the hydrocarbon substrate (isobutane)Subsequently the complex 6 then leads to the formed hydride abstractionproducts As described more thoroughly in Chapter 5 the proposed super-electrophilic activation is also supported by thermodynamic calculations

About the same time a similar type of activation was observed in thereactions of nitronium salts20 Nitronium salts (such as NO2

+BF4minus or NO2

+PF6

minus) show little or no tendency to reactwith deactivated arenes or alkanes inaprotic media However in szliguorosulfuric acid or HF-BF3 solution nitrationtakes place giving nitration products even nitromethane (eq 15)

IncreasingReactivity

NO O NO O NO OHH Ad+

8

CH4 + NO2H2+ CH

HH

NO2H

H2+

8minusH+ CH3NO2H+

+ + + +

(15)

These results can be interpreted in terms of protosolvation of the nitron-ium ion While the monocationic nitronium ion is a sufTHORNciently polarizibleelectrophile to react with strong nucleophiles such as oleTHORNns and acti-vated arenes it is generally not reactive enough to react with weaknucleophiles including methane Partial or complete protonation of thenitronium oxygen then leads to the superelectrophilic species 8 The

10 GENERAL ASPECTS

heightened electrophilic reactivity of 8 allows the reactions with deac-tivated aromatics and alkanes

The protionitronium ion (8 NO2H2+) and the protioacetyl cation (5CH3COH2+) were the THORNrst examples of superelectrophilic intermediatesTheir electrophilic reactivities are much greater than that of the cor-responding parent monocations22 As such these superelectrophiles arecapable of reacting with weaker nucleophiles than the nitronium (NO2

+)and acetyl (CH3CO+) cations A deTHORNning feature of these superelec-trophiles (and those described subsequently) is the further complexation(solvation) of the monocationic electrophile by Broslashnsted or Lewis acidsAs a result of this interaction neighboring group participation with theelectrophilic center is decreased and the resulting electrophiles are increas-ingly electron deTHORNcient and reactive22 In the limiting cases multiplycharged de facto dications (even multications) may result As discussed inChapter 7 superelectrophiles are distinguished from such distant dicationsin which the two charged groups are isolated Distant onium dicationsexhibit chemistry no different than the monocationic onium ions Theterm superelectrophile previously has been applied occasionally to anumber of other chemical systems including metal complexes in high oxi-dation states electrophiles bearing multiple electron-withdrawing groupsand other highly reactive electrophiles While these systems may exhibitunique chemistry they are not superelectrophiles within the context ofdiscussed acid-base interactions Consequently their chemistry will notbe included in our discussions in this book

Superelectrophilic intermediates have been categorized into two distinctgroups the distonic (distant) and the gitonic (close) superelectrophiles(Table 1)22 Distonic superelectrophiles are deTHORNned as electrophiles in

Table 1 Classes and examples of superelectrophiles

Gitonic Superelectrophiles Distonic Superelectrophiles

N

HO

CH3

OH

OH

OH

Ph

OON

N

F

CH2Cl+

+

++

+

+

++

H CCH3

CH3

CH3

OH2+

+

O

OH2

Ph

PhO OH

H3C Br CH3

H

2+

N+ +

+

+

GENERAL ASPECTS 11

which the positive charge centers are separated by two or more carbonor hetero atoms while gitonic superelectrophiles are characterized by thepositive charge centers being in close proximity Both types of superelec-trophiles and their chemistry will be discussed in subsequent chapters

Theoretical calculations have been done on varied superelctrophilic spe-cies They are often found in deep potential energy wells on the energysurfaces although others are higher lying minima Moreover the calcu-lated gas-phase structures are often only kinetically stable species but withsizable energy barriers to proton loss or other fragmentations These cal-culations have been veriTHORNed by the observation of a number of superelec-trophiles by gas-phase mass spectroscopy studies (vide infra) Reactionsof superelctrophiles in the condensed phase frequently involve discreetlyformed dicationic (or tricationic) species However as noted with theprotioacetyl dication (CH3COH2+ 5) and the protionitronium dication(NO2H2+ 8) formation of effective dications may be the limiting casePartial protonation or weaker donor-acceptor interaction with a Lewis acidwhat we now call electrophilic solvation can also activate electrophilesto produce superelectrophiles Along these same lines there has beenkinetic evidence to suggest varying degrees of protonation in the transi-tions states involving superelectrophiles23 For many superelectrophilesit has not been possible to de facto directly observe these species evenwith fast spectroscopic methods It has been proposed in several of thesestudies that superelectrophiles are formed in only low concentrations Asan explanation for these reactions superelectrophilic transition states maybe involved with no persistent intermediates

Two types of interactions have been shown to be involved in super-electrophilic species Superelectrophiles can be formed by the furtherinteraction of a conventional cationic electrophile with Broslashnsted or Lewisacids (eq 16)23 Such is the case with the further protonation (protosolva-tion) or Lewis acid coordination of suitable substitutents at the electrondeTHORNcient site as for example in carboxonium cations The other involvesfurther protonation or complexation formation of a second proximal oniumion site which results in superelectrophilic activation (eq 17)24

O OH+ +

+

OH2

9

H+H+

(16)

12 GENERAL ASPECTS

N

O

HH+ H+

HN

O

H

10

+ HN

OH

H+

+

(17)

Both types of dicationic species (910) exhibit the properties and reac-tivities of superelectrophiles

It should be noted that it was Pauling who predicted the viability of adoubly charged molecular structure in the 1930s by suggesting the kineticstability of the helium dimer dication (He2

2+)25 Despite the large esti-mated exothermic energy of dissociation (200 kcalmol) theoretical cal-culations predicted a substantial energy barrier to dissociation (332 kcalmol) The recent mass spectrometric observation of the helium dimerdication He2

2+ conTHORNrms Paulings prediction25b The kinetic stabilityof the helium dimer dication can be understood by the bonding interac-tion (He2

2+ is isoelectronic with the hydrogen molecule) offsetting thelarge electrostatic charge-charge repulsion Molecular orbital theory alsopredicted the stability of aromatic dications including the cyclobutadi-ene dication the biphenylene dication and the cyclooctatetrene dicationThese dicationic species (1113)

Ph

PhPh

Ph

2+

11

2+

12

2+

13

as well as many other related systems have since been observed as stableions in under high-acidity low nucleophilicity conditions19ab

Superelectrophilic onium dications have been the subject of exten-sive studies and their chemistry is discussed in chapters 47 Othermultiply charged carbocationic species are shown in Table 2 Theseinclude Hogeveens bridging nonclassical dication (14)26 the pagodanedication (15)27 Schleyers 13-dehydro-57-adamantane dication (16)28the bis(szliguroenyl) dication (18)29 dications (17 and 19)19a trications(2021)19a30 and tetracations (2223)31 Despite the highly electrophiliccharacter of these carbocations they have been characterized as persistentions in superacids

In solutions of low nucleophilicity multiply charged electrophiles canfrequently exhibit deep-seated rearrangements and fragmentation reac-tions These reactions often stem from the electrostatic repulsive effectsinvolving the charge centers and they have precluded the observation of

GENERAL ASPECTS 13

Table 2 Some persistent multiply charged carbocations

Dications

2+

CH3

CH3H3C

H3C

H3C CCH3

2+2+

2+

16

18

14 15

19

17

Higher Cations

Ph Ph

Ph

PhPh Ph

Ph

Ph

20

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

21

R

R R

R

R

R

22 23

+ ++

+

+

+

+

+

++

+ ++

+

+ +

some multi-charged ions For example a long-sought goal in carbocationstudies was the generation of an aliphatic 13-carbodication Whereas ion-ization of 25-dichloro-25-dimethylhexane gives the stable 14-dication(24 eq 18) ionization of 24-dichloro-24-dimethylpentane (25) leads onlyto the 2-pentenyl cation (27 eq 19)32 It is thought that the 13-dication(26) if formed undergoes rapid deprotonation to give ion 27 Similarlyionization of the diol (28) gives the two monocations instead of theexpected 13-dication (eq 20)32 Other reactions of dicationic species aredescribed in chapters 47

ClCl

SbF5

SO2ClFminus78degC

+

+

24

(18)

27

Cl + ++

Cl

25 26

SbF5

SO2ClFminus78degC

(19)

OHOH ++

HO

28

SbF5

HSO3F

SO2ClFminus78degC

+

(20)

14 GENERAL ASPECTS

The concept of superelectrophilic activation was THORNrst proposed 30 yearsago20 Since these early publications from the Olah group superelec-trophilic activation has been recognized in many organic inorganic andbiochemical reactions22 Due to the unusual reactivities observed of super-electrophiles they have been exploited in varied synthetic reactions andin mechanistic studies Superelectrophiles have also been the subject ofnumerous theoretical investigations and some have been directly observedby physical methods (spectroscopic gas-phase methods etc) The resultsof kinetic studies also support the role of superelectrophilic activationBecause of the importance of electrophilic chemistry in general and super-acidic catalysis in particular there continues to be substantial interest inthe chemistry of these reactive species It is thus timely to review theirchemistry

REFERENCES

(1) (a) A Lapworth Nature 1925 115 625 (b) C D Nenitzescu in Car-bonium Ions vol 1 G A Olah and P v R Schleyer Eds Wiley NewYork 1968 chap 1 and references therein (c) C K Ingold Recl TravChim Pays-Bas 1929 42 797 (d) C K Ingold Chem Rev 1934 15 225(e) C K Ingold Structure and Mechanism in Organic Chemistry CornellUniversity Press 1953

(2) (a) J F Norris Am Chem J 1901 25 117 (b) F Kehrman F WentzelBer Dtsch Chem Ges 1901 34 3815 (c) A Baeyer V Villiger BerDtsch Chem Ges 1901 35 1189 3013

(3) (a) G A Olah Angew Chem Int Ed Engl 1973 12 173 (b) G A OlahCarbocation and Electrophilic Reactions VCH-Wiley Weinheim NewYork 1973 (c) G A Olah Nobel Lecture Angew Chem Int Ed Engl1995 34 1393 (d) G A Olah K K Laali Q Wang G K S PrakashOnium Ions Wiley New York 1998

(4) (a) L P Hammet Physical Organic Chemistry 2nd Ed McGraw Hill NewYork 1970 (b) H H Jaffe Chem Rev 1953 53 191

(5) C G Swain C B Scott J Am Chem Soc 1953 75 141(6) R Lucius R Loos H Mayr Angew Chem Int Ed 2002 41 92 and

references cited therein(7) (a) N C Deno J J Jaruzelski A Schriesheim J Am Chem Soc 1955

77 3044 (b) E M Arnett T C Hofelich J Am Chem Soc 1983 1052889 and references cited therein

(8) D H Aue M T Bowers in Gas Phase Ion Chemistry M T Bowers EdAcademic Press New York 1979 Vol 2 chap 9

(9) (a) J E Hofmann A Schriesheim A in Friedel-Crafts and Related Reac-tion G A Olah Ed Wiley New York NY 1964 vol 2 pp 597-640

REFERENCES 15

(b) J March Advanced Organic Chemistry 4th Ed Wiley New York 1992pp 548549

(10) (a) Chem Abstr 1979 90 86986u (b) U S Pat Appl 891872 (1978)(c) W D Kray R W Rosser J Org Chem 1977 42 1186

(11) (a) G A Olah G K S Prakash J Sommer in Superacids Wiley NewYork 1985 (b) G A Olah A Molnar G K S Prakash J Sommer inSuperacids Revised 2nd Ed Wiley New York in preparation

(12) (a) G A Olah Angew Chem 1963 75 800 (b) G A Olah in CarbocationChemistry G A Olah and G K S Prakash Eds Wiley New York 2004chap 2

(13) (a) G A Olah J Org Chem 2001 66 5943 (b) Reference 3b

(14) (a) J B Lambert S Zhang C L Stern J C Huffman Science 1993 2601917 (b) C A Reed Acc Chem Res 1998 31 325

(15) (a) M R Rosenthal J Chem Ed 1973 50 33 (b) G A Olah G RasulH A Buchholz X-Y Li G K S Prakash Bull Soc Chim Fr 1995 132569 (c) I Krossing I Raabe Angew Chem Int Ed 2004 43 2066

(16) S Strauss Chem Rev 1993 93 927

(17) E Y-X Chen T J Marks Chem Rev 2000 100 1391

(18) (a) T Kato C R Reed Angew Chem Int Ed 2004 43 2908 (b) K-CKim C A Reed D W Elliot L J Mueller F Tham L Lin J BLambert Science 2002 297 825 (c) G K S Prakash C Bae G RasulG A Olah J Org Chem 2002 67 1297 (d) I Zharov B T KingZ Havlas A Pardi J Michl J Am Chem Soc 2000 122 10253

(19) (a) G K S Prakash T N Rawdah G A Olah Angew Chem Int Ed Engl1983 22 390 (c) R M Pagni Tetrahedron 1984 49 4161 (c) Reference3c chap 10 (d) V G Nenajdenko N E Shevchenko E S BalenkovaChem Rev 2003 103 229

(20) G A Olah A Germain H C Lin D Forsyth J Am Chem Soc 197597 2928

(21) (a) D M Brouwer A A Kiffen Recl Trav Chim Pays-Bas 1973 92 689(b) D M Brouwer A A Kiffen Recl Trav Chim Pays-Bas 1973 92 809(c) M Brouwer A A Kiffen Recl Trav Chim Pays-Bas 1973 92 906

(22) (a) G A Olah G K S Prakash K Lammertsma Res Chem Intermed 1989 12 141 (b) G A Olah Angew Chem Int Ed Engl 1993 32 767(c) G A Olah D A Klumpp Acc Chem Res 2004 37 211

(23) (a) M Volpin I Akhrem A Orlinkov New J Chem 1989 13 771(b) S Saito Y Sato T Ohwada K Shudo J Am Chem Soc 1994 1162312

(24) D A Klumpp Y Zhang P J Kindelin S Lau Tetrahedron 2006 625915

(25) (a) L Pauling J Chem Phys 1933 1 56 (b) J D Dunitz T K HaJ Chem Soc Chem Commun 1972 568

16 GENERAL ASPECTS

(26) H Hogeveen P W Kwant Acc Chem Res 1975 8 413(27) G K S Prakash V V Krishnamurthy R Herges R Bau H Yuan

G A Olah W-D Fessner H Prinzbach J Am Chem Soc 1986 108836

(28) M Bremer P v R Schleyer K Schoetz M Kausch M Schindler AngewChem Int Ed Engl 1987 26 761

(29) (a) J L Malandra N S Mills D E Kadlecek J A Lowery J AmChem Soc 1994 116 11622 (b) N S Mills J L Malandra E E BurnsA Green K Unruh D E Kadlecek J A Lowery J Org Chem 199762 9318

(30) S Ito N Morita T Asao Bull Chem Soc Jpn 2000 73 1865(31) (a) N J Head G K S Prakash A Bashir-Hashemi G A Olah J Am

Chem Soc 1995 117 12005 (b) R Rathore C L Burns I A GreenJ Org Chem 2004 69 1524

(32) G A Olah J L Grant R J Spear J M Bollinger A Serianz G SiposJ Am Chem Soc 1976 98 2501

2STUDY OF SUPERELECTROPHILES

21 INTRODUCTION

Many of the methods used in the study of electrophiles can also be appliedin studies of superelectrophiles As noted in the introduction superelec-trophiles often exhibit very high reactivities when compared with conven-tional electrophiles The heightened reactivities can consequently be usedto estimate the degree of superelectrophilic activation in the chemistryof superelectrophiles In this respect several reports have characterizedsuperelectrophiles based on kinetic studies Reaction rates were shownto increase with acidity for certain types of acid-catalyzed conversionsindicative of superelectrophilic activation Although superelectrophilesaffecting reactions are generally present only in low concentrations somepersistent superelectrophiles have been studied using varied spectroscopictechniques Low-temperature NMR and gas-phase techniques have beenused in studies of several types of superelectrophiles Theoretical calcula-tions have been used to characterize many superelectrophilic systems Inaddition to proving their intermediate nature as energy minima they alsohave provided ground state geometries and energies Calculations havealso indicated signiTHORNcant energy barriers to dissociation for a variety ofdicationic and tricationic superelectrophiles This chapter describes the


17

copy

18 STUDY OF SUPERELECTROPHILES

various methods of study of characteristic superelectrophilic systems thathave been studied Other techniques such as isotopic labeling studiescalorimetric measurements and various physical measurements are alsodiscussed when relevant

22 REACTIVITY PROFILES

One of the deTHORNning features of superelectrophiles is the often-observedhigh level of reactivity towards nucleophiles of low strength1 This experi-mental observation is frequently used as an indication for the involvementof a superelectrophiles To illustrate the following examples show how theelectrophiles reactivity can be characterized to indicate superelectrophilicchemistry

It was the enhanced reactivities of nitronium and acetylium salts insuperacidic media that lead Olah to THORNrst propose in 1975 the concept ofsuperelectrophilic activation2 As mentioned in Chapter 1 nitronium saltsexhibit markedly enhanced reactivities in strong acids when comparedwith reactions in aprotic solvents Even the slow nitration of methane canbe accomplished using nitronium hexaszliguorophosphate (NO2

+PF6minus) in

superacidic FSO3H while nitronium salts in aprotic solvents are unreac-tive This increased reactivity in superacid was suggested to involve pro-tosolvation of the nitronium cation forming the limiting superelectrophileNO2H2+ In a similar respect nitration of strongly deactivated arenes isonly effected by nitronium salts in superacidic media For example nitro-nium tetraszliguoroborate (NO2

+ BF4minus) does not nitrate m-dinitrobenzene in

nitromethane solvent but in FSO3H it gives 135-trinitrotoluene (eq 1)3

NO2O2N

+ NO2BF4

FSO3HNO2O2N

NO2

150degC

62

(1)

When nitronium tetraszliguoroborate was attempted to be reacted withpentaszliguorobenzene in the triszligic acid CF3SO3H (H0 minus141) no nitrationoccured However using the much stronger superacid triszligatoboric acid(2 CF3SO3H-B(O3SCF3)3 H0 minus205) nitration occurs in high yield (thenitronium ion being in situ generated from nitric acid eq 2)3

F

+ HNO3

2 CF3SO3HndashB(O3SCF3)3FO2N

F

25degC

89

FF

FF

F

F

F(2)

REACTIVITY PROFILES 19

Even the trityl cation has been successfully nitrated using superacidicactivation of nitronium salts (eq 3)4

1) CF3SO3H 0degCNO2BF4

Ph

PhNO2

2) H2O

BF4minus

OH

H2OndashBF3

Et3SiH

Ph

PhNO2

H

64

+ (3)

Due to the delocalization of the cationic charge into the phenyl rings theyare only very weakly nucleophilic The reaction of nitronium tetraszliguo-roborate with triphenylcarbenium tetraszliguoroborate in excess CF3SO3Hhowever gives the mononitration product which can then be reducedusing ionic hydrogenation (Et3SiH) The same reaction in an aproticmedium (CH2Cl2) gives no nitration product These results are all consis-tent with the protolytic activation of the nitronium cation in the superacidsMethane m-dinitrobenzene pentaszliguorobenzene and the trityl cation areall weak nucleophiles and the nitronium cation (1) does not possess suf-THORNcient electrophilic reactivity to attack these nucleophiles Increasing theacidity of the reaction medium however leads to an equilibrium with theprotosolvated nitronium ion (2) (or even the protonitronium ion 3)

NO O NO O NO OHH A

31 2

d++ + + +

which is a signiTHORNcantly more reactive electrophile Thus nitration ofthese weak nucleophiles suggest the involvement of the superelectrophilicspecies (2 or 3) A more detailed discussion of the superelectrophilicnitronium ion is found in Chapter 5

Friedel-Crafts type reactions of strongly deactivated arenes have beenthe subject of several recent studies indicating involvement of super-electrophilic intermediates Numerous electrophilic aromatic substitutionreactions only work with activated or electron-rich arenes such as phe-nols alkylated arenes or aryl ethers5 Since these reactions involve weakelectrophiles aromatic compounds such as benzene chlorobenzene ornitrobenzene either do not react or give only low yields of products Forexample electrophilic alkylthioalkylation generally works well only withphenolic substrates6 This can be understood by considering the resonancestabilization of the involved thioalkylcarbenium ion and the delocaliza-tion of the electrophilic center (eq 4) With the use of excess Lewis acidhowever the electrophilic reactivity of the alkylthiocarbenium ion can be


greatly enhanced indicating superelectrophilic activated species (4)6c Thegreater electrophilic reactivity allows for the electrophilic alkylthioalky-lation of even benzene and halogenated arenes in good yields (eq 5)

SR1

R2

R3

SR1

R2

R3

AlCl3

SR1

R2

R3

AlCl3

4

dminus

d++ ++ (4)

Cl SCH3

2 Equivalents AlCl3CH2Cl2 0degC

SCH3

87(5)

Similarly hydroxyalkylation with aldehydes or ketones is best accom-plished with activated aromatic compounds such as phenols7 Howeverreaction even with chlorobenzene has been carried out with either para-banic acid or isatin using triszligic acid (eqs 67)89

N

N

O

O

OH

H CF3SO3H

C6H5Cl

65

N

NO

OH

H

Cl

Cl

(6)

N

O

O

H

CF3SO3H

C6H5Cl

NO

H

ClCl

99

(7)

Diprotonated superelectrophilic intermediates were suggested to beinvolved in both conversions Considering protonated aldehydes benzal-dehyde gives a carboxonium ion that is signiTHORNcantly resonance stabilizedand thus unreactive towards aromatic substrates such as o-dichlorobenzeneor nitrobenzene Pyridinecarboxaldehydes however show much higherelectrophilic reactivities due to their ability to form via N -protonation thesuperelectrophile (5 eq 8)10 A similar situation is seen in the hydrox-yalkylation reactions of acetyl-substituted arenes Acetophenone is fullyprotonated in excess triszligic acid but the resulting carboxonium ion (6) is


not sufTHORNciently electrophilic to react with benzene (eq 9)11 Yet acetyl-substituted pyridines (and other N -heterocycles) give the related conden-sation products in excellent yield under the same conditions (eq 10) Thehigher reactivity of the pyridine system is attributed to the formation ofdication (7) In the superacid catalyzed acylation of arenes with methylbenzoate even nitrobenzene is acylated in high yield suggesting the for-mation of a superelectrophile (8 eq 11)12

N O

H

CF3SO3H

C6H5NO2N OH

H

H N

HNO2

O2N10

5

+ +(8)

CH3

O

CF3SO3H

C6H6

no reactionwith C6H6

6

CH3

OH+

(9)

NCH3

O

CF3SO3H

C6H6

NCH3

OHHN

CH3

Ph Ph

93

7

++

(10)

OCH3

O

CF3SO3H

C6H5NO2OCH3

OH

H

O

NO2

8

82

+

+

(11)

Although electrophilic reactions involving dications with deactivatedarenes may suggest the formation of superelectrophilic intermediates thereare a number of well-known examples of monocationic electrophiles thatare capable of reacting with benzene or with deactivated aromatic com-pounds For example 222-triszliguoroacetophenone condenses with benzenein triszligic acid (eq 12)13 A similar activation is likely involved in the H2SO4

catalyzed reaction of chloral (or its hydrate) with chlorobenzene givingDDT (eq 13)


CCF3

O

CF3SO3H

C6H6

CCF3

OH

CF3

Ph Ph+

(12)

HC

CCl3

O H2SO4

CCCl3H

C6H5Cl

Cl Cl

HC

CCl3

OH+

(13)

The inductive effects of the triszliguoromethyl and trichloromethyl groupsincrease the electrophilic reactivities of the carboxonium ions when com-pared with those formed from acetophenone or acetaldehyde

As mentioned in Chapter 1 some superelectrophiles are even capableof reacting with the σ -bonds of alkanes or alkyl groups σ -Donor alka-nes are of course weak nucleophiles But in reactions with exceedinglystrong acids or electrophiles σ -bonds can act as electron donors This wasdemonstrated in the study of the superacid catalyzed reactions of alkaneswith the protosolvated acetyl cation (Scheme 1 Chapter 1) Olah et alshowed carbon monooxide can react with isobutane to give methyliso-propyl ketone in high yield upon rearrangement of formed pivaldehyde(Scheme 1)14 Other branched alkanes react similarly The results areconsistent with the formation of the protosolvated formyl cation (9)which reacts directly with the tertiary CH bond via a THORNve coordinatecarbocation (10) Subsequent rearrangement yields the methylisopropylketone product Although it is conceivable that the carbonylation mightoccur by initial formation of a tert-butyl cation (via reaction of isobu-tane with superacid) followed by trapping it with carbon monooxide thispathway is unlikely because no carboxylic acids are detectable in theproduct mixtures An analogous superelectrophilic formylation has also

CCH3

CH3CH3H

CO

H

COH

HC

CH3

CH3CH3

H

HFBF3

CO

H9

COH+

H 2+

CCH3

CH3CH3

COH

HminusH+

minusH+

minusH+

H+

C

CH3

CH3CH3

COH2

HC

H3C CH3CH3

COH2

HCH3C

CH3

CH3

COH

HCH3C

CH3

CH3

CO

H

10

91

+ +

+

+

+

+

+

++

Scheme 1


been observed in the reactions of adamantane and carbon monooxide togive 1-formyladamantane (eq 14)15

H

1) CF3SO3HCO (15 atm)

H E

2) H2O

+

E+ = HCO+ or HCOH2+

CHO

minus2H+

(14)

The reaction yield increases with acid strength further suggesting the inter-mediacy of the protosolvated superelectrophilic formylating species (9)

Superelectrophilic activation has also been proposed to be involvedbased upon the reactivity of carbocations with molecular hydrogen (a σ -donor)16 This chemistry is probably even involved in an enzymatic systemthat converts CO2 to methane It was found that N5N10 menthyl tetrahy-dromethanopterin (11) undergoes an enzyme-catalyzed reaction with H2by hydride transfer to the pro-R position and releases a proton to givethe reduced product 12 (eq 15) Despite the low nucleophilicity of H2cations like the tert-butyl cation (13) are sufTHORNciently electrophilic to reactwith H2 via 2 electron-3 center bond interaction (eq 16) However due tostabilization (and thus delocalization) by adjacent nitrogen atoms cationslike the guanidinium ion system (14) do not react with H2 (eq 17)

11 12

HN

NH

N

NHs

O

H2N

CH3

CH3

H

Hr

H2

ENZYMEHN

NH

N

NH

O

H2N

CH3

CH3

H

H

A

+

++ H+

(15)

CH3

H3C CH3H2

CH3

H3C CH3

HH

13CH3

H3C CH3

H

H

++

+

+ +

(16)


H2

NN

N

H

14

H+

+N

NN

+ +(17)

Since N5N10 menthyl tetrahydromethanopterin (11) should also exhibitsigniTHORNcant delocalization of the cationic site its reactivity with molecularhydrogen is remarkable It is suggested that protonation (protosolvation)of one or both of the adjacent basic nitrogen sites by the enzymatic systemcould generate an enhanced electrophilic system (Scheme 2) This super-electrophilic system would be the result of decreased neighboring groupparticipation and thus resulting in increased reactivity A more detaileddiscussion of this system is found in Chapter 5

The above examples are illustrative of how activated electrophilic chem-istry involving weak nucleophiles can indicate involvement of superelec-trophiles Chemical reactivity with weak nucleophiles however by itselfcannot be considered sufTHORNcient evidence for superelectrophilic intermedi-ates or reactive dicationic intermediates Many reactions of alkanes forexample occur by oxidative free radical reaction pathways Strong acidsystems may also cause medium effects such as for example increasingthe solubility of reagents which can lead to higher yields or increasedreaction rates However when these effects can be ruled out and the elec-trophilic reactions of weak nucleophiles give higher yields and increasedreaction rates (eg in conversions dependent on acid strength) superelec-trophilic activation is indicated

23 KINETIC STUDIES

Kinetic studies have been important in the characterization of varied elec-trophilic reactions such as electrophilic aromatic substitutions addition

N

NH

ring

ring

H3C R

HH

Protonation

N

NH

ring

ring

H3C R

HH

H

11

H2

N

N H

ringring

H3CR

HH

++

Scheme 2 Proposed mechanism for the activation of the stabilized cation (11)

KINETIC STUDIES 25

reactions to alkenes and various carbonyl reactions Several superelec-trophilic reactions have also been studied using kinetics experimentsThese reactions typically show dramatic increases in reactions rates (andyields) with increasing acidity Some representative examples are dis-cussed here Divinyl ketones are known to cyclize to 2-cyclopentanonesin acid-catalyzed electrocylization reactions17 The Nazarov and relatedreactions often require forcing conditions of high acidity and elevated tem-peratures O-Protonated cationic intermediates have been proposed in thereactions With a series of 1-phenyl-2-propen-1-ones in superacid-catalyzedreactions 1-indanones were obtained in generally good yields (eq 18)18

Ph

O

Ph

O

Ph

5 hrs 0degC

91

15

18

16minus2 H

CF3SO3H CF3SO3H

OH2

Ph

OH2

Ph

17

2+

Ph

OH

Ph

+ +

+

+

(18)

The reactions were also carried out in solutions of varying acidity and inall cases the cyclization required highly acidic conditions Cyclization of15 gives 91 yield of 18 in 100 CF3SO3H (H0 minus141) and 48 yieldin 6 ww CF3SO3H 94 CF3CO2H (H0 minus87) Attempted reactionsin CF3CO2H (100 H0 minus27) gave no cyclization In kinetic studies1-phenyl-2-propen-1-ones were reacted in solutions of varying acidityand in all cases the cyclizations were found to exhibit pseudo THORNrst-orderkinetics The rate constants were found to be directly proportional to acidstrength over the range of acidities from H0 minus9 to minus13 These results areconsistent with the Zucker-Hammett hypothesis which states that reac-tion rates are linearly proportional to acidity if the reactive species (iethe present protonated intermediates) are formed in low concentrationsand are involved in the rate-determining step Given however that thecarbonyl group is essentially fully protonated at H0 minus9 an increasing rateconstant with acidity indicates formation of the diprotonated intermediate(17)

13-Diphenyl-1-propanone (19) is found to give the cyclization product22 in good yield when the reaction is carried out in superacid19 Thisacid-catalyzed cyclization also shows a dramatic dependence on the acid-ity of the reaction medium a yield of 72 in 100 CF3SO3H (H0 minus141)a yield of 7 in 6 ww CF3SO3H 94 CF3CO2H (H0 minus87) a yield


Ph Ph

O

Ph

19

22

H+

Ph Ph

OH

21

Ph Ph

OH2

OH2

PhH

slow orno reaction

rate-determining

80degC Ph Ph

OH22+

72

20

CF3SO3H

+ +

+

+

+

Scheme 3 Proposed mechanism for the cyclization of 13-diphenyl-l-propanone (19)

of 0 in 100 CF3CO2H Using NMR and UV titration methods thepK BH+ value of ketone 19 was estimated to be minus59 Thus 19 is fullyprotonated in the solution of acidity H0 minus9 and at higher levels of acid-ity the monocationic species (20) is in equilibrium with the diprotonatedspecies (21) The cyclodehydration reaction was also examined in kinet-ics studies Between the range of H0 minus82 and minus141 the reaction rateconstant was found to increase linearly with acidity These results indi-cate that the superelectrophilic species 21 is formed and is involved inthe rate-determining cyclization step (Scheme 3) The monoprotonatedspecies (20) itself is stabilized by inductive and resonance effects andtherefore the cyclization does not occur A second protonation at the car-bonyl group is needed to give the superelectrophile (21) which leads tothe cyclization

In a study involving an intramolecular Houben-Hoesch reaction (eq 19)

CF3SO3HCF3CO2H

CNH+

O

23 24 25

CN

H +

C

NHH+

+

(19)

kinetic evidence suggested the involvement of superelectrophilic diproto-nation of nitriles20 4-Phenylbutyronitrile (23) was found to cyclize at anappreciable rate only in solutions more acidic than H0 = minus10 The THORNrst-order rate constant was found to be linearly proportional to acidity over arange of H0 = minus105 to minus13 In fact the rate increases 100-fold over thisrange of acidity The monoprotonated nitrile (24) itself is approximatelyhalf protonated in solutions of acidity H0 = minus10 However at this acid

KINETIC STUDIES 27

strength there is little or no cyclization This is consistent with the forma-tion of the superelectrophilic intermediate 25 with increasing acid strengthThe kinetic data also indicate that the superelectrophilic intermediate 25 isformed (even if in low concentration) and is involved in the rate-limitingreaction step These experiments also suggest that the rapid increase in reac-tion rate with acidity is probably due to the degree of protonation where inthis case protonation is nearly complete In the study of the intramolecu-lar cyclization of 13-diphenyl-1-propanone (Scheme 3) a similar increasewas found in reaction rate with acidity but the reaction rate increase wasin this case not as large This was interpreted in terms of a more limiteddegree of protonation or the protosolvation of the activated complex

When the unsaturated acetal 26 was reacted with superacid at minus60Cand irradiated a photostationary state is observed consisting of the twostereoisomers 26a and 26b (Scheme 4)21 Evaluation of the kinetics ofstereomutation shows good THORNrst order kinetics and the rate constant in-creases with acidity Based on the kinetics results it was proposed thatprotonation of the carboxonium group of 26b leads to the dication (27)and this facilitates isomerization through delocalization of the positivecharge

The Pictet-Spengler and Bischler-Napieralski reactions are used to pre-pare biologically and pharmocologically important isoquinoline ring sys-tems Versions of these reactions have also been proposed in biosyntheticpathways Under mildly to strongly acidic conditions the cyclizations

OCH3

OCH3

FSO3HSbF5

minus60degC

hn

minusH+H+

26 26a 26b

2727

k1

OCH3

+

OCH3+

OCH3

H

++OCH3

H

+

+

Δ

Scheme 4 Role of superlectrophile (27) in the stereomutation of the oxonium ion (26b)


require activating groups (R) on the aryl-substituent of the imine (eq 20)

N

RprimeR

H+

NH

RprimeR

(20)

From studies of the Pictet-Spenger reaction using superacidic conditionskinetic evidence for superelectrophilic intermediates was reported22 WhileN -methylene-2-phenethylamine (28a) reacts slowly or not at all withstrong acids in 90 CF3SO3H10 CF3CO2H (ww H0 minus125 100equivalents) the cyclization product is obtained in 76 yield (eq 21)When a variety of aldimines were reacted in 100 CF3SO3H the cycliza-tion occurred in good yields For example compounds 28b and 28c gavethe cyclized products (eqs 22 and 23)

N

90 CF3SO3H 10 CF3CO2H

NH50degC 1 h

7628a

(21)

N

CF3SO3H

NH

69

28b

150degC

(22)

N

Ph

28c

NH

Ph 90

29 30

CF3SO3H

150degC

31

N

Ph

H+

N

Ph

HH

++

(23)in CF3SO3H In 100 CF3CO2H the starting aldimines (28b-c) wererecovered unreacted NMR analysis indicated that the imines are com-pletely protonated in CF3CO2H The proton bound to the imine nitrogenappears as a doublet at δ 112 for ion 29 The authors noted that despitebeing fully protonated in CF3CO2H 28b and 28c were unreactive towardscyclization In kinetic studies the imines were dissolved in solutions ofvarying acidity and the formation of products was monitored by 1H NMRIt was found that cyclizations occur at signiTHORNcant rates when the solutionsare more acidic than H0 minus105 The cyclizations showed good THORNrst-orderkinetics with reaction rates increasing steadily as the acidity of solutionincreased (Figure 1) Reaction rates should level off if the monoproto-nated imine is the intermediate leading to cyclization because the imines

KINETIC STUDIES 29

28a28c28d28e

minusH0

log

k

minus55

minus5

minus45

minus4

minus35

105 11 115 12 125

28a

28c

N

N

28d

28e

N

N

Cl

CH3

Figure 1 Acidity-rate proTHORNles of the superacid-catalyzed Pictet-Spengler cyclizations22

are fully protonated at acidities as low as H0 minus27 (CF3CO2H) Electrondonating groups (alkyl) on the phenethyl aryl group increased the reactionrate suggesting that cyclization is involved in the rate-determining stepThe linear correlation between acidity and reaction rates indicates thatdiprotonated superelectrophilic intermediates such as 30 were involvedin the cyclization leading to the cyclized product 31

A hallmark of superelectrophilic reactivity is often the greatly increasedyields and reaction rates dependent on increasing acidity While absolutereaction rate constants can be obtained from kinetic studies and indicateevidence for superelectrophilic activation qualitative evidence can also beobtained from realitive reaction rates For example in a study involving anacetophenone derivative 222-triphenylacetophenone (32) was convertedto 910-diphenylphenanthrene (36) in quantitative yield in reactions car-ried out in superacid (Scheme 5)23 The relative reaction rate is foundto increase with acidity and the exclusive product (36) is formed only insolutions more acidic than about H0 minus12 (limit of superacidic solutionTable 1) Acetophenone is fully protonated in acidic media stronger thanH0 minus1224 and 222-triphenylacetophenone should exhibit a similar basic-ity This suggests the involvement of the diprotonated superelectrophilicspecies 34 Formation of the superelectrophile 34 leads to a retro-pinacolrearrangement and subsequent cyclization


PhPh

PhPh

OCF3SO3H

PhPh

minus2 H+

minusH2O

32 34

36

99

33 35

PhPh

Ph

H2OPh

+

+

PhPh

PhPh

OH2

+

+PhPh

PhPh

OH+

Scheme 5 Proposed mechanism for the condensation of ketone 32

Table 1 Relative yields of product 36 with varying acidity

Acid System

Acidity (H0)

(CF3SO3H-CF3CO2H

ww

)Product

Ratio (3236)

minus141 100 CF3SO3H 0100minus125 728 0100minus115 435 3070minus106 221 1000minus27 100 CF3CO2H 1000

Reaction conditions compound 32 (50 mg) benzene (05 mL) and acid(05 mL) reacted at 25C for 24 h

Superelectrophilic intermediates were also proposed in the cyclizationreaction of α-(methoxycarbonyl)diphenylmethanol (37) with superacid(eq 24)25 The yield of cyclized product is found to increase dramaticallywith increasing acidity of the reaction medium The conversion is believed

ACID

O

OCH3

minus40degC

YIELD

minus27

0

minus118

20

minus132

94

H037 38

O

OCH3

HOOH

OCH3

+

+

(24)

KINETIC STUDIES 31

to involve the dicationic intermediate (38) that further reacts by a con-rotatory electrocyclization The involvement of the superelectrophile wasfurther supported by kinetic experiments and theoretical calculations asdescribed in more detail in Chapter 5

Several types of 12-dicarbonyl compounds have been studied in super-acid and their chemistry indicates the involvement of superelectrophilesOne of the earliest studies involved the chemistry of 23-butanedione(39) which condenses rapidly with benzene in CF3SO3H (Scheme 6)in good yield26 It was proposed that the dicationic intermediates (40)and (41) are formed under the superacidic conditions and these superelec-trophiles lead to product formation As expected with superelectrophilicactivation the reactivity of 39 drops off rapidly with decreasing acidstrength While the yield of product 42 is 94 in CF3SO3H (H0 minus141)and 94 in 50 CF3SO3H 50 CF3CO2H (H0 minus120) the reactionis slower in the later case The product yield falls to 62 at H0 minus11(20 CF3SO3H 80 CF3CO2H) and no reaction is observed at H0 minus8(6 CF3SO3H 94 CF3CO2H) Further evidence for superelectrophile40 was obtained from 1H and 13C NMR studies in superacid solutionsof 39

In acid-catalyzed reactions of cyanides with arenes (Gattermann reac-tion) the yield of products and relative reactions rates are found to cor-relate with the acid strength of the media20 The reaction of either NaCNor trimethylsilyl cyanide (TMS-CN) with benzene in superacid gave thebenzaldimine which upon hydrolysis yielded benzaldehyde (eq 25) Thereactions were found to give reasonable yields (gt 40) of product only

H3CCH3

O

OCF3SO3H

C6H65 min

H3CCH3

O

OHH

H3CCH3

O

94

39

42 41

++

40

H3CCH3

OH

OH+

+

H3CCH3

OH+

+

Scheme 6


when the acidity of the solution was stronger than H0 = minus14 and gaveexcellent yields when acidity was H 0 lt minus18 (Table 2) Since the pKBH+of hydrogen cyanide (43) is between minus10 and minus11 hydrogen cyanideis more than half protonated in CF3SO3HCF3CO2H (5050 H0 = minus12)This suggests that it is not the monoprotoned hydrogen cyanide (44 eq 26)

acidC

NH2

H

H2OC

O

HNaCN orTMS-CN

+

(25)

H+

H C NH+

H+

H C N H+ ++

H C NH

H

NaCN orTMS-CN

4443 45

(26)

that reacts with benzene but a second protonation generates the superelec-trophilic species (45) which is sufTHORNciently reactive to give the product

As noted previously in Chapter 1 the electrophilic reactivities of acetylsalts increase dramatically as the acidity of the reaction medium increasesThis was one of the observations that lead Olah and co-workers to THORNrstpropose the concept of superelectrophilic activation or protosolvation ofthe acetyl cation in 19752 This seminal paper described the chemistryof acetyl hexaszliguoroantimonate (CH3CO+SbF6

minus) and the reaction withalkanes in various solvents In aprotic solvents such as SO2 SO2ClFAsF3 and CH2Cl2 there was no reaction However in HF-BF3 acetylsalts react with iso-alkanes and efTHORNcient hydride abstraction is observed27

This was interpreted by Olah as evidence for protonation of the acetyl

Table 2 Reaction of benzene with cyanides to give benzaldehde

Cyanide Acid H0 Time min Yield

NaCN 23 TfOH 77 TFA minus106 300 055 TfOH 45 TFA minus118 300 380 TfOH 20 TFA minus127 300 11100 TfOH minus140 30 441 SbF5 99 TfOH minus168 30 655 SbF5 95 TfOH ltminus18 5 92

TMS-CN 20 TfOH 80 TFA minus100 720 055 TfOH 45 TFA minus118 300 280 TfOH 20 TFA minus127 30 17100 TfOH minus140 30 555 SbF5 95 TfOH ltminus18 5 99

TfOHCF3SO3H TFACF3CO2H

SPECTROSCOPIC STUDIES 33

Table 3 Yields of acetylated product from the reaction ofchlorobenzene with CH3CO+SbF5

minus in solutions of varyingacid strength

Acid H0 Yielda

100 CF3CO2H minus27 020 CF3SO3H 80 CF3CO2H minus100 940 CF3SO3H 60 CF3CO2H minus120 21100 CF3SO3H minus141 321 SbF5 99 CF3SO3H minus168 485 SbF5 95 CF3SO3H lt minus18 82

salts Similarly acetyl salts show heightened reactivities with aromaticsubstrates in solutions of increasing acidity For example it was found byShudo and Ohwada that acetyl hexaszliguoroantimonate (CH3CO+SbF6

minus)and benzoyl hexaszliguoroantimonate (C6H5CO+SbF6

minus) salts acylate aro-matic compounds most effectively in highly acidic solution20 In the caseof chlorobenzene the acetylated product is formed in 0 to 32 to 82yield for progressively stronger acid systems (Table 3) NMR studiesruled out solubility of the salts as an explanation for the increased reac-tivity Similar results were obtained with the benzoyl cation Togetherwith the results obtained from other work these data suggest theformation of the protioacyl dications 46 and 47 in the highly acidicsolutions

H3C C O H3C C OH

46

C O C OH

47

H+H++ + + + + +

These examples illustrate how electrophilic systems can exhibit en-hanced reaction rates and yields with increasing strength of the acidicreaction media Both qualitative and quantitative kinetic studies stronglysuggest the involvement of superelectrophilic species in reactions

24 SPECTROSCOPIC STUDIES

Similarly as spectroscopic techniques have been used to study manylong-lived electrophilic species such as carbocations acyl and carbox-onium ions and various onium ions they have also been used in anumber of reports directed to characterization of superelectrophiles Bothcondensed and gas phase techniques have been used to study superelec-trophilic systems In the condensed phase however superelectrophiles are


generally formed in equilibria containing only low concentrations or withvery short lifetimes Consequently their direct observation has frequentlynot yet been possible In some cases however they are persistent enoughfor spectroscopic methods even NMR studies

Nuclear magnetic resonance (NMR) spectroscopy has been used todirectly observe varied persistent superelectrophilic species Although 1Hand 13C NMR have been the most often used techniques there have alsobeen applications of 15N 17O and 19F NMR in their structural char-acterization Coupled with theoretical computational methods capable ofestimating NMR chemical shifts these studies have been very useful inthe study of superelectrophiles

It was reported that arylpinacols (48a) can undergo a superacid-catalyzed dehydrative cyclization to give the aryl-substituted phenan-threnes (eq 27)23 Superelectrophilic intermediates were proposed in theconversion Tetraarylethylene dications have been studied by several meth-ods and were observed directly by NMR as well as by UV-vis spec-troscopy and X-ray crystallography28 The low temperature oxidation oftetraarylethylenes gives the dicationic species (50 eq 28)

XXCF3SO3H

48a X = OH 49

(27)

SbF5

RR

R R

SO2ClF

minus78degC

RR

R R

50R = H NMe2 OCH3

Heat

minus2H+

RR

R R

+ +

(28)

1H and 13C NMR studies of the dichloride (48b X = Cl) with Lewis acid(SbF5 or SbCl5) showed only the cyclized phenanthrene product Theincipient dication (50) in this case was not observed


In several recent studies nitro-substituted oleTHORNns have been shown toexhibit high electrophilic reactivities in superacid-promoted reactions29

NMR studies have been used to identify some of the superelectrophilicintermediates in these reactions For example it was found that nitroethy-lene reacts with benzene in the presence of 10 equivalents of CF3SO3Hto give deoxybenzoin oxime in 96 yield (eq 29) Since the reactiondoes not occur with only one equivalent of TfOH it was proposedthat the NN -dihydroxy-iminium-methylium dication (51) is generatedIn spectroscopic studies 1-nitro-2-methyl-1-propene (52) was dissolved inCF3SO3H and at minus5C the stable dication (53) could be directly observedby 1H and 13 C NMR spectroscopy (eq 30)

NO

O

CF3SO3H

C6H6

0degC

NOH

OH

N OH

51 96

++

(29)

53

NO

O

H3C

CH3

52

13C NMR Data (ppm)

NOH

OH

H3C

CH3

266 1999 1303

296

CF3SO3H

NOH

OH

H3C

CH3

++

+ +

C6H6

minus5degC

(30)

Based on chemical shift data it is clear that a considerable amountof positive charge resides at the C-2 position of the nitrooleTHORNn The twomethyl groups on dication 53 are however nonequivalent indicating slowrotation around the C1C2 bond (partial double bond character) Simi-larly diprotonated intermediates were suggested to be involved in thereactions of β-nitrostyrene and nitro-substituted naphthalenes (Scheme7 and 8) Superelectrophilic intermediates 54 and 55 were proposed inthe reactions with superacidic CF3SO3H The involvement of these inter-mediates was supported by their direct observation using 1H and 13CNMR in superacidic solvents When (E )-β-nitrostyrene is dissolved inCF3SO3H at minus20C spectral data are consistent with the diprotonatedspecies 54 Double protonation at the nitro group generates positive chargeat the C-2 position which is reszligected in the deshielding of this car-bon When the same NMR experiment was done with (Z )-β-nitrostyrenethe NN -dihydroxyiminium benzyl dication (54) is likewise observed


NO

O

CF3SO3H NOH

OH

NOH2

OHNOH

C6H6

1651 128313C NMR Data (ppm)

54

C6H6

C6H6

+minus N

OH

OH+

+ + +

++

Scheme 7

NO2

C6H60degC

NH2

Ph

NH2

Ph

NH2

Ph

Ph

NHO OH

NHO OH

55

CF3SO3H+ +

+

+

++

Scheme 8

indicating free rotation about the C1-C2 bond In the reaction of1-nitronaphthalene with CF3SO3H (30 equiv) and benzene phenylatedproducts were obtained (Scheme 8)30 These Freidel-Crafts-type reactionsare consistent with the formation of dicationic electrophilic intermediates(55) The dication 55 was characterized by 1H 13C and 15N NMR spec-tra When compared with the spectrum from the weaker acid CF3CO2Hthe naphthalene ring carbons are more deshielded in the superacid(CF3SO3H) indicating delocalization of positive charge into the ring sys-tem Similar results were obtained for the 2-nitronaphthalene system


In a study involving the superacid-catalyzed reaction of amino-alcoholsa chiral dicationic electrophile was observed by low temperature 13CNMR31 Ionization of benzylic alcohols in superacids can generate stablecarbocations such as the trityl cation Because of the resonance stabi-lization of the carbocationic centers they are fairly weak electrophilesincapable of reacting with benzene (eq 31) However it was shown thatadjacent ammonium groups can increase the electrophilic reactivities ofthe diphenylethyl cations (eq 32)

CH3

HOPh

Ph

CF3SO3H

C6H6

CH3

Ph

Ph

Aqueous

Workup

Ph

Ph+ (31)

PhNH2

OH

CH3

Ph

PhNH2

CH3

PhPh

CF3SO3H

C6H6

PhNH3

CH3

Ph

80

56 57

C6H6+

+ (32)

When the amino alcohol (56) is ionized in FSO3HSbF5SO2ClF atminus40C a clean NMR spectrum is observed for the reactive dicationicelectrophile (57 Figure 2) showing the carbocationic resonance at δ13C2115

Carboxonium ions are indicated to be involved in a number of super-electrophilic reactions In several cases the direct observation of thesuperelectrophiles and reactive dications has been possible using low

200 180

57Ph

d 6-A

ceto

ne

d 6-A

ceto

ne

++Ph

CH3

H3N

160 140 120 100 80 60 40 20 ppm

Figure 2 13C NMR spectrum of dicationic electrophile 57


temperature stable ion conditions For example the condensations of theketones and aldehydes occur in high yields in CF3SO3H (eqs 3337)3234

CH3

N

O

H3CCH3

N

OH

H3C H3C

NOH

CH3

PhPh

75

HO HHO

58

CF3SO3H

C6H6

+

+

(33)

N

O

O

CH3 N

HO

OH

CH3 N

O

CH3

Ph

Ph

59

CF3SO3H

C6H6

75

+

+

(34)

CF3SO3H

C6H6

99 PhP

PhPh

CH3

Ph

Ph

Cl

Ph P OH

PhPh

Ph P O+ + ++

minus

minusPh

PhCH3

Br

60

CH3(35)

N

H

O N

H

HN+ +

H

OH

61

C6H3Cl2

C6H3Cl2CF3SO3H

o-C6H4Cl

87

(36)

CF3SO3H

C6H6

74ndash99

NN

Rprime

R

O

H

NN

Rprime

R

HO

H

+

+

H NN

Rprime

RH

PhPh

62

(37)

The proposed dicationic carboxonium ion intermediates (5862) havebeen directly observed by 13C NMR A more detailed description of thissuperelectrophilic chemistry is found in chapters 5-7

A comprehensive series of ionic hydrogenation reactions have beenstudied by Koltunov Repinskaya and co-workers and superelectrophilicintermediates have been proposed34 Some of these intermediates havebeen characterized by 1H and 13C NMR (Table 4) Many of these dica-tionic intermediates have been shown to react with cyclohexane by hydrideabstraction indicating superelectrophilic character

As mentioned previously superelectrophilic intermediates were pro-posed in the reaction of α-(methoxycarbonyl)diphenylmethanol (37)


Table 4 Superelectrophilic intermediates observed by 1H and 13C NMRspectroscopy and capable of hydride abstraction from cyclohexane34

(1)

(2)

(3)

(4)

(5)

(6)

(7)

Entry Superelectrophile

NOH

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

HF-SbF5

minus30degC

HF-SbF5

minus30degC

ACID

minus30degC

NOH H

H H

OH OHH H

OHH H

HH

78 22

OH OHH H

HH

33 67Cl

Cl

Cl

HF-SbF5

OHH H

80 20Cl

Cl

OHH

H

Cl

OHH

HH

H

FSO3H-SbF5

0 100

OH

N

OH

N

OHH H

H

N

OH

N

OH

H H H

OH

NH2

OH

NH3H H

+ +

+

++

+

+

+

+

+

+ +

+

+

+

H+

+

H+

H+


and related compounds with superacid (eq 38 R=H)25

CF3SO3H

minus20degC

O

OCH3OH

OCH3

65 R = minusOCH3

O

OCH3

HO

37 R = H64 R = minusOCH3

R

R

R

R

R

R63 R = H

+

+

(38)

Both kinetic and theoretical studies support the involvement of dica-tionic intermediates Spectroscopic studies were also used to conTHORNrm theinvolvement of superelectrophiles However compound 37 does not pro-duce an NMR observable superelectrophilic intermediate in FSO3HSbF5at minus50C Because the cyclization reaction occurs so rapidly only thecyclized product 63 (in its protonated form) is seen in the low tem-perature NMR experiments When the system was further stabilized bypara-methoxy groups the dicationic intermediate (65) however wasobserved as a cleanly formed species in CF3SO3H In the 13C NMR spec-trum the carbenium ion resonance is observed at δ13C+ 1760 while thepara-carbons are at δ13C 1747 Based on the chemical shifts the authorsconcluded that the carbocation is largely delocalized in the para-methoxyphenyl rings The delocalization of charge is thought to be important inthe activation of the electrocyclization reaction step leading to productformation

In addition to the direct observations of some dicationic superelec-trophilic intermediates NMR spectroscopy has been also used in someof the previously discussed kinetic studies For example in the case ofthe szliguorene cyclization (eq 38) the alcohol (37) was dissolved in mix-tures of CF3SO3H and CF3CO2H (using large excess of acid ) at lowtemperature25 The cyclization reaction rates were then determined by1H NMR by following the disappearance of the starting material Thecyclization was found to exhibit good pseudo-THORNrst order kinetic behav-ior By repeating the experiments with differing ratios of CF3SO3H andCF3CO2H the acidity of the media was systematically varied and thereactions rate constants were shown to increase linearly with acidity Thisobservation strongly supports the proposed role of superelectrophiles inthe conversions

In superacids many superelectrophiles capable of π -delocalization gen-erate vividly colored solutions Despite the strong absorptions in the


visible range of the electromagnetic spectrum there have been so far nosystematic studies of the UV-visible spectra of superelectrophilic speciesNeither has UV-visible spectroscopy by itself been used to study super-electrophiles UV-visible spectroscopy has been however used in somestudies to estimate the pKBH+ of monoprotonated species such as pro-tonated ketones36 Based on pKBH+ values it then becomes possible toestimate the acidity range at which a substrate is completely protonatedIf increasing acidity of the medium leads to new chemistry or increasingreaction rates then it can be used to probe for diprotonated or superelec-trophilic intermediates Superelectrophiles as mentioned generally areformed in low concentration and may be in equilibrium with stronglyabsorbing monocationic species Therefore UV-visible spectroscopy isexpected to have only limited value in the studies of π -delocalized super-electrophiles

Infrared and Raman are also rapid spectroscopic techniques that havebeen useful in the characterization of electrophiles in the condensed phaseMany superelectrophiles are expected to possess characteristic or newvibrational modes The harmonic vibrational frequencies and infraredintensities for the nitronium ion (NO2

+) and protonitronium ion (HNO22+)

have been estimated using ab initio molecular orbital calculations(Table 5)37 Although the vibrational modes for the superelectrophile(HNO2

2+) clearly differ from that of the monocation data were so far notreported for the superelectrophile using infrared and Raman spectroscopyWhen nitronium salts were dissolved in excess HF-SbF5 no apparent

Table 5 Calculated harmonic vibrational frequencies(cm1) and infrared intensities (KM mol1)37

HF6-31G MP26-31GHF6-31G MP26-31G

ω I ω I

O = +N = O 2760 190 2526 1717

2660 1773 2415 191426 3 1246 21006 540 884 408682 0 553 21630 50 541 51

O = +N = OH 2654 919 2566 62

1682 0 1302 0750 5 601 3


changes were observed in the Raman frequencies and no new absorptionswere observed in the infrared spectrum The failure to observe the super-electrophile (HNO2

2+) by vibrational spectroscopy may be attributed toits formation in only low equilibium concentration

An impressive application of infrared and Raman spectroscopy wasdemonstrated in studies of superelectrophilic diprotonated thiourea[H3NC(SH)NH2]2+bull2AsF6

minus The Raman spectrum (taken at minus110C)corresponded reasonably well with calculated vibrational bands predictedby density functional theory38 Coupled with computational methods forpredicting vibrational frequencies it is expected that vibrational spectro-scopic techniques will be useful for the observations of these and othersuperelectrophiles

25 GAS PHASE STUDIES OF SUPERELECTROPHILESAND RELATED IONS

There has been continuing interest in the study of multiply charged speciesin the gas phase using mass spectroscopic techniques39 The small dica-tionic and tricationic structures in these gas phase studies are clearlyrelated to superelectrophiles generated in the superacidic condensed phaseAmong the techniques used in these studies electron ionization (EI) is wellknown as a source of persistent multiply charged ions of small size Inthe case of dicationic species these ions can be generated by direct ion-ization of neutral molecules with the loss of two electrons or by stepwiseelectron ejection processes involving THORNrst a monocation and then a dica-tion Multiply charged ions have also been generated by photoionizationHowever this technique can be problematic because the multiply chargedcations are sometimes generated in an excited state which can lead torapid dissociation due to Franck-Condon effects Another useful approachhas been through the use of charge stripping (CS) techniques39 Goodthermochemical data have also been obtained using CS experiments In atypical CS experiment a mass-selected monocation M+ is collided with asuitable target gas (often O2) to provide the dication M2+ (eq 39) Anal-ysis of the kinetic energies of the cation M+ and dication M2+ can thenprovide a good approximation of the vertical ionization energy of mono-cation M+ A similar approach is used in double-charge transfer (DCT)spectroscopy (eq 40)

M+ + T minusrarr M2+ + T + eminus (39)

P+ + M minusrarr Pminus + M2+ (40)

GAS PHASE STUDIES OF SUPERELECTROPHILES AND RELATED IONS 43

DCT experiments involve colliding a monocationic projectile (P+) with atarget molecule of interest (M) The dicationic product (M2+) is formedfrom the collision and kinetic energy analysis of the anionic product (Pminus)can give information about the electronic states of M2+ Electrosprayionization (ESI) is another method of generating multiply charged ionsin mass spectral studies This technique involves generating ions from asolvation sphere However there is the limitation that the highly chargedspecies can either react with the solvent or resist decomplexation fromthe solvent An interesting approach suggested by Schroder and Schwarzinvolves the direct use of liquid superacids as solvents for electrosprayionization techniques with the goal of generating superelectrophiles fromdesolvation39a Present ESI technology however limits the use of highlycorrosive superacidic solvents

Unlike superelectrophiles generated in the condensed phase the gasphase species are not stabilized by solvation or association to counterions The stabilities of multiply charged small ions are dependent on theirtendencies to dissociate into fragments in the gas phase39 For diatomicsystems there are two possible routes of dissociation to atomic fragmentsthe cleavage to a pair of monocations (eq 41) or cleavage to a dicationand neutral species (eq 42)

XY2+ minusrarr X+ + Y+ (41)

XY2+ minusrarr X2+ + Y (42)

Cleavage of the dication (XY2+) to a pair of monocations is sometimesreferred to as coulombic explosion Cleavage of the dication (XY2+)to a dication and neutral species is simply the reverse reaction of anelectrostatic intereaction between the dicationic X2+ and a neutral atomSmall dicationic (or tricationic) species may be observable in gas phasestudies when the dication rests in a global energy minimum or rests in alocal minimum protected from dissociation by an energy barrier

Several types of densely charged cationic molecules have been gener-ated and observed using mass spectrometry techniques (Table 6) Rare gasclusters have been of interest to experimentalists and theoreticians sinceas mentioned Linius Pauling THORNrst predicted the stability of He2

2+ in the1930s A number of these clusters have been experimentally observed40

Other types of dicationic and trication species studied in the gas phaseinclude metal halides oxides sulTHORNdes selenides diatomic species andhalogenated carbons Among the oxides the protonitronium dication(HONO2+) was observed by Schwarz and associates in the gas phaseby dissociative electron ionization41 Attempts to observe HONO2+ by


Table 6 Experimentally observed gas phase dicationic andtricationic speciesa

Rare Gas Clusters GeNe2+ GeAr2+ GeKr2+ PtHe2+ He22+

XeNe2+ KrHe2+ XeHe2+ ArNe2+ VHe2+

Metal Halides MgF2+ AIf2+ SiF2+ TiF2+ BaF2+UF2+ MgCI2+ FeCI2+ SrCI2+ BaCI2+CaBr2+ BaBr2+ Bal2+ SF3+ TIF3+VF3+ UF3+ UF2

3+

Oxides SulTHORNdesand Selenides

UO2+ HONO2+ VO3+ COS3+ SO23+

CS3+ CS23+ CSe2

3+

Diatomics B23+ S2

3+ CI23+ Br23+ I23+

Halogenated Carbon CCI22+ CF22+ CF3

2+

aAdapted from reference 39a references cited therewithin

charge stripping methods were so far not successful as this ionizationmethod produces a species in a vibrationally excited state leading to rapiddissociation to monocationic fragments The protonitronium dication wasgenerated in the gas phase from electron impact (100-eV electrons) ofHNO3 The resulting ion at mz 235 is assigned to the protonitroniumdication (HONO2+) The observation of the protonitronium dication isconsistent with theoretical calculations that predict the structure to residein a potential energy well slowing the deprotonation reaction path to H+and NO2

+ or the dissociation reaction path leading to OH+ and NO+In another study the C2H4O2+ dications were studied by theoretical andexperimental methods42 These gas phase experiments found evidencefor the protioacetyl dication (CH3COH2+) which could be produced bycharge stripping experiments from CH3COH+bull The mass spectroscopystudies conTHORNrmed theoretical predictions that the protioacetyl dication wasat a potential energy minimum protected by a signiTHORNcant barrier to dissoci-ation As mentioned the protonitronium dication and the protioacetyl dica-tion were the THORNrst superelectrophiles to be proposed in superacid-catalyzedchemistry Subsequent gas phase techniques have proven to be useful inthe direct study of these superelectrophiles

Mass spectrometric techniques also enable experimentalists to reactdications and trications with neutral substrates in the gas phase to explorethe chemical reactions of these multiply charged species Although onlya few superelectrophiles have thus far been examined experimentally fortheir gas phase chemical reactivities other electrophilic gas phase reac-tions have demonstrated the potential of these methods For example the


nobium dication can be generated in the gas phase and it reacts withmethane by a dehydrogenation reaction to produce a stable NbCH2

2+species (eq 43)43

Nb2+ + CH4 minusrarr NbCH22+ + H2

CH4minusminusrarrminusH2


NbC5H62+ + NbC6H6

2+

(43)The dicationic product (NbCH2

2+) is itself highly electrophilic and reactsfurther with up to six molecules of methane to yield dicationic productslike NbC6H6

2+ There have also been a number of reports of stable dica-tionic systems in which an electrophilic species coordinates with substrates(6668)44

[CF2bullH2]2+ [CCl2bullCl2]2+ [CrbullO2]2+66 67 68

For example when CF22+ was generated and reacted with H2 a long-lived

intermediate (66) was observed It is proposed to have a structure in whichH2 is coordinated with the CF2

2+ although new covalent bonds are notbelieved to be formed The complex itself dissociates to the monocationsCHF2

+ and H+ When dicationic carbon tetrachloride is generated theion rearranges to a C2v structure thought to involve coordination of Cl2and CCl22+ (67) Similarly side-on coordination of O2 was proposed inthe chromium complex 68 A gas phase reaction has also been describedfor HCBr2+ and molecular hydrogen44e

Roithova and Schroder have demonstrated that a dicationic species canparticipate in carbon-carbon bond forming reactions in the gas-phase andthat this is a potential route to polycyclic aromatic hydrocarbons45 WhenC7H6

2+ is generated (from double ionization of toluene) and allowed toreact with acetylene new ions C9H7

2+ and C9H62+ are detected (eq 44)

C6H5CH3

minus2eminus

C7H62+

HC CH

+ C9H62+C9H7

2+ (44)

Experiments with deuterated species show extensive HD scramblingwhich implies longer-lived intermediates in the reaction Calculationsat the B3LYP6-311+G(2dp) level suggest that the reaction pathwayinvolves bond formation between the cycloheptatrienylidene dication andacetylene followed by isomerization and hydrogen loss (Scheme 9) Theauthors of this study note the possibility of similar chemistry generatingpolycyclic aromatic compounds in interstellar space


C

CC C

CCC

HH

H

H

HH

2+

HC CH

Erel = 000 eV Erel = minus068 eV Erel = minus040

C

CC C

CCC

HHH

H

HH

C C HH 2+

C

CC

C

CC

CC

CH H

H

HH

H

H

H2+

Erel = minus144 eV

C

CC

C

CC

CC

CH

H

HH

H

H

H2+

Erel = minus126 eV

C

CC

C

CC

CC

CH

H

HH

H

H2+

minusHminusH2

+

Scheme 9

Although there are many experimental challenges to observing super-electrophiles by mass spectrometry gas phase techniques have someapparent advantages over condensed phase studies Mass spectroscopicstudies are extremely sensitive and consequently dicationic or tricationicsuperelectrophiles can be detected and studied despite being short-livedAs noted previously many superelectrophiles are formed in very low con-centrations in equilibria with conventional monocationic electrophiles (inthe condensed phase) Depending on the methods by which the super-electrophiles are generated gas phase studies may be able to excludethe effects of these equilibrium reactions Finally gas phase studies havealready been demonstrated to provide good thermochemical data and thesedata can be compared with those from theoretical calculations

26 CALCULATIONAL METHODS

Quantum mechanical calculations are an essential part of chemistry andthese methods have been extremely useful in studies of superelectrophilicchemistry For example computations have been used in some stud-ies to show that the formation of dicationic superelectrophiles lowers

CALCULATIONAL METHODS 47

the activation energy for chemical conversions when compared withthe similar reaction involving singly charged cationic electrophiles Inother studies high-level calculations were used to estimate the amountof positive charge at each of the relevant atoms of a superelectrophileThe centers of highest positive charge were then shown to also be thelocations of nucleophilic attack Studies have also been done to relatesuperelectrophilic character to global electrophilicity indexes and localelectrophilicity (related to its electrophilic Fukui function fk+) In con-junction with spectroscopic studies theoretical methods are often used topredict NMR chemical shifts or spectral absorption frequencies of super-electrophiles Many superelectrophiles have also been studied using highlevel ab initio calculations to THORNnd optimized geometries and the energiesof the optimized structures

An example of the application of theoretical methods comes from astudy of diphenylmethyl cations having electron-withdrawing substituentsOver the years somewhat conszligicting reports were published related tothe chemistry involving diphenylmethyl cations Depending on the condi-tions of the experiment three types of major products have been reportedfor the reaction of the diphenylmethyl cation 69 (eq 45)25 Products 70and 71 are thought to form by conrotatory electrocyclization reactionsinvolving cationic intermediates For monocation 69 the transition stateenergy for the szliguorene cyclization is estimated to be 805 kcalmol abovethe transition state for the benzofuran cyclization (B3LYP6-31+ZPE)These results are consistent with experimental studies in that less acidicconditions tend to favor monocationic intermediates and benzofuran (70)products When the O-protonated dicationic species (72) is studied theenergy barrier to szliguorene cyclization dramatically decreases

OHacid

+ +

+O

69

CF3SO3H +

+OH

70

O+

OO

71

69 72(45)

Dication 72 is estimated to have a szliguorene cyclization barrier of 852 kcalmol compared with a value of 2504 kcalmol for the cyclization of


monocation 69 The theoretically predicted barriers to cyclization are alsoin accord with the thermodynamic values obtained from kinetic experi-ments Moreover these results are consistent with the high yield formationof the szliguorene product (71) in superacid

In a study of the Nazarov cyclization and related reactions theoreticalcalculations were used to show that formation of dicationic superelec-trophiles signiTHORNcantly lowers the energy barriers for concerted electrocy-clization reactions18 In ab initio calculations at the B3LYP6-31G theorylevel 14-pentadien-3-one (73) and 1-phenyl-2-propen-1-one (78) wereused as models for the acid-catalyzed cyclization (Scheme 10) Whencomparing monocationic (74 and 79) and dicationic intermediates (75and 80) the energy barriers for the conrotatory 4π -electrocyclizationsare considerably lower for the dications Cyclization of the dication 75is estimated to have an energy barrier about 12 kcalmol less than thecyclization involving the monocation 74

Computational methods have also been used frequently to estimate thethermodynamic stabilities of superelectrophiles These calculations haveoften involved the estimation of barriers to gas phase dissociation ordeprotonation and the proton afTHORNnities of conventional electrophilic inter-mediates Other useful studies have calculated the heats of reactions forisodesmic processes An interesting example of these calculations comesfrom a study of the protoacetyl dication (CH3COH2+)42 In calculationsat the 6-31G4-31G level of theory the protoacetyl dication (83) is esti-mated to react with methane by hydride abstraction with a very favorable

O

78

+OH

+OH2OH

O

73

+OH +OH2

+

+OH2

+ + + +

ΔE = 1827 kcalmol

ΔE = 616 kcalmol

ΔE = 1827 kcalmol

OH

74 7975

+OH2

ΔE = 1237 kcalmol

80

76 77 81 82Transition State Structures

Scheme 10


enthalpy of reaction (eq 46)

H3CC

OH

H3CC

OH

HCH4

ΔHdegR = minus160 kcalmol

CH3

46 83 84

++

+

+

++

(46)

It was concluded that separation of charge is the dominant driving forcefor the reaction

In superacid catalyzed reactions of hydroxyquinolines and isoquino-lines dicationic superelectrophiles were proposed as intermediates in theirreactions (see Table 4)35d In order to explain differences in relativereactivities between the isomeric superelectrophiles the energies of thelowest unoccupied molecular orbitals (εLUMO) the square of the coefTHORN-cients (c2) at the reactive carbon atoms and the NBO charges (q) onCH groups were determined by MNDO and DFT computational methodsFor example 8-hydroxyquinoline (85) is found to be more reactive than6-hydroxyquinoline (87) in the superacid catalyzed reactions with benzeneand cyclohexane (eqs 4748)

N

OH

CF3SO3H-SbF5

NH

OH85 86

++ (47)

NH

HO

88

N

87

HOCF3SO3H-SbF5

+

+(48)

When the εLUMO for dication 86 is compared with the εLUMO for dication88 dication 86 has a LUMO of much lower energy Thus lower εLUMOvalues correspond to increased electrophilic reactivities These studies alsosuggested the importance of atomic charge q at a reaction center indetermining the reactivity from a kinetic point of view A more detaileddiscussion of this chemistry is found in Chapter 7

Calculations by Perez have examined superelectrophilic species withinthe context of both electron deTHORNciency and polarizability of the activesites of superelectrophiles46 Using the model equation proposed by Parrand associates

ω = μ22η


where μ is the electronic chemical potential and η is chemical hard-ness (these values being estimated by the one-electron energies derivedfrom the frontier molecular orbitals HOMO and LUMO) the global elec-trophilicity index (ω) was calculated for several types of superelectrophilicsystems (Table 7) In all cases the superelectrophilic species (H4O2+H2C(OH2)2+ and HC(OH)(OH2)2+) are found to have signiTHORNcantly great-er electrophilicities than the corresponding neutral or monocation speciesIt is noted that the calculations indicate the enhanced electrophilicitymainly results from their remarkably high electronegativity Further cal-culations were done to estimate the local electrophilicities at potentialreaction centers and this was done by taking into account the electrophilicFukui function (fk+) The results from these calculations show good agree-ment between the local electrophilicity index (ωc) and calculated NMRchemical shifts

Over the years computational methods have become increasingly accu-rate in their predictions of NMR chemical shifts for given structures47

The combination of ab initio-optimized geometries theoretically calcu-lated chemical shifts and experimental NMR data affords a powerfultool for structural determination Noncorrelated chemical shift methodssuch as IGLO (individual gauge for localized orbitals) and LORG (local-ized orbitallocal origin gauge) allow the prediction of NMR chemi-cal shifts and have been applied extensively to carbocationic structuresMore recently correlated chemical shift calculations have been used(GIAO-MP2 and SOPPA gauge-independent atomic orbital method andsecond-order polarization propagator approximation respectively) and a

Table 7 Estimated chemical hardness (η) electronic chemical potential (μ) andelectrophilicity indexes (ω)46

HOMO LUMO η (eV) μ (eV) ω (eV)

H4O2+ minus12954 minus06021 1886 minus2582 1767H4O+ minus07489 minus02700 1303 minus1386 737H2O minus02911 minus00627 963 minus311 050

H2C(OH2)2+ minus10243 minus06891 912 minus2331 2997H2COH+ minus06727 minus03773 804 minus1429 1270H2CO minus02685 minus00421 616 minus423 145

HC(OH)(OH2)2+ minus09377 minus05899 946 minus2078 2282HC(OH)+2 minus06400 minus03085 902 minus1290 922HCO2H minus02917 minus00008 792 minus398 100

aCalculations done at the B3LY6-31G(d) level


multiconTHORNgurational SCF version of IGLO has been applied to prob-lems requiring an MCSCF wave function There has been generally goodagreement between calculated NMR chemical shifts and experimentallydetermined values for a variety of NMR active nuclei and electrophilesFor example acetic acid mono and diprotonated acetic acid (89) theacetyl cation and the protioacetyl dication (46) have all been studied usingcomputational methods (Table 8 MP26-31GGIAO-MP2tzpdz levelof theory)48 In the case of protonated acetic acid fast proton exchangeleads only to one averaged 17O NMR signal and the experimentally deter-mined 13C and 17O NMR chemical shifts agree reasonably well with thosecalculated by theory Although the superelectrophilic species (89 46)havenot been observable using NMR experiments theory predicts the 17ONMR signals to be signiTHORNcantly deshielded by protonation Computationalstudies were also done on nitric acid the nitronium cation and the pro-tionitronium dication (3) with respect to 15N NMR spectra49 Comparsionto the experimentally determined 15N NMR chemical shifts of HNO3 andNO2

+ shows good agreement between experiment and theory Although15N NMR has not yet provided evidence for the protionitronium dication(3) 17O NMR suggests protosolvation in superacid and formation of 349b

The geminal superelectrophile H4O2+ (90) has likewise not been observedby NMR experiments but theory has been used to estimate the chemicalshift values of δ17O 507 and δ1H 136 for 1H NMR Although with the-oretical methods it has become possible to include solvation spheres incalculations of molecular structures and properties little or no effort hasbeen made to apply these types of calculations to the solvation of elec-trophiles in superacidic solvents If such calculations were to be donethen the predicted NMR chemical shifts for electrophiles in superacidswould become increasingly accurate

Many of the superelectrophiles that have been proposed in chemicalconversions have been studied by ab initio-computational methods Thesecalculations generally determine the optimized geometry of the superelec-trophile and calculate the potential energy of the species These results arethen used to further understand the superelectrophilic chemistry Many ofthe structures calculated to date are shown in Table 9 The table generallylists only the highest-level calculations and references to earlier calcu-lations or those at lower-levels may be found in the cited manuscriptsMoreover a vast number of doubly and multiply charged species havebeen proposed from mass spectroscopy studies and related plasma studiesThese charged species have often been studied in both ground and excitedstates by high-level computational methods A comprehensive descriptionof these species is outside the scope of this text but the interested readermay consult one of the recent reviews39


Table 8 Calculated and experimental NMR chemical shiftsa

Calculated NMR Chemical Experimental NMR ChemicalCompound Shifts (δ ppm)b Shifts (δ ppm)b

CH3CO2H 13C1 1719 13C2 207 13C1 1769 13C2 20817O1 1943 17O2 4134 17O12 2510

CH3C(OH)2+13C1 2020 13C2 217 13C1 203717O1 2283 17O2 2312 17O 1930

CH3C(OH)(OH2)2+ 13C1 2034 13C2 247 Not Observed

89 17O1 1482 17O2 2942

CH3CO+ 13C1 1557 13C2 63 13C1 150317O 3438 17O 2995

CH3C(OH)2+ 13C1 1576 13C2 48 Not Observed

46 17O 1946

HNO315N 3668 15N 3770

NO+2

15N 2683 15N 25101

NO2H2+ 15N 2728 Not Observed

3

H3O+ 17O 300 17O 1021H 72 1H 95-106

H4O2+ 17O 508 Not Observed

90 1H 136

aAcetic acid protonated acetic diprotonated acetic acid (89) acetyl cation and the protioacteylcation (46) were calculated at the MP26-31GGIAO-MP2tzpdz level of theory nitric acidnitronium cation and the protionitronium cation (3) were calculated at the HF6-31G II6-31Glevel of theory hydronium ion and the tetrahydridooxonium ion (90) were calculated at theMP26minus31GGIAO-MP2tzpdz level of theorybChemical shifts referenced to the following 13C (CH3)4Si 17O H2O 15N NH3


Table 9 Superelectrophiles studied by theoretical methods

Structurea Level of Theory Calculated Properties References

Carboxonium-Based Systems

HC

OH2

H

+

+

MP26-31GMP26-31G

Geometry energy frequencyproton afTHORNnity of H2COH+isodesmic reactiondeprotonation barrier IGLO-IIand GIAO-MP2 NMR chemicalshifts

48505152

H3CC

OH2

H

+

+

MP26-31GMP26-31G

Geometry energy isodesmicreaction frequency protonafTHORNnity of CH3CHOH+IGLO-II and GIAO-MP2 NMRchemical shifts

4850

H3CC

OH2

CH3

+

+

MP26-31GMP26-31G

Geometry energy isodesmicreaction frequency protonafTHORNnity of (CH3)2COH+IGLO-II and GIAO-MP2 NMRchemical shifts

4850

HC

OH

OH2

+

+

MP26-31GMP26-31G

Geometry energy isodesmicreaction frequency protonafTHORNnity of HC(OH)2+ IGLO-IIand GIAO-MP2 NMR chemicalshifts

4850

H3CC

OH

OH2

++

MP26-31GMP26-31G

Geometry energy isodesmicreaction frequency protonafTHORNnity of CH3C(OH)2+IGLO-II and GIAO-MP2 NMRchemical shifts

4850

HOC

OH

OH2

+

+

MP26-31GMP26-31G

Geometry energy isodesmicreaction frequency protonafTHORNnity of C(OH)3+ IGLO-IIand GIAO-MP2 NMR chemicalshifts

485053

H+O=C=+

OH MP26-31GMP26-31G

Geometry energy isodesmicreaction frequency protonafTHORNnity of OC(OH)+deprotonation barrier IGLO-IIand GIAO-MP2 NMR chemicalshifts

4850

CO2bull2AICl3 B3LYP6-311+GMP26-311+G

Geometry energy vibrationalfrequencies

54


Table 9 (continued )



H3NC

OH

OH+

+

MP4(SDTQ)6-311GMP26-311G

Geometry energy IGLOand GIAOMP2 NMRchemical shifts

55

F3CC

OH2

OH+

+ MP26-31GMP2(fu)6-31G

Geometry energyenthalpy ofCF3C(OH)2+protonation

56

FC

OH2

OH+

+ MP2(SDTQ6-31GMP26-31G

Geometry energytransition state structureleading to proton lossand barrier todeprotonation IGLOand GIAO-MP2 NMRchemical shifts

57

H3CC

O

OH

H

CH3+

+ MP4(SDTQ)6-31GMP26-31G

Geometry energy 58

H3CC

O

O

CH3

CH3

H3C +

+


Geometry energy 58

H3CC

O

O

H

CH3

H3C

+


Geometry energy 58

OH

HO

HO

OH

+

+

B3LYP6-31GB3LYP6-31G

Geometry chargedensities IGLO NMRchemical shifts

59





NH

OH+

+B3LYP6-31GB3LYP6-31G

Geometry energy NBOcharges LUMOenergy(MNDO)

35c

NH

OH++


Geometry energy NBOcharges LUMOenergy (MNDO)

35c

NH

OH

+

+ B3LYP6-31GB3LYP6-31G


35c

NH

OH

+



35c

HN

H

OH+


Geometry energy 60

O

OOO

+


Geometry energyrotational energybarriers IGLO andGIAO-MP2 NMRchemical shifts

61

OO

O

OO

O+

+

+



61





CCH

H

H

OH

+

+ HF6-31GHF 4-31G Geometry energy protonafTHORNnity of H2CCHO+charge densities

62

CCH

H

OH

OH

+

+ HF6-31GHF 4-31G Geometry energy protonafTHORNnity charge densities

62

CCHO

OH

OH

OH

+

+ MP26-31GMP26-31G

Geometry energy IGLONMR chemical shifts

63

CCHO

NH2

OH

NH2

+

+ MP26-31GMP26-31G


63

CCH3CO

OCH3

OCH3

OCH3+

+

HF6-31GHF 6-31G Geometry energy IGLONMR chemical shifts

63

OH

OH

HO

HO

+

+


63

H3NC

NH2

OH+

+ MP4(SDTQ)6-311GMP26-311G


64

H3NC

NH3

OH+

+

+



64





HN OHHO

+ + B3LYP6-31GB3LYP6-31G

Geometry energy NBOcharges LUMO energy

65

HN OHHO



65

N OHHO

Cl+ +


Geometry energy energeticsfor Cl+ dissociation

66

N OHHO

ClH+ + + B3LYP6-31G

B3LYP6-31GGeometry energy energetics

for Cl+ dissociation66

OH2

+


Geometry energy transitionstate structure leading toelectrocyclization andenergy barrier forcyclization

18

OH2

+



18

OH2

CH3+



18

H3CC

CO

H

CH3

CH3

HH

+

+


Geometry energy 14b

CC

CO

H

H

H

H

H

H+

+

HF6-31GHF4-31G

Geometry energy protonafTHORNnity of CH2CHCHOH+

24





HOC

COH

OH

OH

+ + MP26-31GHF6-31G

Geometry energy energetics ofbond rotation

67

Acylium and Related Systems

H3Cminus+C=+

OminusH MP26-31GMP26-31G

Geometry energy IGLO andGIAO-MP2 NMR chemicalshifts

425270


CC

CO

H HH

H+

+ MP26-311+GMP26-311+G

Geometry energy transitionstate structure and energybarrier leading to proton lossNBO chargesGIAO-CCSD(T) andGIAO-MP2 NMR chemicalshifts

69

CC

CO

H HH3C

CH3++ MP4(SDTQ)

6-311+GMP26-311+G


69

CO

CO+


Geometry charge densitiesIGLO NMR chemical shifts

59

Hminus +C=

+OminusH MP26-31G

HF6-31GGeometry energy energy

barrier leading to proton lossproton afTHORNnity of HCO+isodesmic reaction

50

Fminus +C=

+OminusH MP4(SDTQ)

6-31GMP26-31G


57




Oxonium-Based Systems

O H

H

HH

2+MP4(STDQ)6-311++GMP26-311G

Geometry energyprotonafTHORNnity of H3O+ transitionstate structures fordissociation IGLO-II andGIAO-MP2 NMR chemicalshifts

48507071

O H

H

HF

2+QCISD(T)6-311GQCISD(T)6-311G

Geometry energy protonafTHORNnity of H2FO+ transitionstate structure and energybarrier to proton lossGIAO-MP2 NMR chemicalshifts

72

O H

H

FF


Geometry energyprotonafTHORNnity of HF2O+ transitionstate structure and energybarrier to proton lossGIAO-MP2 NMR chemicalshifts

72

O H

H

CH3

H3C2+

MP26-31GMP26-31G

Geometry energy protonafTHORNnity of (CH3)2OH+IGLO-II and GIAO-MP2NMR chemical shifts

4850

O CH3

H

CH3

H3C2+

MP26-31GHF6-31GMP4(STDQ)6-311++GMP26-311G

Geometry energy isodesmicreaction frequency protonafTHORNnity of (CH3)3O+IGLO-II and GIAO-MP2NMR chemical shifts

4850

H3CC

COH2

HCH3

CH2 ++


Geometry energy 14b

H3CO

OCH3

CH3

CH3

+

+

MP26-31GMP26-31G


73




Hypercoordinate Systems

C C OH

HH H

+

+


Geometry energy 68

C CO

HHH H

CH H

++


Geometry energy 68

C CO

HHH H

CH CH3

++


Geometry energy 68

C

CO

HHH

HC

CH3

CH3+

+


Geometry energy 68

CH3C

CH3H3C

H

CO

H

H+

+


Geometry energy 14b

C NH

HH H

H

HH

+

+

HF6-31GHF6-31G Geometry energy 74

C NNH

HH H

+

+


C NH

HH H

CH

H

H+

+

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75





C CH

HH H

N

H

H

H

+

+MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

CN

H

CH3

H

CHH

H

H++

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

H3CN

C

C

H HH

H

H H

++

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

C FH

HH H

H+

+


Geometry energy NBO chargesGIAO-MP2 NMR chemicalshifts

7677

C ClH

HH H

H+

+



7677

C BrH

HH H

H+

+



7677

C IH

HH H

H+

+



7677

Si CH

HH H

H

H

+

+

QCISD(T)6-311GMP26-311G

Geometry energy energetics ofdissociation

78

Si S iH

HH H

H

H

+

+



78





CH53+ MP26-31G

MP26-31GGeometry energy NBO

charges79

CH62+ MP4(SDTQ)6-311G

MP26-311GGeometry energy transition

state structure and energybarrier to proton loss

80


MP26-311GGeometry energy

energetics of cleavageprocesses

81

C C

H

H

H H HH

HH +

+


Geometry energyenergetics of cleavageprocesses

80

HC

CC

HH H

H HH H++



80

HC

CC

CH

HH

H H

HH

H H

HH

+

+ MP4(SDTQ)6-311GMP26-311G


80

HC

CC

HH CH3

H HH H++



80

C C

H

H

H HH

H+

+


Geometry energyenergetics of dissociation

78

C C

H

H

H H H

CH3+

+

MP46-31GMP26-31G

Geometry energy 82

C C

H

H

H H H

CH

HH

+

+MP46-31GMP26-31G

Geometry energy 82





C OH

HHH

H H

+

+

MP26-31GMP26-31G

Geometry energydissociation pathwaysGIAO-MP2 NMRchemical shifts protonafTHORNnity of CH3OH2

+isodesmic enthalpies

48507477

C SH

HHH

H H

+

+

MP26-31GHF6-31G

Geometry energyGIAO-MP2 NMRchemical shifts protonafTHORNnity of CH3SH2


5077

C OCH3

+CH3H

HH H+

MP4(STDQ)6-311++GMP26-311G

Geometry energy 75

SH53+ CCST(T)cc-pVTZ

QCISD(T)6-311GGeometry energy

energetics of dissociationpathways

83

BH52+ and BH6

3+ CCST(T)6-311GQCISD(T)6-311G

Geometry energy NBOcharges

79a

NH52+ and NH6


Geometry energyenergetics of dissociationpathways

718485

PH52+ and PH6



7185

AsH63+ and AsH3+

6 CCST(T)6-311GQCISD(T)6-311G


7185

CH3N

CH3

CH3

CH

HH

H+ +

QCISD6-311GQCISD6-311G

Geometry energy 84





HC

CCH3

CH3

H H++

MP4(SDTQ)6-31GMP2(fu)6-31G

Geometry energy 86

H

+

+


Geometry energy GIAO NMRchemical shifts

87

Carbocationic Systems

C CH

H

H

H++

MP36-31GHF6-31G

Geometry energy energeticsof cleavage processestransition state structure andenergy barrier to proton loss

88

C CF

F

F

F++

MP26-31GHF6-31G

Geometry energy energeticsof bond rotation

67

HC

CC

CH

H

H

H H

H H

+

+


Geometry energy IGLO NMRchemical shifts

89

+ +


Geometry IGLO NMRchemical shifts

90

OH

CH3

+ +


Geometry energy transitionstate structure and energybarrier leading toelectrocyclization NBOcharges

25





OH

OCH3

+ +


Geometry energytransition statestructure and energybarrier leading toelectrocyclizationNBO charges

25

OH

H

+ +



25

+

+


Geometry energy 87

+

+

+


Geometry energy GIAONMR chemical shifts

91

CH3

H3C +

+



91

2+ MP23-21GHF3-21G Geometry energy IGLONMR chemical shifts

89

CH2

CH3

CH3H3C

H2C++ B3LYP6-311G

B3LYP6-311GGeometry energy IGLO

NMR chemical shiftsNBO charges

92





HN

+


Geometry energy NBOcharges energy ofLUMO (MNDO)

35c

HN +



35c

NH

SCH3

+

+


Geometry energy 93

NH

SCH3H

+

+


Geometry energy 93

Nitrogen-Based Systems

H2NN

NH2

NHH

+


Geometry energy NBOcharges transitionstate structure andenergy barrier toproton lossvibrational frequenciesand IR intensities

94

N3N

N3

NN

N+

+



94

+

+H2N

CNH3

NHH MP4(SDTQ)6-31G


energy barrier toproton loss IGLO andGIAOMP2 NMRchemical shifts

94





H3NC

NH3

NHH

+ +


Geometry energy energybarrier to proton loss IGLOand GIAO-MP2 NMRchemical shifts

95

H2NC

N

NHH

H H

CH3+

+ B3LYP 6-311+GB3LYP6-311+G

Geometry energy Wibergbond indices NBO chargesGIAO-MP2 NMR chemicalshifts

96

H2NC

N

NHH

H H

BH4+

+ B3LYP6-311+GB3LYP 6-311+G

Geometry energy Wibergbond indices NBO chargesGIAO-MP2 NMR chemicalshifts energetic ofdissociation processes

96

H2NC

N

NHH

H H

AlCl4+

+ B3LYP6-311+GB3LYP6-311+G


96

O=+N=+

OH MP26-31GMP26-31GCASSCF6-31G

Geometry energy atomiccharges transition statestructure and energy barrierto proton loss vibrationalfrequencies and IRintensities energetics ofdissociation pathways

3741

O=+N=+

Ominus +He B3LYP6-31G

B3LYP6-31GGeometry energy NBO

charges transition statestructure and energy barrierto proton loss vibrationalfrequencies and IRintensities

97

[O=NminusHe]3+ B3LYP6-31GB3LYP6-31G

Geometry energy NBOcharges transition statestructure and energy barrierto proton loss vibrationalfrequencies and IRintensities

97





Hminus +Nequiv+

NminusH MP4(SDTQ)6-31GMP26-31G

Geometry energy NBO chargestransition state structure andenergy barrier to proton lossIGLO NMR chemical shifts

98

Hminus +Nequiv+

NminusOH MP4(SDTQ)6-31GMP26-31G

Geometry energy NBO chargesIGLO NMR chemical shifts

98

Nequiv+Nminus+

NH3 MP4(SDTQ)6-31GMP26-31G


98

C N NH

H

H

H+ + MP4(SDTQ)6-31GMP26-31G

Geometry energy NBO chargestransition state structure andenergy barrier to protonlossGIAO-MP2 NMR chemicalshifts

98

C C NH

HH

++

HF6-31GHF4-31G

Geometry energy chargesdensities proton afTHORNnity of+CH2CN

62

H3C CNH3

H

++ MP4(SDTQ)6-31G

MP26-31GGeometry energy 99

C CNH3H

H HH

+

+


Geometry energy 99

H3C CNH3

CH3

++



99

HC

HN

H

HH

++

MP26-31GMP26-31G

Geometry energy transition statestructure and energy barrier toproton loss isodesmic reactionwith hydride donor protonafTHORNnity of CH2NH2+

51





HONH2

OH

NH2+

+ MP26-31GMP26-31G

Geometry energyenergetics of bondrotation

67

H2NNH2

OH

OH+

+ MP26-31GMP26-31G


67

H2NNH2

NH2

NH2+

+ MP2 6-31GMP26-31G


67

NN

+

+

HF6-31GHF6-31G

Geometry charge Mullikencharges

100

Phosphonium Systems

HC

PH

HH

H+ +

MP26-31GMP26-31G

Geometry energy transitionstate structure and energybarrier to proton lossisodesmic reaction withhydride donor protonafTHORNnity of CH2PH2+GIAO-MP2 NMRchemical shifts

51

HC

PH

H

HH

2+

MP26-31GMP26-31G


51

Sulfur-Based Systems

S2+8 and S2+

n (n = 37) B3PW916-311+G(3 df)B3PW916-311+G

Geometry energy spectralabsorption bands

101





2+

HS

H

HH

MP4(SDTQ)6-31GHF6-31G

Geometry energy transitionstate structure and energybarrier for proton loss

50102

2+

CH3

SH3C H

H MP26-31GHF6-31G

Geometry energyenergetics for dissociation

50

2+

CH3

SH3C CH3

H MP26-31GHF6-31G

Geometry energyenergetics fordissociation protonafTHORNninty of +S(CH3)3

50

2+

CH3

SH3C CH3

CH3 MP26-31GHF6-31G


50

2+

CH3

SH3C OH

CH3 B3LYP6-311+GB3LYP6-311+G

Geometry energyenergetics fordissociation GIAO NMRchemical shifts

103

2+

H3CS

H3CO

H

CH3B3LYP6-311+GB3LYP6-311+G


103

2+

H3CS

H3CO

H

H B3LYP6-311+GB3LYP6-311+G


103

2+

H3CS

H3CO

CH3



103

H2NC

NH3

SH+


Geometry energyenergetics for proton lossIGLO and GIAO-MP2NMR chemical shiftsvibrational frequenciesand IR intensities

38





H3NC

NH3

SH+

+

+


Geometry energyenergetics for protonloss IGLO andGIAO-MP2 NMRchemical shiftsvibrational frequenciesand IR intensities

38

H2NC

NH3

SH2+

+

+



38

HSC

SH

SH 2+ (P)MP4(SDTQ)

HF6-31GGeometry energy

hydride afTHORNnityrotational barriers

104

2+

CH3

SH3C H

H MP26-31GHF6-31G

Geometry energyenergetics fordissociation

50

HSC

CSH

SH

SH

++

MP26-31GHF6-31G


67

Boron-Based Systems

HN

BH

HH

++ MP46-311G(dp)

MP46-311G(dp)Geometry energy

transition statestructure and energybarrier for proton loss

105




Halonium Systems

H

H

H F 2+B3LYPLANL2DZB3LYPLANL2DZ

Geometry energy transitionstate structure and energybarrier leading to protonloss NBO charges protonafTHORNnity of H2F+

76106

H

H

H Cl 2+B3LYPLANL2DZB3LYPLANL2DZ

Geometry energy transitionstate structure and energybarrier leading to protonloss NBO charges protonafTHORNnity of H2Cl+

76106

H

H

H Br 2+B3LYPLANL2DZB3LYPLANL2DZ

Geometry energy transitionstate structure and energybarrier leading to protonloss NBO charges protonafTHORNnity of H2Br+

76106

H

H

H I 2+B3LYPLANL2DZB3LYPLANL2DZ

Geometry energy transitionstate structure and energybarrier leading to protonloss proton afTHORNnity of H2I+NBO charges

76106

CH3

CH3

H3C F 2+B3LYPLANL2DZB3LYPLANL2DZ


76

Cl 2+

CH3

CH3

H3CB3LYPLANL2DZB3LYPLANL2DZ


76

Br 2+

CH3

CH3



76

I 2+

CH3

CH3



76




Halonium Systems

HC

F

H

H+ +MP26-31GMP26-31G

Geometry energy transitionstate structure and energybarriers of dissociationprocesses proton afTHORNnity ofCH2F+ GIAOMP2tzpdzNMR chemical shiftsisodesmic reactions

51

HC

Cl

H+ + H

MP26-31GMP26-31G


51107

+

+F

CF

F

HMP4(SDTQ)6-31GMP26-31G


107

+Cl

CCl

ClH

+


Geometry energy transitionstate structure and energybarrier for proton lossGIAO-MP2 NMR chemicalshifts isodesmic reaction

107

+Br

CBr

BrH

+

MP4(SDTQ)LANL2DZMP2LANL2DZ


107

+I

CI

IH

+



107

+ +Cl

CCl

ClHH +



107

+ +Br

CBr

BrHH +



107




Halonium Systems

+ +I

CI

IHH +



107

+

+

++Cl

CCl

Cl

HH

H MP4(SDTQ)6-31GMP26-31G

Geometry energy transitionstate structure and energybarrier for proton lossGIAO-MP2 NMRchemical shifts isodesmicreaction

107

BrC

Br

Br

HH

H

++

+

+ MP4(SDTQ)LANL2DZMP2LANL2DZ


107

IC

I

I

HH

H

++

+



107

ClC

Cl

H

H++MP26-31GMP26-31G

Geometry energy transitionstate structure and energybarriers of dissociationprocesses proton afTHORNnityof CH2F+GIAOMP2tzpdz NMRchemical shifts isodesmicreactions

107

ClC

Cl

H

HH +

+ +

MP26-31GMP26-31G


107

aCalculated structures found to be at potential energy minima (zero imaginary frequencies)

REFERENCES 75

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(5) (a) Friedel-Crafts and Related Reaction G A Olah Ed Wiley NewYork 1964 (b) J March Advanced Organic Chemistry 4th Ed WileyNew York 1992 chap 12

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(16) A Berkessel R K Thauer Angew Chem Int Ed Engl 1995 34 2247(17) H Pellissier Tetrahedron 2005 61 6479(18) T Suzuki T Ohwada K Shudo J Am Chem Soc 1997 119 6774(19) S Saito Y Sato T Ohwada K Shudo J Am Chem Soc 1994 116

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(21) C Blackburn R F Childs J Chem Soc Chem Commun 1984 812(22) A Yokoyama T Ohwada K Shudo J Org Chem 1999 64 611(23) D A Klumpp D N Baek G K S Prakash G A Olah J Org Chem

1997 62 6666(24) T Ohwada N Yamagata K Shudo J Am Chem Soc 1991 113 1364(25) T Ohwada T Suzuki K Shudo J Am Chem Soc 1998 120 4629(26) T Yamazaki S Saito T Ohwada Tetrahedron Lett 1995 36 5749(27) D M Brouwer A A Kiffen Recl Trav Chim Pays-Bas 1973 92 689(28) G A Olah J L Grant R J Spear J M Bollinger A Serianz G Sipos

J Am Chem Soc 1976 98 2501(29) (a) T Ohwada A Itai T Ohta K Shudo J Am Chem Soc 1987 109

7036 (b) T Ohwada K Okabe T Ohta K Shudo Tetrahedron 199046 7539

(30) T Ohta K Shudo T Okamoto Tetrahedron Lett 1984 25 325(31) D A Klumpp S L Aguirre G V Sanchez Jr S de Leon Org Lett

2001 3 2781(32) T Ohwada T Yamazaki T Suzuki S Saito K Shudo J Am Chem

Soc 1996 118 6220(33) (a) D A Klumpp R Rendy Y Zhang A Gomez A McElrea Org Lett

2004 6 1789 (b) Y Zhang S A Aguirre D A Klumpp TetrahedronLett 2002 43 6837

(34) (a) D A Klumpp Y Zhang P J Kindelin S Lau Tetrahedron 2006 625915 (b) D A Klumpp P J Kindelin A Li Tetrahedron Lett 2005 462931

(35) (a) K Y Koltunov L A Ostashevskaya I B Repinskaya Russ JOrg Chem (Engl Transl) 1998 34 1796 (b) K Y Koltunov G KS Prakash G Rasul G A Olah J Org Chem 2002 67 8943 (c) K YKoltunov G K S Prakash G Rasul G A Olah J Org Chem 2002 674330 (d) K Y Koltunov G K S Prakash G Rasul G A Olah Hete-rocycles 2004 62 757 (e) K Y Koltunov I B Repinskaya Zhur OrgKhim 1995 31 1579 (f) K Y Koltunov I B Repinskaya Russ J OrgChem (Engl Transl) 2000 36 446 (g) K Y Koltunov I B RepinskayaRuss J Org Chem (Engl Transl) 2002 38 437 (h) L A OstashevskayaK Y Koltunov I B Repinskaya Russ J Org Chem (Engl Transl) 200036 1474

(36) E M Arnett Prog Phys Org Chem 1963 1 223(37) G A Olah G Rasul R Aniszfeld G K S Prakash J Am Chem Soc

1992 114 5608(38) G A Olah A Burrichter G Rasul K O Christe G K S Prakash

J Am Chem Soc 1997 117 4345

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(40) (a) L Pauling J Chem Phys 1933 1 56 (b) J D Dunitz T K HaJ Chem Soc Chem Commun 1972 568 (c) See also reference 39c

(41) T Weiske W Koch H Schwarz J Am Chem Soc 1993 115 6312(42) W Koch G Frenking H Schwarz F Maquin D Stahl Int J Mass Spec

Ion Proc 1985 63 59(43) H Schwarz Angew Chem Int Ed Engl 1991 30 820(44) (a) K A Newson S D Price Chem Phys Lett 1998 294 223

(b) Z Dolejsek M Farnik Z Herman Chem Phys Lett 1995 235 99(c) C Guenat F Maquin D Stahl W Koch H Schwaz Int J Mass SpecIon Proc 1985 63 265 (d) A Fiedler I Kretzschmar D Schroder HSchwarz J Am Chem Soc 1996 118 9941 (e) J Roithova J ZabkaZ Herman R Thissen D Schroder H Schwarz J Phys Chem A 2006110 6447

(45) J Roithova D Schroder J Am Chem Soc 2006 128 4208(46) P Perez J Org Chem 2004 69 5048(47) H-U Siehl V Vrcek in Calculation of NMR and EPR Parameters (2004)

M Kaupp M Buehl V G Malkin Eds Wiley-VHC Weinheim 2004pp 371394

(48) G A Olah A Burrichter G Rasul R Gnann K O Christe G K SPrakash J Am Chem Soc 1997 119 8035

(49) (a) G A Olah G Rasul R Aniszfeld G K S Prakash J Am ChemSoc 1992 114 8035 (b) G K S Prakash G Rasul A BurrichterG A Olah in Nitration-Recent Laboratory and Industrial Developments L F Albright R V C Carr R J Schmitt (Eds) ACS Symposium Series623 American Chemical Society Washington DC 1996 p 10

(50) N Hartz G Rasul G A Olah J Am Chem Soc 1993 115 1277(51) G Rasul G K S Prakash G A Olah Theochem 1999 466 245(52) B F Yates W J Bouma L Radom J Am Chem Soc 1986 108 6545(53) G Rasul V Prakash Reddy L Z Zdunek G K S Prakash G A Olah

J Am Chem Soc 1993 115 2236(54) G A Olah B Torok J P Joschek I Bucsi P M Esteves G Rasul

G K S Prakash J Am Chem Soc 2002 124 11379(55) G A Olah T Heiner G Rasul G K S Prakash J Am Chem Soc

1998 120 7993(56) G K S Prakash G Rasul A Burrichter K K Laali G A Olah J Org

Chem 1996 61 9253(57) G A Olah A Burrichter T Mathew Y D Vankar G Rasul G K S

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(58) G A Olah N Hartz G Rasul A Burrichter G K S Prakash J AmChem Soc 1995 117 6421

(59) N J Head G Rasul A Mitra A Bashir-Heshemi G K S PrakashG A Olah J Am Chem Soc 1995 117 6421


(61) V Prakash Reddy G Rasul G K S Prakash G A Olah J Org Chem 2003 68 3507

(62) T Ohwada K Shudo J Am Chem Soc 1989 111 34(63) G A Olah J Bausch G Rasul H George G K S Prakash J Am

Chem Soc 1993 115 8060(64) G Rasul G K S Prakash G A Olah J Org Chem 1994 59 2552(65) K Y Koltunov G K S Prakash G Rasul G A Olah Eur J Org

Chem 2006 21 4861(66) G K S Prakash T Mathew D Hoole P M Esteves Q Wang G

Rasul G A Olah J Am Chem Soc 2004 126 15770(67) G Frenking J Am Chem Soc 1991 113 2476(68) G A Olah A Burrichter G Rasul G K S Prakash M Hachoumy

J Sommer J Am Chem Soc 1996 118 10423(69) G Rasul G K S Prakash G A Olah J Phys Chem A 2006 110 1041(70) (a) A I Boldyrev J Simons J Chem Phys 1992 97 4272 (b) W Koch

N Heinrich H Schwarz F Maquin D Stahl Int J Mass Spec Ion Proc1985 67 305

(71) G A Olah G K S Prakash M Barzaghi K Lammertsma P v RSchleyer J A Pople J Am Chem Soc 1986 108 1032

(72) V Prakash Reddy E Sinn G A Olah G K S Prakash G Rasul JPhys Chem A 2004 108 4036

(73) G A Olah G Rasul A Burrichter M Hachoumy G K S PrakashR I Wagner K O Christe J Am Chem Soc 1997 119 9572

(74) K Lammertsma J Am Chem Soc 1984 106 4619

(75) G A Olah G Rasul A Burrichter G K S Prakash Proc Nat AcadSci USA 1998 95 4099

(76) G A Olah G Rasul M Hachoumy A Burrichter G K S PrakashJ Am Chem Soc 2000 122 2737

(77) G Rasul G K S Prakash G A Olah Proc Nat Acad Sci USA 200299 9635

(78) G Rasul G K S Prakash G A Olah J Phys Chem A 2005 109 798

(79) (a) G A Olah G Rasul J Am Chem Soc 1996 118 12922 (b) G AOlah G Rasul Acc Chem Res 1997 30 245

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(83) G A Olah G Rasul G K S Prakash Chem Eur J 1997 3 1039

(84) G A Olah A Burrichter G Rasul G K S Prakash J Am Chem Soc1997 119 4594

(85) (a) G Rasul G K S Prakash G A Olah J Am Chem Soc 1997 11912984 (b) G Rasul G K S Prakash G A Olah J Phys Chem A 1998102 8457

(86) G A Olah N Hartz G Rasul G K S Prakash J Am Chem Soc 1993115 6985

(87) G Rasul G A Olah G K S Prakash Proc Nat Acad Sci USA 2004101 10868

(88) K Lammertsma M Barzaghi G A Olah J A Pople A J Kos P vR Schleyer J Am Chem Soc 1983 105 5252

(89) R Herges P v R Schleyer M Schindler W-D Fessner J Am ChemSoc 1991 113 3649

(90) G A Olah V Prakash Reddy G Rasul G K S Prakash J Am ChemSoc 1999 121 9994

(91) C Taeschler T S Sorensen Tetrahedron Lett 2001 42 5339

(92) (a) G A Olah T Shamma A Burrichter G Rasul G K S PrakashJ Am Chem Soc 1997 119 3407 (b) G A Olah T Shamma ABurrichter G Rasul G K S Prakash J Am Chem Soc 1997 11912923

(93) A Li P J Kindelin D A Klumpp Org Lett 2006 8 1233

(94) G Rasul G K S Prakash G A Olah Inorg Chem 2002 41 5589

(95) G A Olah A Burrichter G Rasul M Hachoumy G K S PrakashJ Am Chem Soc 1997 119 12929

(96) G Rasul G A Olah G K S Prakash Inorg Chem 2003 24 8059

(97) G A Olah G K S Prakash G Rasul Proc Nat Acad Sci USA 199996 3494

(98) G Rasul G K S Prakash G A Olah J Am Chem Soc 1994 1168985


(100) R A Cox D Y K Fung I G Csizmadia E Buncel Can J Chem 2003 81 535

(101) I Krossing J Passmore Inorg Chem 2004 43 1000

(102) G A Olah G K S Prakash M Marcelli K Lammertsma J Phys Chem 1988 92 878

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(104) R Glaser G S-C Choy G S Chen H Grutzmacher J Am Chem Soc1996 118 11617


(105) T Drewello W Koch C B Lebrilla D Stahl H Schwarz J Am ChemSoc 1987 109 2922

(106) A I Boldyrev J Simons J Chem Phys 1993 99 769(107) G A Olah G Rasul A K Yudin A Burrichter G K S Prakash

A L Chistyakov I V Stankevich I S Akhrem N P Gambaryan ME Volpin J Am Chem Soc 1996 118 1446

3GENERATINGSUPERELECTROPHILES

As discussed in Chapter 1 many electrophiles are stable in solventsand the presence of substances of moderate Lewis basicity Even rela-tively strong electrophiles can be generated and handled under appropriateconditions1 A wide variety of electrophilic carbocationic and onium ionsalts have been prepared and characterized by spectroscopic methodsX-ray crystallography kinetic studies and other techniques Several typesof these electrophilic salts are even available commercially (such as variedonium iminium and carbocationic salts etc) Electrophiles are generallygenerated by the reactions of suitable precursors with Broslashnsted or Lewisacids They can be sometimes isolated but for synthetic conversions theyare more often generated in situ and reacted directly with nucleophilicreagents

When superelectrophilic reagents are involved in condensed phase reac-tions they are usually generated in situ in highly acidic systems2 Super-electrophiles are generally not isolated as persistent stable salts althoughsome highly stabilized onium dicationic systems have been isolated (videinfra) Both Broslashnsted and Lewis acid containing systems including solidand liquid acids have been shown suitable to form superelectrophilesBecause superelectrophilic activation often involves interaction of a sub-strate with two or more equivalents of acid superelectrophilic conversionsare often carried out in the presence of excess acid Among the Broslashnsted


81

copy

82 GENERATING SUPERELECTROPHILES

acids sulfonic acids and their Lewis acid conjugate systems have beenmost frequently used for the reactions involving superelectrophiles Directspectroscopic observation of superelectrophiles in these acids have alsobeen reported Although sulfuric acid and oleum are known to catalyzeconversions involving reactive dications (vide infra) H2SO4 (H0 minus12) andH2SO4-SO3 (H0 ge minus145) have seen relatively limited use in superelec-trophilic reactions as they themselves can react with many of the involvedsystems (sulfonation oxidation etc) HF-based superacid systems havebeen important in the study of many superelectrophilic systems TheirLewis acid conjugates such as HF-BF3 and HF-SbF5 were used in exten-sive fundamentally important studies of many systems Acid systemsbased on AlCl3 and AlBr3 have also been useful in various superelec-trophilic reactions

Triszliguoromethanesulfonic acid (CF3SO3H triszligic acid) is an effectiveand most widely used catalyst and activating agent in superelectrophilicchemistry Triszligic acid is a stable nonoxidizing (or weakly oxidizing)superacid with a useful liquid range (mp minus40C bp 161162C) andwith an acidity of H0 minus 1413 It has been used to protolytically generatesuperelectrophiles from varied electrophiles (Table 1) Triszligic acid hasbeen shown inter alia to protolytically activate nitronium salts as wellas nitrosubstituted oleTHORNns and arenes (entries 13)46 In a study ofthe cyclization of imines triszligic acid was found to be an effective cat-alyst and superelectrophilic activating agent (entry 4)7 A number ofcarboxonium-type superelectrophiles have been generated using triszligicacid including those from 12-dicarbonyl compounds (entries 57)810

enones (entries 810)1113 ketones (entry 1113)1416 unsaturated car-boxylic acids (entries 1415)17 amides (entries 1618)121819 and esters(entry 19)20 Because the acidity of hygroscopic triszligic acid is signiTHORNcantlydecreased by water the importance was noted to freshly distill it prior touse Water can also be produced in some triszligic acid catalyzed reactionsleading to decreased acidity This water-induced decrease of acidity mustbe taken into account for reactions requiring high levels of acidity aswell for quantitative studies such as kinetic experiments Using the triszligicacidtriszligic anhydride system can remedy this problem

The acidity of triszligic acid solutions can be greatly increased with addedLewis acids2 For example mixtures of triszligic acid with either SbF5 orB(O3SCF3)3 have been estimated to have H0 minus 168 (with SbF5) andH0 minus 185 (with B(O3SCF3)3) These conjugate Broslashnsted-Lewis super-acids have been used to generate superelectrophiles from varied substratesIn a study related to the Gattermann and Houben-Hoesch reactions super-electrophiles 1 and 3 were suggested as the intermediates in reactionswith CF3SO3HSbF5 (eqs 12)21 When the hydroxyester (4) is ionized

GENERATING SUPERELECTROPHILES 83

Table 1 Superelectrophiles generated in solutions of CF3SO3H

Ph Ph

O

Ph Ph

OH2

Ph Ph

O

Ph Ph

OH2

H3CCH3

O

O

H3CCH3

OH

OH

N

Ph

N

Ph

H

H

(1)

(2)

(3)

(4)

(5)

(10)

(11)

(7)

Ph OH

O

Ph OH

OH

(12)

(13)

NO

Ph

RN

PhR

OH

H

(15)

ROH

O

O

ROH

OH

OH

(6)

Ph NHPh

O

Ph NHPh

OH

NO

OBF4

NOH

O2 X

Ph CH3

O

Ph CH3

OH

N

O

R

O

N

OH

R

OH

(8)

(9)

(14)

(16)

(17)

R2N

O

O

NOH

OH

NO2 NHO OH

R1

R3

R2

R1

R3

Ph

OH

O

Ph

OH

OH

(18)

Substrate SuperelectrophileEntry Substrate SuperelectrophileEntry

Ph OCH3

O

Ph OCH3

OH

H

N

R

O

O

N

R

OH

OH

(19)

Ph

OH2

PhPh

O

CH3

Ph

OPhPh

Ph Ph

OH2PhPh

Ph

O

O

Ar

Ar

OH2

O

Ar

Ar

+

minus

+minus

++

++

+

+

+

+

+

+

++

+

+

+ +

++

minus

+

+

+

+

+

+

+

+

++

++

+

+

+

+

+

+

+

+

in either CF3SO3HSbF5 or CF3SO3H at low temperature the dication (5)can be directly observed by NMR spectroscopy (eq 3)22

H C NH+ +

H

NaCN orTMS-CN

5SbF595CF3SO3H

1

(1)


CN

CH3

TfOminusC6H6

CN

CH3

H C

O

2 3

5SbF595CF3SO3H

+

++

(2)

OHO

OMe

OMe

MeO

SbF5CF3SO3H

OH

OMe

OMe

MeO4 5

+ + (3)

Triszligatoboric acid (2 CF3SO3HB(O3SCF3)3) can be prepared by the reac-tion of THORNve equivalents of triszligic acid with one equivalent of BCl3 (withHCl gas evolution)23 This very strong conjugate Lewis acid has beenshown to produce superelectrophilic protonitronium ion (6) or its equiv-alent protosolvated species in equilibria (eq 4)23 In a study of the C -alkylation with alkyloxonium ions triszligatoboric acid was found to enhancethe electrophilic reactivity of a trimethyloxonium salt (7) Formation ofa the superelectrophilic species (8) was indicated (eq 5)24 Protosolvatedformyl cation (9) has also been proposed as the active electrophile in reac-tions of carbon monoxide in CF3SO3H CF3SO3HSbF5 or 2 CF3SO3HB(O3SCF3)3 (eq 6)25 The methyloxonium ion was similarly suggestedto be protosolvated in triszligatoboric acid producing a superelectrophilicspecies (eq 7)26

HNO2

2 CF3SO3HB(O3SCF3)3

minusH2OO N O

H+

O N O H

6

+ + +(4)

2 CF3SO3HB(O3SCF3)3

O

+ 2+

CH3

CH3

H3CO

CH3

CH3

H3CH

7 8

(5)

CO H CO+

2 CF3SO3HB(O3SCF3)3or

SbF5CF3SO3H

H CO H

9

+ + (6)


CH3OHH+

CH3OH2 CH3OH2

HA

HA

CH3OH3

2+++

(7)

Shudo and Ohwada have developed and used acid systems composedof varying ratios of CF3SO3H and CF3CO2H in order to obtain solu-tions having acidities between H0 minus 77 and H0 minus 13727 These acidsystems have been used in kinetic studies related to superelectrophiles1013 (eqs 811)7131421

N

Ph

H

H

N+

PhH

CF3SO3H -CF3CO2H

10

++

(8)

11

Ph

OH2

PhPh

OH

PhCF3SO3H -CF3CO3H

+

+

+

(9)

Ph Ph

OH2

12Ph Ph

OH CF3SO3H minusCF3CO2H++

+ (10)

CN

H

CF3SO3H minusCF3CO2H C

NH H

13

+ +

+(11)

Kinetic evidence suggests the formation of increasing superelectrophilicactivity (1013) as the acidity of the reaction media increases from H0 minus77 to H0 minus 137 (vide supra)

Superacidic FSO3H (szliguorosulfonic acid H0 minus 15) has also been usedin some studies involving superelectrophilic activation However due toits tendency for sulfonation and oxidation this acid has found only limiteduse in synthetic conversions involving superelectrophiles Fluorosulfonicacid has been shown effective to activate nitronium salts in their reactionswith weak nucleophiles and again it was suggested that the protosolvatedspecies (6) is involved in the reactions28 Both szliguorosulfonic acid andtriszligic acid have been reported to give the diprotonated species (14) from3-arylindenones (eq 12)29


O

Ph

FSO3H

orCF3SO3H

OH

Ph

14

+

+

OH

OHN

HO

OH

CH3

15 16

+

+

+

+

(12)

The FSO3HSbF5 conjugate superacid (Magic Acid H0 minus 15 to minus25)has been useful in extensive studies of onium cations and dications12 Itsvery high acidity was the basis for the stable ion conditions developedby the Olah group to directly observe many types of reactive electrophilesThe acidity of the magic acid system varies according to the proportionof SbF5 in the mixture (FSO3HSbF5 11 H0 minus 25)2 Magic Acid solu-tions have also been used in several NMR studies of reactive dicationsand superelectrophiles such as ions 15 and 161718 Among the superelec-trophiles generated in FSO3HSbF5 solutions are protosolvated oxoniumions (Table 2) sulfonium ions and related species (1718)3031 carbox-onium ions (1920)3233 and others (2122)3435 In the cases of 1718 and 21 data indicate low-equilibrium concentrations of the superelec-trophiles while 19 20 and 22 are formed in sufTHORNciently high-equilibriumconcentrations to allow their direct observation by spectroscopic methods

HF-based conjugate Lewis acid systems have been particularly impor-tant in the study of superelectrophiles Commercial anhydrous HF is arelatively modest Broslashnsted acid (H0 minus 11) but as shown by Gillespie ifcarefully dried and handled anhydrous HF has H0 minus15 The acidity ofHF is greatly increased with the addition of Lewis acids such as BF3(HF-BF3 H0 minus 11 to minus16) and SbF5 (HF-SbF5 H0 minus 11 to minus28)2 LikeMagic Acid these Lewis acid conjugates vary in strength according tothe ratio of HF and the Lewis acid

As discussed in Chapter 1 Brouwer and Kiffen reported the obser-vation that HF-BF3 promoted hydride transfer from isoalkanes to acylcations These results were later shown by Olah and co-workers to be dueto superelectrophilic activation of the acyl cation (24 eq 13)37 Diproto-nated acetone and aldehydes were also shown to abstract hydride fromisoalkanes in HF-BF3 solutions38 Carboxonium ions (25) are generally


Table 2 Superelectrophilic species generated in FSO3HSbF5 solution

OCH3

OCH3

OCH3

OCH3

H H

HH

OCH3 O

CH3

H

OCH3

H

H3C OCH3

O

H3C OCH3

OH

H

H2N NH2

O

H2N NH3

OH

(1)

(2)

(3)

(4)

XCH3H3C

CH3

+

X = O S Se Te

FSO3HSbF5

FSO3HSbF5

XCH3H3C

CH3

H2+

2+

SDH

HS DH

H

D

(5)

(6)


17

18

19

20

21

22

FSO3HSbF5

FSO3HSbF5

FSO3HSbF5

+

+

+

+

+ +

++

+

+

+

+FSO3HSbF5


not reactive towards weak nucleophiles such as alkanes and deactivatedarenes However a superelectrophilic species (26) is formed in HF-BF3solution (eq 14) and hydride abstraction occurs HF-BF3 has also beenshown to promote synthetically useful reactions (see Chapter 5) such asinvolving the protosolvated formyl cation (9)39 diprotonated pivaldehyde(27)39 and the superelectrophile derived from dimethyl ether (28)40

C

O

H3C OHC

O

CH3

H

C

OH

CH3

HFBF3C

O

CH3

23 24

+

+

+

+ (13)

C

O

R CH3

R = H CH3

HFBF3or HFSbF

C

OH

R CH3

H+

C

OH2

R CH3

25 26

C

OH2

R CH3

2++ +

+(14)

CH3

C

O

CH3

CH3H

HFBF3

CH3

C

OH2

CH3

CH3H

2+

CH3

C

OH2

CH3

CH3H

27

+

+

(15)

CH3OCH3 CH3OCH3

HCH3OCH3

H minusminus

H 2++HF-BF3

BF4 2 BF4

28

(16)

Besides the synthetic utility of the HF-BF3 system both HF and BF3 aregases at room temperature and thus they can be readily recovered fromreaction mixtures

The strongest liquid superacid known so far HFSbF5 has been usedto generate a variety of superelectrophiles In their study of the protosol-vation of oxonium ions Olah and co-workers found evidence even fordiprotonated water41 Hydrogendeuterium exchange of the hydroniumion (H3O+) was observed in DF-SbF5 solution (H0 minus 25) where thereis no deprotonation equilibrium and the diprotonated superelectrophile(29) is indicated to be the key intermediate (eq 17) Hydrogendeuteriumexchange was not observed in somewhat weaker FSO3H-SbF5 solutionEvidence was reported to suggest that carboxylic acids form diprotonatedspecies in HF-SbF5 and these intermediates can subsequently generatesuperelectrophilic acyl dications (eq 18)42


O

H

D

D

O

H

H

D

minusD+O

H+ +

D

D

HHF-SbF5

29

2+

(17)

F3CC

OH

OHFSbF5

F3CC

OH

OHH

F3C F3CC

OH2

OH minus H2O

C

OH++

++

++ (18)

A number of substituted naphthols were studied in HF-SbF5 solution byNMR and their superelectrophilic diprotonated carboxonium ions weredirectly observed (eqs 1920)43 These superelectrophiles are capable ofreacting with weak nucleophiles such as cyclohexane Even alkyl cationssuch as the tert-butyl cation (30) have been shown to undergo protol-ysis in DF-SbF544 When DFSbF5 is added to the previously formedtert-butyl cation (obtained from the alkyl halide in SbF5) it results inhydrogendeuterium exchange (eq 21) Under these conditions no depro-tonation equilibrium with isobutylene can exist to account for this isotopicexchange Deuteration at the C-H σ -bond must occur forming the super-electrophile (31) In studies related to trihalomethyl cations SommerJacquesy and others have demonstrated that HFSbF5 strongly activatesthe trichloromethyl cation in its reactions with CH σ -bonds45 The for-mation of the superelectrophilic species (32) is suggested (eq 22)

OH

Cl

HF-SbF5

OH+

+

Cl

(19)

OH

HF-SbF5

OH

OH OH+

+

(20)

DF-SbF5

31

minus78degC

H3C H3C H3CC

CH3

CH3

CC

CH3

HH

H

D

CCH2D

CH3

minusH+

30

++

+

+

(21)

CCl4HF-SbF5 Cl

CCl

Cl

H+ Cl+ ++

CCl

Cl32

H (22)


A similar type of activated trichloromethyl cation has been generated fromCCl4 in excess Lewis acids (SbF5 or AlCl3 vide infra)

In the above examples the superelectrophiles are formed via protona-tion or protosolvation of the corresponding electrophiles via their electrondonating ligands by superacids There are also a number of examples ofsuperelectrophiles being formed by coordination with strong Lewis acidssuch as SbF5 AlCl3 and AlBr3 In general Lewis acids can participatein the formation of superelectrophiles by two routes

1 The electrophile initially formed is further complexed by a Lewisacid thus decreasing neighboring group participation into the elec-trophilic center generating the superelectrophile

2 An electron donor Lewis base complexes simultaneously with twoLewis acid sites forming a doubly electron-deTHORNcient species orsuperelectrophile

In most of the examples of superelectrophilic reactions involving Lewisacids they are conducted using an excess of the Lewis acid This is inaccord with electrophilic solvation by the Lewis acid ie activation of theelectrophile requires interaction with two or more equivalents of Lewisacid As an example superelectrophilic nitration can be accomplishedwith NO2Cl and at least three equivalents of AlCl3 (eq 23)46 This pow-erful nitrating reagent involves a superelectrophilic complexed nitroniumion (33)

NO2Cl + 3 AlCl3 NO O

AlCl3

Al2Cl7

33

+minus (23)

Complexation between the oxygen lone pair electrons and the AlCl3generates an increasing positive charged bent nitronium ion creating alow-lying LUMO at the nitrogen Using excess aluminum halide VolpinAkhrem and co-workers have developed several types of aproticsuperacids These superelectrophilic reagents are capable of crackinghydrocarbons by their reactions with C-C and C-H σ -bonds vide infraFor example a superelectrophilic acyl cation (34) is formed by the reactionof acetyl chloride with excess AlCl3 (eq 24)47

C

O

H3C Cl AlCl3

AlCl3C

Od+

d+

dminus

dminus

dminus

H3C

AlCl3

CH3COCl bull 2AlCl3

34

AlCl3

Al2Cl7+

+minus (24)


Highly electrophilic species are also generated in the reactions of halo-genated methanes and excess aluminum halides (eq 25) probably involv-ing the superelectrophilic complex (35)48 A reactive thio-methylatingagent has also been developed based on superelectrophilic activation byAlCl3 (eq 26)49 Similarly electrophilic solvation was proposed in thecarboxylation of arenes with CO2AlAlCl3 (eq 27)50

CBr4 bull 2 AlBr3Br

CBr+

minusd+

minus

+

Br

BrC

Br

Br

35

AlBr3

AlBr3

Al2Br7

Al2Br7

(25)

Cl SCH3

SCH3 S

CH3

AlCl3

2 AlCl3

Al2Cl7

Al2Cl7

AlCl3 +minus

minus

+

dminus

d+

(26)

ClAl

ClCl

OC

O

AlCl3

ClAl

ClCl

OC

O

AlCl3 ClAl

ClCl

OC

O

AlCl3

AlCl3AlCl3

2 AlCl3+

++minus minus minus

d+

d+

d+

(27)

These are representative examples (eqs 2327) of superelectrophilicspecies being generated by interactions with Lewis acids The presenceof trace water impurities in Lewis acids such as AlCl3 creates strongprotic Broslashnsted acids to produce superelectrophiles as in reactions withenones (eq 28)51 and αβ-unsaturated amides (eq 29)1252 Superelec-trophilic species have been similarly formed from a variety of naphtholswith excess aluminum halide (eqs 3031)53 These multiply charged inter-mediates are capable of reacting with benzene or cyclohexane (hydrideabstraction) Several studies have also described the use of H2O-BF3 asa strong acid catalyst (H0 minus12) which is believed to act primarily as aBroslashnsted acid54 It has been shown to produce superelectrophilic speciesarising from N -halosuccinimides (eq 32)

H3C CH3

CH3 O 13 equivAlCl3

H3C CH3

CH2 OAlCl3

+

+minus

(28)

R NRprime2

O

R NRprime2

O

H H

X

X = AlCl3minus or AlnCl3n

minus

5 equivAlCl3

+

+

(29)


OH OH H

HH

X3 equivAlCl3

X = H AlCl3minus or AlnCl3n

minus

+

+

(30)

OH

HO

OX

HH

HH

OH

X3 equivAlCl3

+

+

+

X = H AlBr3minus or AlnBr3n

minus

(31)

N

O

O

ClBF3-H2O

N

OH

O

Cl N

OH

OH

Cl N

OH

OH

Cl

HH+H+

+ +

+

+

+

+

(32)

In addition to the discussed Broslashnsted or Lewis superacidic activationin solution chemistry there have been reports to suggest that superelec-trophilic species can be formed with solid acids and even in biochem-ical systems For example Sommer and co-workers have found severalexamples in which HUSY zeolite has exhibited catalytic activity similarto liquid superacids (eqs 3334)12 In the same study the perszliguorinatedresinsulfonic acid NaTHORNon-H (SAC-13) was found to give products consis-tent with the formation of the superelectrophile (36 eq 35)

Ph NEt2

O HUSY

C6H6130degC

Ph NEt2

OX

Ph NEt2

OPh97+

+

(33)

Ph CH3

O HUSY

Ph CH3

OX

Ph CH3

O70

C6H6130degC

+

+

(34)

NH

O

Ph

Nafion-H

NH

OH

Ph

H

NH

O

Ph

70

36

C6H6130degC

+

+

(35)

Although it is still difTHORNcult to correctly determine or estimate the aciditiesof solid acids both NaTHORNon-H and HUSY are considered weaker acids


than typical liquid superacids2 Favorable geometry in rigid systems (ieNaTHORNon-H and HUSY) however can cause bi-dentate or multi-dentateinteraction between the substrate molecule and the solid acid (or acidicenzyme site) which can explain the observed electrophilic activationAccordingly superelectrophiles are generated by multiple interactionswith closely oriented acid sites (both Broslashnsted and Lewis) on the sur-face of the solid acid Consistent with this the structure of NaTHORNon-Hcontains clusters of sulfonic acid groups This type of multi-dentate com-plexation is similar to the discussed catalytic activation of electrophileshaving suitable electron donor ligands in varied liquid acids systems(vide supra) A closely related bi-dentate electrophilic activation has beendemonstrated with carbonyl compounds involving double hydrogen bond-ing Several similar catalytic systems have been developed for exampleGong and Wus enantioselective aldol reaction catalyst (37)55 Theo-retical calculations have shown that the catalyst activates the carbonylgroup of benzaldehyde by double hydrogen bonding (38 Scheme 1)which is shown to be more effective than the proline-catalyzed reactioninvolving only a single hydrogen bond (39) This carbonyl activation isstrikingly similar to Shudo and Ohwadas superelectrophilic activation of13-diphenylpropan-1-one (40) and benzaldehyde (41)1456 Compoundscapable of double hydrogen bonding to carbonyl groups belong to apromising new class of catalysts While these catalysts clearly do notgenerate a full di-positive charge at the carbonyl group the multi-dentateinteraction signiTHORNcantly lowers the energy of the carbonyl LUMO (theC=O π orbital) enhancing the electrophilic reactivities of the carbonylcompounds

As discussed previously superelectrophilic activation in biological sys-tems has been found even with a metal-free hydrogenase enzyme foundin methanogenic archea an enzymatic system that converts CO2 tomethane57 It was found that N5N10 menthyl tetrahydromethanopterin(42) undergoes an enzyme-catalyzed reaction with H2 by hydride transferto the pro-R position and release of a proton to form the reduced product(43 eq 36)

HN

NH

N

N+

+ +

HO

H2N

CH3

CH3

H

42 43

HN

NH

N

NHs

O

H2N

CH3

CH3

H

Hr

H2

H2-formingmethylene tetrahydromethanopterin

dehydrogenaseH+

(36)


Ph H

O

H3C CH3

O

NH

O

NH

OH

Ph

Ph

20 mol

minus25degC Ph CH3

OOH

51 yield 83 ee

N

O

N

O

Ph

Ph

CH3

PhH

OH

H

d

37

38

N

O

O

CH3

PhH

O

H 39Ph Ph

OH2 OH2

H

40 41

+

+

d+

+

+

+

+

+

Scheme 1

It was suggested that protonation of one or both of the adjacent nitrogensites generates an enhanced electrophilic system This superelectrophilicsystem would be the result of decreasing stabilization by neighboringgroups and increasing electron deTHORNciency at the electrophilic site enablingcation 42 to react with molecular hydrogen As noted by Berkessel andThauer a localized highly acidic enzyme active site is formed by properlypositioned acidic functional groups and a nonbasic environment

The vast majority of examples reported so far of superelectrophilicactivation have been found in studies involving liquid superacids withacidities in the range of H0 minus 12 to minus26 Most often these acids havebeen szliguorinated sulfonic acids (CF3SO3H and FSO3H CF3SO3HSbF52 CF3SO3H-B(O3SCF3)3) HF-based Lewis conjugates (HF-BF3 and HF-SbF5) and systems with excess Lewis acids Nevertheless several


examples of superelectrophilic activation were reported in weaker acidsystems such as zeolites and perszliguorinated resinsulfonic acid such asNaTHORNon-H Multi-dentate interaction with weaker acidic sites can extendthe realm of superelectrophilic activation to physiological conditions Inprinciple superelectrophiles (doubly electron deTHORNcient systems) may alsobe generated from two-electron oxidation of neutral substrates A numberof these systems are discussed in subsequent chapters

Besides acidity the involved temperature has also been found to bea factor in the chemistry of superelectrophiles A number of super-electrophilic reactions have been shown to require more elevated tem-peratures in order to accomplish reactions with weak nucleophiles(Table 3)71214235458minus60 In cases lower temperatures fail to allow thereactions However these same electrophilic systems will often react withmore nucleophilic substrates at lower temperatures For example szliguo-robenzene gives p-chloroszliguorobenzene in 95 yield at 25C by reactionwith N -chlorosuccinimide and H2OBF354 3-pyridinecarboxaldehydecondenses with benzene in 99 yield by reaction with CF3SO3H at25C59 and 5-hydroxy-1-methyl-2-pyrrolidinone reacts with o-dimeth-oxybenzene in CF3SO3H giving the arylated product in 67 yield at 0C(compared with entries 1 5 and 6 respectively)60 The need for more ele-vated temperatures however can sometimes be avoided through the useof a different acid system as shown in the cyclization of the cinnamoylamide (entry 3)12 There may be several reasons for the required highertemperatures in some superelectrophilic reactions Since the superelec-trophiles are often higher-energy species it may be necessary to use moreelevated temperatures to generate their appreciable concentrations Evenwith the formation of a dicationic superlectrophile the higher tempera-ture may also be necessary to overcome the signiTHORNcant activation energybarrier associated with their electrophilic attack on weak nucleophilicsubstrates Nitrobenzene for example itself is almost completely pro-tonated in superacidic media (protonated nitrobenzene pKa minus 113) andtherefore electrophilic reactions with nitrobenzene may require that thesuperelectrophilic reagent collide with a protonated nitrobenzene Highertemperatures may be necessary to overcome the electrostatic repulsiveeffects in such reactions

While many superelectrophilic reactions are accomplished at ambient orsomewhat elevated temperatures a signiTHORNcant number of conversions arefound to work better at lower temperatures As some of these reactionsemploy gaseous reagents such as HF BF3 and low molecular weightalkanes the lower temperatures may be necessary to help to keep thereagents in the condensed phase In other reactions the lower tempera-tures are used to control the excessive reactivities of the superelectrophiles


Table 3 Superelectrophilic reactions requiring more elevated temperatures

(1) N

O

O

ClNO2

NO2

Cl

105degC 69

(2)

N

O

Ph

HHUSY

CF3SO3H

130degC

25degC

130degCH3PO4ndashP2O5N

OH

Ph

H N

O

Ph

H(3) 90

90

85

OH

NH2

AlCl3 110degC

OH

NH2

70

NH2

O

(4)

(5)

HNO3 2CF3SO3HndashB(O3SCF3)3

65degC

FF

FNO2

O N OH

FF

FNO2

O2N96

N

O

H

(6)

CF3SO3H 130degCNO2

HN

OH

H10

N

NO2

NO2

(7)

N

O

CH3

OH

CF3SO3H 80degCCl

ClN

OH

CH3N

O

CH3

ClCl

60

Ph Ph

O

CF3SO3H 80degCPh Ph

OH2 Ph 84

(8)N

CF3SO3H 150degC 69NH2 NH

YieldProductProposedSuperelectrophile

phenyl

phenyl

phenyl

phenyl

phenyl

NucleophileTemperatureAcidSubstrateEntry

CH2

H2OndashBF3 N

OH

OHCl

H

+

+

+

+

+

+

+

+ +

+

+

+

+

+

+

++

and increase selectivity For example a number of superelectrophilic sys-tems are based upon halogenated methyl cations such as CCl4-nAlCl3CCl4-nSbF5 and CBr4-nAlBr3 These systems tend to form very reac-tive trihalomethylcation-Lewis acid complex (44) and have been used ina variety of reactions of alkanes and cycloalkanes at lower temperatures


The effect of temperature is clearly seen in the iodination of alkanes andcycloalkanes with CCl4-AlI3-I2 where only monoiodination is observedat minus20C but further products are also obtained at 0C (eq 37)61

CCl4-AlI3 I2

minus20degC

I

70

CXX

X

MXn

44

+

d+dminus

(37)

In other conversions better yields (Scheme 2) and product selectivity(Scheme 3) are obtained at lower temperatures62 In the case of theKoch-Haaf butane carbonylation it was noted the importance of temper-ature on the equilibria between the sec-butyl and tert-butyl cations andtheir derived acyl cations Besides providing better yields and product

CH3CH2CH3+ CO

CCl4SbF5(008 mole ratio)

minus30degC

minus10degC

Temp

CH3OH COCH3O

CHCH3H3C

Yield

50

28

Scheme 2

CCH3H3C

CH3

i-PrOH i-PrOHCO CO

CH3CH2CHCH3

CO O CH(CH3)2 C

O O CH(CH3)2

C(CH3)3

minus20degC

0degC

Temp

525 100

129 100

Product Ratio

CH3CH2CH2CH3+ CO

+CH3CH2CHCH3

CBr4AlBr5(008 mole ratio)

+

Scheme 3


selectivity the lower temperatures also prevent cracking and oligomeriza-tion reactions which are known to occur with trihalomethyl cation-Lewisacid complexes and saturated hydrocarbons Protosolvated nitronium salts(6) are exceptionally reactive electrophiles A number of synthetic conver-sions with superelectrophilic nitronium salts have been carried out at lowertemperatures often to prevent polynitration of the aromatic substratesNitrobenzene and 1-nitronaphthalene can both be prepared effectively atlow temperatures using superelectrophilic nitrations (eqs 3839)63 Goodpositional selectivity is seen in the low temperature nitration of naphtha-lene With the use of a single equivalent of nitronium salt (or its precursor)di and trinitration is suppressed by lower temperatures This is also seenin the superelectrophilc nitration of the trityl cation (eq 40)46

80HNO3 minus78degC

(CF3SO2)2ONO2

(38)O N O

HA

O N OH

6

+

d+

+ +

NO2

94

(CF3SO2)2O

HNO3 minus78degC (39)

NO2NO2

+ BF4minus

CF3SO3H0degC

64

+ + (40)

Several conversions based on superelectrophilic hydroxycarbenium ions(such as 45) were also carried out at lower temperatures including thecondensation reaction (eq 41) and electrocyclization (eq 42)813 A simi-lar electrocyclization reaction with a benzilic acid methyl ester was alsofound to proceed in high yield at minus40C (eq 43)22

H3CCH3

O

O CF3SO3H

C6H6 0degC5 min

H3CCH3

OH

OHH3C

CH3

O

PhPh95

45

+

+ (41)

Ph

O O

Ph

91

Ph

OH2

CF3SO3H

+

+0degC

(42)


PhO

PhHO

OCH3

CF3SO3H

minus40degC PhOH

Ph

OCH3

O

OCH3

9446

+ +

(43)

The reactivity of superelectrophile 46 precludes its direct observation byNMR but as discussed in Chapter 2 stabilization of the carbenium ioncenter with para-methoxyphenyl groups allowed the dicationic species(5) to be observed at low temperature

As discussed previously several types of reactive dications and super-electrophiles have been directly observed using NMR spectroscopy Theseexperiments have all used low temperatures (minus100C to minus30C) andsuperacidic conditions to generate the observable reactive dications andsuperelectrophiles Some reactive dications and superelectrophiles are sta-ble at low temperatures and can be directly observed by NMR but athigher temperatures they readily cleave and decompose The low temper-atures also slow down proton exchange reactions and enable the ions tobe observed as static species

Lower temperatures were also an important aspect of other studies ofsuperelectrophilic chemistry For example Olah and co-workers studiedthe role of superelectrophiles in the acid-catalyzed cleavage of esters34

One of the key experiments was carried out under highly acidic conditionsand at minus40C to prevent nucleophilic attack of monocationic intermediates(eq 44)

H3C

O CH3

O CH3

BF4

CD3SO3FSbF5

minus30degC

47

H3C

O CH3

O CH3

48

D3C

(NuCH3)+

H3C

O CD3

O CH3

Nu+

+

+

minus

+

(44)Under these conditions it is highly unlikely that exchange of the minusCH3

group for minusCD3 could occur by nucleophilic attack on the monocation(47) The superelectrophile (48) is indicated to be involved in the exchangereaction In studies related to the protosolvation of carbocations very highacidities and low temperatures were used to probe the proton-deuteriumexchange of carbocationic electrophiles (Scheme 4 and vide supra)64

Low temperature stable ion conditions are important to prepare the2-propyl cation (49) Despite the low temperatures isotopic exchange wasobserved indicating involvement of the protosolvated superelectrophile


DFSbF5

50

minus78degC

H3CC

C

H

HH

H

D

H3CC

CH2D

H

minusH+

H3CC

CH2

H+ H+

H3CC

CH3

H

49

+ +

+

+

Scheme 4

OCH3

OCH3FSO3HSbF5

minus60degCOCH3

hn

ΔOCH3

OCH3

HOCH3

H

minusH+ H+

51a 51b

5252

k1

+

+

+

+ ++

Scheme 5

(50 see also related study of tert-butyl cation44) The very high aciditiesand low temperatures prevent any deprotonation-deuteration equilibriuminvolving propylene As discussed brieszligy in Chapter 2 low tempera-ture was also important in the study of a protosolvated carboxonium ion(Scheme 5)33 At minus60C a photostationary state is found for the conju-gated oxonium ion 51 As the temperature is increased the Z (51b) -gt E(51a) isomerization rate is increased The isomerization is also found tooccur at an increasing rate at higher acidities In FSO3H at minus5C thestereomutation rate constant is found to be 20 times 10minus4 sminus1 while inFSO3H-SbF5 (41) at minus5C the rate constant is measured to be 69 times10minus3 sminus1 This indicates the involvement of dicationic intermediate (52)Delocalization of the positive charge in the dicationic structure is thoughtto enhance the isomerization rate

REFERENCES 101

In summary superelectrophilic systems are usually generated with anexcess of Broslashnsted and Lewis superacids although examples are knownin which under suitable conditions superelectrophiles are formed by themultidentate interaction of less strong acids Multidentate interactionscan also lead to doubly electron deTHORNcient systems exhibiting superelec-trophilic chemistry Besides the highly acidic conditions solvents for thesuperelectrophilic reactions must be themselves of low nucleophilicitySuperelectrophiles are typically generated from the same precursors andfunctional groups that form the parent electrophiles Indeed the discussedsuperelectrophiles are usually in equilibrium with their corresponding par-ent electrophiles Lower temperatures may be needed in superelectrophilicreactions to control excessive unselective reactivities Higher tempera-tures are found important however in the reactions of superelectrophileswith weak nucleophiles

REFERENCES

(1) G A Olah K K Laali Q Wang G K S Prakash Onium Ions WileyNew York 1998

(2) G A Olah G K S Prakash J Sommer in Superacids Wiley New York1985

(3) P J Stang M R White Aldrichimica Acta 1983 16 15(4) G A Olah K K Laali G K S Sandford Proc Nat Acad Sci USA 1992

89 6670(5) (a) T Ohwada A Itai T Ohta K Shudu J Am Chem Soc 1987 109


(6) T Ohta K Shudo T Okamoto Tetrahedron Lett 1984 25 325(7) Yokoyama A T Ohwada K Shudo J Org Chem 1999 64 611(8) T Yamazaki S-i Saito T Ohwada K Shudo Tetrahedron Letters 1995

36 (32) 5749(9) D A Klumpp M Garza S Lau B Shick K Kantardjieff J Org Chem

1999 64 7635(10) D A Klumpp K Y Yeung G K S Prakash G A Olah J Org Chem

1998 63 4481(11) T Ohwada N Yamagata K Shudo J Am Chem Soc 1991 113 1364(12) K Y Koltunov S Walspurger J Sommer Chem Comm 2004 1754(13) T Suzuki T Ohwada K Shudo J Am Chem Soc 1997 119 6774(14) S Saito Y Sato T Ohwada K Shudo J Am Chem Soc 1994

116 2312(15) D A Klumpp D N Baek G K S Prakash G A Olah J Org Chem

1997 62 6666


(16) D A Klumpp S Fredrick S Lau G K S Prakash K K Jin R BauG A Olah J Org Chem 1999 64 5152

(17) R Rendy Y Zhang A McElrea A Gomez D A Klumpp J Org Chem 2004 69 2340

(18) D A Klumpp R Rendy Y Zhang A Gomez A McElrea Org Lett 2004 6 1789

(19) D A Klumpp R Rendy A McElrea Tetrahedron Lett 2004 45 7959(20) J P Hwang G K S Prakash G A Olah Tetrahedron 2000 56 7199(21) Y Sato M Yato T Ohwada S Saito K Shudo J Am Chem Soc 1995

117 3037(22) T Ohwada T Suzuki K Shudo J Am Chem Soc 1998 120 4629(23) G A Olah A Orlinkov A B Oxyzoglou G K S Prakash J Org Chem

1995 60 7348(24) G A Olah G Rasul A Burrichter G K S Prakash Proc Nat Acad Sci

USA 1998 95 4099(25) O Farooq M Marcelli G K S Prakash G A Olah J Am Chem Soc

1998 120 4629(26) G A Olah A-H Wu Synlett 1990 599(27) S Saito S Saito T Ohwada K Shudo Chem Pharm Bull 1991 39(10 )

2718(28) (a) G A Olah H C Lin J Am Chem Soc 1976 96 549 (b) G A Olah

H C Lin Synthesis 1974 444(29) S Walspurger A V Vasilyev J Sommer P Pale Tetrahedron 2005 61

3559(30) (a) G A Olah J R De Member Y K Mo J J Svoboda P Schilling

J A Olah J Am Chem Soc 1974 96 884 (b) K Laali H Y ChenR J Gerzina J Organomet Chem 1988 348 199

(31) G A Olah G K S Prakash M Barzaghi K Lammertsma P v RSchleyer J A Pople J Am Chem Soc 1986 108 1032 (b) G A OlahG K S Prakash M Marcelli K Lammertsma J Phys Chem 1988 92878

(32) I B Repinskaya K Y Koltunov M M Shakirov V A Koptyug ZhurOrg Khim 1992 28 1013

(33) C Blackburn R F Childs J Chem Soc Chem Commun 1984 812(34) G A Olah N Hartz G Rasul A Burrichter G K S Prakash J Am

Chem Soc 1995 117 6421(35) G Rasul G K S Prakash G A Olah J Org Chem 1994 59 2552(36) (a) D M Brouwer A A Kiffen Recl Trav Chim Pays-Bas 1973 92

809 (b) D M Brouwer A A Kiffen Recl Trav Chim Pays-Bas 197392 906

(37) Olah G A Germain A Lin H C Forsyth D A J Am Chem Soc1975 97 2928

REFERENCES 103

(38) D M Brouwer A A Kiffen Recl Trav Chim Pays-Bas 1973 92 689(39) (a) G A Olah G K S Prakash T Mathew E R Marinez Angew Chem

Int Ed 2000 39 2547 (b) G A Olah T Mathew E R Marinez P MEsteves M Etzkorn G Rasul G K S Prakash J Am Chem Soc 2001123 11556

(40) A Bagno J Bukala G A Olah J Org Chem 1990 55 4284(41) G A Olah G K S Prakash M Barzaghi K Lammertsma P v R

Schleyer J A Pople J Am Chem Soc 1986 108 1032(42) G K S Prakash G Rasul A Burrichter K K Laali G A Olah J Org

Chem 1996 61 9253(43) I B Repinskaya M M Shakirov K Y Koltunov V A Koptyug Zhur

Org Khim 1988 24 1907(44) G A Olah N Hartz G Rasul G K S Prakash J Am Chem Soc 1993

115 6985(45) (a) J C Culman M Simon J Sommer J Chem Soc Chem Commun

1990 1098 (b) A Martin M-P Jouannetaud J-C Jacquesy TetrahedronLett 1996 37 2967 (c) J Sommer J Bukala Acc Chem Res 1993 26370

(46) (a) G A Olah Q Wang A Orlinkov P Ramaiah J Org Chem 199358 5017 (b) G A Olah A Orlinkov P Ramaiah A B OxyzoglouG K S Prakash Russ Chem Bull 1998 47 924

(47) M Volpin I Akhrem A Orlinkov New J Chem 1989 13 771(48) G A Olah G Rasul A K Yudin A Burrichter G K S Prakash

A L Chistyakov I V Stankevich I S Akhrem N P Gambaryan M EVolpin J Am Chem Soc 1996 118 1446

(49) G A Olah Q Wang G Neyer Synthesis 1994 276(50) G A Olah B Torok J P Joschek I Bucsi P M Esteves G Rasul

G K S Prakash J Am Chem Soc 2002 124 11379(51) K Y Koltunov I B Repinskaya Zhur Org Khim 1995 31 1723(52) (a) K Y Koltunov S Walspurger J Sommer Tetrahedron Lett 2004 45

3547 (b) K Y Koltunov S Walspurger J Sommer Eur J Org Chem 2004 4039

(53) K Y Koltunov L A Ostashevskaya I B Repinskaya Russ J Org Chem(Engl Transl) 1998 34 1796

(54) G K S Prakash T Mathew D Hoole P M Esteves Q Wang G RasulG A Olah J Am Chem Soc 2004 126 15770

(55) Z Tang F Jiang L-T Yu X Cui X Cui L-Z Gong A-Q Mi Y-ZJiang Y-D Wu J Am Chem Soc 2003 125 5262

(56) S Saito T Ohwada K Shudo J Am Chem Soc 1995 117 11081(57) A Berkessel R K Thauer Angew Chem Int Ed Engl 1995 34 2247(58) K Y Koltunov G K S Prakash G Rasul G A Olah Tetrahedron 2002

58 5423


(59) D A Klumpp S Lau J Org Chem 1999 64 7309(60) D A Klumpp unpublished results(61) I Akhrem A Orlinkov S Vitt A Chistyakov Tetrahedron Lett 2002 43

1333(62) I Akhrem A Orlinkov L Afanaseva P Petrovskii S Vitt Tetrahedron

Lett 1999 40 5897(63) G A Olah V Prakash Reddy G K S Prakash Synthesis 1992 1087(64) G A Olah N Hartz G Rasul G K S Prakash M Burkhart

K Lammertsma J Am Chem Soc 1994 116 3187

4GITONIC GEMINALSUPERELECTROPHILES

41 STRUCTURAL CONSIDERATIONS

As noted in the THORNrst chapter superelectrophiles are divided into two basiccategories gitonic (close) and distonic (distant) superelectrophiles Thedistonic superelectrophiles are characterized by structures having twoor more carbon or hetero atoms separating the positive charge centerswhile the gitonic superelectrophiles have the two charges in close prox-imity Gitonic superelectrophiles thus can be characterized according tothe distance between the two (or more) charge centers This chapter dis-cusses systems in which the charges are located on (or around) the sameatom (ie H4O2+) These are referred to as geminal systems Chapter5 deals with vicinal superelectrophiles having greater charge separationcorresponding to 12-dicationic systems Distonic superelectrophiles arediscussed in Chapter 7

Although gitonic superelectrophiles may be viewed as closely locateddi- or polycationic systems in fact the positive charges are often stronglydelocalized through resonance conjugative and inductive interactionswith involved ligands For example in the case of water natural bondanalysis (NBO) derived atomic charges from DFT calculations showcharges of minus0916 and +0458 on the oxygen and hydrogen atoms1


105

copy

106 GITONIC GEMINAL SUPERELECTROPHILES

HO

H

HH

+070

+070

+070

+070

minus080

Td

2+

HO

H+0458

+0458

minus0916

C2v

HS

HH

+049

+056

+056

+056

+035

3+

Cs

+049HH

1 2

Figure 1 Calculated NBO charges on water diprotonated water (1) and pentahydrido-sulfonium trication (2)

respectively while similar calculations show charges of minus080 and +070on the oxygen and hydrogen atoms for the gitonic superelectrophilicdiprotonated water (H4O2+ 1 Figure 1)2 Similarly theoretical studiesof the pentacoordinate sulfonium trication H5S3+ (2) have shown thatmost of the positive charge is delocalized on the hydrogen atoms3 It hasalso been noted that in systems like H4O2+ and H5S3+ the distributionof the positive charge on the periphery atoms leads to a large decrease inthe quantum mechanical Coulombic repulsion energy4

In a similar sense charge delocalization through resonance-type con-tributions is important in the nature of some superelectrophiles and inthe understanding of their chemistry For example the superelectrophilicNazarov-cyclization is also considered to involve delocalization of posi-tive charge in a gitonic superelectrophile (Scheme 1)5 Although doubleprotonation of the carbonyl group can be represented as the geminal-typedication 4a this is only a minor contributing resonance structure The defacto best representation of this superelectrophile involves the 12-dication4b and delocalized structure 4c which leads directly to the transition statestructure of the 4π -electrocyclization (5) Compared with a cyclization

CH3

OCF3SO3H

25degC

CH3

OH

CH3

OH H

O HH

CH3

O

CH3

+

97

3

CH3

OH H

4a 4b

2+

5

++

+

+

+

CH3

OH H

4c

+

+

Scheme 1

STRUCTURAL CONSIDERATIONS 107

reaction involving the monoprotonated intermediate (3) it was shown (byab initio calculations) that the reaction involving the superelectrophile hasa signiTHORNcantly lower energy barrier to the cyclization (vide supra)5

It should be clear when considering superelectrophilic chemistry thatfully formed dicationic superelectrophiles are only the limiting case Thereis always a varying degree of protolytic (or Lewis acids complexat-ing) interaction involved in superelectrophilic condensed phase reactions(Figure 2)6 While much evidence has been accumulated for the de factorole of varied superelectrophiles their direct observation (in most cases)has not yet been accomplished in the condensed phase Besides beingenergetic high lying and therefore by necessity short-lived species thiscould also suggest either incomplete protonation to a superelectrophilicstate (ie 6) formation of low concentrations of fully formed dicationicsuperelectrophiles (7) or an equilibium system involving both structuresBased on the results of kinetic studies Shudo and Ohwada have found evi-dence to suggest the varying degree of protonation of superelectrophiles(vide infra) In one of the studied systems it was proposed that protontransfer at the transition state is about 507

In the following we describe geminal gitonic superelectrophilesincluding carbo azo oxo and sulfo and halodicationic gitonic super-electrophiles There is even evidence for the protonation and alkylation ofnoble gases and thus superelectrophiles based on them are a possibility8

Though doubly ionized noble gases (ie Xe2+) are well known therehave been no reports yet describing geminal gitonic superelectrophilescentered at noble gases although they have been studied by ab initiocalculations4 As noted in Chapter 1 metal atoms in high oxidation statesare not considered geminal gitonic superelectrophiles within the contextof this discussion


H3CO

CH3

CH3 H3CO

CH3

CH3

H Ad+ dminus

H3CO

CH3

CH3

H

2+

6 7

++

Figure 2 Degree of protosolvation of the oxonium cation


42 GEMINAL SYSTEMS

421 Geminal Carbodications

One of the foundations of organic chemistry is Kekules concept (sug-gested independently by Couper) of the tetravalency of carbon The struc-ture of higher bonded (coordinated) carbon systems such as alkyl-bridgedorganometallics [Al(CH3)2]2 or carbonium ions of which CH5

+ is theparent however cannot be explained by Kekules four-valent conceptinvolving only two electron-two center bonding (2e-2c) Extensive exper-imental and theoretical studies have provided evidence for the involvementof two-electron three center (2e-3c) bonding in such systems showingthat carbon atoms can be simultaneously coordinate to more than fourgroups or atoms9 Diprotonated methane CH6

2+ (8) or its analogues canbe considered as gitonic superelectrophiles with multiple 2e-3c bond-ing Ab initio calculations at the HF6-31G level have shown CH6

2+to have a C2v symmetrical structure with two orthogonal 2e-3c interac-tions It was shown to be kinetically stable with a calculated barrier of63 kcalmol to deprotonation10 Despite this kinetic stability and the factthat CH5

+ is readily observed in gas-phase studies CH62+ has not yet

been observed in condensed phase studies However a remarkably stableanalogous gold complex (9) has been prepared and even isolated as a crys-talline compound allowing X-ray structure determination by Schmidbaurand co-workers11 Compound 9 may be considered an isolobal analog ofthe CH6

2+ ion In addition to CH62+ the CH7

3+ ion (10 triprotonatedmethane) has been studied computationally at the MP26-31G level12

HC

HH

H

H H 2+

8

CAuPPh3

AuPPh3Ph3PAu

Ph3PAu

AuPPh3

AuPPh3

2+

2 X minus

9

HC

HH

H

H H3+

10

H

The ab initio calculations determined the C3v structure to be a kineticallystable minimum

Varied one carbon geminal dications have been generated in the gas-phase and studied by theoretical methods For example mass spectroscopicstudies of methane have detected dicationic species CH4

2+ CH3bull2+CH2

2+ and CHbull2+ while other studies have examined the structuresof halogenated one carbon geminal dications13 The halogenated systems

GEMINAL SYSTEMS 109

(11a-b) have been studied by both theoretical and experimentalmethods14

H C F2+

H C Cl2+

H C Br2+

H C I2+

11a 11b 11c 11d

In gas-phase studies these dicationic species were found to react by com-peting electron and proton transfer routes15 These studies found that forion-molecule reactions involving CHX2+ and nonpolar molecules (N2 andO2) or rare gas atoms the electron transfer reaction dominates at theexpense of proton transfer if the electron transfer process is signiTHORNcantlyexothermic (gt2 eV) However in reactions involving CHX2+ species andpolar molecules (H2O CO and HCl) proton transfer becomes far moreimportant The difference in reaction paths was attributed to an increasingstabilization of the encounter complexes involving the CHX2+ speciesand polar molecules This stabilization tends to favor the formation of thethermodynamic products from proton transfer versus the kinetic productsfrom electron transfer reaction

In other theoretical and experimental studies CF22+ and CF3

2+ havebeen examined for their gas-phase chemistry16 The gas-phase reactionof CF2

2+ with molecular hydrogen has been extensively studied as wasbrieszligy mentioned in Chapter 216a In chemistry that is characteristic ofseveral superelectrophilic systems (vide infra) the gas-phase reaction ofCF2

2+ with hydrogen leads to the formation CHF2+ and H+ products in

which the two formal positive charges are separated by a fragmentationprocess Other reaction pathways have been described for gas-phase colli-sions involving CF2

2+ and diatomic molecules including non-dissociativeelectron transfer dissociative electron transfer and collision inducedcharge separation16a The carbodication CCl22+ (13ab) may be involvedin the conversion of trichloroszliguoromethane to methylene chloride by theaction of SbF5 in the presence of a hydride donor17 Such a reactionwould involve superelectrophilic solvation of the trichloromethyl cationby SbF5 (Scheme 2) producing an equilibrium involving the incipienttrichloromethyl dication (12) and the geminal dication (13ab) Subse-quent reactions with the hydride donor then give the reduced productThe CCl22+ ion (13ab) has also been studied by theoretical calcula-tions and mass-spectroscopic experiments18 Calculations have estimatedthe carbon-halogen bond length to be quite short indicating a signiTHORNcantamount of charge delocalization (ie 13b) Interestingly superelectrophile13 is isoelectronic with carbon disulTHORNde (S=C=S)


CClCl

Cl

SbF5CClCl

Cl

SbF5or H+

12

Cl C Cl2+

13a

FCCl3SbF5 RH

HCCl3 bull SbF5

HCCl2

minus SbClF5minus

RHCH2Cl2

RHCl C Cl

13b

+ +dminusd+

++ +

Scheme 2

Table 1 Observed gas-phase one-carbon dications and trications

Dicationic Species Tricationic Species

CCl2 middot Cl22+ CF32+ CHCl32+ CCl22+

CBr22+ CI22+ CH2Cl22+CH3Cl2+ CO2+ CO2

2+CS2

2+ CF2+ CS22+

COS3+ CS23+ CSe2

3+ CS3+

Gas-phase experiments have been used to detect a variety of doublyand triply-charged one carbon species (Table 1)19 While many of thesespecies presently do not have a direct analog in condensed phase chem-istry studies of their generation stability (including determinations ofelectronic states structures and energies) and gas-phase reactivities mayprovide further insight towards the behavior of gitonic superelectrophilesespecially geminal-type systems

422 Geminal Azodications

The formal expansion of the valence octet involving hypervalent andhypercoordinate THORNrst row elements has been a subject of considerableinterest Some of these species can be directly observed (ie BH5 andCH5

+) The gitonic superelectrophile NH52+ (14 doubly protonated

ammonia) has been studied by experimental and theoretical methods20

At both MP2(fu)6-31G and QCISD6-311G levels of theory struc-ture 14 (C4v symmetry) is found to be a minimum on the potential energysurface The dissociation of 14 into NH4

+ and H+ is estimated to beexothermic by 991 kcalmol however the gitonic species (14) has a con-siderable kinetic barrier to dissociation estimated to be about 25 kcalmolInterestingly the same study suggests the possibility of directly observ-ing NH5

2+ in mass-spectrometry experiments as theoretical calculations

GEMINAL SYSTEMS 111

indicate that the NH32+ species (16) reacts with molecular hydrogen in a

highly exothermic reaction (eq 1)

N

H

H H

H

H2+

C4v

14

NLAuLAu

AuL

AuL

AuL

2+

2 BF4minus

15L = P(C6H5)3

NH32+ + H2

H=minus143 kcalmolminusminusminusminusminusminusminusminusminusminusrarr NH52+

16 14(1)

No evidence for the gitonic superelectrophile 14 has yet been obtainedfrom condensed phase superacidic experiments In experimental studiesammonium chloride NH4

+Clminus was reacted with DSO3FSbF5 in solutionat 100C for 14 days but no hydrogendeuterium exchange was observedHowever a gold (I) stabilized species (15) analogous to 14 has been pre-pared and characterized by X-ray crystallography in work by Schmidbaurand associates21 It was found that the central nitrogen atom is coordinatedto THORNve (C6H5)3PAu ligands in a trigonal-bipyramid geometry

Besides the hypervalent or hypercoordinate gitonic ammonium dica-tions such 14 there is considerable experimental and theoretical evidencefor trivalent dicationic nitrogen species of which NH3

2+ (16) can beconsidered the parent system The NH3

2+ dication (16) itself has beenobserved in the gas-phase by charge-transfer mass spectroscopy22 Relatedgitonic superelectrophiles have also been generated in the condensed phaseby superacid-promoted reactions of hydroxylanilines aniline N-oxidesand nitrosobenzene23 For example when N-phenylhydroxylamine (17) isreacted in superacid with benzene diphenylamine (18) and the amino-biphenyls (19) are formed as products (Scheme 3)23a With CF3CO2Hthe major product is diphenylamine (18) while in CF3SO3H the major

NOH

H

C6H6

acid NH

NH2

Ph

18 19

CF3CO2H

CF3SO3H trace 43 para23 ortho

56 9 para8 ortho

17

+

Scheme 3


products are the aminobiphenyls (19) In the reaction with CF3CO2H(H0 minus27) it is proposed that monocationic intermediates (20 21 or22) lead to diphenylamine (19) (Scheme 4) Although the divalent anile-nium ion (21) cannot be ruled out the authors favor either an SN2-likebimolecular substitution (A2) mechanism or one that involves a cationicspecies having partial anilenium ion character (22) In the reaction withCF3SO3H (H0 minus141) dicationic intermediates are thought to be involvedand lead to the biphenyl products 19 (Scheme 5) Protonation of both theN and O-sites provides the diprotonated species 23 which gives a gitonicsuperelectrophile (or iminium-benzenium dication) 24 upon loss of H2OElectrostatic repulsive effects make structure 24b the more important res-onance contributor to the overall structure of 24The reaction of dication24 with benzene produces intermediates 25 and 26 and eventually leadsto the aminobiphenyl products (19) Similarly aniline N -oxide (27) and

NOH

H

H+ NO

HH

H

minus H2O

NH

NH

NH

HSn-2-like

C6H6

minusH+

19

17 20

21 22

NO

H

H

H

C6H6

+

+

+

+

+

Scheme 4

NOH

H

2H+ NO

HH

H

minusH2O NH

17 23

C6H6

HN

H

24a

2+H

H

NH

H

H

HN

H

H

H

Hminus2H+NH2

Ph

19 26 25

24b

+ + +

+

+

++

+

+

Scheme 5

GEMINAL SYSTEMS 113

the nitrosobenzene (29) react in superacid to form superelectrophiles 28and 30 respectively (eqs 23)23b Both superelectrophiles (28 and 29)have been shown to react with benzene in electrophilic aromatic substitu-tion reactions Analogous chemistry was used in the superacid-promotedreaction of the N -oxide (31) in the preparation of the natural productalkaloid (32 eq 4)23c

N

CH3

minusO

CH3CF3SO3H N

CH3

CH3

28b27

NCH3

CH3

28a

2+ ++

+ (2)

NOH

H

30b

NO

NOH

H

30a

2+

29

CF3SO3H

+

+ (3)

N

O

CF3SO3H

31H3CO

NH3CO

H3CO

NH3CO

H3CO

H3CO

NH3CO

H3CO

2+

minusH2O

32

minus

+ +

+

(4)

423 Geminal Oxo and Sulfodications

There are several types of oxygen-based geminal dications that have beenstudied by experiment and theory A fundamentally important system isdiprotonated water ie H4O2+ In superacidic solution the hydroniumion has been shown to be extremely stable by 1H and 17O NMRspectroscopy24 Isotopic hydronium ions have also been prepared fromHSO3FSbF5D2OSO2ClF25 The ions H3O+ H2DO+ and HD2O+ canbe generated and characterized by 1H and 2H NMR spectroscopy andthere is no evidence for any deprotonation or hydrogendeuterium exchangewhen the hydronium ions are formed in the superacid HSO3FSbF5(H0 minus21) However in even stronger superacidic medium (HFDFSbF5


OH

DD

OH

DO

HH

DO

H

HO

HH

H

minusD+ minusD+H+ H++ + +(a)

minusD+ minusD+H+ H++O

HD

DO

HH

D(b) O

HD

DH

2+O

HH

DH

2+O

HH

H

++

Scheme 6 Two possible mechanisms for HD exchange in superacids

H0 minus25) hydrogendeuterium exchange is observed26 1H 2H and17O NMR spectroscopy was used to study the system indicatingisotopomeric ions including D2H17O+ and DH2

17O+ exchange throughD2H2

17O2+ Two mechanisms are possible for the observed HD exchange(Scheme 6) (a) deprotonation-protonation equilibria involving neutralmolecules and monocations or (b) protonation-deprotonation equilibriainvolving monocations exchanging H and D through H4O2+ dicationsBecause HD exchange only occurs at the highest acidities (ie withHFDFSbF5 but not with HSO3FSbF5) and deprotonation to water is nottaking place in these systems the results suggest that isotopic exchangetakes place via isotopomeric H4O2+ or corresponding protosolvated species(H3O+HA) involving the nonbonded electron pair of the oxygen atom

The observed HD is in accord with theoretical studies by Schwarz et aland Olah et al respectively which indicating H4O2+ to be a kineticallystable species27 At the MP4SDTQ6-311++GMP6-31G level cal-culations show that H4O2+ lies in a potential energy well with a barrierfor proton loss estimated to be 396 kcalmol in the gas-phase Calcula-tions at the HF6-31G level likewise indicate a deprotonation barrier of394 kcalmol The optimized geometry is shown to possess Td symme-try (isoelectronic with NH4

+ CH4 and BH4minus) and much of the charge

is located on the hydrogen atoms (calculated charges hydrogen atoms+070 oxygen atom minus080)2 The GIAO-MP2 derived δ 17O for H4O2+has also been calculated and it is estimated to be 392 ppm which is29 ppm deshielded from the experimentally observed 17O chemical shiftfrom H3O+27a Despite the predicted kinetic stability of H4O2+ the ionhas not yet been generated in gas-phase experiments although H3O2+bull

has been observed from charge stripping of the hydronium ion H3O+27b

Other computational studies have investigated the structures and energiesof the szliguorooxonium dications FOH3

2+ and F2OH22+2 Schmidbaur and

co-workers have remarkably succeeded in preparing dipositive tetrahedralgold complexes of O2+ (33)28

GEMINAL SYSTEMS 115

OAuPAr3

AuPAr3

Ar3PAu

Ar3PAu

Ar = C6H5 or (ondashCH3C6H4)

33

2+

The gold complexes were characterized by X-ray crystallography andrepresent isolobal analogs of H4O2+

Other superelectrophilic oxonium dication systems have also been stud-ied For example trialkyloxonium salts (Meerwein salts R3O+ Xminus) inthe presence of strong acids show substantial increase in their reactivi-ties indicating superelectrophilic activation29 Meerwein salts are excel-lent alkylating agents for nucleophiles containing heteroatoms but in theabsence of superacids they are not capable of C -alkylating aromatic oraliphatic hydrocarbons When superacids like FSO3HSbF5 (Magic AcidH0 minus21 to minus24) or CF3SO3HB(O3SCF3)3 (triszligatoboric acid H0 minus20 to21) are added trialkyloxonium ions (34) readily alkylate aromatics suchas benzene toluene or chlorobenzene (eq 5)30

OH3C

CH3

CH3

FSO3H ndash SbF5 C6H6OH3C

CH3

CH3

H2+

C6H5CH3 OH3C

H

CH3++

34

+

(5)Weaker acids do not catalyze the methylation Despite that trialkyloxo-nium ions have a formal positive charge the oxygen atom can still act asa Lewis base resulting in an interaction between the lone pair electronson the oxygen and the highly acidic protosolvating system

Protolytic activations can also be achieved in cases of primary andsecondary oxonium ions Primary alcohols even methanol and ethersform acidic oxonium ions with strong acids Methanol is completelyprotonated in superacids and forms the methyloxonium ion (35) as a sta-ble well-deTHORNned oxonium ion31 The methyloxonium ion requires forcingconditions to C -alkylate arenes such as phenols The methylation of aro-matics including benzene is greatly facilitated by the use of solid or liquidsuperacids32 This is indicative of the activation of the methyloxonium ionthrough protosolvation of the nonbonded electron pair of the oxygen atom(36 or 37 eq 6) or alternatively it may suggest a protosolvated species(39) arising from the dimethyloxonium ion (38 eq 7)


H+ HA

H

3635 37

H O CH3

HO CH3

H

HO CH3

H

A

H O CH3

H

H

+

δminus

δ+

+

2+ (6)

2 CH3OH CH3OCH3

minusH2O

CH3OCH3

H

HAH+

CH3OCH3

H

H

38 39

+ 2+

(7)

The methyloxonium ion CH3OH2+ in superacidic media also readily

undergoes ionic hydrogenation to give methane (eq 8)33

CH3OHCF3SO3HminusB(OSO2CF3)3minusminusminusminusminusminusminusminusminusminusminusminusminusminusrarr

minusH2CH4 (8)

again suggesting the formation of superelectrophilically activated species(36 or 37) Under forcing conditions in varied superacids (even polyphos-phoric acid) methanol undergoes self-condensation to give C3-C9 alkanestoluene and C8-C10 aromatics (Scheme 7)3435 The carbon-carbon bondsare initially formed by a reaction step involving the methyloxonium ionCH3OH2

+ and protosolvated dication CH3OH32+ Due to the superelec-

trophilic nature of CH3OH32+ (37) it is capable of insertion into the

carbon-hydrogen bond of CH3OH2+ (35) with concomitant loss of hydro-

nium ion Subsequent reactions of protonated ethanol readily yield theobserved hydrocarbon products (by further alkylation or through dehydra-tion to ethylene) A similar mechanism has been proposed in the formationof hydrocarbon products from dimethyl ether in superacidic media35 Pro-tosolvation is also suggested in the superacid-catalyzed carbonylation ofdimethyl ether (or methanol) to form methyl acetate (eq 9)36

CH3OCH3 CH3OCH3

H

+CH3OCH3

H

H 2+HF-BF3

CO

BF4minus

O

C

minus2HF

CH3CO BF3OCH3

minusBF3

CH3CO2CH3

382BF4

minus

+ minus

(9)The dimethyloxonium ion (38) is itself not reactive towards CO Howeversuperelectrophilic activation enables it to react with carbon monoxide

A considerable amount of work has also been done to show that super-electrophilic sulfonium dications can be generated For example like the

GEMINAL SYSTEMS 117

CH3OHH+

HO

CH

HH

HH O

CH

HH

HH2+

3537

minusH3O+

CH

HH

OC

HHHH

H

minusH+

C

HHH

OC

HHHH

hydrocarbons

+

+ +

+

+

Scheme 7

protosolvated (protonated) hydronium ion (H4O2+) evidence has beenobtained for protosolvation of H3S+ involving H4S2+37 When HD2S+is generated in FSO3HSbF5(41 H0 minus18) solution it also forms the iso-topomeric products (ie H2DS+) by HD exchange (eq 10)

SH

D

D

SH

H

D

H++ + +2+ 2+minusD+ minusD+minusH+

SH

D

D

H SH

H

D

H SH

H

H(10)

Moreover the exchange rate increases when FSO3HSbF5(11 H0 minus215)is used as the reaction medium The increasing rate of HD exchangeat higher acidities is in accord with exchange occurring by a protosol-vation mechanism involving isotopomeric H4S2+ Ab initio calculationshave been done on the H4S2+ ion and like H4O2+ it was shown to bethermodynamically unstable but kinetically stable The global minimum isfound at the tetrahedral structure (Td symmetry isoelectronic with AlH4

minusSiH4 and PH4

+) with a signiTHORNcant barrier to gas-phase dissociation (592kcalminus1 at the MP4SDTQ6-31GHF6-32G level) Interestingly cal-culations also suggest that the H4S2+ ion may be more readily obtainedthan H4O2+ Although the calculations were done on isolated gas-phasespecies the proton transfer from H4O2+ to H3S+ is estimated to be ther-modynamically very favorable at the MP4SDTQ6-31G level (eq 11)37

OH

HH

H2+ 2++ +

SH

HH

SH

HH

HOH

HH

ΔHdeg = minus277 kcalbullmolminus1

+ +(11)

The increased stability of the sulfonium dication may be due to the largersize of sulfur and thus greater ability to disperse the positive charge


Other stable organosulfurane (IV) dications (4042) were reported38

S SBF3bullOEt2

XeF2

40

SN

N

F

FCH3

CH3

CH3

CH3

42

2+

[S(NP(CH3)4]2+

2Clminus

41

2 BF4minus

2+

2 SbF6minus

Salt 40 is prepared by the oxidation of the neutral organosulfurane withXeF2 to obtain 40 as a crystalline solid38a X-ray diffraction studies of33 reveal a tetrahedral geometry at the sulfur and C-S bond length of1753 ucircA which is comparable to C-S single bond length Laguna andco-workers were able to prepare and study by X-ray crystallography theperchlorate salt of [(C6H5)3PAu]4S2+ (43) an analog of H4S2+39 Thesalt was prepared by the reaction of [(Ph3PAu)2S] with two equivalentsof [AuPPh3ClO4

minus] and exhibits an approximately tetragonal pyramidalframework

Little experimental or theoretical work has been done on the relatedH4Se2+ and H4Te2+ dications (44 and 45)

Se

H

H

H

H

44

43

45

Te

H

H

H

HAu Au

Au

Au

S

2ClO4minus

PhPh3

Ph3P

Ph3P

Ph3P2+

2+ 2+

The tetraaurated species [(C6H5)3PAu]4Se2+ has been prepared and char-acterized however40

Like the trialkyloxonium superelectrophiles the salts of trimethyl sul-fonium (CH3)3S+ selenonium (CH3)3Se+ and telluronium (CH3)3Te+ions have also been shown by Laali et al to undergo superelectrophilicactivation41 These onium salts methylate toluene in FSO3H-SbF5 butwith the weaker Bronsted superacid CF3SO3H (triszligic acid H0 minus141) nomethylation takes place (eq 12)

X

+2+

H3C

CH3

CH3

FSO3HndashSbF5XH3C

CH3

CH3

HC6H5CH3

X = S SeTe

Xylenes(12)

GEMINAL SYSTEMS 119

The need for extremely high acidity is in accord with the protosolvationof the onium salts

There has been some experimental and theoretical work related toeven higher coordinate polycationic geminal superelectrophiles such asH5O3+ and H5S3+42 When triprotonated water H5O3+ was studied at theMP26-31G level of calculation the entire potential energy surface isfound to be repulsive The trication H5O3+ dissociates into H4O2+ and H+upon optimization However with the larger sulfur atom the tricationicspecies (2 H5S3+) is found at a stable minimum At the MP26-31Glevel the Cs-symmetric form of 2 is determined to be the only stablestructure one that resembles a complex between SH3

3+ and a hydrogenmolecule (eq 13)

S

H

H H

H H3+

2

Cs

SH33+ + H2 SH5

3+ ΔH = minus124 kcalbullmolminus1

2 (13)

The structure 2 is isostructural with the Cs-symmetric structure of the pen-tacoordinate carbonium ion CH5

+ involving a 3 center-2 electron bondInterestingly theoretical calculations at the CCSD(T)cc-pVTZQCISD(T)6-311G + ZPE level indicate that the reaction of SH3

3+ and H2may be a viable gas-phase reaction as it is shown to be highly exother-mic (eq 13) Calculations also indicate that SH3

3+ itself is located ata potential energy minima Although SH5

3+ (2) has not yet been thusfar generated experimentally the isolobal gold complex [S(AuPR3)53+]has been reported in the solution phase39 The same study also reportsevidence for the [S(AuPR3)64+] species However neither of the salts[S(AuPR3)53+] or [S(AuPR3)64+] could be characterized by crystallog-raphy These sulfur complexes represent isolobal analogues of the SH5

3+and SH6

4+ respectively

424 Geminal Halodications

Halonium ions are an important class of onium ions43 The dialkylchlorobromo and iodohalonium ions can be prepared and even isolated as sta-ble salts (ie 46) as shown by Olah et al by reacting an excess ofhaloalkane with strong Lewis acid halides in solvents of low nucleophilic-ity (eq 14) In superacid solution dialkylhalonium ions show enhancedalkylating reactivity44 It is considered that this enhanced reactivity is dueto further protolytic (or electrophilic) activation involving the non-bonded


electron pairs of the halogen atom leading to gitonic superelectrophiles(47 or 48 eq 15)

2H3CndashBrSbF5

SO2ClFH3C Br CH3

minus

+

X46

(14)

H3C Br CH3+ 2+

H3C Br CH3

X

HX

H X

H3C Br CH3

H 2 X46 47 48

+

minus minusδminusδ+ (15)

There is further evidence for the involvement of the halogen-centeredgitonic superelectrophiles from isotopic exchange experiments45 Whenbromonium ion 46 (X=SbF6

minus) is generated in a solution containing theisotopomeric CD3FSbF5 methyl interchange is observed (Scheme 8)Under conditions of low nucleophilicity and high acidity it is unlikelythat demethylation of 46 occurs to give free bromomethane (and subse-quently the exchange product 50) Thus methyl exchange is best explainedthrough the methylation of 46 to give the geminal dication 49 Pro-tosolvated dialkylhalonium ions such as 48 have also been studied bytheoretical methods44a

In studies of szliguoro chloro bromo and iodonium ions and their super-electrophilic H3X2+ ions were investigated by density functional theorycalculations at the B3LYP6-31GB3LYP6-31G level The H3I2+H3Br2+ and H3Cl2+ ions were found to be stable minima (C 3v sym-metry) with signiTHORNcant energy barriers to dissociation 358 379 and274 kcalmol respectively In all cases however gas-phase dissociationinto H2X+and H+ is shown to be exothermic The H3F2+species is alsolocated at a potential energy minimum however the optimized geome-try shows D3h symmetry and a signiTHORNcantly lower barrier to dissociation

H3C Br CH3+

minusSbF646

Nu

H3C Br + H3C Nu

CD3F SbF5H3C Br CH3

49

CD3

2+

H3C Br CD3

50

+

Scheme 8

GEMINAL SYSTEMS 121

BrC CH

H

HH

H

H

H

Relative Energy 00 kcalbullmolminus1

2+

BrC CH

HH

H

H

H

217 kcalbullmolminus1

2+H

51 52

Figure 3

86 kcalmol These calculations agree well with earlier calculations doneat the MP2(FU)6-31G level

In the HFSbF5 superacid-catalyzed carbonylation reactions of alkanesSommer and co-workers reported that addition of bromide ion to thereaction mixture leads to greatly increased reaction rates46 This can bebest interpreted to be a consequence of the protolytic activation of H2Br+via the gitonic trihydrobromonium dication H3Br2+ though the authorssuggested that the enhanced reactivity may be due to the formation ofBr+ for which however there is no evidence in the condensed state6a

Thermodynamically H3Br2+ is expected to be more stable in solutionthan in the gas phase due to interaction with the involved counter ions Incomparing H3Br2+ to H4O2+ it has been noted that the calculated protonafTHORNnity of H2Br+ (minus429 kcalmol) is greater than the calculated protonafTHORNnity of H3O+ (minus604 kcalmol) Yet the calculated dissociation barriersare comparable (H3Br2+ 379 kcalmol H4O2+ 382 kcalmol) Giventhe discussed experimental evidence for the formation of H4O2+ in liquidsuperacid it seems likely that H3Br2+ is a viable gitonic superelectrophile

In the case of the dimethylbromonium cation 46 ab initio calcula-tions have found two stable minima for the protosolvated superelec-trophile the bromine and carbon protonated forms 51 and 52 respectively(Figure 3)44a Dication 51 is estimated to be more stable than 52 byabout 21 kcalmol at the B3LYP6-31GB3LYP6-31G level Whendimethylbromonium cation (46) is reacted in DFSbF5 in SO2 at minus78Cno deuterium incorporation is observed into the methyl groups This obser-vation is in accord with the theoretical calculations in that Br-protonationis expected to be the preferred process

The protonated methyl halides have also been studied by ab initio com-putational methods44a Whereas initial protonation occurs on the halogenatom the second protonation occurs primarily on the C-H bonds TheB3LYP6-31G potential energy surfaces (PES) for CH3XH2

2+ (X=FCl Br I) are found to be repulsive


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(2) V Prakash Reddy E Sinn G A Olah G K S Prakash G Rasul J PhysChem A 2004 108 4036

(3) G A Olah G Rasul G K S Prakash Chem Eur J 1997 3 1039(4) A I Boldyrev J Simons J Chem Phys 1992 97 4272(5) T Suzuki T Ohwada K Shudo J Am Chem Soc 1997 119 6774(6) G A Olah D A Klumpp Acc Chem Res 2004 37 211(7) Y Sato M Yato T Ohwada S Saito K Shudo J Am Chem Soc 1995

117 3037(8) (a) A J Heck L J d Koning N M N Nibbering J Phys Chem 1992

96 8870 (b) G A Olah J Shen J Am Chem Soc 1973 95 3582(9) G A Olah G K S Prakash R E Williams L D Field K Wade Hyper-

carbon Chemistry Wiley New York 1987(10) (a) G A Olah G K S Prakash G Rasul J Org Chem 2001 61 2907

(b) G A Olah G Rasul J Am Chem Soc 1996 118 12922 (c) G AOlah G Rasul Acc Chem Res 1997 30 245

(11) F Scherbaum A Grohmann B Huber C Kruger H Schmidbaur AngewChem Int Ed Engl 1988 27 1544

(12) G A Olah G Rasul J Am Chem Soc 1996 118 8503(13) K Lammertsma P v R Schleyer H Schwarz Angew Chem Int Ed Engl

1989 28 1321(14) (a) M W Wong B F Yates R H Nobes L Radom J Am Chem Soc

1987 109 3181 (b) J Roithova J Hrusak Z Herman Int J Mass Spec-trom 2003 228 497

(15) (a) J Roithova J Zabka Z Herman R Thissen D Schroder H SchwarzJ Phys Chem A 2006 110 6447 (b) J Roithova Z Herman D SchroderH Schwarz Chem Eur J 2006 12 2465

(16) (a) Z Herman J Zabka Z Dolejsek M Farnik Int J Mass Spectrom 1999 192 191 (b) S D Price M Manning S R Leone J Am ChemSoc 1987 109 3181 (c) S D Price J Chem Soc Faraday Trans 199793 2451

(17) G A Olah Angew Chem Int Ed Engl 1993 32 767(18) (a) K Leiter K Stephean E Mark T D Mark Plasma Chem Plasma

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(19) D Schroder H Schwarz J Phys Chem A 1999 103 7385

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(21) A Schier A Grohmann J M Lopez-de-Luzuriaga H Schmidbaur InorgChem 2000 39 547

(22) M Hamden A G Brenton Int J Mass Spectrom 1988 84 211(23) (a) K Shudo T Ohta T Okamoto J Am Chem Soc 1981 103 645

(b) T Ohta R Machida K Takeda Y Endo K Shudo T OkamotoJ Am Chem Soc 1980 102 6385 (c) K Shudo T Ohta Y EndoT Okamoto Tetrahedron Lett 1977 105

(24) (a) K O Christe R D Schack R D Wilson Inorg Chem 1975 14 2224(b) G D Mateescu G M Benedikt J Am Chem Soc 1979 101 3959

(25) V Gold J L Grant K P Morris J Chem Soc Chem Commun 1976397


(27) (a) G A Olah A Burrichter G Rasul R Gnann K O ChristeG K S Prakash J Am Chem Soc 1997 119 8035 (b) W Koch N Hein-richH Schwarz F Maquin D Stahl Int J Mass Spec Ion Proc 1985 67305 (c) Reference 4

(28) H Schmidbaur S Hofreiter M Paul Nature 1995 377 503(29) V G Granik B M Pyatin R G Glushkov Russ Chem Rev 1971 40


J A Olah J Am Chem Soc 1974 96 884 (b) G A Olah G RasulA Burrichter G K S Prakash Proc Nat Acad Sci USA 1998 954099

(31) G A Olah A M White D H OBrien Chem Rev 1970 70 561(32) J Kaspi D D Montgomery G A Olah J Org Chem 1978 43 3147(33) G A Olah A-H Wu Synlett 1990 599(34) D E Pearson J Chem Soc Chem Commun 1974 397(35) G A Olah K A Laali Q Wang G K S Prakash Onium Ions Wiley

New York NY 1998 p 435(36) A Bagno J Bukala G A Olah J Org Chem 1990 55 4284(37) G A Olah G K S Prakash M Marcelli K Lammertsma J Phys Chem

1988 92 878(38) (a) S Sato H Ameta E Horn O Takahashi N Furukawa J Am Chem

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(39) F Canales C Gimeno A Laguna M D Villacampa Inorg Chim Acta1996 244 95

(40) S Canales O Crespo M C Gimeno P G Jones A Laguna Chem Comm 1999 679

(41) K Laali H Y Chen R J Gerzina J Organomet Chem 1988 348 199(42) G A Olah G Rasul G K S Prakash Chem Eur J 1997 3 1039(43) G A Olah Halonium Ions Wiley New York 1975(44) (a) G A Olah G Rasul M Hachoumy A Burrichter G K S Prakash

J Am Chem Soc 2000 122 2737 (b) Reference 30a(45) G A Olah et al unpublished result(46) J Bukala J-C Culmann J Sommer J Chem Soc Chem Commun 1992

481

5GITONIC VICINALSUPERELECTROPHILES


Similar to the geminal-type superelectrophiles described in the previouschapter vicinal systems may be formally depicted with adjacent posi-tive charges but these charges are often delocalized by induction andconjugation In the case of the ethylene dication (C2H4

2+ 1) theoreti-cal calculations have shown the perpendicular structure (D2d) to be themost stable geometry1 The two formally vacant orbitals are orthogonaland capable of interacting with the vicinal CH2 groups by hyperconju-gation (Figure 1) This leads to a remarkably short carbon-carbon bond(estimated to be 1432 ucircA) as well as positive charge residing on the hydro-gen atoms Similarly protosolvation of the tert-butyl cation (2) gives theprotio-tert-butyl dication (3) Theoretical calculations (MP26-311+Glevel) of the NBO charges show that much of the positive charge is locatedon the methyl groups2

There have been many studies related to tetraaryl-12-ethylene dica-tions formally gitonic superelectrophiles which show extensive chargedelocalization into the aryl rings (Scheme 1) Low temperature 13C NMRstudies have shown that the para carbons are deshielded from δ13C


125

copy

126 GITONIC VICINAL SUPERELECTROPHILES

C CH

H

H

HC C

H

H+

H+

H

1

CC

CH3

CH3

protio-tert-butyl cation

3

2++

+ +

1432 Aring

etc

NBO charges+052

+027

H3CC

CH3

CH3

tert-butyl cation

2

+058

+014

HH

H

H

+094

D2h

Figure 1 Ethylene dication (1) and calculated NBO charges for the tert-butyl cation (2)and the proto-tert-butyl cation (3)

OCH3

OCH3

OCH3

H3CO

SbF5 SO2ClF

minus78degC

OCH3

OCH3

OCH3

H3CO

OCH3

OCH3

OCH3

H3CO

etc

1583 ppm 1753 ppm

4 5 5

++

+

+

Scheme 1

1583 in the tetrakis(p-methoxyphenyl)ethylene (4) to δ13C 1753 in thecorresponding dication (5)3 This large downTHORNeld shift is best explainedby the delocalization of the positive charge caused by the repulsive inter-action of the two positive charge centers Inductive effects have likewisebeen shown to increase the acidic and electrophilic character of adja-cent groups For example the bicyclic hydrazinium dications react withnucleophiles at the α-carbon instead of at one of the nitrogen centers(eq 1)


N

N

KCN

CNHH

N

N

CN

H

minusHCN

N

N

HNC

+

+

minus

+

minus

(1)

As described previously a fully formed dicationic superelectrophileis generally considered the limiting case and there are likely varyingdegrees of superelectrophilic activation In Chapter 1 the 12-dicationicsystems such as the protoacetyl dication (CH3COH2+) and protonitron-ium dication (NO2H2+) were considered in terms of varying degrees ofprotosolvation Superelectrophilic activation in these systems may involveonly partial protonation or partial Lewis acid coordination to generate thereactive species The kinetic studies of Shudo and Ohwada were describedin Chapter 2 wherein the cyclizations of 4-phenylbutyronitrile (6) and13-diphenyl-1-propanone (9) were compared (eqs 2 and 3)4

CNCF3SO3H

CF3CO2H

CN

H

H+ C

NH H

O

6 7 8

++

+

(2)

Ph Ph

O

Ph Ph

OH

Ph Ph

OH2

80degC

9 10 11

H+CF3SO3H

Ph+

+

+

(3)

While both 4-phenylbutyronitrile (6) and 13-diphenyl-1-propanone (9)cyclizations show a dependence on acid strength the kinetic data sug-gest differing degrees of protonation at their transition states or differingprotosolvation of the activated complexes

Koltunov and Sommer have noted that an important consideration isthe timing of the second protonation in superelectrophilic reactions5 Forexample in the superacid-catalyzed condensation of benzaldehyde withbenzene (vida infra) two studies have proposed superelectrophilic dipro-tonated benzaldehyde (12 or 13) as the reactive electrophile leading tocondensation products (Scheme 2)67 An alternative explanation for this


H

OACID

C6H6

H

OHH

OH

H

HOH2

HH OH2

C6H6

H+

minusH+Products

15

16

H

OH2

12 + C6H6

H

O

CF3SO3H

C6H6

or H

OH

H

Hplus otherproducts

12 13

14

+

+

+

+

+

+

+ +

+

Scheme 2

conversion without invoking superelectrophiles 12 or 13 involves mono-protonated benzaldehyde (14) forming the σ -complex with benzene (15)followed by protonation of the resulting hydroxy group to give the distonicsuperelectrophile (16) This proposal suggests another potentially impor-tant aspect of superelectrophilic chemistry formation of diprotonated (orother multiply charged species) intermediates may lead to favorable shiftsin equilibria leading to products

The vicinal -dicationic intermediates comprise a large group of super-electrophilic species We are subsequently discussing sections on boronaluminum carbon nitrogen oxygen halogen and even noble-gasbased systems Each of these sections is further divided as necessaryFor example the carbon-based systems include vicinal -carbon-carboncarbon-nitrogen carbon-oxygen and carbon-halogen dicationic systems

52 VICINAL SYSTEMS

521 Boron and Aluminum-Centered Systems

There are relatively few examples known of doubly electron-deTHORNcientgitonic superelectrophiles involving boron or aluminum In studies bySchwartz and associates the NBH4

2+ dication has been generated ingas-phase studies using charge stripping mass spectroscopy and its poten-tial energy surface has been studied by theoretical calculations8 The

VICINAL SYSTEMS 129

NBH42+ dication is formed by the collision of the NBH4

bull+ ion withO2 and experimental detection of the NBH4

2+ ion indicates a lifetimegreater than 5times10minus6 s This is in accord with computational studies thatTHORNnd signiTHORNcant energy barriers to decomposition or fragmentation Atthe MP46-311G(dp)6-31G(d)+ZPE level of theory two minima arelocated the ammoniaborene dication NH3BH2+ (17) and its isomerNH2BH2

2+ (18)

B NH

H H

HH B N

H

H

H

2+2+

17 18

C2v

C3v

The ammoniaborene dication NH3BH2+ (17) is estimated to be about60 kcalmol more stable than NH2BH2

2+ (18) Much of the interest inactivated boron and aluminum electrophiles arises from their isoelectronicrelationships to related carbon-centered superelectrophiles (Table 1)9 Forexample a variety of superelectrophilic trihalomethylcations (ie 19)have been proposed in superacid-catalyzed conversions and these specieshave been shown to have signiTHORNcance in the functionalization of alka-nes (vide infra) Isoelectronic boron and aluminum species 20 and 21are thought to be involved in some reactions with weak nulceophilesthe reaction of BCl3 with arenes in the presence of AlCl3 gives phenyl-borondichloride (eq 4)10

C6H6 + BCl3AlCl3minusminusminusminusrarr C6H6BCl2 + HCl (4)

The activity of aluminum chloride as a strong Lewis acid (including itsability to crack or isomerizes alkanes) may be related to the formation ofits mono-bridged dimer (21)11 The carbodication CCl22+ (22) has beensuggested as a possible intermediate in condensed phase reactions12 whilethe carbodication CH2

2+ (25) has been studied by high level ab initio cal-culations and directly observed by mass-spectrometric techniques13 Theisoelectronic boron and aluminum species (2324) have likewise beenstudied by theoretical methods14 while cation 26 has also been observedin gas-phase experimental studies15 Carbodication 27 has also been stud-ied extensively by experimental and theoretical work and computationshave shown 27 to have planar structure (C2v)16 Similarly the isoelectronicboron species 28 was studied theoretically and it was proposed as an inter-mediate in the condensed phase17 Evidence for the boron analog (29) tothe protosolvated tert-butyl dication (3) has also been suggested from con-densed phase superacid chemistry18 Diprotonated carbonic acid (30) may


Table 1 Carbon superelectrophiles and their isoelectronic boron and aluminumsystems

CCl++ d+ dminus

d+ dminusd+ dminus

Cl

Cl

SbF5CClCl

Cl

SbF5B ClCl

Cl

AlCl3

19 20

Cl C Cl2+

2+ +

22 23

Cl B Cl+ +

H C H25 26

H B H

24

Cl Al Cl

CHH

H H

2+

27

BHH

H H

+

28

H3C +

+

+

CH3C

CH

H

H H

3

H3C

++

BH3C

CH

H

H H

29

Al ClCl

Cl

AlCl3

21

OH2

CHO OH

30

+OH2

BHO OH

31

HCHH

HH H 2+

32

HBHH

HH H +

33

Superelectrophile Isoelectronic Boron or Aluminum Systems

be involved in the superacidic cleavage of carbonates or bicarbonates19

The isoelectronic boron species protonated boric acid (31) has beenobserved in gas-phase studies and examined by theoretical methods20

Even the methonium dication CH62+ (32 diprotonated methane) has an

analogous boron species (BH6+ 33) which has been observed in gas-phase

studies and been examined by computational methods21 The BH6+ (33)

VICINAL SYSTEMS 131

ion is generated in a szligowing afterglow-selected ion szligow tube apparatus bythe gas-phase reaction of BH2

+ (26 previously generated from molecularoxygen and B2H6) with two dihydrogen molecules Calculations at theMP2(fu)6-311G9 dp)MP2(fu)6-311G(dp) level of theory indicate thatBH2

+ binds to two H2 molecules in reaction steps that are exothermic by145 kcalmol (THORNrst reaction) and 176 kcalmol (second reaction)17b Thereactions of BH2

+ (26) and BCl3-AlCl3 (20) with weak nucleophiles (H2and C6H6) indicate that the isoelectronic boron and aluminum speciespossess a high level of electrophilic reactivity Although these boronand aluminum systems are monocationic they can be good models forcarbon-centered gitonic superelectrophiles or other doubly electron-deTHORNcient systems

522 Carbon-Centered Systems

Vicinal 12-carbodicationic systems are some of the most important andthoroughly studied superelectrophiles They include inter alia 12-ethylenedications related carbon-nitrogen superelectrophiles (diprotonated iminesand nitriles) protosolvated carboxonium ions and superelectrophilic tri-halomethyl cations It is understood that many of these systems involveextensive charge delocalization and in a sense may not be consideredformal 12-dicationic systems For example diprotonated 23-butanedione(34) may be represented formally as a 12-ethylene dication (35a a gitonicsuperelectrophile) but even in monocationic carboxonium ions there is asigniTHORNcant amount of double-bond character retained in the carbon-oxygenbond (eq 5)22

H3CCH3

O

O

CF3SO3H

H3CCH3

+OH

+OH

35a 35b34

H3CCH3

OH

OH

++

(5)

Charge-charge repulsive effects increase the importance of the resonanceform (35b) having dione-type structure (a 14-dication and representing adistonic superelectrophile) Despite the importance of the charge separatedstructure 35b the system is included here with other 12-ethylene dicationsand gitonic superelectrophiles

5221 Carbon-Carbon Vicinal-Dications Ethylene dications are amajor group of carbon-centered superelectrophilic systems The parentethylene dication (CH2CH2

2+ 1) has been studied experimentally inthe gas-phase as well as in several theoretical studies1 Two electron


ionization of ethylene in the gas-phase produces the ethylene dication1 Calculations at the HF6-31G(d) and MP26-31G(d) levels indicatethe D2h structure as the most stable geometry Other two carbon sys-tems studied include the acetylene dication (36) the ethane dication (37MP46-311G optimized structure) and diprotonated ethane (38)1323

1 36

H CC H2+

Dinfinh

37

C C

H

H

H

H

HH

Cs

38

2+2+

C C

H

H

HH

C2

H

H

H

H

C CH

H H

H+ +

Halogenated ethylene dications have also been studied in theoretical andgas-phase studies24 Although the ethylene dication (1) can be detectedin mass spectrometric experiments by charge stripping of the ethyleneradical cation with molecular oxygen 1 could not be generated yet in thecondensed phase On the other hand substitution by good n- or π -donorgroups leads to ethylene dications that can be readily generated in solution

Among the stabilized ethylene dications produced the aryl-substitutedethylene dications have received most attention (Table 2) These havebeen prepared by the direct oxidation of the ethylene derivatives or byionization of suitable functional groups In the case of tetraanisylethylene(4) oxidation by SbCl5 Br2 or I2CCl4 produces the remarkably stabledark green ethylene dication 5 which has been characterized by X-raycrystallography25 Other organic oxidants such as anthracene-based rad-ical cations have also been used to generate 5 The tetraanisylethylenedication (5) can itself oxidize hydrocarbon substrates (octamethylbipheny-lene and cyclooctatetraenes) to their radical cations by electron-transferreactions26 The reversible oxidation of the chiral tetraaryl ethylene (50)provides a chiral tetraaryldication (51) which may be useful in chiropticalswitching and memory devices (eq 6)27

O

OO

O

SbCl5

25degC

5150

O

OO

O

+

+

(6)

The (R)-alkyl groups induce left-handed helicity in dication 51 whichgives an intense Cotton effect in the circular dichroism (CD) spectrumAs in the case of the tetraanisylethylene dication (5) the X-ray crystal

VICINAL SYSTEMS 133

Table 2 Generation of aryl-substituted 12-ethylene dications

Ar Ar

ArAr

Ar Ar

Ar Ar

PhPh

Ph Ph

CH2CH3Ar

CH3CH2 Ar

OHPh

Ph Ph

OHPh

Ph OCH3

OHAr

Ar OCH3

OHPh

Ph OH

SbCl5 Br2 or I2

SbCl5 or AgNO3

SbF5

ElectrochemicalOxidation

CF3SO3H

Ag (I) CF3SO3H

CF3SO3H-SbF5

CF3SO3H

Reagent DicationSubstrate

40

42

44

45

46

47

48

CF3SO3H or FSO3HAr Ar

HO OH

Ar = p-methoxyphenyl49

Ar Ar

ArAr

Ar Ar

Ar Ar

PhPh

Ph Ph

CH2CH3Ar

CH3CH2 Ar

OPh

Ph Ph

OPh

Ph OCH3

OAr

Ar OCH3

OPh

Ph OH

HO

Cl

HO

HO

Ar = p-methoxyphenyl

Ar = p-dimethylaminophenyl



4 5

39

43

Ar Ar

O O


41

+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +


structure of the chiral dication 51 shows extensive delocalization (and thusstabilization) of the positive charges Another related and important systemis the tetrakis-(p-dimethylaminophenyl)-ethylene dication (40) which canbe readily prepared by the chemical oxidation (by Ag (I) salts or SbCl5)of the oleTHORNn (eq 7)28

NMe2

NMe2

NMe2

Me2N

NMe2

NMe2

NMe2

Me2N

39 40

SbCl5

NMe2

NMe2

NMe2

Me2N+

+

+

+

(7)

The stability of dication 40 is seen in the fact that it can be studied inDMSO solution and isolated with counter-ions having somewhat highernucleophilic nature The X-ray crystal structure of the bis-triiodide salt ofdication 40 reveals that the C=C bond length increases from 135 ucircA instarting compound 39 to 150 ucircA for the dication (40) reszligecting a chargedelocalized structure and roughly a single bond between the two centralcarbons28 While the stabilized tetraarylethylene dications such as 5 51and 40 do not possess the high electrophilic reactivities typical of gitonicsuperelectrophiles the reactivities of these systems are greatly increasedin structures having substituents that are less electron donating

The tetraphenylethylene dication (42) can be generated by the directoxidation of the oleTHORNn or by other routes (Scheme 3)29 Ionization of ben-zopinacol tetraphenylethylene oxide and 222-triphenylacetophenone intriszligic acid gives the ethylene dication 42 by dehydration of the carbenium-oxonium dication (52)30 Although dication 42 can be directly observedunder stable ion conditions at low temperatures warming of the solutionscontaining dication 42 leads to cyclization with proton loss giving quanti-tatively 910-diphenylphenanthrene The same 910-diphenylphenanthreneis also produced from the reaction of 12-dichloro-1122-tetraphenyl-ethane with SbCl5 a reaction that likely involves dication 42 For dication42 the 13C NMR spectrum (minus75C SbF5-SO2ClF) shows δ13C reso-nances at C+1986 Cipso1401 Cortho1430 1484 Cmetal1433Cpara1529 When compared to the 13C NMR spectrum of tetraphenylethy-lene it is clear that the positive charge is delocalized into the phenylrings 42 It is however also apparent that the charge delocalization isconsiderably less in 42 than in the tetraanisylethylene dication (5) or thetetrakis-(p-dimethylaminophenyl)ethylene dication (40)

VICINAL SYSTEMS 135

42

SbF5 SO2ClF

ndash78degC

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph

CF3SO3H

OHHO

Ph

Ph Ph

PhO

PhPh

O

PhPh

CF3SO3H

CF3SO3H

52

ndash2 H+

H H

Ph

Ph Ph

PhH2O+

++ +

++

Scheme 3

The dication 44 was generated by the reversible electrochemical oxida-tion of the corresponding oleTHORNn (43)26 It was also prepared by chemicaloxidation using the ethanoanthracene derivative (53 eq 8)


CH2CH3Ar

CH3CH2 Ar+

44

CH2CH3Ar

CH3CH2 Ar

+

OCH3

OCH3

+

2+ + CH2CH3Ar

CH3CH2 Ar

43 54

(8)

Dication 44 decomposes at room temperature The poor stability is thoughtto arise from the liable α-protons of the ethyl groups of dication 44 Aseries of 12-ethylene dications have been generated and studied involvingboth aryl-stabilized and oxygen-stabilized carbocationic centers (4549(Table 2) When the hydroxyketone is reacted with a substantial excess ofCF3SO3H at minus50C two cyclization products (5556) are obtained (eq9)31 The reaction is thought to occur through the dication 45 Similarlythe szliguorene products (5960) are obtained from the hydroxyester (57)and acid (58) via the dications 46 and 48 (eq 10)

PhO

Ph

Ph

HO CF3SO3H

Ph OH

8

55 5645 45

PhOH

Ph

Ph

++

Ph OHPh

Ph

+ + +

O

Ph

74

(9)


PhO

Ph

OR

HO CF3SO3H

O

OR

R = CH3 46R = H 48

R = CH3 59 81R = H 60 65

ndash45degC

R = CH3 57R = H 58

OH

OCH3

OCH3

H3CO

47

+ +

Ph OH

Ph

OR

+ +

(10)

Several lines of evidence in the studies of Ohwada and Shudo support theinvolvement of these gitonic superelectrophiles An analagous dicationicspecies (47) has been directly observed by 1H and 13C NMR at low tem-perature in both CF3SO3HSbF5 and CF3SO3H solutions With dication47 the NMR spectra show an equivalence of the aromatic rings suggest-ing a perpendicular relationship between the two cationic centers Thedications having the 4-methylphenyl substituents (6162) have likewisebeen directly observed by NMR at low temperature and upon warmingthe solutions the expected cyclization products are formed (eqs 1112)

ArO

Ar

Ar

HO

Ar = p-methylphenyl

CF3SO3H-SbF5

ndash30˚C

61

O

Ar

Ar OH

70 14

0degCAr

OHAr

Ar

+ + +

(11)

ArO

Ar

OH

HO

Ar = p-methylphenyl 62

O

OH

82

CF3SO3H

ndash20degC30 min

ArOH

Ar

OH

+ +(12)

In the case of dication 62 the cyclization reaction was found to exhibitTHORNrst order kinetics (k = 403 times 10minus3 sminus1) The activation parameters werealso calculated (H = 111 kcalmol and S = minus287 eu)32a

Evidence for the dicationic intermediates was also obtained from kineticexperiments involving the hydroxyester 5732a The yield of the cyclizationproduct (59) increases considerably with the acidity of the reaction media(Scheme 4) The szliguorene product 59 is formed in appreciable quantitiesonly in superacids H0 le minus12) Following this observation the kinetics ofthe szliguorene cyclization was also studied in solutions of varying acidityWhen compound 57 is reacted in solutions with acidity in the H0 minus11 tominus13 range the cyclization rate is found to increase linearly with acidity

VICINAL SYSTEMS 137

PhO

Ph

OCH3

HO

O OCH3

5957

ACID

ndash40degC YIELD

ndash27 ndash118 ndash132H0

0 20 94

Scheme 4

The linear rate proTHORNle provides strong evidence for the second protonationof the monocationic intermediate and a rate-determining step involvingthe dicationic superelectrophile 46

In addition to the above kinetics studies the szliguorene cyclizationwas studied using ab initio computational methods32a It was foundthat the theoretically predicted barriers to the cyclizations for the dica-tionic intermediates agree well with the values obtained from the kineticexperiments For example geometry optimization and energy calculationsat the B3LYP6-31 level estimated that the activation energy (Ea) is140 kcalmol for the 4π -electron conrotatory electrocyclization reactioninvolving compound 57 and the diprotonated intermediate (46 eq 13)

HO OCH3

Ea = 140 kcalbullmolndash1

57

46

2 H+

Ph OH

Ph

OCH3

+ +

+ ++

+(13)

This is reasonably close to the experimentally determined value ofH = 111 kcalmol for the superelectrophilic cyclization of 62(eq 12) Another computational study showed that the energy barriersdramatically decrease for the electrocyclization when the monocationsare protonated to form superelectrophiles In the case of 63 cycliza-tion provides the acetyl-substituted szliguorene in 70 yield from CF3SO3H(Scheme 5) At the B3LYP6-31 level of theory dication 64 is estimatedto have a cyclization barrier to szliguorene of 85 kcalmol compared to avalue of 25 kcalmol for the cyclization of monocation 65

The described superelectrophilic activation and szliguorene-cyclization isthought to involve a lowered energy of the LUMO and concomitant delo-calization of positive charge into the aryl ring(s)32b Calculations at the4-31GSTO-3G level on a model system (Figure 2) have shown that theamount of positive charge in the phenyl ring increases upon formation ofthe dication (67) when compared to the monocation (66) and the benzylcation (calculations are based on fully planar structures) It is well known


HO CH3



63 64

2 H+

PhO

PhHO

CH3

O CH3

63 65

H+

CH3

PhO

PhHO

63

PhO

PhHO

CH3

CF3SO3H

ndash40degC

OCH3

70

Ph OH

Ph

CH3

+ +

PhO

Ph

CH3

+

+

+

+

++

++

Scheme 5

66 67

67a 67b 67c

Total ring charge (planar structures)

+0594 +0635 +1063

LUMO energies ndash013875 au ndash034115 au

+

OH

H

H

+OH

H

H

+

+ OH

H

H

+

++

O

H

H

+ OH

H

H

+

+

Figure 2

from experimental studies that charge-charge repulsive effects can leadto separation of the charge centers The calculations also show that theLUMO energy decreases considerably upon formation of the dicationicsystem (minus013875 au for the monocation 66 and minus034115 au for thedication 67) Moreover calculations of the LUMO coefTHORNcients indicatethat resonance forms such as 67b and 67c are important to the description

VICINAL SYSTEMS 139

of the dicationic structure These two aspects LUMO lowering and chargedelocalization are critical factors in the superelectrophilic activation ofthese 4π -electron controtatory electrocyclizations

Further experimental evidence for gitonic superelectrophiles comesfrom the catalytic activation of the monocationic species32a When theα-chloro ester (68) is reacted with AgBF4 or Ag(O2CCF3) the mono-cationic intermediate (69) is cleanly formed This is evident from theobserved trapping product (57 eq 14)

Ph

Ph

O

OCH3Cl

Ag+

CF3SO3H

H2O

Ph

Ph

O

OCH3HO

5996

68 69

46

57

Ph

Ph

O

OCH3+

(14)

With the monocationic species no szliguorene cyclization is observed How-ever upon addition of CF3SO3H the cyclization occurs almost quanti-tatively This is consistent with formation of the protonated dicationicintermediate (46) leading to the cyclization product (59) In this samestudy it is noted that other stable monocationic 11-diarylethyl cations(ie the 11-diphenylethyl cation) do not readily form the szliguorene ringsystem indicating the importance of superelectrophilic activation

Besides the szliguorene cyclization the 12-ethylene dications are known toundergo another type of electrocyclization reaction to produce the phenan-threne ring system (see eqs 9 and 11 and Scheme 3)32a Although derivedcarbenium-carboxonium dications (70) will give the phenanthrene-typeproducts (albeit in low yield eq 15) the bis-carboxonium dication 71 doesnot Moreover the szliguorene cyclization occurs readily in 11-dihydroxylicsystems (eq 10)

Ph Ph

OHO CF3SO3H

Ph Ph

OH

Ph Ph

OH

OH

11

70 70

+ +

+

+ (15)

7171

Ph Ph Ph Ph Ph Ph

O O HO OH HO OHCF3SO3H nocyclization

+ +

+ + (16)

In order to understand this apparent difference in reactivities two isomericdications (72 and 73) were studied calculationally


OC C

H

H O

H

H

HC C

H OH

O H

72 73

Relative Energies 0 kcalbullmolminus1 25 kcalbullmolminus1

+ + + +

Calculations at the 4-31G level of theory found that the 12-bis-carboxonium ion (72) is signiTHORNcantly more stable than the carbenium-carboxonium dication (73) Thus when compared with the 11-dihydroxylicstructure 73 the 12-dihydroxylic structure 72 ismore effective at stabilizingthe 12-ethylene dication This effect leads to the stabilization of dication 71(eq 16) and not to phenanthrene cyclization

Other oxygen stabilized ethylene dications have been prepared and stud-ied using stable ion conditions For example Olah and White were able toobserve as early as 1967 diprotonated oxalic acid (74) in FSO3HSbF5solutions33 This species and related dications were also studied subse-quently by theoretical methods Diprotonated α-keto acids and esters havelikewise been generated in superacidic media such as 757734

HO OH

OHHO OHHO

HO OH Ph OH

OHHO OCH3HO

Ph OH

HO OCH3

OH

HO OCH3

OH

H3C H3C

74 74 75 76

77 77

+

+

+ + + + + +

+ + +

+

For each of these ions the 1H and 13C NMR spectra are consistent withdicationic species In the case of dication 77 the 13C signal for thepara-carbon is found at δ13C 1775 (CF3SO3HSbF5 solution at minus20C)This again indicates a signiTHORNcant amount of positive charge delocalizationarising from charge-charge repulsive effects

Similar oxygen stabilized ethylene dications were proposed in sev-eral types of superacid-catalyzed condensation reactions involving 12-dicarbonyl compounds For example 23-butanedione condenses in highyield with benzene and the superelectrophile (35) is considered to bethe key intermediate because the monoprotonated species (78) is notsufTHORNciently electrophilic to react with benzene (eq 17)35 Several biologi-cally important α-ketoacids were also found to generate superelectrophiles

VICINAL SYSTEMS 141

H3CCH3

O

O

CF3SO3H

C6H65 min 0degC

H3CCH3

OH+

+

+

++

O

H3CCH3

OH

OH

H3CCH3

OH

OHH3C

CH3

O

Ph Ph

95

357834(17)

H3COH

O

OCF3SO3H

C6H6H3C

OH

OH

OH

H3COH

OH

OH

H3COH

OH

Ph PhPh

Ph

79

+ CO + H2O

+

++

+

+

(18)

(7982) in CF3SO3H all of which condense with benzene (eq 18 and videinfra)36 In the case of 81 and 82 it is likely that these superelectrophilesare in equilibrium with diprotonated species

Ph OH

OH

OH

Ph OH

OH

OH

80 80

HO OH

OH

OH

OH

HO OH

OH

OH

OH

81 81

HOOH

OH

OHHO

OH

OH

OH

82 82

OHOH

OHHO OHHO

83 83

+

+

+ ++ +

+

+

+ +

+

+ +

++ +

+

++

+

Dication 79 has been observed by low temperature NMR fromFSO3HSbF5 solutions34 Although diprotonated quinones (8384) areexpected to have extensive delocalization of the positive charges sev-eral have been reported and their condensation chemistry suggests arelatively high level of electrophilic reactivity (eq 19)37 Diprotonatedacenaphthenequinone and aceanthrenequinone (83 and 84) have been


proposed as intermediates in superacid-catalyzed condensation reactionsHigh molecular weight polymers have also been prepared by superelec-trophilic condensations involving 8337bc Both superelectrophiles 83and 84 were studied by calculations while 83 has been directlyobserved by spectroscopic methods In each case calculations at theB3LYP6-311GB3LYP6-311G level show that the global minimainvolve protonation at both carbonyl oxygen atoms38 Aceanthrenequinoneand acenaphthenequinone have been shown to condense with moderatelydeactivated arenes in the superacid-promoted reactions (eq 19)

O O

O

CF3SO3H

C6H5Cl

94

HO OH

Cl

Cl

HO O+ + +

+ +HO OH

84 84

(19)

This indicates that strong electrophilic species (ie 84) are generated fromthe quinones

Besides oxygen and aryl-stablized ethylene dications there havebeen several reports of nitrogen-stabilized systems For example Olahand co-workers described the oxamide dication (85) using theoreti-cal and experimental studies (eq 20)39 When oxamide is dissolved inFSO3HSbF5 solution at minus78C the 13C NMR of dication 85 is obtainedwith a single 13C signal at δ13C 1579 This experimental result agreesreasonably well with the IGLO-calculated chemical shift of δ13 C 1657for the dication 85

H2NNH2

O

O

FSO3H-SbF5

minus78degC H2NNH2

OH

OHH2N

NH2

OH

OH

H2NNH2

OH

OH

85 85 85

+

+

+

+

+

+

(20)

Calculations at the MP26-31GMP26-31G level indicates that the C2h

fully planar structure is about 8 kcalmol more stable than the C2v perpendic-ular form (a transition state) Likewise condensation reactions with isatinshave suggested the involvement of the superelectrophile 86 (eq 21)40 Thissuperelectrophilic chemistry has been successfully applied in the prepa-ration of hyperbranched polymers and other macromolecules40bminusd Other

VICINAL SYSTEMS 143

synthetic studies have used the isatin condensations to prepare biologicallyactive products40e The monooxime of 23-butanedione is protonated twicein CF3SO3H to generate the dication 87 (eq 22)41

N

O

O

H

CF3SO3H

86

N

OH

OH

H

+

+

86

N

OH

OH

H

+

+(21)

H3CCH3

N

O

HO

CF3SO3H-SbF5

87

H3CCH3

N

OH

HO H+

+

87

H3CCH3

N

OH

HO H

+ + (22)

Both of these superelectrophiles (8687) are capable of reacting with ben-zene in condensation reactions Dication 87 can be directly observed bylow-temperature NMR being generated by dissolving the oxime inCF3SO3HSbF5 solution at minus30C Based on the NMR studies the pKa ofdication 87 is estimated to be aboutminus17 tominus19 suggesting that inCF3SO3H(H0 minus 14) a low but signiTHORNcant concentration of the dication is present

Another ethylene dication with signiTHORNcant nitrogen stabilization is thetetrakis(dimethylamino)ethylene dication (88) By reaction of the sub-stituted-ethylene with Cl2 or Br2 (eq 23)

N

NN

N N N N N N N

Cl2

88 88 88

NN+ +

NN+

+NN

+ +

2 Clminus

(23)

the dication salt (88) can be formed and its X-ray crystal structure has beendetermined42 Shortening of the CN bonds and twisting of the NCNsub-units 76 relative to each other is consistent with almost complete delo-calization of the positive charges The same dication (88) can be preparedas a 12 salt by the reaction of tetrakis(dimethylamino)ethylene and tetra-cyanoethylene The stability of this dication is evident from the formationof stable salts with counter ions having relatively high nucleophilic nature

An unusual class of gitonic superelectrophiles (having vicinal -dicationicstructure) are the protosolvated alkylcarbenium ions (of carbenium-car-bonium dication nature) Several studies have shown that alkylcarbenium


DFSbF5

3

minus78degC

H3CC

CH2D

CH3

minusH+

H3CC

CH2

CH3

2

H3CC

CH3

CH3

+ H3CC

C

CH3

HH

H

D

+

+

+

+ H+

Scheme 6

ions can undergo protosolvation of the CH σ -bonds in superacidicmedia43 For example the tert-butyl cation (2) is a remarkably stablespecies in superacids with no deprotonation to isobutylene Howeverwhen it is generated in an SbF5SO2ClF solution and then 11 DFSbF5 isadded the tert-butyl cation undergoes slow but well-characterized (by 1Hand 2H NMR) hydrogen-deuterium exchange (Scheme 6)43a To accountfor the isotopic exchange in superacid protonation (deuteration) of thetert-butyl cation (2) to the protio-tert-butyl dication (3) or the correspond-ing protosolvation must occur Theoretical calculations have estimated thatCH protonation of 2 is more favorable than CC protonation by about14 kcalmol

In a similar respect 2-chloropropane can be ionized in SbF5SO2ClF atminus78C to the 2-propyl cation (89)43b Subsequent addition of 11 DFSbF5

again leads to slow hydrogen-deuterium exchange The exchange is envis-aged to occur by reactions at the CH bond via the dication 90 (eq 24)

DFSbF5

90

minus78degC

H3CC

C

H

HH

H

D

H3CC

CH2D

H

H3CC

CH3

D

89

++minusH++

+H3C

CCH3

H

+

(24)

Alkyl cations like the tert-butyl cation (2) and 2-propyl cation (89) are sig-niTHORNcantly stabilized by hyperconjugative CH and CC σ -back donationinto the empty carbocationic p-orbitals Protosolvation involving σ -bondscan diminish this hyperconjugative stabilization and thus lead to super-electrophilic carbocationic species

VICINAL SYSTEMS 145

5222 Carbon-Nitrogen Vicinal-Dications There are several types ofgitonic superelectrophiles having the 12-dicationic structure involvingcarbon-nitrogen bonds As described in Chapter 2 diprotonated nitrilesand cyanides have been proposed as intermediates in superacid-catalyzedreactions44 The Gatterman reaction (the acid-catalyzed reaction ofcyanides with arenes) is known to provide improved yields of prod-ucts with increasing acidity of the catalyst Shudo and Ohwada studiedthe superacid catalyzed reaction of trimethylsilyl cyanide with aromaticsand found signiTHORNcantly increased reaction rates and yields with strongersuperacids (eq 25)

(CH3)3SiCN

acid 20degCCl Cl

H2OCHO

+CHO

Cl

100 CF3SO3H (H0 minus 14)

95 CF3SO3H 5 SbF5 (H0 lt minus 18)

acid system product yield (ca 25 ortho 75 para)time

30 min

10 min

2

93

(25)

Based on these results the diprotonated superelectrophile (92) is suggestedto be involved in the reactions (eq 26)

H+

H C NH+ H+

NaCN orTMS-CN

9291

H C N H+

H C NH

H

+ +

(26)

Theoretical studies of dication 92 have shown it to reside in a deep poten-tial energy well with a gas-phase barrier to deprotonation estimated to beabout 42 kcalmol (MP46-311G level)45

The nitrilium salt 93 is known to react with activated arenes but inrelatively weak acids (CF3CO2H H0 minus27) it does not react with benzeneor deactivated arenes However in 5 SbF5 95 CF3SO3H H0 minus18solution the nitrilium salt 93 gives with benzene benzophenone in 55yield (eq 27)

C6H6

ACID

C

O

93 94

H2OC N CH3

CF3SO3

+

minusC

N

CH3

H

++

(27)

Since the reaction only occurs in highly acidic media it is suggested thatthe gitonic superelectrophile (94) is formed and leads to product44


Kinetic evidence suggests the involvement of gitonic superelectrophilesalso in superacid-promoted Houben-Hoesch reactions44 As discussed pre-viously 4-phenylbutyronitrile (6) is found to cyclize at an appreciable rateonly in solutions more acidic than H0 minus10 (eq 28)

CN CF3SO3H

CN

H

H

O

6

8

CN

H

slow

fast

H2O

H2O

+

++

(28)

This is indicative of the formation of the diprotonated intermediate 8 andits involvement in the rate-limiting step of the cyclization

Protonated iminium dications have also been studied by theoretical andgas-phase experimental studies46 For the methyleniminium ion (95) theN -protonated species (96) was found to be a stable minimum A seconddicationic species was also located as a minimum corresponding to thenonclassical structure 97 but it lies 27 kcalmol above 96 on the potentialenergy surface (MP26-31G level)

95 96 97

NHC

H

H

H+ N

HCH

H

H H

++

NHC

H

H

H H+

+

Using charge stripping mass spectrometry Schwarz and co-workers foundevidence for the formation of the gitonic superelectrophile 96 in the gasphase (generated from the ethylamine radical cation CH3NH2

+bull)47 Theethyleniminium and related dications have also been studied using theo-retical methods46 Three types of structures have been found at the globalenergy minima from their respective iminium ions (eqs 2931)

H3CC

NH

H

H

98

Relative Energy kcalmol 00 60

99

+

H+

CC

NH

H

HH

H

HH

+

+H3C

CN

H

H

HH

++

(29)

VICINAL SYSTEMS 147

H3CC

NH

CH3

H

100

+

H+

H3CC

NH

CH3

HH

++

(30)

H3CN

CH

CH3

H

H+

101

+

CN

CH

CH3

H

H

HH

H+

+

(31)

the nitrogen-protonated charge-separated dication (98) the nitrogen pro-tonated dications (99 and 100) and the CH protonated dication (101)The preferred type of structure is evidently determined by the pattern ofsubstitution of the iminium ion In the case of the isopropyleniminum ion(eq 30) nitrogen protonation leads to a carbenium ion center (100) that isstabilized by hyperconjugation with the methyl groups Similar stabiliza-tion occurs with dication 99 (eq 29) However the repulsive effects of thepositive charges lead to charge separation and stabilization of structure 98

In superacidic reactions diprotonated imines form gitonic super-electrophiles48 As described in Chapter 2 kinetic experiments have shownthat diprotonated intermediates are involved in these conversions Otherexperiments showed that the reaction provides higher yields in strongeracid systems (eq 32)

N

Ph

H3C

CH3

acid


100 CF3CO2H (H0 minus 27)

acid system product yieldtime

2 h

26 h

94

50

104

N

Ph

H3C

CH3

HN

Ph

H3C

CH3

H

HN

H

PhCH3

H3C

temperature

60degC

72degC

102 103

++

+

(32)

indicating the involvement of vicinal -superelectrophiles (ie 104) Inorder to further probe the superelectrophilic activation compound 105was reacted in deuterated triszligic acid (CF3SO3D 23C for 24 hrs) anddeuterium incorporation was only seen in the phenethyl group (Figure 3)This HD exchange must occur through intermediates such as 106 Thussuperelectrophilic ring closure does not occur via dications 107 or 108but rather involves an NN -diprotonated species (such as 104 or 109)


105

23degC

CF3SO3D

108

N

No DeuteriumIncorporation

DeuteriumIncorporation

NHHD

107

NH

H D

N 106

109

NH

D

H

NH

D

+ + +

+

+ ++

+

Figure 3

Another example of a carbon-nitrogen gitonic superelectrophile is theprotonated guanidinium ion49 The guanidinium ion (110) can be proto-nated in FSO3HSbF5 to give the gitonic superelectrophile (111 eq 33)

110

FSO3HSbF5

minus40degC

111

H2NC

NH2

NH2

+

H2NC

NH3

NH2

+

+(33)

which is a stable dication in the superacidic medium Dication 111 wascharacterized with 13C 1H and 15N NMR spectroscopy

As described in Chapter 2 a unique gitonic superelectrophile is consid-ered to be involved in an enzyme system that converts CO2 to methaneBerkessel and Thauer have studied this metal-free hydrogenase enzymefrom methanogenic archaea and a mechanism is proposed involving acti-vation through a vicinal -superelectrophilic system (eq 34)50

114

H2

112 113

HN

NH

N

NH

O

H2N

CH3

CH3

H

H

AH

HN

NH

N

NH

O

H2N

CH3

CH3

H

AH

+

HN

NH

N

NH

O

H2N

CH3

CH3

H

A

H+ +

(34)

Although the exact nature of the superelectrophilic intermediate is notknown it was suggested that protosolvation of one or both of the iminium

VICINAL SYSTEMS 149

nitrogen atoms leads to the superelectrophile such as 113 This resultsin a decreased neighboring group stabilization and enables reaction withthe weakly nucleophilic molecular hydrogen It was also noted that local-ized highly acidic realms (such as those necessary to produce a super-electrophile) may be possible in an enzymes active site given properlypositioned acidic functional groups and a nonbasic local environmentIn accord with the proposed superelectrophilic activation model studieshave shown that the carbenium ion salts themselves are unreactive towardsmolecular hydrogen even in the presence of added base (eq 35)51

N

NtBu

tBu

H

1 atm H2 DMAP

N

N

tBu

tBu

H

H

Clminus

+ (35)

The metal-free hydrogenase enzyme system was also studied by the-oretical calculations52 This study involved the reactions of two modelsystems (115 and 116) with molecular hydrogen (Table 3) Cation 115

Table 3 Calculated model reactions of the amidinium ions 115 and 116 with H2 inthe absence and presence ofa base ((BLYP6-311G(2 d 2p) level)

149

33

minus57

4

minus87

ΔH (kcalbullmolminus1)

115

NN

H

116

NN

HH

118

N N CH3H3C N N CH3H3C+ H

H2

H2+ H

117

244

H2

H2O

H2

NH3

115

115

116

116

117 + H3O

118 + H3O

117 + NH4

118 + NH4

HH H

H2

H2O

H2

NH3

+

+

+

+

+

+

+

+


represents the resonance stabilized amidinium ion of N5N10 methenyltetrahydromethanopterin (112) while cation 116 serves as a model hav-ing resonance stabilization diminished or eliminated In Berkessel andThauers mechanistic proposal loss of planarity is suggested as one ofthe factors that makes the system (112) more electrophilic and reactivetowards hydrogen Using the BLYP6-311G(2 d 2p) level of theory andsolvation modeling using SCI-PCM (self-consistent isodensity polarizedcontinuum model) it was found that reactions with molecular hydrogenwere energetically more favorable with cation 116 compared with cation115 When the calculations included reaction of base with the protongenerated from the electrophilic reaction the reaction energetics showexothermic or slightly endothemic values (4 kcalmol 115 H2 and NH3)The authors suggest that these data indicate the thermodynamic feasibilityof the Berkessel-Thauer mechanism in the presence of a base Howeverthese studies did not address the possibility of superelectrophilic activa-tion and ascribed reactivtity to decreased neighboring group stabilizationby a folding or bending of the imidazolidine ring rather than due toprotonation of the nitrogen lone pair electrons

Pnictogenocarbenium ions [H2C=XH2]+ (119121 X = P As Sb)and their superelectrophilc dications have been studied using high-levelab initio calculations53 Cations 119121 can be protonated at either theC- or X-sites (Figure 4) and studies of proton afTHORNnities (PA) show anincreasing PA in the order P lt As lt Sb (for both C -protonation andX -protonation) For cation 119 calculations indicate that protonation at the

C PH

H

H

HC As

H

H

H

HC

H

H

H

H

119 120 121

122

2+

C PH

H

H

HH

C PH

H

H

HH

2+

125

123

2+

C AsH

H

H

HH

C AsH

H

H

HH

2+

126

124

2+

CH

H

H

HH

C Sb

Sb

Sb

H

H

H

HH

2+

127

+++

Figure 4

VICINAL SYSTEMS 151

P-site (125) is favored by 33 kcalmol over protonation at the C-site (122)However protonation at the carbon is favored for cations 120 and 121 Allthree dicationic species 123 124 and 125 are predicted to be kineticallystable with signiTHORNcant energy barriers towards homolytic or heterolyticfragmantation reactions In studies of isodesmic reactions with methanethe dicationic species are shown to be far more reactive (eqs 3637)

C

H

H

H+H

H

H

HHC

H

H

H H

119ndash121

X = P As SbH

H

H

HC X C X

+

++ (36)

2+ +

+C CX X

H

H

H

HH C

H

H

H+H

H

H

HHHC

H

H

H H+

125ndash127

X= P AsSb

(37)

For the reactions of cations 119121 with methane all the conversionsare endothermic (eq 36) Hydride abstractions involving the dications(125127) are however strongly exothermic (eq 37) Thus the isodesmicreactions go from being moderately endothermic to strongly exothermicupon changing involvement of monocationic species (119121) to thesuperelectrophilic dicationic species (125127)

5223 Carbon-Oxygen Vicinal-Dications A parent system of thesevicinal -dications is formed upon diprotonation of carbon monoxide Car-bon monoxide can be protonated at carbon to yield the formyl cation (128HCO+) or at oxygen to yield the isoformyl cation (COH+) though thelatter is estimated to be around 38 kcalmol less stable than the formylcation54 The formyl cation has been observed in the gas phase usinginfrared microwave and mass spectroscopy In the condensed phase thedirect observation of the formyl cation has been reported by Gladysz andHorvath in HFSbF5 solution using high-pressure NMR spectroscopy55

While the formyl cation is considered to be sufTHORNciently electrophilic toreact with arenes (Gatterman-Koch formylation) a more activated pro-tosolvated formyl cation (or the protoformyl dication 129) is needed inreactions with saturated hydrocarbons (Scheme 7) For example Olah etal found that isoalkanes are converted to branched ketones in high yieldsby the reaction of carbon monoxide with HFBF356 The carbonylation-rearrangement of isoalkanes to branched ketones is fundamentallydifferent from the Koch-Haaf type carbonylative carboxylation whichexclusively gives branched carboxylic acids A mechanism is suggested


CCH2

CH2CH3CH2CH3H

HFBF3

128 129

CO

2+

CH3CCH2CH3

CH2CH3

C

O

H

130

C

O

H

H

C

OH

HC

CH3

CH2CH3

CH2CH3

H

CCH3CH2

CH2CH3

CH3

C

O

H

+

minusH+

C

CH3

CH2CH3

CH2CH3

C

OH

H

+

H+

C

O

H

++

+

131

Scheme 7 Proposed mechanism for the formylation of isoalkanes and rearrangement toketone

involving the superelectrophilic formyl dication 129 (or its protosolvatedform) and reaction with the σ -donor tert CH bonds of the isoalkanesthrough a 3 center-2 electron bond (130) Rearrangement of the interme-diate products (ie 131) then gives the branched ketones potential highoctane gasoline additives As described in Chapter 2 superelectrophiliccarbonylation has also been demonstrated with adamantane

Further evidence for the protoformyl dication comes from aromaticformylation with CO in superacids57 It has been shown in the formyla-tion of toluenebenzene that the kTkB rate ratio is sensitive to the strengthof acidic catalyst Formylation in HFSbF5 gives a low kTkB rate ratioof 16 and a signiTHORNcant amount of ortho substitution while with lessacidic systems formylation gives a kTkB rate ratio of up to 860 withpredominantly para substitution These data indicate that the formylat-ing agent in HFSbF5 is an extreme reactive electrophilic species asit does not discriminate between toluene and benzene It has been pro-posed that the protoformyl dication (132) or a protosolvated species (129)are involved in these superacid-catalyzed formylations (Scheme 8) Olahand co-workers have also shown that HCOF with excess BF3 is also anexceedingly reactive formylating agent having a signiTHORNcantly enhanced

C

O

H

128 129 132


133

+

C

O

H

H

+

+C

O

H

H Ad+ dminus

C

O

H

BF3

d+ dminus

+BF4

minus+

Scheme 8 Protosolvation of the formyl cation (128)

VICINAL SYSTEMS 153

reactivity over the 11 complex HCOFBF358 The Lewis acid-complexed12 superelectrophile (133) was suggested as the reacting species

In work by Stahl and Maquin the protoformyl dication was observedin the gas-phase by charge-stripping mass spectrometry59 Ionization ofmethanol and reaction with O2 leads to detectable HCOH2+ (or DCOH2+when CD3OH is used) Several theoretical studies have examined thestructure and stability of the protoformyl dication (132) and its isomers60

At the MP46-31G level the protoformyl dication (132) is found tobe in a fairly deep potential energy well The barriers for proton loss are20 kcalmol (OH protonation 134) and 47 kcalmol (CH deprotonation135) above the energy minimum for 132 (Figure 5) In structural studiesthe protoformyl dication is found to have a relatively short CO bondlength suggesting considerable π -bonding

Related classes of gitonic superelectrophiles are the previously men-tioned protoacetyl dications and activated acyl cationic electrophiles Theacyl cations themselves have been extensively studied by theoretical andexperimental methods22 as they are intermediates in many Friedel-Craftsreactions Several types of acyl cations have been directly observed byspectroscopic methods and even were characterized by X-ray crystal struc-ture analysis Acyl cations are relative weak electrophiles as they areeffectively stabilized by resonance They are capable of reacting with aro-matics such as benzene and activated arenes but do not generally reactwith weaker nucleophiles such as deactivated arenes or saturated alkanes

There are several reports of activation of acyl cations by superacidssuggesting the involvement of gitonic superelectrophiles61 As discussedin Chapter 2 hydride transfer from isobutane to the acetyl cation has beenreported when the reaction is carried out in excess HFBF3 At the same

C

O

H HH

H

C-O BondLength Aring 1400 (6-31G)

C

O

H H

H

1232 (6-31G) 1102 (6-31G)1120 (MP3 6-31G)

132

CH HHCinfinv

CH HCHCinfinv

2+

RelativeEnergy(MP46-31G)

00 kcalbullmolminus147 kcalbullmolminus1 20 kcalbullmolminus1

2+

Cinfinv

2+

132135 134

1087 (6-31G)

128

O OO

+

C

O

H Cinfinv

+

C

O

H

H

Cinfinv

+

+

Figure 5 Calculated structuresenergies and C-O bond lengths of protonated formylcations


C

O

H3C OHC+O

CH3

HFBF2C

O+

CH3

136 137

HFBF3

minusH2OC+O

CH3

H F BF3d+ dminus

C+OH

CH3

+

Scheme 9 Protosolvation of the acetyl cation 136 to superelectrophile 137

CnH2n+2CH3COCl bull 2AlCl3

20degC 30 miniminusC4H10 + iminusC5H12 + iminusC4H10COCH3 + C C

m

138 139

C+

O

H3C AlCl4

AlCl3d+ dminus

minusC

O

H3C Cl AlCl3

AlCl3

d++

dminus

dminus

Scheme 10 Electrophilic solvation of the acetyl cation and reactions with alkane

time hydride transfer does not occur with acetyl cation salts in aprotic sol-vents such as SO2 SO2ClF or CH2Cl262 These results are consistent withthe activation by protosolvation of the acetyl cation (generated from aceticacid) by the Broslashnsted superacid (Scheme 9) The monocationic acetyl ion(136) is unreactive while the dicationic species (137) abstracts hydride Inaddition to protosolvation the activation of the acetyl cation can also beaccomplished with Lewis acids As Volpin found reaction of CH3COClin the presence of two or more equivalents of AlCl3 with alkanes leads toready isomerization and other electrophilic reactions (Scheme 10)63 Sincethe reaction does not occur when only one equivalent of AlCl3 is used theresults indicate evidence for electrophilic solvation involving a dicationiccomplex (138 or 139) In a similar respect pivaloyl chloride was foundto give methyl isopropyl ketone in reactions with hydride donors and alarge excess of AlCl3 (eq 38)64

CCO

ClCH3

H3CH3C

2 AlCl3C

CO

CH3

H3CH3C

AlCl4minus

CC

O

CH3

H3CH3C

AlCl4minus

AlCl3

(CH3)3CHH C(CH3)3

CCO

HCH3

H3CH3C

AlCl3

140

+ +

+ +minusminus

(38)

A proposed mechanism involves hydride abstraction by the superelec-trophilic pivaloyl-AlCl3 dicationic complex (140) which in turn undergoesthe mentioned rearrangement to methyl isopropyl ketone

VICINAL SYSTEMS 155

As discussed in Chapter 2 Shudo and Ohwada found that acetyl andbenzoyl hexaszliguoroantimonate salts (CH3CO+SbF6

minus andC6H5CO+SbF6minus

respectively) acylate aromatic compounds with increasing reaction ratesand greater yields in progressively more acidic media44 These data areconsistent with the formation of the superelectrophilic species 137 and 141(eq 39)65

C OH+ minus2H++ + +

C O H

141

ClOH

HCl

O

Cl

+

+

(39)

Like other superelectrophiles protonation of the acyl cations leads to de-crease of neighboring group participation and a lowering of the LUMOenergy level which facilitates reactions with even weak nucleophiles

Although attempts to directly observe the protoacetyl dication (137) bylow temperature NMR spectroscopy have not been successful the stretch-ing frequency of the acetyl cation carbonyl group is signiTHORNcantly shiftedin superacids63 The protoacetyl dication (137) has been observed in thegas phase by charge-stripping mass spectroscopy obtained by the disso-ciative ionization of pyruvic acid to generate CH3COH+bull followed bycharge stripping via collision with O266 The gas phase observation ofthe protoacetyl dication is also consistent with ab initio calculations67

Despite possessing high thermochemical instability towards deprotona-tion calculations indicate a signiTHORNcant kinetic barrier towards such uni-molecular dissociation The protoacetyl dication (137 C3v symmetry) wasfound to be at the global energy minimum for the C2H4O2+ structures(MP26-31G4-31G+ZPE level of theory) Based on the high enthalpyof formation of 137 and the exothermicity of model disproportionationreactions it was predicted that the free protoacetyl dication was unlikelyto exist in solution66 Nevertheless superelectrophilic activation of theacyl salts may not require formation of the discrete fully formed dica-tionic species (137) but may involve partial protonation or protosolva-tion (Scheme 9) in the condensed phase Moreover solvation and ionpairing effects may signiTHORNcantly stabilize these doubly-electron deTHORNcientspecies

Another related class of gitonic superelectrophiles are the superelec-trophilic halocarbonyl dications The halocarbonyl cations (XCO+ X =F Cl Br I) have been prepared under long-lived stable ion conditionsand characterized by 13C NMR spectroscopy68 Sommer and co-workersstudied the bromine-assisted carbonylation of propane in superacids and


C OBr

H-Aor SbF5

C OBr H A+ d+

d+

+

dminus

dminus

+CH3CH2CH3

SbF5 CO

Br2 (---SbF5)

H3CC CH3H

C HBrO

HA

minusHBrminusHA

+

H3C C CH3H

CO

142

Scheme 11

the bromocarbonyl cation was proposed as the reactive electrophilic inter-mediate69 Considering the high acidity of the reaction mixture an alter-native mechanistic proposal involves the superelectrophilic protosolvatedspecies (142) Reaction with propane an extremely weak nucleophileis considered to require further activation of the electrophile by coor-dination with the superacid (Scheme 11) This leads to the carbonylationproduct

Carboxonium ions are an important group of electrophiles in chemistry22

Carboxonium ions are categorized by the number of oxygen atoms boundto the carbon atom (one two or three) and by the groups bonded to the oxy-gen atoms (as acidic or non-acidic carboxonium ions) All of these types ofcarboxonium ions have the potential to form vicinal -dications by protona-tion or complexation of the non-bonded electron pairs of oxygen with acids(eq 40)

RprimeC

Rprime

OH

RprimeC

Rprime

O+

++

H

RprimeC

Rprime

OH H

H+

Rprime= alkyl aryl alkoxy OH

(40)

A wide variety of these superelectrophilic carboxonium ions have beenstudied It has long been recognized that carboxonium ions are highly sta-bilized by strong oxygen participation and therefore are much less reactivethan alkyl cations For example trivalent carbocations are efTHORNcient hydrideabstractors from tertiary isoalkanes (eq 41)

CRR

RRprimeC

RprimeH

RprimeCR

R

RRprimeC

Rprime

RprimeH+ ++ + (41)

VICINAL SYSTEMS 157

CO

R CH3

143a R = H 143b R = CH3

CCH3

CH3CH3H

HFSbF5or HFBF3

COH

R CH3

H+

COH2

R CH3C

CH3

CH3CH3H

COH2

RCH3

CH3C

CH3

CH3H

144 ab 145 ab

NO REACTION

ISOBUTANECOH3

R CH3

2+

+

+ +

+

+

+

Scheme 12 Proposed mechanism for the superacid-catalyzed hydride transfer involvingcarboxonium ions and isobutane

In contrast carboxonium ions do not hydride abstract from isoalka-nes when they are reacted in aprotic solvents However as mentionedBrouwer and KifTHORNn observed that reaction of acetaldehyde or acetone(143ab) with isobutane in HFSbF5 or HFBF3 leads to formation ofthe tert-butyl cation (Scheme 12)70 Under these conditions the carbonylgroup of acetaldehyde or acetone is completely protonated However cal-culations estimate hydride transfer from isobutane to the carboxoniumions (144ab) to be thermodynamically unfavorable These considerationslead to the early mechanistic proposal by Olah et al in 1975 involvingthe protosolvation of the carboxonium ions (144ab) forming superelec-trophilic species (145ab) enabling hydride abstraction to occur62 Similarreactions have also been observed for formaldehyde and its protonatedions71 In gas-phase studies it has been shown that charge-stripping of theradical cation [CH2OH2]+bull leads to the formation of CH2OH2

2+ (dipro-tonated formaldehyde) and quantum mechanical calculations also showthat CH2OH2

2+ sitting in a considerably deep potential energy well72

Several recent reports have described kinetic studies suggesting proto-solvated carboxonium ion intermediates Shudo Ohwada and associateshave described kinetic experiments and theoretical studies to show thatsuperelectrophilic carboxonium ions (ie 146) are involved in superacid-catalyzed Nazarov reactions (Scheme 13 see also Chapter 2)73 Usingdeuterated superacid no deuterium was incorporated into the product sug-gesting protonation only at the carbonyl group rather than at the oleTHORNnicmoiety resulting in an intramolecular Friedel-Crafts-type reaction In abinitio calculations at the B3LYP6-31G level diprotonation is shown tosigniTHORNcantly lower the energy barriers (compared to the monoprotonatedspecies) leading to the products of the 4π -electrocyclizations

Similarly kinetic experiments have shown that superelectrophiliccarboxonium dications are involved in the cyclodehydrations of 13-diphenyl-1-propanones4a Several examples of the cyclodehydrations weredescribed including the triszliguoromethyl-substituted system (Scheme 14


OCF3

acid

100 CF3SO3H (H0minus14)

94 CF3CO2H 6 CF3SO3H (H0minus9)


5 h

5 h

99

43

temperature

0degC

0degC

OHCF3 OH2

CF3 O

CF3

146

+ +

+

Scheme 13

see also Chapter 2) The reactions exhibit signiTHORNcantly increased yieldsand reaction rates in more highly acidic media Along with the resultsfrom kinetic studies these data indicate the involvement of superelec-trophilic carboxonium ions (ie 148) Monocationic carboxonium ionssuch as 147 are in contrast signiTHORNcantly stabilized and they either donot give the cyclization products or they react very slowly The acti-vation parameters from the superacid-promoted cyclization (CF3SO3HH0 minus141) of 13-diphenyl-1-propanone were also determined in thisstudy (H 20 kcalmol G 29 kcalmol and S minus 26 calKbullmol)

The acid-catalyzed condensation reactions of benzaldehyde with ben-zene have been well studied A gitonic superelectrophile has been pro-posed in one study6 while distonic superelectrophiles have been suggestedin others57 When benzaldehyde (149) is reacted with CF3SO3H andC6H6 four products are obtained (150153 Table 4) The relative yieldsof the products vary with conditions For example no anthracene is formedwhen large excess of C6H6 is used in the reaction In studies using catalyticsystems of varying acidities it was found that overall product formation( yield) increased with acidity Given that the pKBH+ of benzaldehyde149 is minus68 the carbonyl group should be almost completely protonatedat H0 minus9 or minus10 Since the product yields increase with systems more

O

acid

OH

F3C F3C

OH2

F3C F3C

product yieldtime

20 min

20 min

68

2

temperature

80degC

80degC

147 148

+ +

+



acid system

Scheme 14

VICINAL SYSTEMS 159

Table 4 Products and yields of the reactions of benzaldehyde (149) with benzene atvarying acidities

CF3SO3H

C6H6

O

H

OH

+150

149

151

152

153

100 CF3CO2H

5 CF3CO2H 95 CF3SO3H




100 CF3SO3H

minus27

minus90

minus10

minus12

minus13

minus14

0

4

15

40

77

83

Acid Acidity H0

Total YieldProducts

150+151+152+153

acidic than H0 minus10 it is suggested that diprotonated benzaldehyde is thesuperelectrophilic intermediate responsible for the condensation chem-istry In considering the mechanism the THORNrst protonation of benzaldehydeoccurs at the carbonyl oxygen while the second protonation could be at thering positions (ortho meta para or ipso) or at the carbonyl group Whenbenzaldehyde is reacted even with a large excess of CF3SO3D at 50C for19 h no deuterium incorporation is observed either on the phenyl ring oraldehyde group of compound 149 Based on these considerations it wasproposed that the OO-diprotonated species (12) is the key intermediateinvolved (eq 42)


OH+

+ + + +

++++

2+ +

+H H+

OH2

H

OH2

H

14 12 12

OH

H

13

OH

H

154

OH

H

156

OH

H

155

HH

H

H

H

HH

(42)

In theoretical studies of the benzaldehyde condensation the diproto-nated structures were calculated at the MP26-31GMP26-31G leveland THORNve structures were found at energy minima (1213 and 154156)The global minima for the gas-phase C7H8O2+ structure are found at 13and 155 (distonic superelectrophiles same relative energies) both beingCO-diprotonated benzaldehyde isomers The OO-diprotonated species(12) is found about 20 kcalmolminus1 above 13 and 155 in energy while154 and 155 are 14 and 5 kcalmolminus1 above the global minima repec-tively The condensed phase experiments with CF3SO3D and benzalde-hyde argue however against the involvement of 13 Consequently analternative explanation has been suggested involving neither 12 or 13based also on the results from analogous chemistry with acidic zeolites5

In the latter case benzaldehyde was found to give triphenylmethane whenreacting with benzene in the presence of HUSY zeolite a solid acid cata-lyst with an acidity estimated at H0 sim minus6 Benzaldehyde is also found toreact with cyclohexane (a hydride source) using the same zeolite catalystIt was argued that the relatively low acidity (and low density of acidicsites) of HUSY makes it improbable to form diprotonated benzaldehyde(12 or 13) and a mechanism was proposed involving only monoproto-nated benzaldehyde (14 Scheme 2) These considerations assumed thesame mechanism to be involved in liquid superacid-promoted condensa-tion It should be noted however that conTHORNnement effects associated withzeolite-catalysis may also have a role in the reactions

Besides promoting reactions with weak nucleophiles several molecularrearrangements have been reported with superelectrophilic carboxoniumions suggested as intermediates This includes the superacid promotedrearrangment of 222-triphenylacetophenone (157) with subsequent for-mation of the 910-diphenylphenanthrene (160 eq 43)30

VICINAL SYSTEMS 161

PhPh

O

PhPh

CF3SO3H

PhPh

OH

PhPh

PhPh

OH2

PhPh Ph

PhPh

Ph

H2OPh Ph

157 158 159 16052

+ +

++

+

(43)

As described in Chapter 2 the superacid produces the diprotonated gitonicsuperelectrophile (159) which undergoes a retropinacol rearrangementPhenyl migration is driven by the resulting charge-charge separation Sub-sequent reaction steps then give the THORNnal cyclization product (160)

A related reaction was reported in the discussed acid-catalyzed formy-lation of isobutane with rearrangement to methyl isopropyl ketone (apotentially signiTHORNcant gasoline additive)74 Following the insertion of theprotosolvated formyl cation into isobutane (vide supra) a key step in theformation of the methyl isopropyl ketone involves the superelectrophilicOO-diprotonated species (162 Scheme 15) Methyl shift is driven byCoulombic repulsion to give initially the charge-separated species (163)Quantum mechanical calculations indicate that the methyl shift is veryfavorable energetically (H = minus48 kcalmol for the gas-phase reaction)Upon undergoing deprotonation subsequent hydride shift then gives pro-tonated methyl isopropyl ketone (166) in another energetically favorablestep (estimated gas-phase H = minus24 kcalmol) Interestingly calcula-tions also suggest that the hydride shift is unlikely to involve the distonicdication 165 because such a step would be signiTHORNcantly endothermic (H= 24 kcalmol) due to charge-charge repulsive effects in 165 Althoughaccording to calculations the fully formed gitonic superelectrophile 162is not a stable minimum in the gas-phase at the B3LYP6-31G levelof theory partial proton transfer (protosolvation) is also likely to acti-vate the electrophilic center Moreover ion pairing may also stabilize thesuperelectrophile 162 in the condensed phase

C CH3

CH3

CH3

HCO

HFminusBF3

C CH3

CH3

CH3

C

H

HO

C CH3

CH3

CH3

C

H

OH

H

CCH3

CH3

CHO

HH

H3C

CCH3

CH3

CHHO

H3C

H+

minusH+CCH3

CH3

CHO

H3C

HCCH3

CH3

CO

H3C

H CCH3

CH3

C

H3C

OH

HH

161 162

163164166 165

minusH+

+ +

+

+

+

+

+

+

+

Scheme 15


Table 5 Results of the CF3SO3HCF3CO2H catalyzed isomerization ofpivaldehydea

H 0 Acid System ww Pivaldehyde Methyl Isopropyl Ketone

minus109 269 CF3SO3H 0 100minus97 114 CF3SO3H 17 83minus94 80 CF3SO3H 29 71minus84 31 CF3SO3H 68 32minus77 09 CF3SO3H 83 17minus27 100 CF3CO2H 100 0

aReaction conditions 2 h 25C 15 pivaldehyde acid

Further support for the involvement of the superelectrophile (162) wasobtained from experimental studies establishing the effect of acidity on therearrangement The yield of methyl isopropyl ketone from pivaldehyde isfound to increase in proportion to acidity (Table 5) with complete con-version occurring at H0 minus109 The pKa for the protonated pivaldehydeis estimated to be minus80 indicating that more than half of the aldehydeis in its monoprotonated form (161) at H 0 minus109 Thus protosolvationof the monoprotonated species (161) should lead to the formation of thesuperelectrophile (162) albeit in low concentrations

Another OO-diprotonated gitonic superelectrophile has been proposedin the condensation chemistry of ninhydrin (Scheme 16)75 It was shownthat ninhydrin condenses with arenes in H2SO4 to give the 22-diaryl-13-indanediones (167) while reaction in superacidic CF3SO3H give the 3-(di-arylmethylene)isobenzofuranones (168) If the 22-diaryl-13-indanedioneproducts are isolated and then reacted with CF3SO3H they isomerizecleanly to the 3-(diarylmethylene)isobenzofuranones As triszligic acid (H0minus141) is more than 100 times more acidic than anhydrous H2SO4 (H0minus12) it suggests the involvement of a protosolvated superelectrophile(169) in the formation of the 3-(diaryl-methylene)-isobenzofuranonesThere may be several other factors contributing to the protosolvated dica-tion 169 undergoing rearrangement Ring-opening serves to spread out thepositive charge between the acyl cation and a protonated enol group (170)Moreover the acyl cation is in conjugation with the diphenylmethylenegroup as shown by the resonance structure This stabilizing effect of thegem-diphenyl group may be also an important aspect in the rearrangementbecause when 2-phenyl-13-indanedione is reacted in CF3SO3H no rear-rangement is observed and the starting material is recovered quantitatively

As discussed in Chapter 2 kinetic evidence has been reported to indicatethe involvement of the diprotonated product 174 from the unsaturated acetal171 formally a superelectrophilic carboxonium dication (eq 44)76

VICINAL SYSTEMS 163

Ph

Ph

O

O

OH

OH

O

O

PhOH

OPh

PhOH2

OPh C

PhOH2

O

Ph

O

O

PhPh

C

Ph

OH2

O

Ph

C

Ph

OH2

O

Ph

C

Ph

OH

O

Ph

O

OH

PhPh

C6H6

H2SO4

C6H6

CF3SO3HO

O

PhPh

Ph

Ph

O

O

CF3SO3H

C6H6

CF3SO3H

minusH+

H+

167 168

169

170170

minusH+

+ +

+

+

+

+

+

+

+

+

+

Scheme 16

OCH3

OCH3 FSO3HSbF5 H+hn

Δminus60degCOCH3

OCH3 OCH3H

171 172 173 174

+

+ ++

(44)

Protonated carbonic acid (H3CO3+ 175) is recognized as a stable

species in superacids and even a salt was isolated with its X-ray crys-tal structure obtained In strong superacids diprotonated carbonic acid(30) was found to undergo ionic hydrogenation to methane (eq 45)77

HOC

OH

OH HOC

OH2

OHHO C OH CH4

175 176

H+ 4H2

minus2H3O+

H+

H3O+

30

+

+

+ + +

(45)

This has been interpreted as a protosolvation of 175 to give the super-electrophile 30 which itself undergoes protolytic cleavage to give pro-tosolvated carbon dioxide (176) The gitonic superelectrophile 176 thenreacts with H2 to eventually give methane In gas-phase studies dicationicspecies such as CO2

2+ and OCS2+ have been generated using mass spec-trometry techniques78 Both of these dicationic species have been shown


to react with molecular hydrogen (deuterium) for example producingDCO+ DCO2

+ and OD+ ion products (reaction of CO22+ and D2)

5224 Carbon-Halogen Vicinal-Dications Trihalomethyl cations areshown to have enhanced reactivities in superacid solution while poly-halomethanes in the presence of excess AlBr3 or AlCl3 exhibit the proper-ties of aprotic superacids79 The trihalomethyl cations CX3

+ (178 X=ClBr I) have been characterized by NMR and IR spectroscopy The stabil-ity of these species is attributed to substantial resonance-stabilization byback-donation from the nonbonded electron pairs of the halogen atoms22

Trihalomethyl cations are capable of hydride abstraction from alkanes andalkyl groups when the reactions are carried out in the presence of Bronstedor Lewis superacids (eq 4648)80

CCl4ndashSbF5

minus123degC(SbF5 Matrix)

+ (46)

CCl4ndashSbF5


+(47)

H3C NCH3

CH3

O

HH3C N

CH3

CH3

OH

H

1) HFndashPyridine2) Na2CO3 H20

H3C NCH3

CH3

O

H

F

80

CCl4ndashHFndashSbF5

minus30degC

+

+

(48)

Sommer et al has noted that the reactivities of the chloromethyl cationsdecrease in the order CCl3+ gt CHCl2+ CH2Cl+81Since increasingchloro-substitution should give less reactive electrophiles (due to reso-nance stabilization) this trend has been interpreted to be a consequenceof protosolvationelectrophilic solvation involving the halogen nonbondedelectron pairs (178 and 179 (Scheme 17) Complexes such as CBr4bull2AlBr3 CCl4 bull2AlCl3 and others have been shown to efTHORNciently cat-alyze the cracking isomerization and oligomerization of alkanes and

VICINAL SYSTEMS 165

XC

X

X XC

X

X

SbF5

HFndashSbF5

XC

X

X

SbF5

X = Cl Br I

XC

X

XH

179

178177 177

++

+d+

+

+

dminus

Scheme 17 Superelectrophilic activation of trihalomethyl cations

cycloalkanes82 Electrophilic solvation similar to 178 can also be envis-aged for these systems17

Theoretical studies have examined the structures and energies of thevicinal -carbon-halogen dications such as 178 and 17983 An ab initiocomputational study described the structures energies and reactivities ofprotonated halomethyl cations In the case of the trichloromethyl cation(181) calculations at the MP26-31G level reveal a shortening of theCCl bond length when compared with carbon tetrachloride (Scheme18) This is consistent with delocalization of the positive charge among thethree chlorine atoms Upon protonation the vicinal -dication 182 is formedshowing further shortening of the C-Cl bonds (indicating a stronger p-pinteraction) and a lengthening of the C-ClH bond due to charge-chargerepulsive effects Calculations estimate a gas-phase energy barrier to pro-ton loss of 695 kcalmol suggesting that 182 should be a viable species inmass-spectrometric studies Diprotonated (CCl3H2

3+ 183) and triproto-nated (CCl3H3

4+ 184) ions were also found at energy minima In the case

ClC

Cl

ClCl

ClC

Cl

Cl

ClC

Cl

ClH+

++ + +

+++

+ +

ClC

ClH

ClH

HClC

ClH

ClH

C-Cl Bond Length(s) Aring

Energy Barrierto H+ Loss kcalmol

1766 1648 183916061603

17791575

1732

NA 695 274 43NA

184183182181180

Scheme 18 Calculated structural and energy parameters of prototrichloromethyl cations


of 184 however deprotonation is highly exothermic (minus2617 kcalmol)and having a barrier to proton loss of only 43 kcalmol In the same study13C NMR chemical shifts were calculated for the species (181184)18

To evaluate the impact of superelectrophilic activation of halogenatedmethyl cations a series of isodesmic reactions were studied by ab initiocalculations (Table 6)83b For the trichloromethyl cation (181) protonationleads to dramatically more reactive electrophiles This is evident from thecalculated reaction enthalpies in hydride transfer from propane to givethe 2-propyl cation Indeed protosolvation of 181 to give the superelec-trophile 182 leads to an increasingly exothermic reaction more favorableby more than 140 kcalmol (gas-phase) Another signiTHORNcant trend is seenin the calculated reaction enthalpies for the trichloromethyl cation (181)dichloromethyl cation (185) and the chloromethyl cation (186 entries13) In the series 181 rarr 185 rarr 186 the reaction enthalpy is pro-gressively more exothermic minus39 rarr minus119 rarr minus266 kcalmol This isconsistent with the observation that halogen substitution on a carbeniumcarbon leads to increasing stabilization and the trichloromethyl cation isthe most stable cation in the series However reactions of halogenatedmethanes in superacid show that the tetrahalogenated methanes producethe most reactive electrophilic systems This has been interpreted as evi-dence for activation involving superelectrophilic species like 182 and183

Another computational study examined the structures and energies ofthe trichloromethyl cation-AlCl3 complexes by semi-empirical and ab

Table 6 Calculated isodesmic reactions between chloromethyl cations(181186) and propane

Entry Reaction H (kcalmol)

(1)+

H2CCl +CH3CH2CH3 minusrarr CH2Cl2++

CH3CHCH3 minus266186

(2)+

HCCl2 +CH3CH2CH3 minusrarr CH2Cl2++


(3)+

CCl3 +CH3CH2CH3 minusrarr HHCl3++

CH3CHCH3 minus39181

(4)2+

CCl3H +CH3CH2CH3 minusrarr+

HCCl3 H++


(5)3+

CCl3H2 +CH3CH2CH3 minusrarr2+

HCCl3H2 ++


(6)4+


HCCl3H3 ++


VICINAL SYSTEMS 167

initio calculations84 In contrast to the study of protosolvated superelec-trophiles (182) this study could THORNnd no evidence for the formation ofthe CCl3+ rarr AlCl3 complex(es) or donor-acceptor complexes analo-gous to 178 The superelectrophilic character of the CCl4-2AlCl3 systemwas attributed to formation of a bidentate complex with substantial chlore-nium ion character AlCl4 minus ClCCl2+ AlCl4 minus or CCl3+ AlCl4 minusinvolvingC-Cl rarr Cl-Al interactions As described in Chapter 4 protonation of thedimethylbromonium cation (187) has been studied by ab initio calcula-tions and two stable minima were found ie the carbon and bromineprotonated forms 188 and 189 (Figure 6)85 Dication 188 is estimatedto be more stable than 189 by about 21 kcalmol Monoprotonation ofmethyl halides occurs on the halogen atom to give the protohaloniumion Diprotonation is shown by calculations to give the vicinal -dications(190) involving also protonation at a C-H bond forming a 2e-3c bondCalculations also show that the halogen atoms carry signiTHORNcantly morecharge in the dications (190 CH4XH2+) than in the respective monoca-tions (CH3XH+) In the case of bromomethane the NBO charge on thebromine atom increases from 046 to 070 with formation of 190 fromthe monoprotonated species Thermodynamically diprotonation of szliguo-romethane is determined to be the least favorable while diprotonation ofiodomethane is found to be the most favorable

Other types of vicinal carbon-halogen dications have been studied bygas-phase and theoretical methods Their full discussion is beyond the scopeof this chapter and many can be found in published review articles86

Charge-stripping experiments have been shown to provide CH2XH2+(X=FCl Br I) dications in the gas-phase and their structures have been stud-ied by computational methods87 The CX3

2+ (X=F Cl) dications can alsobe generated in the gas-phase and have also been studied by theoreticalinvestigations The chemistry of CFn

2+ is considered important in plasmaetching processes and these ions may also be important in ozone deple-tion chemistry88 In the case of CF3

2+ it can be generated in the gas-phaseby electron impact on CF4 The CF3

2+ ion is shown to react with neu-tral collision partners and yield products from bond forming reactions

BrC CH

HH

H

H

H


2+

BrC CH

HH

H

H

H


2+H

188 189

BrC CH

HH

H

H

H

187

HXC H

H

H

H

2+

H

190 Cs

X = F Cl Br I

+

Figure 6


such as DCF2+ and OCF2

+ by respective reactions with D2 and O279

High-level quantum chemical calculations have been carried out on ionssuch as CF3

2+88 As noted in the previous chapter the CX22+ (X = F

Cl) ions have also been the subject of gas-phase and theoretical studies89

Likewise CX2+ dications have been examined47 While these novel CX2+n

dicationsmay not necessarily be described as vicinal -type gitonic superelec-trophiles their demonstrated gas-phase reactivities are remarkably similarto the high electrophilic reactivities of condensed-phase superelectrophiles

523 Nitrogen-Centered Vicinal -Dications

There are a number of well-characterized nitrogen-centered vicinal -dications that can be considered gitonic superelectrophiles For exampleOlah and co-workers showed that tetramethylammonium ions undergoslow hydrogen-deuterium exchange when reacted with DF-SbF5 at 20C(Scheme 19)90 Theoretical calculations suggest that C-H protonation(deuteration) (192) is the most likely mechanism of exchange ruling outthe intermediacy of 191 Structure 192 was characterized as a stableminimum (Cs symmetry) at the MP2(fu)6-31G level of theory Tetra-methylammonium ion did not undergo methyl exchange with CD3F-SbF5indicating that there is no involvement of a penta-coordinate nitrogen (ieN(CD3)(CH3)42+)19

Hydrazinium dications and their related systems can be readily formedand show remarkable stability These vicinal -dications show enhancedelectrophilic reactivities compared to their monocationic precursors Theirchemistry has been recently reviewed91 therefore only a brief overview iswarranted here Hydrazine itself can be doubly protonated with HCl When

DF-SbF5

20degC

NCH3CH3

H3C

CH3D2+

2+

+

N CH3CH3

H3C

D

not formed191

N CCH3

H3C

CH3

N CH3CH3

H3C

CH3

DH

HH N CH2D

CH3

H3C

CH3

minusCH3+

minusH+

192

+

+

Scheme 19

VICINAL SYSTEMS 169

tetramethyl hydrazine was reacted with strong methylating agents how-ever only monomethylation was achieved (eq 49)92 If the monomethy-lated product (193) is then reacted in 70 H2SO4 the hydraziniumdication is formed to an extent of about 50 (eq 49)

H3CN

NCH3

CH3

CH3

CH3SO3F

CH3SO3F

H3CN

NCH3

CH3

CH3H3C

No Reaction

70 H2SO4

H3CN

NCH3

CH3

CH3H3C

H

193

+ ++

(49)

Several bicyclic hydrazinium ions have been prepared and two syntheticstrategies have emerged as generally useful ie electrochemical oxida-tion and Lewis or Broslashnsted acid-promoted cyclization93 Oxidation of16-diazabicyclo[444]tetradecane for example (194) gives the interme-diate radical cation (195) and the bicylic dication (196 eq 50)93a

N

N minuseminus

+ +

+minuseminus

N

N

N

N

NndashN Distance Aring 281 230 153

194 195 196

(50)

X-ray crystal structures have been obtained for them and the nitrogen-nitrogen distance decreases with successive oxidation When 15-diazabi-cyclo[330]octane is reacted with 3-bromo-1-propanol followed byreaction with 40 HBF4 the hydrazinium dication (197) is obtained in80 yield (eq 51)93b The 13C labeled hydrazinium dication (198) wasprepared through double alkylation of tetramethyl hydrazine the secondalkylation being assisted by the silver (I) salt (eq 52)93c

N

N

Br OH

40 HBF4

N

N

197

2BF4minus

+

+(51)


BrBr +

CH3

13C

H3C

NN

CH3

CH3

CH3AgBF4

HBF4N

NH3C

CH3

CH3

CH3

CH3

198

2BF4minus

+

+

(52)

Although acyclic and monocyclic hydrazinium dications are readilyobtainable the propellane-type structures (ie 196 and 197) have beenshown to be the most easily prepared hydrazinium dications There havebeen no examples reported of direct nucleophilic attack at the nitrogensof the hydrazinium ions Nucleophilic reactions generally occur at theα-carbon atoms or at hydrogens Even water has been shown to be capa-ble of deprotonating the α-carbon in some of the bicyclic hydraziniumdications This is consistent with the delocalization of positive charge ingitonic superelectrophiles and signiTHORNcant positive charge on the neighbor-ing hydrogen atoms

A related category of vicinal -dications involves aromatic systemshaving adjacent nitrogen atoms The diquaternary salts of diazenes anddiazoles can be prepared using strong alkylating agents (eqs 5354)94

Compound 199 is prepared in 52 yield by alkylation with trimethylox-onium salt with some of the positive charge being delocalized onto thesulfur (eq 54)

N

NCH2CH3BF4

minus

(CH3)3O BF4+N

NCH2CH32 BF4

minus

CH3

++

+

+

minus (53)

N N

S

N N N N

S

H3C CH3

S

H3C CH3

1992 BF4

minus2 BF4minus

(CH3)3O BF4++

+

+

+ +

minus

(54)

No systematic study of the reactivities of these electrophiles has beendone but they are known to be easily reduced to their radical cationsThe NN -bipyridiniums and related systems have not yet been studiedin detail but some have been prepared such the 1-pyridinopyridiniumdication 20095 Little is known about the electrophilic reactivities of thesecompounds but 200 has been shown to react with water at a ring carbon(eq 55) An unusual gitonic superelectrophile has been proposed involving

VICINAL SYSTEMS 171

N+ +

+N Cl

2 Clminus

H2O

N N O

Clminus

+ 2 HCl

200

(55)

N

NCH3

CF3SO3H

N

NCH3H

H

H+

N

NH

HHH N

NCH3H

HHH

201

+

+ +

++

+

CH3

++

(56)a tricationic intermediate 201 (eq 56)96 Deuterium labeling suggests tripleprotonation of the pyrazine ring with delocalization of positive charge intothe propenyl group

Diazenium dications may also be considered gitonic superelectrophilesbut only a limited number of them have been prepared and studied97 Inprinciple diazenium dications could be prepared by double alkylationor protonation of various azo-compounds To date only monalkylationhas been achieved with strong alkylating agents (eq 57)97a HoweverOlah et al showed that diazenium dications can be produced by doubleprotonation of azobenzenes in FSO3HSbF5 at low temperature97b It hasalso been demonstrated that the diazenium dications are prepared fromelectrochemical and chemical oxidations (eqs 5859)97cd

Ph N N PhCF3SO3CH3

Ph N NPh

CH3CF3SO3

minus+

(57)

N Nminus2eminus

NaClO4

N N

2 ClO4minus

++

(58)

NN

2NO+ PF6minus

CH3CN N

N

202 203

81

2PF6minus

+

+

(59)

In the oxidation of 202 the tetracyclodiazenium ion 203 is produced in81 yield Like the hydrazinium dications the diazenium dications exhibitrelatively high acidities of their α-hydrogen atoms

Diazonium dications have been studied extensively in both experi-mental and theoretical work The parent system for diazonium dications


is doubly protonated dinitrogen (204) Calculations at the QCISD6-311++GQCISD6-311++G level show that dication 204 (DinfinVsymmetry) is a kinetically stable species in the gas-phase having a barrierof about 30 kcalmol for dissociative proton loss98 Although monoproto-nated dinitrogen has been observed directly in gas-phase studies (and it isgenerated from protonated diazomethane vide infra)99 dication 204 hasnot yet been detected Diazomethane is observed to be diprotonated underconditions of kinetic control in extremely acidic FSO3HSbF5100 Theexperimental studies suggest protonation at both termini of diazomethane(208 eq 60)

204 205 206 207

N N NH

HH

+ +N N N

H

H

H+ +

CN H

H

NH

H+

+N N HH

++

CN H

H

N FSO3H-SbF5

minus120degC

SO2ClF SO2ClFCH3OSOClF +

++

++

minus

N2minusH+

CN H

H

NH

H

208

(60)

Calculations at the MP2(FU)6-31GMP2(FU)6-31G level havefound that the global minimum is the NN -diprotonated species 205 (gas-phase structure) while the C N -diprotonated species (208) is 11 kcalmolhigher in energy98 From kinetic studies it is known that the displacementof nitrogen from the methyldiazonium ion (CH3N2

+) is a nucleophilicsubstitution type reaction Weakly nucleophilic SO2ClF is also knownto displace nitrogen from methyldiazonium ion with a reaction rate thatincreases with the acidity of the solution This is in accord with theformation of the protosolvated gitonic superelectrophile 208 leading tonucleophilic attack by SO2ClF (eq 60) Similarly Olah and co-workersdemonstrated the use of azide salts as effective aromatic aminating agentswith excess HCl-AlCl3101 Diprotonated hydrazoic acid (206) has beenproposed as an intermediate in the conversion This gitonic superelec-trophile (206) was also studied by theory at the MP2(FU)6-31GMP2(FU)6-31G level and found to be a global minimum at least20 kcalmol more stable than structure 20798

Aryldiazonium dications are thought to be intermediates in the Wallachrearrangement97b Azoxybenzene is shown to form the monoprotonated

VICINAL SYSTEMS 173

NN

OHF-SbF5

SO2

minus78degC

NN

OH

NN

OH

H

minusH2O

211

N NN NH2ON

NHO

209 210

+++

++

++

Scheme 20

ion (209) in FSO3H at low temperature while the dicationic species (210and 211) are directly observable by NMR in HF-SbF5 at low temperature(Scheme 20)97b In the Wallach rearrangement delocalization of the posi-tive charges then leads to nucleophilic attack by water at a ring carbon ThepKa of ion 209 is estimated to be minus9 indicating that the azoxybenzene iscompletely monoprotonated under the conditions required for the Wallachrearrangement being likely in equilibrium with the diprotonated interme-diate 210 Water elimination then gives the diazonium dication 211 Therehas been a report showing that superelectrophilic intermediates like 211can react with relatively weak nucleophiles such as benzene102

An important class of nitrogen-based gitonic superelectrophiles are theprotonitronium dication (214) and related systems (Scheme 21) Thesegitonic superelectrophiles are highly efTHORNcient for nitration of very weaknucleophiles (vide infra) In 1975 the observation of the enhanced elec-trophilic reactivity of nitronium salts in superacids was reported by Olah etal and protosolvation of the nitronium ion (212) was suggested (Scheme27)62 While the often used nitronium tetraszliguoroborate reagent reacts witha large variety of arenes it does not react with highly deactivated ones(such as meta-dinitrobenzene) under aprotic conditions In contrast thereaction in superacid gives 135-trinitrobenzene in 70 yield103 Thissuggests the formation of an activated protosolvated species or even thede facto protonitronium dication NO2H2+ (214) A convenient system ofnitration for deactivated aromatics is a mixture of nitric acid and triszligato-boric acid (2 CF3SO3H(CF3SO3)3B H 0 minus 205)104 This system readilynitrates deactivated arenes such as inter alia pentaszliguorobenzene nitroben-zene and methyl phenyl sulfone in high yields (7899) Nitronium saltsare reported to nitrate the trityl cation (215) in superacid to give 216(eq 61)105



NO O NO O NO OHH A

213 214212

+ + δ++ +

Scheme 21 The nitronium ion (212) and the protonitronium dication

215

1) NO2BF4 CF3SO3H 2) (CH3CH2)3SiH 64

H

NO2

216

1) NO2Cl 3 AlCl3 2) (CH3CH2)3SiH 100

+ BF4minus (61)

When nitronium tetraszliguoroborate was attempted to react with the tritylcation in CH2Cl2 or sulfolane no nitration occurred due to the deactivat-ing effects of the carbenium ion center in 215 Nitration of deactivatedsubstrates is also readily accomplished by reaction with NO2Cl with threemole excess AlCl3 suggesting Lewis acidic electrophilic solvation of thenitronium cation (217 eq 62)105

NO2Cl ++ d

+

dminus

minusNO O

AlCl3

Al2Cl7217

3 AlCl3(62)

Remarkably nitronium salts have been shown to react even with methaneunder superacidic conditions106 Nitronium hexaszliguorophosphate (NO2PF6)reacts with methane albeit in low yields when the reaction is carried outin the presence of boron tris(triszligate) in triszligic acid (eq 63)

CH

HH

NO2H

H2+

CH3NO2H+ + H+

214

218

B(O3SCF3)3NO2

+CF3SO3H

NO2H2+ CH4

(63)

The reaction is suggested to proceed via a two-electron three-center boundcarbocationic transition state (218) formed by insertion of dication 214into the C-H σ -bond of methane

The activation of the nitronium ion (212 NO2+) can be understood

as a consequence of the interaction of the oxygen lone pair electrons

VICINAL SYSTEMS 175

with superacidic Broslashnsted or Lewis acids Because the linear nitroniumcation has no vacant orbital on the nitrogen atom nor low-lying unoc-cupied molecular orbital extremely weak nucleophiles such as methaneor deactivated arenes are unable to initiate the necessary polarizationof the nitrogen-oxygen π -bond Protonation (or coordination by Lewisacid) weakens the N-O π -bond character and results in the bending ofthe linear nitronium ion and rehybridization of the nitrogen from sp tosp 2 The rehybridization creates a developing p orbital on the nitro-gen which is capable of interacting with weak π -donor or even σ -donornucleophiles High-level theoretical calculations have shown the protoni-tronium ion (214) to be a kinetically stable species with an estimated(gas-phase) barrier to deprotonation of 17 kcalmol107 These calculationsalso found the optimized structure to be bent with a ONO bond angle ofabout 172 The protonitronium ion (214) was experimentally observed bySchwarz in the gas phase by electron impact mass spectrometry of nitricacid108 Attempts to directly observe 214 under superacidic conditionsby 15 N NMR and FT-IR (Raman) spectroscopy as a stable species havebeen inconclusive but the 17O NMR signal is deshielded from that of thenitronium ion NO2

+107b This suggests that the protonitronium ion (214)is formed only in low-equilibrium concentrations even in the strongestsuperacids

524 Oxygen- and Sulfur-Centered Vicinal -Dications

A signiTHORNcant number of vicinal -dicationic systems containing oxygensuch as superelectrophilic carboxonium ions acylium ions and nitroniumions have been previously discussed Few systems have been reportedinvolving only oxygen cationic centers Other than doubly ionized O2

(known in gas-phase studies) scarce indications for such oxygen-basedvicinal -dications have been reported Hydrogen peroxide has been studiedby low temperature NMR in HF-SbF5 solution but no direct evidence fordiprotonated species was reported and only the monoprotonated species(219) was observed (eq 64)109 Even at very high acidity (ca H0 minus20)proton exchange is fast compared with the NMR time scale as both oxy-gen atoms are found to be equivalent by 17O NMR In a similar respectdimethylperoxide forms trimethylperoxonium ion (220) under superacidicmethylating conditions (eq 65)110

H2O2

HF-SbF5

minus25degC HO

OH

H

XminusH

OO

H

H

2 XminusH219+

+

+(64)


H3CO

OCH3

CF3F-SbF5-SO2

minus50degC H3CO

OCH3

CH3

220

H3CO

OCH3

CH3

221

CH3

+

++ (65)

No NMR evidence (1H and 13C) could be obtained for the vicinal -dication(221) Calculations at the MP26-31G level however show dication 221to be a stable minimum Its structure has D2symmetry with the two COCunits in an almost perpendicular arrangement (dihedral angle betweentwo COC units is 837) Protonated ozone O3H+ was studied by Olahet al and by Italian researchers111 In the superacid catalyzed reactions ofozone diprotonated ozone is however possibly involved as the de factointermediate

In contrast to the vicinal -oxonium dications vicinal -sulfonium dica-tions are well known dicationic systems Many examples have been pre-pared and studied As discussed in review articles91 the disulfoniumdications can be readily prepared by electrochemical or chemical oxi-dation of appropriate disulTHORNdes (eq 66) by reactions of mono-S-oxideswith acidic reagents (eq 67)

S

S

S

S

2 CF3SO3

2 (CF3SO2)2O

+

+

minus(66)

S

S

2 CF3CO2

S

S

O

CF3CO2H +

+ minus

(67)

and other methods112 The reactions of mono-S-oxides with acidic reagentshave been the subject of mechanistic studies Some of these studies sug-gest a complex mechanism in the formation of the vicinal -disulfoniumdications On the other hand experimental and theoretical studies of theprotonated and alkylated dications of dimethylsulfoxide (vide infra) havesuggested the possibility of OO-diprotonation of the sulfoxide group113

Thus formation of the vicinal -disulfonium dication could involve dipro-tonation of the sulfoxide bond of 222 forming the gitonic superelec-trophile 224 which upon intramolecular nucleophilic attack gives thevicinal -disulfonium dication (225 Scheme 22) It has been shown thatdications such as 225 possess moderately high electrophilic reactivitiesFor example 225 (X=CF3SO3

minus) has been shown to react with activated

VICINAL SYSTEMS 177

S

S

S

S

2 Xminus

2 Xminus

OHX

S

SHO

S

SO

H

H

222 223 224

225

minusH2O

Xminus

HX+

++

+

+

Scheme 22

arenes (phenols and anilines) at the sulfonium center (eq 68)114

S

S

2 CF3SO3

225

OH

OHSSminusH+

+

+

++

minus

(68)

Similar chemistry has been described for the vicinal -dications of seleniumtellurium and mixed chalcogen systems both for the preparation andreactions of these vicinal -dications91

Vicinal -sulfoxonium-oxonium dications have been studied by experi-mental and theoretical methods speciTHORNcally the dicationic species fromdimethylsulfoxide (DMSO)113 The structures and energies for the pro-tonation products of DMSO were calculated at the B3LYP6-311+GB3LYP6-311+G level (Figure 7) For the monoprotonated productsthe O-protonated structure (226) is found to be 37 kcalmol more stablethan the S -protonated structure (227) Similar results are obtained frommethylation of DMSO The second protonation of O-protonated DMSOcan take place on either oxygen or sulfur Both the OO-diprotonatedspecies (228) and the OS -diprotonated species (229) are found to beminima on the potential energy surface However the OO-diprotonatedspecies is found to be 2087 kcalmol more stable than the isomeric OS -diprotonated species (229) Not surprisingly there is a signiTHORNcant length-ening of the OS bond with the second protonation (226 rarr 228 1641ucircA rarr 1817 ucircA) due to electrostatic repulsive effects In addition to struc-tures and energies 13C 17O and 32S NMR chemical shifts were calcu-lated using the correlated GIAO-MP2 method with the DFT optimizedgeometries Comparison of the calculated chemical shift values with the


H3CS

CH3

OH

H3CS

CH3

O

HH3C

SCH3

OH

H3CS

CH3

O

H

2+ 2+HH

226 227 228 229

Calculated 13CChemical Shift 400 ppm 434 ppm 560 ppm 478 ppm

+ +

Figure 7 Protonated dimethylsulfoxide (DMSO) and calculated 13C NMR chemical shiftvalues

experimentally determined data in FSO3HSbF5-SO2ClF media indicatepredominant formation of the monoprotonated species (226) For examplethe experimentally determined value for the 13C chemical shift of 226 isfound at δ13C 343 while GIAO-MP2 value is estimated to be δ13C 40(δ13C 35 at the GIAO-SCF level) The diprotonated species is estimatedto be further deshielded to δ13C 560

525 Halogen-Centered Vicinal -Dications

Despite the importance of halogens in synthetic and mechanistic chem-istry there has been very little work on the superelectrophililc activation ofhalogens of vicinal -halogen dications and related systems Gas-phase andtheoretical studies have demonstrated the possibility of multiply-ionizationof diatomic halogens such as producing I23+ Br23+ and Cl23+115 Inthe condensed phase acid-catalyzed halogenation of weak nucleophilesis thought to occur by interaction of halogen lone pair electrons with theacid (eq 69)

Cl ClAlCl3

Cl Cl AlCl3AlCl3

Cl Cl AlCl3AlCl3

HA

230

231

Cl ClH

A

HACl ClH

A

H

A

d+

d+

dminus

dminus

dminus

d+

d+

dminus

dminus

d+

d+

dminus

(69)

Complexationwith a second equivalent of Lewis acid could produce a super-electrophilic species (230) having the vicinal -dication structure or alterna-tively doubleprotonationcould conceivablygenerate superelectrophile231Olah andRasul recently reported a calculational studyof both protonated andmethylated vicinal dihalogen dications (HXXH2+ CH3XXCH3

2+ etc)116

Superelectrophilic activation can also be envisaged for hypohalogen sys-tems and other oxygenated halogens Diprotonation of iodosyl systems or

VICINAL SYSTEMS 179

hypochlorous acid could potentially form the vicinal -dications (232234)(eqs 7071)

X OH+

X O HH+

X OH

HX O Hor

H232 233

+ + + + +IIII (70)

H ClH+ H+

HO Cl

H

HO Cl

HH

234

+ + +O (71)

Protonation of perchloric acid could form the corresponding dication 235and trication 236 (eq 72)

HO ClH+ H+ H+

O

O

O HO Cl

O

O

OH HO Cl

O

OH

OH HO Cl

OH

OH

OH

235 236

+ ++

+

++ (72)

These systems await future studies

526 Noble Gas-Centered Vicinal -Dications

As noted in Chapter 1 the helium dimer dication He22+ was predicted

by Pauling to be a stable species117 This unusual dication indeed canbe generated in the gas-phase and it has been studied by several the-oretical investigations118 Many other noble gas diatomic species havebeen observed by gas-phase studies including Ne2

2+ ArNe2+ XeNe2+and KrHe2+86c Dicationic species have also been observed with noble gasbound to other atoms For example noble gas chloride dications (NeCl2+KrCl2+ and XeCl2+) are reported in mass spectrometric studies86c Bond-ing to metal and nonmetal centers have also been seen in dicationic andtricationic species for example in GeNe2+ PtHe2+ VHe3+ SiNe2+and CAr2+86bc Other related dicationic and tricationic species have beenstudied by theoretical methods Not surprisingly the vicinal-dications (andtrications) of noble gas clusters are limited to the gas-phase and no anal-ogous condensed phase species have been reported It may be possible toform a doubly electron deTHORNcient species (237 eq 73)

F FSbF5

F F SbF5

SbF5F Xe F SbF5SbF5

237

Xe Xed+

dminus

dminus

dminus

d++

(73)


by complexation of xenon szliguorides by Lewis acids although it is uncertainif such a species could be persistent in the condensed phase

Olah and colleagues have studied the heliomethonium dicationCH4He2+ (238)

HC

H

H

H

He

2+

238

by ab initio calculations at the MP26-31G and MP26-311+G(2 dp)levels119 This gitonic superelectrophile 238 is a stable minimum (Cs sym-metry) on its potential energy surface and its structure is isoelectronic withCH5

+ The transition state structure for proton loss was calculated anddication 238 is protected from dissociation by a signiTHORNcant energy barrier(213 kcalmol) Based on calculations it is suggested that dication 238may be produced by the reaction of CH4

2+ and He

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489 209

6GITONIC 13-SUPERELECTROPHILES


Multiply charged onium cations have been actively studied over the years1

With the development of the concept of superelectrophiles and the stud-ies of varied related onium dications and trications it has become clearthat electrophilic reactivities drop off rapidly with an increasing distancebetween the charge centers A large enough separation of the chargecenters in onium dications leads to electrophilic reactivities similar tomonocationic electrophiles As discussed in the previous chapters gemi-nal and vicinal-type dications are very reactive gitonic superelectrophilesA number of studies have also demonstrated that 13-dicationic systemscan exhibit superelectrophilic activity despite the increased charge-chargeseparation These 13-dicationic superelectrophiles are discussed in thischapter First superelectrophiles composed of 13-carbodications specif-ically containing carbenium and carbonium ion centers are consideredThis is followed by those containing oxonium and carboxonium ions acyldications and azacarbodications

62 13-DICATIONIC SYSTEMS

621 13-Carbodications

The destabilization and connected superelectrophilic character of some13-carbodications can be seen in the unsuccessful attempts to prepare


187

copy

188 GITONIC 13-SUPERELECTROPHILES

certain persistent 13-carbodications For example the tert-butylcation(1) is known to be a remarkably stable species in superacidic solution(eq 1)2 In contrast ionization of 2334-tetramethyl-24-pentanediol (2)does not produce the expected 13-carbodication (3) but instead dispropor-tionation products 23-dimethyl-2-butyl cation (4) and protonated acetone(5) are formed (eq 2)3

(CH3)3C-Xsuperacid

CCH3

CH3

H3C

1

(1)

OHHO

FSO3HSbF5

2

OH

4 5

minus78degC

3

+++

++

(2)

In a similar respect ionization of 24-dichloro-24-dimethylpentane (6)does not give the 13-carbodication (7 eq 3)3 Despite the superacidicconditions deprotonation occurs to give the allylic cation (8) Even sub-stitution by phenyl groups is not enough to stabilize the 13-dicationFor example 1133-tetraphenyl-13-propanediol (9) also undergoes thedeprotonaton or disproportionation reactions (eq 4)3

In an attempt to prepare an adamanta-13-diyl dication 12 only themonocationic donor-acceptor complex (11) could be observed experimen-tally in the superacid-promoted reaction of the diszliguoride (10 eq 5)4

ClCl

6 8

minus78degC

SbF5

7

minusH+

+ + +(3)

Ph Ph

Ph PhOHHO

9Ph

Ph Ph

Ph

FSO3HSbF5

minus130degC

FSO3HSbF5

minus78degCPh CH3

Ph

Ph Ph

OH

++

+

+(4)

FF SbF5 Fexcess

SbF5

10 11 12

+ + +d+

dminus

(5)

13-DICATIONIC SYSTEMS 189

Although the fully formed dicationic structure (12) is not formed thedonor-acceptor complex 11 may have partial superelectrophilic characterby interaction with SbF5 The adamanta-13-diyl dication 12 has beenfound to be the global minimum structure on the C10H14

2+ potentialenergy surface5 Theoretical studies at the B3LYP6-31G level haveshown 12 to be 04 kcalmol more stable than the isomeric 14-dication13 The loss of stabilization on going from the 3 carbocationic centerto the 2 carbocationic center is compensated by an increasing distancebetween charge centers The next most stable structure is the 15-dication14 which is found to be 33 kcalmol less stable than 12 The struc-tures and energies for the protio-adamantyl dications (C10H16

2+) werealso studied by theoretical calculations5 At the B3LYP6-31G levelTHORNve energy minima were located The global energy minimum for theprotio-adamantyl dication was found for structure 15 which can be con-sidered as the C(3)C(9) protonated 1-adamantyl cation The structurecontains a two electronthree center (2e3c) bond involving two car-bons and a carbenium center separated by a methylene group The otherC10H16

2+ structures are energy minima with considerably higher energy(gt 18 kcalmol) than dication 15

12 13 14

Rel Energy(kcalmol)

00 04 33 15

HH

HH+ + +

+++

++

As in the case of vicinal dications stabilization of the carbocationiccenters has provided several examples of observable 13-carbodicationsFor example Olah and co-workers were able to generate the cyclopropylstabilized 13-carbodication (17) by ionization of the diol (16) in FSO3HSbF5 at low temperature (eq 6)6

OHOH

FSO3H-SbF5

SO2ClF minus78degC

d13C

16 17

262

+ +

(6)CH3

274

18

d13C

+

The carbocationic centers of 17 exhibit a δ13C resonance of 2628 whichagrees reasonably with the calculated IGLO DZB3LYP6-31G


chemical shift of δ13C 2826 The cationic centers of the carbodication (17)are shielded by 12 ppm when compared with the 11-dicyclopropylethylcation (18) showing an increased delocalization of the charge from thecationic centers into the cyclopropyl groups The trimethylenemethanedication (20) is an interesting example of a prepared 13-dication7 Ion-ization of the diol (19) in FSO3HSbF5 produces the dication (20) whichwas observed by NMR (eq 7)

Ph

Ph

Ph

Ph

PhPh

OH OHFSO3H-SbF5

SO2ClF minus78degC

Ph

Ph

Ph

Ph

PhPh

or

Ph

Ph

Ph

Ph

PhPh

2+

19 20

+ +

(7)

Another class of gitonic superelectrophiles (based on the 13-carbodica-tion structure) are the Wheland intermediates or sigma complexes derivedfrom electrophilic aromatic substitution of carbocationic systems (eq 8)

Ph

Ph

Ph

O O HA

or

O OH

Ph

PhH

NO2 Ph

PhH

NO2 etc

21 22 23

minusH+

N+

++ +

+ d+

+ + ++

N

(8)

Few examples of such intermediates have been reported but one exampleinvolves the superelectrophilic nitration of the trityl cation8 Attack ofthe trityl cation (21) by the protosolvated nitronium ion (22 HNO2

2+)leads to a sigma complex (23) having the 13-dicationic structure It isexpected that delocalization of the charges leads to signiTHORNcant contribu-tions from charge separated resonance forms (eq 8) In general these typesof dicationic sigma complexes will also be formed when the reacting arenecontains a potentially cationic substituent group This would include thesuperacid-catalyzed reactions of nitrobenzenes aryl ketones aryl aldehy-des and anilines many of which are fully protonated in superacids Thenitration of phenalenone is another example in which a dicationic specieshas been proposed as a key intermediate (eq 9)9

O

HNO3

70 H2SO4

OH OHO2N H

minus2H+

O

NO2

24

++ +

(9)


In strongly acidic media 2-nitrophenalenone is produced which is consis-tent with formation of dication 24 There are also examples of diprotonatedphenalenones similar to intermediate 24 that have been directly observedby NMR spectroscopy

A similar type of intermediate has been proposed in the superacid-catalyzed hydrogen-deuterium exchange involving 9-substituted-9-szliguo-renyl cations10 For example 9-methyl-9-szliguorenyl cation (25) can begenerated in deuterated szliguorosulfonic acid solution from ionization ofthe 9-methyl-9-szliguorenol (Scheme 1) Deuterium exchange is observed atthe C-27 C-45 and at the methyl carbon These exchange products havebeen rationalized by formation of the ring-deuterated dicationic species(26) Formation of the dicationic species likely increases the acidity ofthe methyl hydrogens (making them superelectrophilic) and deprotonationgives monocation 27 which undergoes subsequent deuteration

There are several other carbodications that may be represented as 13-dicationic systems (or nonclassical highly delocalized systems) includingSchleyers 13-dehydro-57-adamantanediyl dication (28)11 Hogeveenspyramidal dication (29)12 diallyl dications (ie 30)13 dicationic ethers(ie 31)14 diprotonated pyrones (32)15 as well as various aromatic dica-tions

2+

2828

CH3

CH3

CH3

H3C

H3CC

CH3

CH3

CH3

CH3

H3C

H3CC

CH3

29 29

2+

CH3

CH3

CH3H3C

30

N

NO

N

N

CH3

CH3

H3C

H3C

31

O OH

CH3H

H

O OH

CH3H

H

32 32

+

++ +

+ +

+ +++++

Though interesting as dicationic species these ions are not generallyconsidered gitonic superelectrophiles Several recent reviews have sum-marized their chemistry16

As described in the case of the 1-adamantyl cation protosolvation ofcarbon-carbon and carbon-hydrogen sigma bonds can lead to cationic2e3c bonding and the formation of carbonium ion centers The role ofthis interaction in the chemistry of superelectrophiles is typiTHORNed by proto-solvation of the tert-butyl cation (1) in superacid to provide the dicationic


HO CH3DSO3F

SO2ClFminus78degC

CH3 CH3

H

D

H

D

D+

minusH+D+

minusH+

CH2D

H

D

CH2D

D

CD3

DD

DD

25 26 27

+ + + +

+++ +

Scheme 1 Superacid-promoted deuterium-hydrogen exchange on the 9-methyl-9-szliguo-renyl cation (25)

species (33 eq 10)17 As described in the previous chapter this leadsto isotopic exchange when deuterated superacid is used Although suchprotosolvation of trialkylcarbenium ions has only been reported for thetert-butyl cation and 2-propyl cation similar dicationic species should alsobe possible for larger systems leading 13-dicationic superelectrophilesFor example the 3-ethyl-3-pentyl cation (34) should preferentially be pro-tosolvated at the methyl groups (35) instead of the methylene groups (36)due to the charge-charge repulsive effects (eq 11)

DFSbF5

33

minus78degC

H3CC

CH3

CH3

H3CC

C

CH3

HH

H

D

H3CC

CH2D

CH3

minusH+

1

+ +

+

+

(10)

HFSbF5CH3CH2 CCH2CH3

CH2CH3

34 35

CH3CH2 CC

CH2CH3

HH

H

H

C

HH

36

CH3CH2 CC

CH3CH2

CH3H

H

H

++ + + +

+

(11)

In addition to the carbenium-carbonium dications (ie 35) bis-carbonium dications have been studied by theoretical methods Exami-nation of the potential energy surface of C3H10

2+ (diprotonated propane)THORNnds three structures at energy minima18 The global minimum corre-sponds to the structure (37) in which both terminal carbons are involvedin electron-deTHORNcient 2e3c bonds The next most stable C3H10

2+ structure(38) lies 67 kcalmol higher in energy and it possesses two 2e3c bonds


one involving the CH bond and the other involving the CC bond Ina similar respect the global minimum on the C4H12

2+ potential energysurface is found at a structure (39) involving 2e3c bonds of the terminalcarbons18

37 38 39

CC

C

H H

HH

HH

H

H

H

H

+ +C

CC

H H

H

H

HHH

HH

H

++ C

CC

H CH3

HH

HH

H

H

H

H

+ +

It might be argued that structures such as 37 and 39 should actuallybe described as distonic superelectrophiles because three carbon atomsseparate the protosolvated 2e3c bonds However as it is understood thatsome of the positive charge resides at the carbon atoms of the CH4

+groups the designations as gitonic superelectrophiles can be consideredappropriate for 37 and 39

622 Carboxonium-Centered 13-Dications

There have been a signiTHORNcant number of reports of gitonic superelec-trophilic systems involving carboxonium-centered dications Many ofthese can be represented as 13-dicationic systems although charge delo-calization may increase the distance between charge centers Somesuperelectrophiles of this type could be considered gitonic or distonicdepending upon which resonance form predominates in describing thestructure For example acidic carboxonium ions can be described as eitherthe carbenium or oxonium structures (40a and 40b respectively)

H3CC

CC

CH3

O CH3

HHH3C

CC

CCH3

O CH3

HH

40a 40b

HH

+ +

+

+

With the adjacent carbocationic center structure 40a would be consid-ered a gitonic superelectrophile while 40b would be a distonic super-electrophile Although it is generally recognized that the oxonium-typestructure (40b) is the more important resonance form in the description ofmany carboxonium ions1b for demonstrating the raised point we use thehydroxycarbenium ion form for some of the dicationic structures in thissection These include carboxonium dications from 13-dicarbonyl groupsαβ-unsaturated carbonyl compounds and others The oxonium-type ofrepresentation is however used in the section describing gitonic super-electrophiles from diprotonated esters and carboxylic acids


6221 Carboxonium-Carbenium Dications The protonation of mesityloxide (41) has been studied by several groups19 It has been proposed thatmesityl oxide can form equilibria in superacid with the OO-diprotonatedspecies (42) and (at more elevated temperatures) with the CO-diprotona-ted species (40 eq 12)19a

H3CC

CC

CH3

O CH3

H

H+ H+

41

H3CC

CC

CH3

OH CH3

H

H3CC

CC

CH3

OH2 CH3

H

H3CC

CC

CH3

OH CH3

H

H+

HH3C

CC

CCH3

OH CH3

HH

42

40b 40a

H3CC

CC

CH3

O CH3

HH

43

Cl3Al

+ +

+

++

+

++

+minus

(12)

Evidence for the involvement of the diprotonated species 40 and 42includes 13C NMR data which shows deshielding of the involved car-bons as the acidity of the media increases from H0 minus8 to minus26 (mesityloxide is estimated to be fully monoprotonated in acids of about H0 minus8)Dication 42 has been shown to be capable of reacting even with very weaknucleophiles for example abstracting hydride from cyclohexane19b Ananalogous species (43) has been proposed in interaction with excess AlCl3Protonated cyclohex-2-enone is converted to 3-methylcyclo-pent-2-enonein HFSbF5 solution at 50C20 The reaction mechanism is thought toinvolve the dicationic intermediate 44 (eq 13) Likewise aryl-substitutedindenones are converted to the dications by reaction in superacid (eq 14)21

O

HF-SbF5

OH OH OH

CH3

O

CH344 44

+

+ +

+

+

+(13)

O

R

Rprime

CF3SO3H

OH

R

Rprime

45

OH

R

Rprime

45

+

+

+

+

(14)


Dications (45) can be directly observed in some cases (R= CH3 andOCH3) Depending on the substituents the carboxonium carbon (C-1)is observed between δ13C 214217 C-2 is observed at δ13C 4446 andC-3 is observed at about δ13C 197 These data are consistent with theformation of diprotonated species 45 For αβ-unsaturated ketones bothCO-diprotonated and OO-diprotonated species have been observed Forexample dication 46 arising from CO-diprotonation is the product from4-phenyl-3-buten-2-one in superacid22 while dication 47 arising fromOO-diprotonation is the product from chalcone in superacid23

Ph CH3

OH

Ph Ph

OH2

46 47

+

+ +

+

Carboxonium-carbenium dications have also been proposed in the reac-tions of aryl ethers phenols and naphthols with superacids When2-naphthol is reacted with an excess of AlCl3 (3 equivalents) and cyclo-hexane the product of ionic hydrogenation is observed in 59 yield(eq 15)24 This conversion is thought to occur by double protonation ofthe 2-naphthol ring to give the dication 48 which is capable of abstract-ing hydride from cyclohexane Similar intermediates are formed by thereactions of HFSbF5 with naphthyl ethers (eq 16)25

OH 3 equivAlCl3

C6H12

OX

H H

H

H

OC6H12

48 X = H AlCl3minus AlnCl3n

minus

+

+(15)

OCH3

Ph

HF-SbF5OCH3

Ph

49

SO2ClFminus30degC

OCH3

Ph

49

+

++

+ (16)

Dication 49 can be directly observed by low temperature NMR Like othercarboxonium ions dication 49 forms an equilibrium mixture of the E andZ stereoisomers

A variety of 13-dicationic carboxonium superelectrophiles have beengenerated from protonation of carboxylic acids and their derivatives Forexample carboxonium-carbenium dications have been proposed in thesuperacid promoted reaction of cinnamic acid (50) and related


compounds26 When cinnamic acid is reacted with triszligic acid and benzenethe indanone product 51 is formed in good yield (eq 17)

OH

O

Ph

50

CF3SO3H

C6H6

O

Ph

51

(17)

OH

OH

Ph OH

OH

Ph OH

OH

Ph

Ph

53

OH

OH

Ph

52 53 5554

OH

OH2

Ph

+

+

+

++ +

+ +

Mechanistically it is suggested to involve protonation of the carboxylicacid group to give the monocation 52 followed by a second protona-tion at the C-2 position to give the superelectrophile 5326a Cyclizationof the propionic acid derivative (55) then gives the indanone productAb initio calculations suggest that 53 is the key intermediate rather thandication 54 (arising from OO-diprotonation)26a Structure 54 is foundto lie 28 kcalmol above 53 on the potential energy surface Althoughsuperelectrophile 53 could not be directly observed using low tempera-ture 13C NMR the dication (57) from β-phenylcinnamic acid (56) canbe observed in FSO3HSbF5SO2ClF solution26a The superelectrophiliccharacter of dication 57 is seen by comparing it with a monocationic ana-logue the 11-diphenylethyl cation 59 While dication 57 reacts readilywith benzene and gives the indanone (58) in high yield from a cyclization(eq 18) the 11-diphenylethyl cation (59) is unreactive towards benzene(eq 19)

O

Ph PhOH

OH

Ph

57

Ph

OH

O

Ph

56

CF3SO3H

C6H6

Ph

OH

OH

Ph

58

PhPhC6H6

+

+ +

(18)

CH3Ph

59

Ph

Ph

CF3SO3H

C6H6

PhNo Reaction

C6H6

+ (19)

This suggests that the protonated carboxylic acid group enhances theelectrophilic reactivity of the carbocationic site (ie makes it superelec-trophilic) despite the resonance stabilization by the two phenyl groups


Several types of unsaturated amides have produced gitonic superelec-trophiles in superacidic media For example reaction of the cinnamamide(60) with benzene in CF3SO3H gives the addition product in quantitativeyield (eq 20)27

Ph NH2

OCF3SO3H

C6H6 Ph NH2

OHC6H6

Ph NH2

OPh

60 61

+

+

(20)

The dicationic species (61) is proposed as the key intermediate in thereaction Dicationic intermediates such as 61 have also been proposedin conversions of unsaturated amides with polyphosphoric acid sulfatedzirconia and zeolite catalysts such as HUSY28 Likewise ionic hydro-genation of 2-quinolinol (62) can be best understood by the involvementof the dicationic species (63) which is sufTHORNciently electrophilic to reactwith cyclohexane (eq 21)29

C6H12

N OH AlCl3N O

H

X

62 63

H

H

N O

H

X = H or AlnCl3nminus

80

90degC

+

+

(21)

64

N O

H

X

H AH

H

d+

+

dminus

It was also noted that dications like 63 may only be discrete intermediatesin reactions in very strong liquid superacids while protosolvated specieslike 64 may be more likely intermediates in reactions involving weakersuperacids or zeolites

There have been two reports involving gitonic superelectrophiles com-posed of carboxonium ions and vinylic carbocations in a 13-relationshipIn the reaction of 3-phenylpropynoic acid (65) with benzene in superacidthe novel carboxonium-vinyl dication 66 is generated followed by reac-tion with benzene and then cyclization (eq 22)26a Likewise the unsatu-rated amide (67) gives the cyclization product in high yields (7097)in very strong acids (polyphosphoric acid CF3SO3H NaTHORNon SAC-13 orHUSY eq 23)30


CO2H

O

Ph Ph

65

99

CF3SO3H

C6H6Ph

HOOH

H

66C6H6

58

Ph

HOOH

H

66

OH

OH

Ph

57

Ph

Ph +

+

++

+

+(22)

CPh

67

C6H6

Acid

Ph NH

O

Ph

H

HN

H

O

Ph68

NHPh

O+

+

(23)

The carboxonium-vinylic dication (68) is considered the key intermedi-ate leading to the cyclization product The analogous vinylic dications(6971) have also been generated in superacid31 Each of the speciesexhibits high electrophilic reactivity

P

Ph

Ph

PhN

H

Ph

Ph

69 70

NNN

H

71

+ +

++

+

+

6222 Bis-carboxonium Dications A number of reports describegitonic superelectrophiles arising from carboxonium ion groups sepa-rated by a carbon oxygen or nitrogen atom (Table 1) As noted acidiccarboxonium ions can be represented as either the oxonium-type orhydroxycarbenium-type structures Depending on which resonance formis considered these bis-carboxonium dications are considered either agitonic or distonic superelectrophiles For example aliphatic 13-diketonescan be diprotonated in FSO3HSbF5SO2 solution at low temperature(eq 24)32a

H3C CH3

O O FSO3H-SbF5-SO2

minus60degC H3C CH3

OH OH

H3C CH3

OH OH

73a 73b

+ +

+ +(24)

The two important resonance structures for the dication are the bis-oxonium structure (73a a distonic superelectrophile) and the bis-carbenium structure (73b a gitonic superelectrophile) Although it isunderstood that various factors should favor structure 73a (including


charge-charge repulsion) a considerable amount of positive charge residesat the carbon Thus due to their (partial) 13-dicationic character thesetypes of dicationic species are considered as gitonic superelectrophiles

Bis-carboxonium ions such as 73 can be directly observed using low-temperature NMR In the case of 73 24 pentanedione is dissolved inFSO3HSbF5SO2 solution at minus60C and the 1H NMR shows threeabsorptions including the carboxonium protons32 In some cases (espe-cially in weaker superacid systems) the diprotonated species formequilibrium mixtures with the monoprotonated species When either 13-cyclohexane-dione or 2-methyl-13-cyclopentanedione is reacted in verystrong superacids only the monoprotonated species are observed32 Thisis attributed to increased stability of the enol-type cations 90 and 91when compared with the acyclic systems

HO OHCH3

HO OH

90 91

OH

OH

OH

OH

OH92 93

++

+ +

+

++

However diprotonated and triprotonated indane derivatives (92 and 93)have been reported33

The dicationic species have also been obtained from β-ketoacidsβ-ketoesters and β-ketoamides in superacid solutions (Table 1entries 24) Diprotonated acetoacetic acid (75) can be observed bylow-temperature NMR under stable ion conditions34 Likewise diproto-nated methylacetoacetate (77) can be observed by NMR at temperatureslower than minus80C in FSO3HSbF5SO2 solution35 With ethyl acetoac-etate in HFSbF5 the equilibrium constant for the dication-monocationequilibrium has been estimated to be at least 107 indicating virtuallycomplete conversion to the superelectrophile35 The β-ketoamide (78) isfound to give the condensation products 95 in good yield from CF3SO3Hand the superelectrophile 79 is proposed as the key intermediate in thecondensation reaction (eq 25)27

H3C NH2

O O

H3C NH2

OH OHCF3SO3H

78 79

C6H6

H3C NH2

O

95

PhPh

99

H3C NH2

Ph OH

94

+ + +

+

(25)


Table 1 Dications formed upon protonation of 13-dicarbonyl groups and relatedprecursors

HO OH

O O

HO OH

OH OH

O OO O OHHO

XN OHHO

XN OO

H3C CH3

O O

H3C CH3

OH OH

H3C OH

O O

H3C OH

OH OH

H3C OCH3

O O

H3C OCH3

OH OH

H3C NH2

O O

H3C NH2

OH OH

N N

OO

O

HH N N

OHO

OH

HH

Precursor Dication AcidEntry

(1)

(2)

(3)

(4)

(5)

(6)a

(7)

(8)

72 73

74 75

76 77

78 79

80 81

82 83

84 85

86 87

OH

OH

OH

OH88 89

(9)

X = H Cl Br I

CF3SO3H

CF3SO3H

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

HF-SbF5

CF3SO3H

FSO3H-SbF5

BF3-H2O

aCyclic dication 83 is in equilibrium with open chain dication see text

+ +

+ +

+ +

+ +

+

+ +

+ +

+

+

+

+

+


Following electrophilic attack on benzene the carbenium-carboxoniumdication 94 is generated which then gives the product 95 There havebeen several studies of the chemistry of malonic acid (80) and its estersin superacidic media It has been shown that diprotonated products (ie81) are formed (Table 1 entry 5)36

A number of cyclic systems have produced bis-carboxonium dications(Table 1 entries 69) In the case of succinic anhydride (82) howeverthe product formed at minus80C in FSO3HSbF5SO2 solution was theacyl-carboxonium dication (96 eq 26)37

O OHHO

83

OC OH

OH

COHO

OH

96 96

+

+ + + +

+ (26)

When the solution is warmed to minus40C NMR suggests that the acyl-carboxonium dication 96 rearranges through the bis-carboxonium dication83 leading to the acyl-carboxonium dication 96

The succinimide ring system is also thought to form diprotonatedbis-carboxonium type dications (entry 7)3839 When succinimide (84 X =H) is dissolved in FSO3HSbF5SO2 solution the dicationic species (85X = H) can be directly observed by low temperature NMR39 RecentlyOlah and co-workers demonstrated that N -halo-succinimide (84 X = ClBr I)BF3H2O is a highly effective halogenating system for arenes39

A remarkable aspect of this halogenating system is its ability to evenreadily halogenate deactivated arenes For example 2-szliguoronitrobenzeneis converted to the halogenated products (97 X = Cl Br I) in high yieldsfrom the corresponding N -halosuccinimides and BF3H2O (eq 27)

NO2

F N OO

XBF3-H2O

NO2

F

X = Cl Br I84

X

819592

X Yield

ClBrI

97

+ (27)

To account for these conversions two mechanistic proposals have beenmade either the halogenating system involves a highly reactive and sol-vated X+ or the reaction involves X+ transfer from a protonated formof N -halosuccinimide In the later case X+ transfer could occur fromthe neutral N -halosuccinimide monoprotonated or multiply protonatedsuperelectrophilic species These mechanistic possibilities were furtherexamined using DFT calculations For N -chlorosuccinimide and its pro-tosolvated intermediates a series of calculations were done at the B3LYP


Table 2 Calculated reaction enthalpies for the generation of Cl+ fromN -chlorosuccinimide and its protonated forms

N OO

Cl

N OOCl+

N OO

Cl

N OHOCl+

H

N OO

Cl

N OHHOCl+

H

H

N OO

Cl HN OHHO

Cl+H H

H

ΔH kcalmol

3244

1922

702

minus1020

98

+

++

+

++

+

+

+

minus

+

+

+

+

6-311++GB3LYP6-31G level to estimate the reaction enthalpiesfor the generation of Cl+ (Table 2)39b Optimized structures and energieswere calculated for N -chlorosuccinimide its mono- di- and triproto-nated forms and the dehalogenated product Not surprisingly cleavageof the nitrogen-chlorine bond to form Cl+ becomes increasingly favor-able with a greater degree of protonation of N -chlorosuccinimide Onlyin the case of the triprotonated species (98) however is the release ofCl+ predicted to be exothermic Although it is not presently clear whetherthis particular halogenating system involves the release of solvated Cl+or the direct transfer of Cl+ to the arene nucleophile the calculations sug-gest that protosolvation of the N -chlorosuccinimide leads to ground statedestabilization If Cl+ is directly transferred to the arene nucleophilesthis estabilization of the N -chlorosuccinimide by superelectrophilic acti-vation should lead to lowered activation barriers leading to the productcompared to the uncatalyzed reactions (eqs 2829)

H

Cl

N OO

Dagger

N OO

Cl

H Cl

N OO

ΔG1Dagger

d+ _

_

+

(28)


ΔG1Dagger ΔG2

ΔG2δ+

Daggergt

H

Cl

N OO

H H

H

DaggerN OO

Cl

H H

H

H Cl

NH

OHHO

Dagger

+ ++

++

+

+

+ +

(29)

Transfer of Cl+ to the arene provides some relief of the Coulombic repul-sion in the multiply charged superelectrophilic system Under the reactionconditions it is not yet known to what extent the N -halosuccinimides areprotonated in BF3H2O but this acid-catalyst has an estimated acidityaround H0 minus12

Parabanicacid (86)hasbeenshowntoproducehighlyelectrophilic speciesin superacidic CF3SO3H and the resulting electrophile is capable of reactingwith C6H6 and moderately deactivated arenes40 The superacid-promotedcondensation reaction of parabanic acid with benzene (and other arenes) inCF3SO3H provides satisfactory yields of the 55-diarylhydantoins (eq 30)

N N

OO

O

HH N N

OHO

OH

HH

86 87

CF3SO3H

C6H6

2 C6H6

N N

O

O

HH

Ph

Ph

+

+

(30)

well known for their use as anticonvulsant drugs To explain the high elec-trophilic reactivity of parabanic acid in CF3SO3H the superelectrophilicintermediate (87) is suggested as the key intermediate Alternatively aprotosolvated ion with partial dicationic character may also be involved

A series of protonated napthalenediols have also been studied and insome cases the bis-carboxonium dications can be observed by low temper-ature NMR from HFSbF5 solution25 In the case of 13-napthalenediol(88) the bis-carboxonium ion (89) is formed having the 13-dicationiccharacter (Table 1 entry 9)

6223 Carboxonium-Ammonium and Related Dications A wide vari-ety of species have been generated in which the 13-dicationic structurearises from carboxonium ion centers being adjacent (separated by one car-bon) to an ammonium or related charge center These intermediates maybe described as reactive dications yet they have been shown to exhibitelectrophilic reactivities comparable to superelectrophiles


It was demonstrated that α-aminoacids can be protonated in superacidsto form well-deTHORNned dicationic species (99 eq 31)41 It is not known ifracemization of the α-aminoacid dications occurs from deprotonation atthe α-carbon Given the high acidity of the media however this seemsunlikely Triprotonated amino acids were likewise observed with aminoacids lysine methionine aspartic acid and glutamic acid Interestinglythere were no examples of the α-aminoacid dications (ie 99) cleavingto the corresponding acyl dications (ie 100) Increasing the charge sep-aration of the cationic centers however facilitates the dehydration to theacyl dication (102 eq 32)

H3NO

O

CH3FSO3H-SbF5-SO2

minus60degC H3NOH

OH

CH3

H3NO

CH3

99 100

minusH2O

+ ++ +

+minus (31)

H3N OH

OH

minusH2O H3N

O

101 102

+

+

++

(32)

The different chemistry of the dications 99 and 101 seems to reszligectthe superelectrophilic nature of the gitonic dication It has also beenshown that simple peptides may be multiply protonated in acids likeFSO3HSbF5 generally being protonated at the terminal amino groupthe carboxyl group and at the peptide bonds In a study of the chemistryof N -tosylated phenylalanine derivatives the diprotonated intermediate(103) was proposed in a reaction with superacid CF3SO3H (eq 33)42

Ph OH

NHTs

OCF3SO3H Ph OH

N

OH

SH

H Ar

O

O

103

+

+ (33)

It has also been shown that gitonic dications may be generated fromsuperacid-promoted reactions of aminoacetals (eq 34)43

H2NOCH3

OCH3

CF3SO3H

C6H6

H3NOCH3

H3NOCH3

H3NPh

C6H6 minusCH3OH

H2NPh

Ph95

104 105 105

106107

++

+

+

+

+

(34)


Reaction of acetal 104 with benzene in the presence of CF3SO3H leadsto product 107 in high yield This conversion involves formation of theammonium-carboxonium dication (105) a reactive dication possessingsome 13-dicationic character Reaction with benzene and subsequent lossof methanol generates another reactive dication (106) which then gives theproduct The superelectrophilic character of the ammonium-carboxoniumdications is indicated by their reactions with moderately deactivatedarenes such as o-dichlorobenzene

The N -heterocyclic systems have likewise been shown to produce reac-tive dications having 13-dicationic character Piperidones and relatedsystems are diprotonated in superacid and the resulting intermediatesare capable of reacting with benzene in condensation reactions(eq 35)44

N

O CF3SO3H

N

OH

H

N

OH

H

+

+

+

+(35)

Several types of nitrogen-containing heteroaromatic compounds are alsocapable of producing carboxonium-centered dications (Table 3)45 Amongthe dications 108113 all have been shown to react with weak nucle-ophiles such as benzene deactivated arenes and even saturated hydro-carbons Moreover their reactivities greatly exceed that of comparablemonocationic electrophiles In the case of dication 111 for example it isshown that it will condense with benzene in a hydroxyalkylative conver-sion (eq 36)45d

NO

CH3

X

CF3SO3H

C6H6

N

CH3

X

PhPh

92

+ +

minusminus

(36)

Under the same reaction conditions however protonated acetone does notreact with benzene Dications 112 and 113 have been shown to undergoionic hydrogenation in the presence of cyclohexane an exceptionally weaknucleophile45ef

The chemistry of N-acyliminium ions has great synthetic value andmany of the conversions are done in highly acidic media46 There are sev-eral examples of N-acyliminium ion reactions that likely involve gitonicsuperelectrophiles For example reaction of the 3-chlorophthalimidine114 with excess AlCl3 produces an electrophile capable of reacting withm-dichlorobenzene (eq 37)47


Table 3 Dicationic species (108113) arising from diprotonation ofN -heteroaromatic compounds

N

O

H

N

OH

H

H

N

S O

CH3 N

S OH

CH3

H

NH

O

NH

OHH

NO

CH3

Xminus

NOH

CH3

N

OH

N

OH H

N

OH

N

OH

X

CF3SO3H

CF3SO3H

CF3SO3H

CF3SO3H

CF3SO3H-SbF5

HBr-AlBr3

X = H or AlnBr3n

108

109

110

111

112

113

(1)

(2)

(3)

(4)

(5)

(6)

Substrate Dication AcidEntry

+

+

+

+

+

+

++

+

+

+

+

+

minus

NH

O

Cl

14-20 equivAlCl3

m-C6H4C12

N

OAlCl3

H

AlCl3 NHO

Cl

Cl80

116114 115

N

O

H+ +

d+

dminus

(37)


As a reasonable explanation for the high electrophilic reactivity theN-acyliminium ion (115) may be interacting with excess Lewis acid toproduce the gitonic superelectrophile (116) Another superelectrophilicN-acyliminium ion is involved in the superacid-promoted Tscherniacamidomethylation reaction of aromatic compounds48 It was observedthat N -hydroxymethylphthalimide reacts with benzene and deactivatedarenes in superacidic CF3SO3H (Scheme 2) Given the high electrophilicreactivity the gitonic superelectrophiles (117 and 118) were proposed asprobable intermediates The cyclic N-acyliminium (120) ion is obtainedfrom ionization of the 5-hydroxypyrrolidone (119) and indirect evidencesuggests the formation of the gitonic superelectrophile (121) in superacids(eq 38)49 A dramatic acidity effect is seen in the reactions of 119 witharenes and CF3SO3H (H0 minus14) or CF3CO2H (H0 minus27) Compound119 reacts with a moderately deactivated arene p-dichlorobenzene inCF3SO3H In contrast the same reaction with CF3CO2H gives no ary-lated product (122) However when an activated arene is used in thereaction with 119 and CF3CO2H the arylated product (123) is obtained(eq 39) indicating that the N-acyliminium ion (120) is generated in theCF3CO2H media This is in accord that the superacidic CF3SO3H pro-tosolvates the N-acyliminium ion (120) to produce the superelectrophile(121 eq 38) This chemistry was also studied by calculations (Figure 1)that indicate that the superelectrophilic N-acyliminium ion (121) is farmore reactive towards benzene than the monocationic N-acyliminium ion(120) Calculations using gas-phase modeling indicate that formation ofthe σ -complex from the monocationic N-acyliminium ion (120) and ben-zene is signiTHORNcantly endothermic (at the MP26-31+G level no minimum

N

O

O

OH CF3SO3HN

OH

O

OH2N

OH

O

CH2 N

O

OCH2

N

OH

O

CH2N

OH

O

CH2

H

117 118

117 117

N

OH

O

CH2

117

N

O

O

OH CF3SO3H

C6H6

N

O

O

++

+

+

+

+

++

+

+

++

Scheme 2


could be found for the σ -complex and without a THORNxed ring-ring bondthe structure reverts to benzene and 120) However formation of theσ -complex from the superelectrophilic N-acyliminium ion (121) and ben-zene is found to highly exothermic The more favorable thermodynamicsis clearly the result of effective charge dispersal in the formation of theσ -complex from the superelectrophile Given the highly acidic conditionsand high temperatures often used in the reactions of N-acyliminium ionswith arenes it is likely that other examples of superelectrophilic interme-diates arising from protosolvation or interaction with excess Lewis acidsare to be found

N

O

OH

CH3

CF3SO3H

p-C6H4Cl2

N

O

CH3

Cl

66

80degC Cl

N CH3

O

120

N CH3

OH

121119 122

+

+

+

(38)

123

N

O

OH

CH3

CF3CO2HN

O

CH3

OCH3

67

80degC H3CO

N CH3

O

120119

p-C6H4(OCH3)2

+

(39)

A series of phosphonium-carboxonium dications have also been studiedin superacid catalyzed reactions31a When the dicationic electrophiles arecompared with similar monocationic species it is clear that the phos-phonium group enhances the electrophilic character of the carboxoniumcenter For example protonated acetone is incapable of reacting withbenzene in condensation reactions however the phosphonium-substitutedcarboxonium ion (124) reacts in high yield (eq 40)

PhP

O

PhPh

CH3

PhP

PhPh

CH3

Ph

Ph

X

88CF3SO3H

C6H6

PhP

OH

PhPh

CH3

124

+ + +

minus

(40)

Phosphonium groups are well known for their ability to stabilize adjacentanionic sites (ie Wittig reagents) but the results with the dicationicspecies indicate that phosphonium groups can also destabilize adjacentcationic groups producing their superelectrophilic reactivities


N CH3

O

++

N CH3

OH

HH

+

TheoryLevel

Energy + ZPE (Hartrees)

HF6-31+G minus230711092 minus323093601 minus55769292 +222

MP26-31+G minus231472004 minus324061503 minus555513348(ring-ring bond fixed)

+126

N CH3

OH

+

+

+

N CH3

OH

HH

2+


HF6-31+G minus230711092 minus323236421 minus557016575 minus433

MP26-31+G minus231472004 minus324183270 minus555743085 minus551

120

121

TheoryLevel

ΔHreaction(kcalmol)


Figure 1 Calculated energetics for the reactions of monocation 120 and superelectrophile121 with benzene to form the initial σ -complexes

6224 Diprotonated Esters and Carboxylic Acids A signiTHORNcant classof 13-dicationic gitonic superelectrophiles are the diprotonated estersand carboxylic acids Acid-catalyzed ester cleavage has been extensivelystudied in organic chemistry and evidence has emerged to suggest thatsuperelectrophiles can play a role in this chemistry The acid catalyzedAac1 cleavage mechanism involves initial protonation at the acyl oxy-gen followed by proton transfer to the ether oxygen followed by directcleavage to the acyl cation and alcohol (eq 41) In low-temperature NMRstudies methyl acetate is found to be completely protonated at the acyloxygen (125) in superacidic FSO3HSbF5SO2 solution50 There is noindication of an equilibrium with the neutral ester or the ether protonatedisomer (126) However even at minus78C protonated methyl acetate under-goes slow acyl oxygen cleavage to acetyl cation and methyloxonium ion(eq 42)

H3C OCH3

O

H3C OCH3

OH

H3C OCH3

O

HH3C

O

+acid

CH3OHAac1

125 126

+

+ +

(41)


H3C OCH3

O

H3C OCH3

OHFSO3HSbF5

SO2minus78degC

H+

H3C OCH3

OH

127H

H3C

O

+ CH3OH2

125

+++

++

(42)

This is indicative of further protolytic activation via the superelectrophilicgitonic carboxonium dication (127) The protonated species arising frommethyl acetate were also studied by calculational methods50 Consistentwith the experimental results the most stable monoprotonated species isfound to be the acyl-oxygen protonated monocation (125) Several dipro-tonated structures were found as minima on the potential energy surface(MP4(SDTQ)6-31GMP26-31G level) and a stereoisomer of 127 isfound to be the most stable Structurally the second protonation on 125leads to a lengthening of the oxonium centers oxygen-carbon bond and ashortening of the oxygen-carbon bond of the acyl center Another mini-mum on the potential energy surface is the dication arising from doubleprotonation at the acyl oxygen It is found just 30 kcalmol higher inenergy than the global minimum (ie 127)

Further evidence for dicationic intermediates comes from a study of the11-di-methoxyethyl cation (128) and its reaction with CD3FSbF5SO2

(eq 43)50 At minus30C slow methyl exchange occurs at the methoxy oxy-gen Since demethylation (to form the neutral ester) is unlikely in suchhighly acidic solution the methyl exchange is best interpreted by elec-trophilic solvation of 128 by the CD3FSbF5 and methylation to give thedication 129 Subsequent demethylation then gives the exchange product130 The superacid-promoted ring opening of the β-lactone 131 has alsobeen shown to produce the distonic acyl-oxonium dication 13351

H3CO CH3

O CH3

BF4

CD3FSbF5SO2

minus30degC

128

H3CO CH3

O CH3

129

D3C

H3CO CD3

O CH3

130

(NuCH3)+Nu

++

+

+

minus(43)

O

H3CCH3

O

HF-BF3

O

H3CCH3

HOOH

H3CCH3

HO OH2

OC

CH3H3C

131 132 133

++++

+ (44)

This ring opening may likewise involve the gitonic superelectrophile 132


Superelectrophilic intermediates have further been proposed in the reac-tions of some esters For example a recent report describes the conver-sions of methyl benzoate to benzophenone products (7093 yields) inreactions with superacid (eq 45)52

OCH3

O

CF3SO3H

C6H5NO2

O

NO2

82

(45)

OCH3

OH

H

OCH3

OH2

134 135

+

+

+

+

To explain the high level of electrophilic reactivity of this system theprotosolvated species 134 and 135 are proposed as probable intermediates

Like the diprotonated esters gitonic superelectrophiles are thought toarise from the reactions of some carboxylic acids in superacidic mediaProtosolvation of the monoprotonated carboxylic acids has been suggestedin the superacid-catalyzed formation of acyl cations from the correspond-ing carboxylic acids For example tetraszliguoromethane is formed in thereaction of triszliguoroacetic acid (CF3CO2H) with FSO3HSbF5 (50 mol SbF5 eq 46)53

F3CC

OH

OFSO3HSbF5

F3CC

OH

OHH

F3CC

OH2

OH minusH2O

F3CC

OHCF4

136 137 138

minusSbF5

minusCOH+

CF3

139

+ ++

+

+

+

SbF6minus

+

(46)

With decreasing mol of SbF5 and thus decreasing acidity the yield ofCF4 diminishes and at 10 mol SbF5 no CF4 is detectable These resultsare interpreted as the protonation of CF3CO2H to form the carboxoniumion 136 and subsequent protosolvation involving the gitonic dication 137Formation of 137 then leads to cleavage to the protiotriszliguoroacetyl cation138 which ultimately leads to CF4 Theoretical calculations found thedication 137 to be a stable minimum structure at the MP26-31G level53

However calculations at the same level of theory could not THORNnd a stableminimum for the protiotriszliguoroacetyl dication 138 because of its sponta-neous dissociation into CF3

+ and protonated carbon monoxide (COH+)


This suggests that the formation of the CF3+ cation and szliguoride abstrac-

tion from SbF6minus leads to the product CF4

In a similar respect protosolvation has been suggested in the superacid-induced formation of the acetyl cation from acetic acid and the for-mation of the formyl cation from formic acid54 In theoretical studiesrelated to such processes both diprotonated acetic acid and diprotonatedformic acid were found at a minimum on the potential energy surfaces(MP26-31G level) In the case of acetic acid the global minimumstructure involves protonation at both oxygen atoms (140) and the struc-ture is characterized by a long COH2 bond and relatively short COHbond13C and 17O NMR chemical shifts were also calculated using IGLOGIAO-SCF and GIAO-MP2 methods The gitonic superelectrophile (140)can be considered as a donor-acceptor complex of H2O and the pro-tonated acetyl cation (CH3COH2+) A similar structure (both Cs pointgroup) is found at the global minimum for diprotonated formic acid (141)

HC

O

O

141

H

H

H

H3CC

O

O

140

H

H

H

1207 Aring1221 Aring


2+2+

Although monoprotonated acetic and formic acid can be directly observedas persistent species in superacids at low temperature55 the diprotonatedions 140 and 141 have not been detectable in the condensed phase as theycleave to their acyl cations

623 Oxonium 13-Dications

Like gitonic 12-dicationic species analogous superelectrophiles havingtwo oxonium cationic centers in a 13-dicationic structure are so far vir-tually unknown There have been no reports of persistent bis-oxonium13-dicationic species such as 142143 This may be due to the facilecleavage pathways that are available to such systems In the case of13-dioxane reaction in superacid does not lead to the gitonic superelec-trophile 143 but rather ring opening products such as 145 and 146 areobserved56 These are thought to arise from monocationic intermediateslike 144 (eq 47)

H3CO O

CH3

CH3 CH3 O OHH

142 143

++

++


O HF-SbF5

SO2

O OOH

HO O

HO O

H

HO O

H H

H144

145

146

+ +

+

+

+

+ +

(47)

Several gitonic superelectrophiles have been reported having closelyoriented oxonium and carboxonium ion centers some of which may beconsidered 13-dications A series of hydroxy-substituted carboxylic acidswere studied in FSO3HSbF5 in solution and the oxonium-carboniumdications could be directly observed at low temperature57 In the case oflactic acid dication 147 is a persistent ion at minus80C but at temperaturesabove minus60C formation of the diprotonated lactide (148) is observed(eq 48)

HOCH3

OH

OFSO3HSbF5

SO2minus80degC

HOCH3

OH2

OH

minus30degC

minus2 H3O+ O

O

CH3

CH3

OH

HOHO

CH3

OH2

OH

147 147 148

+

+

+

+

+

+

(48)

Although no mechanism is proposed for the dimerization of lactic acidin the FSO3HSbF5 solution the process may very well involve thesuperelectrophile 147 Other oxonium-carbenium 13-dications have beensuggested in superacid promoted pinacolone rearrangments of diproto-nated aliphatic glycols and alkoxy alcohols (eqs 4950)58

HO

CH2CH2

OH

FSO3H SbF5

SO2minus80degC

O

CH2CH2

O

H

H

H

H

minusH2O

O

CH2C

H

H

H

H

~H

minusH+ HC

CH3

OH

149 150 152

O O

H

H

H

H

151

C C

H H

HH

2+

+ + +

+ +

+ d+

d+

(49)

O

CH2CH2

O

H

H

H

HminusH2O

149

O

CH2C

H

H

H HC

CH3

OH

152

+ +

+ +

minusH+ (50)


Ethylene glycol is shown to be diprotonated in FSO3HSbF5 solution atminus80C giving the distonic superelectrophile 149 When the solution of149 is warmed to 25C NMR indicates that protonated acetaldehyde (152)is generated This conversion can be understood as the loss of water withan accompanying shift of a hydride and subsequent proton loss Althoughthe gitonic superelectrophile 150 may only be a short-lived species or atransition state structure (ie 151) this conversion is novel with respectto the formation of a gitonic superelectrophile (150 or 151) from a dis-tonic dicationic species (149) An alternative mechanism may also beproposed involving equilibration with the monoprotonated species in thedehydration step (eq 50) Similar conversions have been reported for thesuperacid-promoted rearrangements of alkoxy alcohols59 For example2-methoxy-ethanol is also diprotonated in FSO3HSbF5 solution formingthe observed bis-oxonium dication (153) at minus80C (eq 51)

CH3O

CH2 CH2

OH

FSO3H SbF5

SO2

minus80degCO

CH2 CH2

O

H

H3C

H

H

minusH2O

HC

CH3

O

153 154

H3C

+ +

+

(51)

When the solution is warmed to 70C dication 153 rearranges to thecarboxonium ion 154 (t12 = 30 min) This conversion likely follows amechanistic pathway similar to the superacid-promoted conversion ofethylene glycol to acetaldehyde (eq 49)

Further insight into the above reactions may be found in the previouslydiscussed conversion of pivaldehyde (155) to methyl isopropyl ketone(160 Scheme 3) and in the closely related superacid-catalyzed prepara-tion of methyl isopropyl ketone from isobutane and carbon monoxideThese conversions involve formation of the OO-diprotonated species(156) which triggers a methyl shift to produce a oxononium-carbenium13-dication (157)60 Theoretical calculations indicate that 13-dication157 is the global minimum on the potential energy surface and thata direct hydride shift producing 158 is highly improbable energetically(H = 237 kcalmol) Charge-charge repulsive effects lead to the desta-bilization of 158 relative to 157 To explain the formation of methylisopropyl ketone (160) it is suggested that the monocationic interme-diate (159) is formed and the hydride shift occurs in a rapid ener-getically favorable step (H =minus197 kcalmol) This suggests that thesuperacid-promoted rearrangements involving glycols and alkoxy alcoholsdescribed above may likewise involve formation of a oxonium-centeredsuperelectrophile (ie 150) followed by the deprotonation step


C

CH3

CH3

CH3

C

OH

H C

CH3

CH3

CH3

CH C

H3C CH3

CH3

C

H

CH3CCH3

CH3

C

O

H

C

CH3

CH3

CH3

C

O

HH+ H+

minusH+

C

H

CH3

CH3

CH3CC

H3C CH3

CH3

C

OH

HCH3C

CH3

CH3

C

H

155 156 157

158159160

+

OH+

OH2

+OH2

+

OH2

+

+

+

++

Scheme 3 Proposed mechanism for the superacid-catalyzed isomerization of pivaldehyde(155) to methyl isopropyl ketone (160)

Another novel class of oxonium dications involves the superacid-promoted ring opening reactions of oxazolines and related conversions61

Oxazolines are well known for their ability to react with strong nucle-ophiles (ie alcohols) when protonated at the ring nitrogen62 It was shownthat the dicationic species (161 or 162) are capable of reacting with weaknucleophiles such as benzene (eq 52)

O

NH3C

Ph

H3CN

O

H

Ph

Ph

CF3SO3H

O

NH3C

Ph

CF3SO3H

H H

H

H3CN

OH

H Ph

C6H6O

NH3C

Ph161

162163

C6H6

+ +

+

+

+

(52)

In this conversion protonation at both the ring nitrogen and oxygen atomsleads initially to the 13-dication (161) Although benzene may attack thesuperelectrophile 161 directly to give the ring opened product it seemsmore likely that ring opening precedes nucleophilic attack Ring openingeffectively separates the two positive charge centers A similar conversionwas reported in which isoxazolidine 164 was reacted with an excess of alu-minum chloride in benzene to give product 167 in good yield (eq 53)63


NO

S

PhPh

2 equiv AlCl3

C6H6 NO

S

PhPh Ph N

Ph

AlCl3

AlCl3S

AlCl3

OAlCl3Ph N

PhS

OH

Ph

76

164 167165 166

+

+minus

minus

+

+

minus

minus

(53)

It was proposed that product 167 arises from coordination of theisoxazolidine (164) to AlCl3 to generate the dicationic superelectrophilicintermediate (165) which undergoes ring-opening to give product 167by a Friedel-Crafts type reaction

624 Acyl-dications

There have been several types of gitonic superelectrophiles having acylcationic groups as part of a 13-dicationic system Monocationic acylcations (168) can be prepared as persistent species in superacidic mediaand salts have even been studied by X-ray crystallography1b Much of theinterest in superelectrophilic species from acyl cations has focused on theprotioacyl dications (169 vide supra)67

RC

O

RC

O

168a 168b

HR

COH

169

+

+ +

++

In principle gitonic superelectrophiles may also be possible in struc-tures that have two acyl cationic groups or in structures having an acylcation adjacent to another cationic center Like the superelectrophilic car-boxonium dications there is also some ambiguity here in distinguishingbetween gitonic and distonic superelectrophiles as there are two impor-tant representations of acyl ions (168ab) For the purposes of the presentdiscussion it is assumed that both the acyl oxygen and carbon atoms havepartial positive charge

Diacyl dications have been examined in both experimental and theoret-ical studies Attempts to directly observe the oxalyl dication (174) werenot successful as ionization of oxalyl chloride (170) with SbF5 leads to thechlorocarbonyl cation (172 Scheme 4)65 The initially formed chloroxa-lyl cation 171 immediately decarbonylates under the reaction conditionsInterestingly complexation of the chloroxalyl cation 171 with excessLewis acid is expected to generate superelectrophile 173 Theoretical cal-culations (MP26-31G level) indicate that the oxalyl dication (174) is ata minimum on the potential energy surface66 Calculated bond lengths for


ClC

CCl

O

O

SbF5 SO2ClF

minus80degC ClC

C

O

O

SbF5

ClC

C

O

OSb F5

minusCOCl

CO

C

C

O

O

170 171 172 172

173 174

+ ClC

O+

+

+

+

+

dminus

d+

Scheme 4 Reaction of oxalyl chloride with SbF5 and the attempted generation of theoxalyl dication 174

the species (174) are estimated to be 1442 ucircA for the carbon-carbon bondand 1145 ucircA for the carbon-oxygen bonds

As expected separation of the acyl groups leads to increasing stabilityof the diacyl dications Malonyl szliguoride (175) reacts with excess SbF5 togive the donor-acceptor complex (176) which is in equilibrium with thedicationic species (177 eq 54)67

FC

CC

F

O O

HH

SbF5 SO2ClF

minus80degCC

CC

F

O O

HHSbF5

CC

CO O

HH

CC

CO O

HH

175 176 177

+ + +

++

FC

CH2C

F

O O

178n

SbF5C

CH2C

O O

nn ge 3 2 SbF6

+ +minus

d+

dminus

(54)

Larger systems (178) produce persistent diacyl ions that may be observeddirectly by NMR and IR spectroscopy and in some cases are considereddistonic superelectrophiles (Chapter 7) Increasing distances between theacyl ion centers lead to structures with electrophilic reactivities similar tomonocationic acyl ions

Several types of onium dications have been studied in which a singleacyl cationic center has been part of 13-dicationic superelectrophilesFor example pyruvic acid has been studied in FSO3HSbF5 solutionat low temperatures34 Initially the diprotonated species is observed inequilibrium with some of the monocation (eq 55)


H3C CC

OH

O

OFSO3H

H3C CC

OH

OH

O

H3CC

COH

OH

OH

H3C C CO

OH

H3CC

CO

OH

H3CC

O

179

180

181

SbF5 +

+

+

+

+

+

+ +

(55)

The diprotonated species (179) is then observed slowly cleaving to theacetyl cation (181) in a process thought to involve dication (180) A num-ber of β-carbenium-acyl dications have also been studied by experimentand theory Reaction of the 4-chloro-butanoyl cation (182) in superacidicHFSbF5 or HSO3FSbF5 leads to formation of the 2-butenoyl cation(185 eq 56)68

HF-SbF5H2C C

OH3C

CO

H3C CO

CO

185184182 183

186

Cl CO+

+

+ +

+

+ +

(56)

One of the proposed intermediates in this transformation is the super-electrophilic species (184) which undergoes deprotonation to give the2-buten-oyl cation Further evidence for the superelectrophile 184 isobtained from experiments in which the 2-butenoyl cation (185) is gen-erated in DSO3FSbF5 SigniTHORNcant deuterium incorporation is found atthe α and γ positions suggesting equilibria involving 184186 In a sim-ilar respect formation of the 4-chloro-3-methylbutanoyl cation (187) insuperacid leads to the two acyl dications (188189 eq 57)69

HF-SbF5

187

H3C CO

188

CH3

H3C CO

189

H3C CO

CH3

H3C CO

productsCl CO

CH3

++

+ +

+ +

++

+ +

CC

CO

H

HH H

CC

CO

H

H

H

H

190 191 192

CC

COH

H

H

H+

+ + +

+

+ (57)


Carbenium-acyl dications have also been investigated by theoreticalmethods70 The structures of the propenoyl (CH2 = CHCO+) andthe isopentenoyl ((CH3)2C=CHCO+) cations and their superelec-trophilic protonated dications were calculated at the MP26-311+Gand MP2cc-pVTZ levels In the case of the propenoyl cation calcu-lations THORNnd three structures for the protonated dications (190192) atminima on the potential energy surface The global minimum is found tobe the Cα protonated structure (191) while the oxygen protonated (190)structure is 153 kcalmol higher in energy Gas-phase proton loss from191 is calculated to be endothermic by 30 kcalmol and the transitionstate for deprotonation is estimated to be 778 kcalmol higher in energythan structure 191 Thus dication 191 is predicted to be a kineticallystable species in the gas-phase Structure 191 may be visualized as aproduct from the reaction of carbon monoxide with the ethylene dication(CH2CH2

2+) Calculations of NBO charges indicate that the CO groupbears +090 of charge (including +108 on carbon) and the terminal CH2group bears +102 of charge With the isopentenoyl ((CH3)2C=CHCO+)cation three isomeric protonated dications were located at minima theoxygen protonated species (193) the Cα protonated structure (187) andthe methyl CH protonated species (193) In the case of Cβ protonation(analogous to 191) all attempts to locate a stationary point for the productdication were unsuccessful and the ion spontaneously rearranges to dica-tion 195 The structure 195 is less stable than the global minimum (188)by only 104 kcalmol Again the most stable product from protonation ofthe alkenoyl cation corresponds to the one producing the carbenium-acyldication (188) It is estimated to be 328 kcalmol more stable than dication193 and 314 kcalmol more stable than dication 194

CC

CO

CH3

H3CH H

CC

COH

CH3

H3C

HC

CC

OC

H3C

H

193 188 194

HH

H

HC

CC

OH

CH CH3

195

H

HH

CC

CH3

H3CH H

196

H

H

++ + +

+

++ + + +

In dication 188 the NBO charge at the carbenium ion center is +069and at the acyl carbon is +109 The tert-butyl cation has been found tohave NBO charge at its carbenium center of +067 suggesting a modestsuperelectrophilic activation of the carbenium ion center in 188 comparedwith the tert-butyl cation When charges on the methyl groups are alsoconsidered structure 188 is similar to the protosolvated tert-butyl cation196


625 Aza-carbo Dications

As seen in the gitonic and vicinal systems ammonium and related cationiccenters may be components of superelectrophiles and reactive dicationshaving the 13-dicationic structure Several types of superelectrophilicaza-carbo dications have been studied in which protonated nitro groupsare involved For example it was found that nitroethylene reacts with ben-zene in the presence of 10 equivalents of CF3SO3H to give deoxybenzoinoxime in 96 yield (eq 58)71 Since the reaction does not occur with onlyone equivalent of CF3SO3H the formation of the NN -dihydroxyiminium-methyl dication 197 was proposed In spectroscopic studies the stabledication (199) can be directly observed by 1H and 13C NMR spectroscopyfrom solutions of 1-nitro-2-methyl-1-propene (198) in CF3SO3H (eq 59)

NO

O

CF3SO3H

C6H6

0degC

NOH

OH

NOH

197

96

NOH

OH

197

++

+

+

(58)

NO

O

CF3SO3HN

OH

OH

199

H3C

CH3

H3C

CH3

198

+ +

(59)

NOH

OH

2+ +

197

H

H

H

N

N N

H H

H

H

H

H

200

It was further proposed that dications 197 and 199 are stabilized byY-delocalization involving six π -electrons (four lone pair electrons fromthe oxygen and oleTHORNnic electrons) This stabilization is thought to besimilar to that of the guanidinium ion 200 Ab initio calculations werecarried out to estimate the Y delocalization stabilization energies of 197and 200 By studying the energies of conformational isomers the totalπ -stablization energy was estimated to be 8950 kcalmol for 197 and11317 kcalmol for the guanidinium ion 200 at the 4-31G level of the-ory Similarly 2-nitropropene (201) reacts with C6H6 in CF3SO3H andfollowing a methanol then water quench α-phenylacetone is formed in85 yield (Scheme 5)72 It is proposed that the superelectrophilic inter-mediate 202 is formed by diprotonation and arylation gives the aci nitro


Ph

NO

OCF3SO3H

C6H6N

OH

OH

PhN

OH

CH3CH3 CH3

OH

CH3OH

minus40degC

Ph NOHCH3

OHOCH3CH3OH

OCH3

CH3

OCH3

C6H6

H2OPh

CH3

O

85

201 202 203

+ + + +minus

Scheme 5

species 203 Quenching of the reaction mixture yields the ketal and withwater the ketone product is obtained The arylated product is also formedin high yield if chlorobenzene is used indicating that the electrophilicintermediate (202) is highly reactive When nitro-substituted cyclic oleTHORNnsare reacted with benzene and CF3SO3H at minus40C similar products areformed 1-Nitrocyclohexene (204) reacts to give 2-phenylcyclohexanonein 72 (eq 60)72

NO

OCF3SO3H

2) H2O

minus40degC

1) CH3OH

2 hr72

Ph

O+

minusC6H6

(60)

If the nitro oleTHORNns are reacted with benzene at higher temperatures theproduct mixtures are dominated by the formation of 4H -12-benzoxazinesFor example compound 204 reacts in CF3SO3H at 40C to give the4H -12-benzoxazine (206) in 87 yield (Scheme 6) It was proposed thatthe cyclization involves the dicationic intermediate (207) with positivecharge substantially delocalized into the aryl ring Intramolecular reactionof the hydroxy group then provide the novel heterocyclic product 208Further evidence for the proposed dicationic intermediates comes froma study in which β-nitrostyrenes are found to generate stable diproto-nated species in CF3SO3H73 When (E )-β-nitrostyrene 209 is dissolvedin CF3SO3H at low temperature the spectroscopic data are consistent withthe formation of OO-diprotonated species (210 eq 61)

NO2

NO2

CF3SO3H

minus20degC

CF3SO3H

minus20degC

209 211

NOH

OH

210

21

+

+ (61)


NO

O

CF3SO3H

C6H6

40degC4 hr204

NOH

OH

C6H6

NOH

OH

205 206

NH

OHN

O

208

NH

OH

207a207b

minus2H+

minusH2O

+

+

+

+ +

+

++

H+

minus

Scheme 6

13C NMR spectroscopy shows the C2 resonance at δ13C 1651 andC1 resonance at 1283 As expected with the formation of dication210 (Z )-β-nitrostyrene 211 gives the identical spectra from CF3SO3HCryoscopic experiments also conTHORNrmed the formation of the dicationicspecies in the superacid

An analogous series of dicationic species have been proposed in thereactions of nitro-substituted arenes in superacid For example 2-nitro-naphthalene (212) reacts in superacid to give the arylated product (214)in good yield (eq 62)74

CF3SO3H

C6H6

Ph

NH2NO2 50N

OH

OH

N

OH

OH

212

213

214

+

+

+ +

(62)

Although no detailed mechanism for the conversion was proposed theinitial step likely involves the formation of the superelectrophilic dipro-tonated species (213) which reacts with benzene by electrophilic attackThere is some 13-dicationic character in 213 however it is understoodthat the positive charge is delocalized throughout the naphthalenering-system Evidence for the dicationic species comes from cryoscopic


measurements as well as 1H13C and 15N NMR spectroscopy All ofthese data conTHORNrm the formation of 213 in CF3SO3H In a similar respect1-nitronapthalene (215) is found to produce the dicationic species (216) inCF3SO3H and the superelectrophile 216 can be directly observed by spec-troscopic studies When 1-nitronapthalene (215) is dissolved in CF3SO3Dno deuterium is incorporated onto the ring positions indicating that dipro-tonation occurs at the nitro group Intermediates like 213 and 216 havealso been found to be involved in the superacid-promoted reactions ofhydroxylanilines and aniline-N -oxides (eq 64)

NO2

CF3SO3H

215

N

216

OHHON

216

OHHO+

+ +

+ (63)

NOH

H

CF3SO3H NH

H2+ 2+ 2+

++

NH

H

NH

H

minusH2O

(64)

The chemistry of these species is discussed in Chapter 4It has been demonstrated that nitronic acids and α-carbonyl nitro-

methanes can form superelectrophilic intermediates in strong acids andthe resulting species are capable of reacting with benzene (eqs 6567)23

H3C NONa

OHF

C6H6

H3C NOH

OH

H3C NOH

OH2

H3C NOH

OH2

Ph N

CH3

OH

C6H6217

+

+ +

+

+

+

minus

(65)

EtONO2

O CF3SO3H

C6H6 EtON

OH

OH

OH

EtON

OH

OH2

OH

C6H6

EtON

O OH

Ph219218

+

+++

+

(66)


PhNO2

O

PhN

OH

OH

OH

PhN

OH

OH2

OH

C6H6

PhN

O OH

Ph22 0 221

CF3SO3H

C6H6++

+

+

+

(67)

It has been proposed that the gitonic superelectrophiles (217 219 221)arise from double protonation at the nitro group and in the case ofα-carbonyl nitromethanes (eqs 6667) protonation also occurs at the car-bonyl group to form highly reactive tricationic superelectrophiles (219and 221) Because weaker acids are capable of forming the diprotonatedspecies but do not lead to arylated products tricationic reactive superelec-trophiles are thought to be involved in limited equilibria concentrationsThe dicationic species 218 can be directly observed by NMR spectroscopy

It has been shown that ammonium-carbenium 13-dications can begenerated from superacid-promoted reactions of some amino-alcohols76

Reactions of compounds such as 222 in CF3SO3H lead to the formation ofammonium-carbenium dications which have been shown to possess super-electrophilic reactivities Dication 223 reacts in high yield with benzene(eq ) while the analogous monocationic electrophile 11-diphenylethylcation (59) does not react with benzene When compound 222 is reactedin FSO3HSbF5 at low temperature the dication 223 can be observedby NMR spectroscopy The para-carbon atoms are deshielded in the 13CNMR (by about 10 ppm from the alcohol 222) indicating signiTHORNcant delo-calization of the carbocation charge into the phenyl rings Interestingly anumber of biologically important compounds possess the phenethylaminesubstructure and it has been shown that some of these compounds canionize to the dicationic electrophiles in superacid For example adrenaline(224) leads to dication (225) in FSO3HSbF5 NMR studies suggest thatthe dication is best represented as the charge separated distonic superelec-trophile (225a) although it is expected that some 13-dicationic characteris also present in the structure (ie 225b)

PhNH2

CH3

OHPh

PhNH3

CH3

Ph

PhNH2

CH3

PhPh

222 223 80

CF3SO3H

C6H6+

+ (68)

PhC CH3

Ph

59

+


HN

CH3

OH

OH

HO

224

FSO3H-SbF5

225b225a

NCH3

OH

HO

H H

++

NCH3

OH

HO

H H+

+

(69)

Ammonium-carbenium dications and related species are also generatedreadily from oleTHORNnic precursors77 For example the tetrahydropyridine(226) leads to the 13-dication (227) and vinyl-substituted N-heteroaro-matics can give dications (ie 228) in superacid both of which showhigh electrophilic reactivities (eqs 7071)

N

CH3

CH3

CF3SO3H

C6H6 N

CH3

CH3HN

CH3

CH3

Ph

87

226 227

+

+(70)

NHN

CH3N

CH3

Ph

228

CF3SO3H

C6H6

+ +

(71)

It was previously noted that superelectrophilic carboxonium ionsmay be generated from suitable precursors including amino-ketonesN-heteroaromatic ketones and aldehydes amino-acetals and othersubstrates45 In their superacid-promoted condensation reactions thesecompounds often produce ammonium-carbenium superelectrophiles asintermediates in the reactions As an example the amino-acetal (229)reacts with arenes in the presence of superacid to give the arylated product(231 eq 72)43

NOCH2CH3

OCH2CH3

CF3SO3H

o-C6H4Cl2

N Cl

Cl

Cl

Cl

CH3CH2

CH3CH2N

OCH2CH3CH3CH2

CH3CH2

H N

CH3CH2

CH3CH2

H Cl

Cl

CH3CH2

CH3CH2

229 230

231

+

+ + +

(72)


Initial ionization gives an ammonium-carboxonium dication which thenproduces the ammonium-carbenium dication (230) A variety of dicationicelectrophiles like 230 have been proposed

Several studies have examined the possibility of generating carbenium-nitrilium dications Ionization of benzophenone cyanohydrin (232) inFSO3HSbF5SO2ClF at minus78 C leads to the formation of the monoca-tionic species (233) which was characterized by NMR spectroscopy(eq 73)78 Despite the superacidic conditions no direct evidence for thegitonic superelectrophile (234)wasobtainedWhencompound232 is reactedwith benzene in CF3SO3H the phenylated product (236) is obtained in goodyield (eq 74)

PhC

CN

OHPh FSO3H-SbF5

PhC C

PhN

PhC C

PhN H

232 233 234

orPh

C CPh

N

235

H Ad+ dminus+ + + +

(73)

PhC

CN

OHPh CF3SO3H

236

C6H6 PhC CN

PhPh

237

74 (74)

Based on related observations it was concluded that the superelectrophile234 is not involved in the phenylation reaction However weak interaction(solvation) of the nitrile lone pair (ie 235) with the superacid may gen-erate increasing dipositive character and the observed superelectrophilicreactivity

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(55) G A Olah A M White D H OBrien Chem Rev 1970 70 561 andreferences cited therein

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7DISTONIC SUPERELECTROPHILES


In distonic superelectrophiles the two (or more) electrophilic chargecenters are separated by at least two carbon or other heavy atoms Asdiscussed earlier increasing separation of charge leads to decreasing elec-trophilic activation Depending on the electrophilic system and the distancebetween charge centers distant onium dications may exhibit chemistry nodifferent than isolated onium monocations For example it was shown that4-acetylpyridine will condense with benzene through the distonic super-electrophile (1 eq 1) but the analogous more charge-separatedspecies (2) is unreactive towards weakly nucleophilic benzene1

N

H3C

OCF3SO3H

C6H6 N

H3C

Ph Ph

Reactive to C6H6

1

N

H3C

OH

H

+

+ (1)


231

copy

232 DISTONIC SUPERELECTROPHILES

Unreactive to C6H6

NH

HO

CH3

2

+ +

While structure 2 is an onium dication it can not be considered a super-electrophile Only if the electrophilic site(s) exhibit signiTHORNcantly increasedreactivities due to interaction of the onium charge centers can the speciesbe classiTHORNed as distonic superelectrophiles

Several examples of superelectrophiles have already been described inwhich delocalization of charge may lead to structures that could be consid-ered gitonic or distonic superelectrophiles depending on which resonanceform is being considered predominant While the bis-oxonium structure(3a) is formally a distonic superelectrophile the bis-carbenium structure(3c) is considered a gitonic superelectrophile (eq 2) These types of sys-tems have been previously discussed and therefore will not be includedin this chapter In a similar respect there are examples of equilibrationbetween gitonic (4) and distonic (5) superelectrophilic systems (eq 3)2

3a 3c3b

H3C CH3

OH OH+ +

H3C CH3

OH OH+

+ H3C CH3

OH OH

+ + (2)

4 5

N O

CH3

PhPh

H H+

H3C NPh

OH

H Ph

+

++

(3)

Although there have been almost no systematic studies of these equilibriait is expected that for many of these systems the distonic superelectrophileshould be preferred in the equilibria due to favorable separation of posi-tive charge Besides the number of atoms separating charge centers anotherimportant consideration is the actual distance between charges If a partic-ular conformational or structural effect leads to charge centers being forcedinto closer proximity then this may lead to superelectrophilic activationSeveral examples of this effect are described in subsequent sections

72 DISTONIC SYSTEMS

721 Carbodicationic Systems

There has been considerable experimental and theoretical work re-lated to carbodications many of which may be considered distonic

DISTONIC SYSTEMS 233

superelectrophiles3 In the absence of aryl stabilization of the positivelycharged centers long-lived acyclic carbodications can be formed only ifthe charge bearing carbons are separated by at least two carbon atomswhile the carbenium centers are tertiary4 For example the 22prime-ethyl-enediisopropyl dication 6 has been prepared by the ionization of 25-dichloro-25-dimethylhexane in SbF5SO2ClF (eq 4)

H3CCH3

CH3

CH3

Cl

Cl

SbF5

SO2ClFndash78degC

6

H3CCH3

CH3

CH3

++

(4)

The 13C NMR spectrum shows a characteristic absorption of δ13C 3313for the carbenium centers

The instability (and superelectrophilic nature) of aliphatic 14-dicationicsystems can be seen in the failure to prepare some analogous cyclopropyland 25-dimethyl-substituted 25-norbornadiyl dications (eqs 5 and 7)4

H3C

CH3

OH

H3C

CH3HO

H

H

FSO3H

SbF5SO2ClF

87

H3C CH3

CH3 CH3

+ (5)

FSO3H

SbF5SO2ClFndash78degC

9

OH

HO

H

H

10

H

H

+

+(6)

CH3

OHHO

H3C

11 12

CH3

H3C

++

(7)

Despite the stabilizing effects of the cyclopropyl ring diol 7 ionizes insuperacid to give only the heptadienyl cation (8) from ring opening andproton loss4 It is only with further stabilization by cyclopropyl groupsthat the 14-dication was found to be persistent (eq 6)5 Likewise ion-ization of diol (11) does not provide the 25-dimethyl-25-norbornyldiyldication (12 eq 7)6 Only with more powerful electron donating groups


such as aryl or hydroxy groups is the 25-norbornadiyl dication persistent(vida infra) The 14-dialkyl-14-cyclohexyl dications are also found to beunstable6 For example diol (13) does not give the expected 14-dication15 but instead forms the allylic cation 14 (eq 8) and 14-di-n-butyl-14-cyclohexanediol (16) leads to the rearranged dication (18 eq 9)6 It is notclear if the distonic superelectrophile (17) is formed initially but never-theless rearrangement leads to the more stable charge separated species(18) Stabilization of the carbocationic centers with cyclopropyl groupshowever leads to a persistent 14-dication (eq 10)7

CH3

OH

H3C

HO

FSO3H

SbF5SO2ClF

13 14 15

CH3

H3C

H +

CH3

H3C not formed+

+

(8)

FSO3H

SbF5SO2ClF

OH

HO

16 17 18

+

++

+

(9)

H

H

H

H

HO

OH SbF5SO2ClF

ndash78degC++ (10)

The above examples of the 25-norbornadiyl dication (12) and the14-dialkyl-14-cyclohexyl dications (15 and 17) illustrate the importanceof distance between charge centers implicating stability Another inter-esting example of this effect is in the isomerization of the 15-manxyldication (19 eq 11)

19 20CH3

H3CFSO3H

SbF5SO2ClF

RelativeEnergies 00 kcalbullmolndash1 ndash268 kcalbullmolndash1

+

+ +

+ (11)

21

+ +


It was observed that dication 19 was stable at minus105C but upon warm-ing to minus60C the 37-dimethylbicyclo[331]nona-37-diyl dication (20)is cleanly formed89 The 13C NMR of dication 20 shows a resonanceat δ13 C 323 for the cationic carbons Calculations at the B3LYP6-31Glevel indicate that the isomerization increases the distance between chargecenters from 280 ucircA in 19 to 358 ucircA in 20 and this leads to a concomitantdecrease in potential energy of more than 26 kcalmol The increasingdistance between the charge centers is thought to be the driving forcefor the isomerization and it is consistent with the superelectrophilic char-acter of dication 19 Interestingly bicyclic dications (1920) are shownto have charges in closer proximity than the 26-dimethyl-26-heptadiyldication (21 charge-charge distance 521 ucircA) Though each of these sys-tems (19-20) are considered 15-dications the structural constraints ofthe bicyclic framework force the positive charge centers closer to eachother This enhances their distonic superelectrophilic character A sulfur-stabilized dication (22) has also been reported from the superacid-promoted reaction of tetramethylhexathiaadamantane (eq 12)10

S SS

SS S

CH3

CH3

H3C

H3C

CF3SO3H

22

S SS

SS

CH3

CH3

H3C

H3C +

+

(12)

Like the structurally similar dication 20 dication 22 has been observed by13C NMR in superacidic solutions (FSO3HSbF5 or CF3SO3H) and thecarbocationic centers are found at δ13C 230 This large shielding comparedto that of dication 20 (δ13C 323) is indicative of the sulfoxonium-typeinteraction AM1 calculations estimate the distance between the chargecenters to be 388 ucircA which is slightly longer than the distance (358 ucircA)found in dication 20

In addition to the 15-manxyl dication (19) the 14-bicyclo[222]octadiyl dication (25) has been claimed to have been observed (eq 13)11c

Cl

Cl

SbF5

SO2ClFndash80degC

23 24 25Cl

+ +

+(13)

Subsequent NMR experiments indicate that the monocationic species (24)is formed initially as a donor-acceptor complex and then a second chlorideabstraction could provide the dication (25) At temperatures above minus60C


2527261

4

C1-C4Distance 259 Aring 234 Aring 199 Aring

28

+ +

+

Figure 1

dication 25 is found to be unstable The carbenium ion centers are foundat δ13 C 307 MINDO calculations11c estimate the C1- C4 distance tobe 199 ucircA Interestingly calculations show a shortening of this distanceupon progressing from the parent uncharged bicyclo[222]octane (26) tothe monocation 27 and to the dication 25 (Figure 1) Although it mightbe expected that strong coulombic repulsion would lead to an increasingdistance between C1 and C4 this is not observed The shortening of theC1-C4 distance in the dication 25 is attributed to hyperconjugative transferof electron density to the carbocationic centers which leads to symmetryallowed 14 bonding (ie 28) Calculations indicate that more than half ofthe positive charge is delocalized over the 12 hydrogen atoms as a resultof hyperconjugative effects

The 26-adamantadiyl dication systems have likewise been studied andthe results are consistent with the superelectrophilic character of somethese 15-carbodications When diol 29 was reacted in superacid the 26-adamatanediyl dication 31 was not formed (eq 14)12 Despite the superacidic conditions only the dioxonium ion (ie diprotonated diol 30) couldbe observed Structure 31 and other adamantadiyl dications (C10H14

2+)have been also been studied by theoretical calculations13 As describedin Chapter 6 dication 31 is found to be 33 kcalmol less stable than the13-dication having the two carbocationic centers located at the bridgeheadcarbons Even the ionization of the tertiary-diol 32 gives only a singlecarbocationic center while the other hydroxy group produces an oxoniumcenter (eq 15)12

HOH

HO

H

FSO3H-SbF5

ndash80degC

29 30 31

HOH2

H2O

H

++

H

H

+

+

(14)


CH3

OH

HO

CH3

FSO3H-SbF5

ndash80degC

32 33 34

CH3

H2O

CH3

+

+CH3

H3C

+

+

(15)

Water elimination in the superacidic solution is a highly exothermic stepbut nevertheless the 26-adamantadiyl dication 34 is not formed Thisobservation suggests that structures like 34 can be distonic superelec-trophiles As in the case of other 14- and 15-carbodications the 26-adamantadiyl dications are stabilized and persistent when the carbeniumcenters bear an aryl substitutent (vide infra)

Other adamantane-based dications have also been prepared Althoughsystems such as diadamanta-49-diyl dication (35) and 11prime-bisadamanta-33prime-diyl dication (36) have been prepared (both 16-dications) experimen-tal data suggests that these systems are more related to the monopositiveadamantyl cations rather than distonic superelectrophilic systems14 How-ever the adamanta-13-dimethyldiyl dication (38) has been prepared insuperacid media (eq 16)15

37

CH3

CH3

H3CCH3

OH

OH

SbF5

SO2ClF

38

3635

+ + CH3

CH3

H3C CH3+

++

+

(16)

The 13C NMR data for 38 clearly indicate that due to the close proximityof the cationic centers the positive charges are highly delocalized into thesubstituents and the adamantyl cage

Many of the unstable distonic superelectrophiles discussed here havebeen prepared as stabilized species by incorporating aryl substituents intothem (Table 1)461215 In the cases of 39 and 44 however the analogousmethyl-substituted dications (6 and 38) are also persistent In comparingthe 13C NMR data the aryl-stabilized dications (39 and 44) show largeshieldings of the carbocationic centers when compared to 6 and 38 Forexample the 22prime-ethylenediisopropyl dication 6 has a resonance of δ13C+ 3313 while dication 39 has the resonance of δ13C+ 2224 This isindicative of the signiTHORNcant charge delocalization into the phenyl rings in


Table 1 Aryl-stabilized dicationic systems (3944) and theirδ13C+ data

Structure 13C NMR C+ 13C NMR C+Structure

PhPh

Ph

Ph

2224

PhPh

Ph

Ph

PhPh 2479

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

2451

2523

2456

2209

39

40

41

42

43

44

+

+

+

+

+

+

+

+

+

+

+

+

dication 39 Charge delocalization and stabilization results in diminishingsuperelectrophilic character

There are a number of other aryl-substituted carbodicationic systemsthat can be properly described as distonic superelectrophiles For exampledication 45 has been generated from 22prime-p-phenylenedi-2-propanol inSbF5 at minus78C4 When compared to the dimethyl(phenyl)carbenium ion(cumyl cation) 46 NMR data indicate that the positive charges are dis-persed to a considerable extent into the neighboring methyl groups in thedication 45

CCH3C CH3

CH3

CH3

CH3H3C

45 46

C

d13C NMR Signals d13C NMR Signals

1379

+ + +

14912408

471minusCH3C+

CipsoCring

142414072557

339minusCH3C+

CipsoCortho

Due to coulombic repulsion there is also less charge delocalization intothe phenyl group The diminished neighboring group participation (stabi-lization) is one of the characteristics of superelectrophilic activation16 Inthe case of dication 45 the aryl group is less capable of donating electrondensity to either carbenium center

Other distonic superelectrophiles arise from aryl-substituted carbodica-tionic systems in which the positive charge centers are forced into close


proximity due to structural effects A series of aryl-substituted phenylenediyl dications (4749)

47 48 49

pKR+secondionization minus105 minus99 minus166

Ph

Ph

Ph

Ph+ +

Ph

Ph

Ph

Ph

+

+Ph

PhPh

Ph

+ +

were prepared in sulfuric acid solutions17 Within this series it was foundthat the pKR+ value (for the ionization producing the dication) is signif-icantly higher for the ortho-substituted system (49) This higher pKR+value is attributed to the close proximity of the two charge centers andit suggests some distonic superelctrophilic character in 49 The 18-bis(diarylmethyl)naphthalene dications have been extensively studied andexperimental observations suggest partial distonic superelectrophiliccharacter The 18-bis(diphenylmethyl)naphthalene dication (50) has beenprepared by several methods including Ichikawa and coworkers deoxy-genation method using strong silylating agents (eq 17)18

OPhPh

PhPh

(CH3)3Si-O3SCF3

[(CH3)3Si]2O

2 eminusPh

Ph

Ph

Ph

50 512 Xminus

Ph Ph PhPh+ +

(17)

BBPh Ph PhPh

52

Although formally considered a 15-dication 50 possesses a structure inwhich the carbenium centers are constrained at a distance of separationof 311 ucircA NMR studies show the carbenium ion centers at δ13C 2077consistent with the carbocationic structure 50 In cyclic voltamographicanalysis the compound 51 shows an especially high oxidation potential(two-electron oxidation peak at 110 V) when compared to analogousdications and triarylmethyl monocations19 It has also been shown that


the oxidation potential varies in a predictable manner based on the natureof the aryl rings The high oxidation potentials are considered to be theresult of close proximity of the charge centers Despite the close proximityof the charges dication 50 has been reported as stable in acetonitrilesolutions This suggests a decreased degree of electrophilic reactivity Anisoelectronic neutral boron-containing compound (52) has likewise beenprepared and studied

An interesting application of the dicationic species has been reportedin which 50 has been used as a two-electron oxidant to couple NN -dialkylanilines (eq 18)19

(H3C)2N

CH3

CH3

(H3C)2N

CH3

CH3

N(CH3)2

H3C

H3C95

50 X = ClO4minus

(18)

The oxidative coupling is thought to involve single electron transfer stepsThe use of 50 in this coupling reaction is shown to superior to the useof other oxidizing agents such as Ceric ammonium nitrate (CAN) andPhI(O2CCF3)2 This type of conversion is not possible with triphenyl-methyl (trityl) cation salts indicating that dications like 50 could beconsidered distonic superelectrophiles

More highly stabilized 18-bis(diarylmethyl)naphthalene dications havebeen prepared including the p-methoxyphenyl derivative 5320 This dica-tion is generated from ionization of the diol in HBF4 and (CF3CO)2O20a

Dication 53 has been characterized by experimental studies (single crys-tal X-ray analysis and NMR) and theoretical calculations The carbeniumion centers are found to be separated by just 3076 ucircA (X-ray and ab ini-tio results) and show 13C NMR resonances at δ13C 1918 Two electronreduction is also shown to give the acenaphthene derivative 54

53

2eminus

OCH3H3CO

H3CO OCH3

54

OCH3H3CO

H3CO OCH3minus2eminus+ +

(19)Other 18-naphthalene or acenaphthene dication systems have beendescribed and some have been shown to have useful electrochromic pro-perties20bc


Closely related systems have been studied which are composed of11prime-biphenyl-22prime-diyl dications and 11prime-binaphthalene-22prime-diyl dica-tions In the case of the 11prime-biphenyl-22prime-diyl dications these have beenprepared by the ionizationof related diols (ie 55) in HBF4 and by theoxidation of compound 57 (electrochemically or with reagents such as(p-BrC6H4)3N+bullSbCl6minus)21 Conversely dication 56 is converted back to57 by Mg or by electrochemical reduction

ArAr

ArAr

HO

OHAr = p-MeOC6H4

55

HBF4

56

ArAr

ArAr

Mg

57

ArAr

ArAr

+

+2 (p-BrC6H4)3N

SbCl6

+

minus

(20)

Dication 56 has been isolated and studied by crystallography revealing aseparation of the carbenium ion centers by 366 ucircA

Among the binaphthyl-systems Suzuki and co-workers have reportedtwo methods to prepare these dications (eq 2122)22

OR

ROS

S

HBF4

S

S

Zn

SS

58 59 60

2 (p-BrC6H4)3N

SbCl6minus

++

+

(21)

The diol or diether (58) can be ionized in HBF4 Optical resolution hasbeen achieved to produce the chiral distonic superelectrophilic dication(59) X-ray analysis shows an interplanar separation of the charged ringsby about 353 ucircA Due to its helical structure and the exciton couplingof the dye components there is a very high amplitude of the circulardichroism (CD) signals Along with its redox chemistry the chiropticresponse makes these compounds promising candidates for chiral redoxmemory systems or electrochiroptic materials Another system (62) hasbeen generated from the oxidation of the binaphthylic dioleTHORNn (61) by


iodine (eq 22)23

ArAr

ArAr

Ar = p-(Me2N)C6H4

61

I2

ArAr

ArAr

62

H H

2 I3minus

+ +

(22)

Oxidation leads to formation of the new σ -bond and aryl-stabilized car-bocationic centers in 62 Interestingly there is no evidence of proton lossfrom the dihydro[5]helicene dication 62 and the dication is stable in thepresence of the reasonably nucleophilic counter ion I3minus This again sug-gests that these stabilized systems are considered only as weakly distonicsuperelectrophiles

There is also the possibility of distonic superelectrophilic bis-carbo-nium ions Despite the fact that such species may be important in thesuperacid-catalyzed cracking reactions of aliphatic hydrocarbons therehave been very few studies of such systems The structures and energiesof small distonic alkonium dications have been studied using ab initiocalculations24 For diprotonated n-butane (C4H12

2+) two structures werelocated as stable minima on the potential energy surface Structure 63 isformed by a protonation of the two terminal C-H bonds resulting in apair of two electron-three center bonds The other structure (64) arisesfrom protonation of the terminal C-H bond and the most distant C-Cbond

HC

CC

CHH

H

H H

H H

H H

HH

2+ 2+

HC

CC

CHH

H

H H

H HHH

H

H

63 (C2) 64 (C1)

The gas phase structures are found to be within 2 kcalmol in energy with63 being more stable It is notable that both 63 and 64 are the diprotonatedstructures possible from n-butane having the maximum charge-charge sep-aration Interestingly gas-phase proton loss is estimated to be endothermic


by 503 kcalmol (MP4(SDTQ)6-311GMP26-31G level) while thecarbon-carbon bond cleavage reaction is found to be exothermic by morethan 50 kcalmol (eq 23)

minusH+ minusCH3+

HC

CC

CHH

H

H H

H H

H H

H H2+

63

ΔH = minus504 kcalmolΔH = 503 kcalmol HC

CC

HH

H

HH

H

HH

+

HC

CC

C

H

HH

H

H HH

HH H

+

(23)The product ions are the most stable monocationic carbonium ions thoseprotonated atthe secondary carbon

Another class of distonic superelectrophiles are the carbenium-carbo-nium dications As discussed Olah and co-workers found experimentaland theoretical evidence for the protosolvated tert-butyl dication ([(CH3)2CCH4]2+) and 2-propyl dication ([CH3CHCH4]2+) both gitonic super-electrophiles (vide supra)25 However analogous distonic superelectro-philic systems like 65 and 66 have not yet been studied

H3C

CH3 HH

H

H H3C

CH3

CH3

H

H H

65 66

++

+ +

722 Carbo-onium Dication

Among other distonic superelectrophiles described in the literature thereare carbo-onium dications These include carbo-carboxonium dicationscarbo-ammonium dications and related ions Despite the separation ofcharge in these superelectrophiles some have been shown to have veryhigh electrophilic reactivities Like the carbodications described previ-ously the discussion here is limited to those systems that have beenshown to have electrophilic reactivities greater than the related monoca-tionic onium ions as well as structural criteria supporting their designationas a distonic superelectrophilic species

There have been a wide variety of carbo-carboxonium dications des-cribed in the literature Some of the related distonic superelectrophilescan be used for remote functionalization of appropriate substrates For


H3C CH3

O HF-SbF5

CO 20C

H2O

H3C CH3

O CO2H

+ H3CCH3

O

CO2H

H3C CH3

OH

H3C CH3

OHHH

H

H

H+

H3C CH3

OH

H3C CH3

OH CO H2OCO

67 68

67

H2

H

H3C

CH3OH H

HH

CH4

~HH3C

CH3

OHCO

H3CCH3

OH

CO

H2O

68

69 70 71 72

73 74 75

+

+

+

++

+ +

+

+

++

+

+

+ +

Scheme 1

example it was shown that aliphatic ketones are converted to the ketoacids (67 and 68) by the reactions in superacid in the presence of car-bon monoxide (Scheme 1)26 The two products from 2-heptanone arethought to arise from protolytic cleavage of C-H and C-C bonds Pro-tonation of the carbonyl group leads to the carboxonium ion (69) andfurther protosolvation leads to the carboxonium-carbonium dications (70and 73) and subsequently to the carboxonium-carbenium dications (71and 74) Capture of the carboxonium-carbenium dications by carbonmonoxide and water then gives products 67 (20 relative yield) and68 (74 relative yield) The key step in this conversion is formationof the carboxonium-carbonium dications (70 and 73) and it is notablethat these species are formed with the maximum possible charge-chargeseparation It is not known to what extent each cationic charge inszligu-ences the other charge centers electrophilic character This chemistryhas been shown to be selective and useful in functionalizing remote 3

alkyl carbons (eq 24)26

H3CCH3

O

CH3

HF-SbF5

CO minus20degC

H2O

H3C

CH3O

CH3

CO2H

60

(24)

In chemistry involving conversion of camphor two distonic superelec-trophiles are proposed27 When ketone 76 is reacted with HFSbF5 theenone 80 is produced (eq 25)


CH3

CH3

O HF-SbF5

CH3

CH3

OH H+CH3

CH3

OH

H

H

H

H2

CH3

CH3

OHOH+CH3

CH3

OCH3

CH3

76 77 78

7980

+ + +

+ + +

(25)

The conversion is thought to involve formation of the carboxonium ion(77) by protonation of the carbonyl oxygen and subsequent protona-tion then occurs at the C-H bond The resulting carboxonium-carboniumdication (78) possesses the maximum possible charge-charge separationfor this bicyclic framework Subsequently an intermediate carboxonium-carbenium dication (79) is produced which isomerizes to the tertiary-carbenium ion and deprotonation provides the product enone (80)Similar distonic superelectrophiles are proposed in other rearrangementsof terpenes in superacid28

Another type of carboxonium-carbenium dication is obtained fromremote functionalization of alkylamides (eq 26)29

H3C NCH3

O

H CH3

CCl4 HF-SbF5

minus30degCH3C N

CH3

OH

H CH3

1) HF-pyridine2) Na2CO3 H4O

H3C NCH3

O

H CH3

F

81 82

+

+

(26)In the presence of superelectrophilic trihalomethyl cation the carboca-tionic center is formed by hydride abstraction generating the distonicsuperelectrophile (81) Capture of the superelectrophile with szliguoride leadsto the szliguorinated product (82)

A number of steroidal systems have also been shown to generatecarboxonium-carbenium dications in superacid These intermediates areknown to lead to novel products and their chemistry has been recentlyreviewed28d

Olah and associates demonstrated the oxyfunctionalization of aldehydesand ketones by superacid promoted reactions with ozone30 These con-versions are thought to involve carbo-carboxonium dications and it hasbeen shown to be an effective method for the preparation of bifunctional


products In the case of aldehydes and ketones oxyfunctionalization pro-duces dicarbonyl products (eqs 2728) It has been found that the reactionrequires a minimum separation of two carbons between the carboxoniumand the developing carbonium ion centers in order for product formationto occur Thus pentanal gives dicarbonyl product (84) while no suchreaction occurs with butanal (eq 29)

O FSO3H-SbF5

O3 minus78degC

O O

60(27)

CCH2CH2CH2CH3

H

OFSO3H-SbF3

O3 minus78degCC

CH2CH2

H

HO C CH3

H O O OH

HminusH2O2

CCH2CH2

H

HO CCH3

OH

HCH3

O

O 80

83 84

+

+

++

(28)

CCH2CH2CH3

H

OFSO3H-SbF5

O3 minus78degCC

CH2

H

HO C CH3

H O O OH

HminusH2O2

CCH2

H

HO CCH3

OH

not formed85

+

+

++

(29)The mechanism is thought to involve the reaction of protonated ozone withthe C-H σ -bond and formation of the carboxonium-carbonium dication(83) Evidently formation of the analogous gitonic superelectrophile (85)from butanal is disfavored due to the close proximity of the two positivecharges Like most of the chemistry discussed preceedingly there is astrong preference for functionalization at the site most distant from thecarboxonium ion group (assuming it is a 2 or 3 reaction center)

Carbo-carboxonium dications have also been generated by the directionization of appropriate functional groups by the action of Broslashnstedsuperacids For example unsaturated acids are shown to give the reactivedistonic superelectrophiles which are shown to be moderately reactive31

Protonation of the carboxyl and oleTHORNnic groups give the distonic super-electrophiles (86 and 88 eqs 3031)

CO2HCF3SO3H

C6H6

O

CH38586 87

orH3COH

OH+ +

CH3 O

+

+

(30)


Ph CO2HCF3SO3H

C6H6

O

Ph9888 89

orPhOH

OH+ +

PhO

+

+

(31)

H

H

Ph

HOOH

CF3SO3H

Ph

OH

OH

90 88

++

+ Ph

OH

OH+ +

(32)

It has been shown in another study that protonated carboxylic acids tendto form acyl ions at temperatures above 10C so it is possible that theacyl-carbenium dications (87 and 89) are the electrophiles that lead to theTHORNnal cyclization products32 Based on the ability to react with deactivatedarenes it has been shown that there is a marked decrease in superelec-trophilic character upon going from the gitonic superelectrophile 90 tothe distonic superelectrophile 88 In addition to protonation of the oleTHORNnprotonation of a cyclopropane derivative has also been shown to producethe distonic superelectrophile 8832b There is evidence that these types ofdistonic superelectrophiles are signiTHORNcantly more reactive than analogousmonocationic electrophiles For example the distonic superelectrophile(91) is generated from a condensation reaction with α-ketoglutaric acidand despite the stabilizing effect of the two phenyl groups dication 91reacts withbenzene and gives the phenyl-substituted tetralone (eq 33)33

HO OH

OO

O

CF3SO3H

C6H6

C6H6

HOPh

OH

Ph

minus2H2O

minusCO HO Ph

OH

Ph

Ph

O

Ph Ph8991

+

+

+

(33)

CH3Ph

Ph

92

+

In contrast the 11-diphenyl ethyl cation (92) is unreactive to benzeneThis indicates that the carboxonium group (or the corresponding acyl ion)participates in the superelectrophilic activation of the adjacent carboca-tionic center


Several reports have suggested that carbo-carboxonium superelectro-philes may also be produced from phenols naphthols and related speciesby diprotonation in superacidic media34 For example 1-naphthol isthought to form the distonic superelectrophile (93) with a variety ofacids (excess AlCl3 HFSbF5 and HUSY zeolite)34a In the presenceof benzene the substituted tetralone and with cyclohexane 1-tetralone isproduced (eq 34)

OH

ACID

OH

C6H6

O

Ph O

cyclohexane

93

+

+

(34)

Since benzene and cyclohexane are both fairly weak nucleophiles thischemistry indicates that such dicationic species (ie 93) are indeed super-electrophilic

As mentioned 2-oxazolines may form a ring-opened distonic super-electrophile in reactions in superacid These carboxonium-carbenium dica-tions are capable of reacting with benzene and moderately deactivatedsubstrates2 For example the optically active oxazoline (94) reacts inCF3SO3H to generate the chiral dication (95) and this superelectrophilicspecies is capable of reacting with o-dichlorobenzene in fair to modestyield and diastereoselectivity (eq 35)

O

NH3CPh

Ph

H3CN

O

H

PhPh

61

ClCl

CF3SO3H

o-C6H4Cl2

(86 de)94 95

H3CN

OH

H

PhPh

H

+

+

(35)Carbo-acyl dicationic species have been proposed as intermediates in

several reports but these types of distonic superelectrophiles have not yetbeen sufTHORNciently studied Work by the Olah group has shown that pro-tonated carboxylic acids cleave to the acyl ions in superacidic media attemperatures above minus10C32 In principle ionization of a second group(such as hydroxyl or oleTHORNnic) can generate a carbocationic site adjacent to


the acyl cation producing the carbo-acyl dicationic species Two types ofdistonic superelectrophiles are possible for the carbo-acyl dications theacyl-carbenium dications (ie 97) and acyl-carbonium dications (ie 99)As described in Chapter 6 it has been proposed that the distonic superelec-trophile (97) is formed as a short-lived and reactive intermediate from the4-chlorobutanoyl cation (96 eq 36)35 An acyl-carbonium dication (99)could be produced by protosolvation of an acyl cation (98 eq 37) It hasbeen shown in a closely related study that proto(deutero)solvation of thepropionyl cation (100) occurs in superacid to provide deuterium incor-poration at the methyl group36 Experimental and theoretical evidencedemonstrated that formation of the carbonium ion center occurs preferen-tially at the most distant carbon giving the gitonic superelectrophile (101eq 38)

Cl CO

HF-SbF5 H3CC

OH3C

CO

96 97

H2CC

O+

+

+ + ++

(36)

C OHF-SbF5

98 99

H

HC O

H

H

H+ + +

(37)

DF-SbF5

100 101

C OCH2DCH2minusH+

25 D

20degC12 days

C OCH3CH2

+C OCH2CH2

D H

+

+

+

(38)

This provides maximum charge-charge separation in the dication Thus itis expected that analogous distonic superelectrophiles will likewise tend toundergo protosolvation at the carbon(s) most distant from the acyl cationcenter

A fair number of carbo-ammonium dicationic species and related sys-tems have been reported These distonic superelectrophiles have beendirectly observed and shown to be useful in synthetic methodologies Forexample the acid-catalyzed Grewe-cyclization is a well-known reactionused in the preparation of morphine analogues37 The conversion involvesformation of the distonic superelectrophile (102) from an appropriate


tetrahydropyridine derivative (eq 39)

NR

OH

NR

OCH3

H3PO4

102

N

R

OCH3

H

+

+

(39)Related ammonium-carbenium distonic superelectrophiles (14-dications103104) have been shown to possess strong electrophilic reactiviesundergoing arylation with benzene and dichlorobenzene (eqs 4041)38

NH

CF3SO3H

o-C6H4Cl2

Cl

Cl

42 NH

103

N

H

H +

+

(40)

N Ph CF3SO3H

C6H6

N Ph

Ph

99

104 105

N PhH +

+ (41)

107106 108 109 110

NPhH Ph

+

+ Ph

NPh

CH3H

H

+

+

NH3+

+Ph NCH3

HH

+ +CH3

H3N

+

+

The formation of distonic superelectrophile 104 provides a high-yieldroute to the antispasmodic drug fenpiprane 105 The 14-dication (108)15-dication (106) and 16-dication (107) have likewise been shown toreact with benzene in high yields39 The superelectrophilic vinyl-dications(109110) have also been studied4041

A number of related distonic superelectrophiles have been generatedfrom N -heteroaromatic compounds (Table 2) Vinyl-dications (111112)have been produced from the ethynyl pyridines40 while N -alkenylN -heterocycles provide dications (113115)42a Vinyl-substituted N -heterocycles provide access to distonic superelectrophiles such as dica-tion 11639 Dications 117 and 118 are generated from their precursors andboth intermediates lead to efTHORNcient cyclization reactions with the adjacent


Table 2 Distonic superelectrophiles (111118) formed with CF3SO3H

N+

+

+

+

+

+

+

+

HN

N H

CH3N+

+

+N

Ph

OH

N+

N+ +

Ph

OH

PhN+ +NPh

OHOH

N

S

CH3

N

S

CH3

CH3

H

NNPh

NPh

PhCH3

CH3

N

PhCH3

CH3

H

N

O PhPhPh

H3C

N

O PhPhPh

H3C H

Precursor Distonic Superelectrophile Precursor Distonic Superelectrophile

111

112

113

114

115

116

117

118

NN

CH3

CH3

Ph

119

N

O Ph

H3C

120

N

++

phenyl groups42b43 Products 119 and 120 are obtained from the conver-sions Distonic superelectrophiles 111116 have all been shown to reactwith benzene in Friedel-Crafts type reactions indicating their reactivi-ties as electrophiles As expected the diprotonated species 111118 areformed with the largest possible charge separation with preference forhighly substituted carbenium centers

Some theoretical work has been done to estimate the relative stabil-ities of distonic superelectrophiles with respect to the distance betweenthe charge centers For example compound 121 is ionized in CF3SO3Hto give initially the 13-dication (122) which is found to undergo thekinetically controlled isomerization to the charge separated 14-dication(123 Figure 3)43 Experiments using isotopic labeling indicate that the


122

N

S

PhH

123

N

S

PhH

HCH3 CH3

N

S

Ph

CH3 CF3SO3H

minusH2OOH

12125degC

N

S

Ph

CH3

PhN

S

Ph

CH3

Ph56 26

Relative Energy 00 kcalmol+160 kcalmol

+

C6H6 C6H6

+ ++

Figure 2

charge migration occurs via successive deprotonation-reprotonation stepsCalculations at the B3LYP 6-311GB3LYP 6-311G level of theoryestimate that the 14-dication (123) is about 16 kcalmol more stable thanthe 13-dication (122) for the gas-phase geometry-optimized structuresIn another study the oleTHORNnic quinoline (124) was found to preferentiallygive the charge separated 15-dication (126) rather than the 14-dication(125 Table 3)44 As described subsequently dication 125 leads by cycliza-tion to a very efTHORNcient conversion to benz[c]acridine The two dications(125126) were studied using calculational methods to determine their rel-ative stabilities (Table 3) Although their relative energies varied with the

Table 3 Calculated energies for dications 125 and 126

Ph

Ph

Ph2H+

NH

+

125 126

Level of Theory Relative Energy kcalmolminus1

HF3-21G

HF6-31G (d)

HF6-311G (d)

PBE16-311G (d)

MP26-311g (d)

MPW16-311G (d)PCMsp

00

00

00

00

00

177

171

179

100

103

7400

124

++

Ph

Ph

NH

+

+

PhN


level of theory used in the calculations all computational methods showedthe charge-separated species (125) to be considerably more stable Besidesthe charge-separation dication 125 also beneTHORNts from favorable benzylicinteraction A calculation was also done using the solvation-sphere modelMPW16-311G(d)PCMsp using sulfuric acid as the solvent While theenergy difference between the two dications becomes even less thissolution phase model still suggests more than a 7 kcalmol difference instabilities between the two dications

Examination of the dication pairs 122123 and 125126 may also sug-gest a further useful deTHORNnition of the distonic superelectrophiles thedistonic superelectrophiles may be distinguished from onium dicationsthat are without superelectrophilic activation (ie two isolated cationiccenters) by comparison of the energies reactivities or structuralelectroniccriteria of two closely related species For example it is expected thatammonium-carbenium dications 127 and 128 should vary considerably interms of energy due to the proximity of the charges

14-dication

15-dication

127

19-dication

110-dication

129

130

HN

HH

CH3+ +

128

HN

HH

CH3+

+ HN CH3

HH

+ +

HN CH3

HH

+

+

Thus dication 127 can be called a distonic superelectrophile Howeverthere is very little difference in energy between the ammonium-carbeniumdications 129 and 130 due to the large distance between charges Dica-tion 129 is therefore not a distonic superelectrophile but rather an oniumdication with isolated electrophilic sites This concept has been demon-strated experimentally for a number of onium dications as in studiesof carbodications having a large distance between the charge centers Inorder to distinguish between distonic superelectrophiles and onium dica-tions an arbitrary energy criteria may be set For example if increasingcharge-charge separation by a single carbon atom leads to a stabilizationgreater than 10 kcalmol then the species may be considered as a distonicsuperelectrophile Likewise the energy levels of LUMO orbitals could becompared and used as a basis for distinguishing between these two typesof closely related dicationic species


H2N

HO

H3CO

HCl ether

H3N

H2O

H3CO

H3N

H3CO H3CO

H3N

H3CO

H2NN

OH

H3CO

Butorphanol

131 132

+

+ +

++

+

Scheme 2

Charge-charge separation has been shown to be a useful driving forcein the reactions of carbo-ammonium dications For example in the com-mercial synthesis of the analgesic drug butorphanol a key step involvesthe ring expansion step of dication 131 to dication 132 (Scheme 2)45

The carbocationic center in 131 is located at a benzylic charge positionbeing adjacent to an electron rich aryl ring It is somewhat unexpectedthat migration should occur to produce dication 132 because the resultingcarbocationic center loses its benzylic stabilization Clearly an importantdriving force for this conversion is the charge-charge separation wherethe 14-dication (131) produces a 15-dication (132) In other studies itwas demonstrated that distonic superelectrophiles 133 and 135 undergocharge migration (eqs 4243)43

NH3C

OH

Ph

NH3C

Ph

Ph

H 98

CF3SO3H

134

C6H6

133

NH3C

Ph

H+

+

NH3C

Ph

H

H

++

(42)

N

PhOH

N

Ph

Ph 97Ph

Ph

CF3SO3H

C6H6

135

N

Ph

Ph

H136

N

Ph

Ph

H+

+

+

+

(43)


The charge-separated species (134 and 136) are then quantitatively trappedwith benzene Interestingly the conversion of 135 to 136 involves themigration of charge from one benzylic position to another benzylic posi-tion This indicates that charge-charge repulsion drives the conversionThe charge migration chemistry has been exploited in the synthesis of avariety aza-polycyclic aromatic compounds (eqs 4445)43

NNPh

Ph

Ph

HO

NNPh

86

CF3SO3H (44)

O

ON N

Ph NN

Ph

60

OHPhO

OCF3SO3H (45)

As shown in Scheme 3 these conversions involve two key reaction stepsFrom the pyridine derivative (137) ionization of the starting materialinvolves protonation of the N -heterocycle and the hydroxyl group withloss of water producing the distonic superelectrophile (138) Charge migra-tion then provides the dicationic species (139) which is able to undergoring closure Ipso-protonation of the phenyl group leads to benzene elim-ination and formation of the condensed aromatic system

Besides carbo-ammonium dicationic systems there have been stud-ies related to carbo-phosphonium dication systems Some of the reportedchemistry suggests that superelectrophilic activation is involved OleTHORNnicphosphonium salts are protonated in superacid to generate dications like140 and these species have been shown to react with benzene in good

N

H

N

PhPh

CH3

CH3CH3

CH3

CH3

OH2

H

CF3SO3H

N

Ph

HNNH

H

minus H2O

138 139

93

CH3

N

Ph

OH

Ph

137

+

+

N

PhPh

H

CH3

+

+

+

+

+

N

PhPh

H

CH3

+

+

+

minusC3H6

minusH+

Scheme 3 Proposed mechanism for aza-polycyclic aromatic compound formation


yields (eq 46)46 In the reaction of the 2-pentenyl system (141) thesuperacid catalyzed addition reaction gives a product arising from a chargemigrationstep (eq 47)

PhP

PhPh

CH3

CH3Br

CF3SO3H

C6H6Ph

P

PhPh

CH3

CH32 X

PhP

PhPh

CH3H3C

140 92

+ + + +

minus 2 Xminusminus

(46)

PhP

PhPh

Br

CF3SO3H

C6H6Ph

P

PhPh

2 X

141

CH3

CH3 PhP

PhPh

2 X

CH3 PhP

PhPh

2 X

CH3

142 143

99

++

minus minus minus

+ + +

minus

+

(47)Initial protonation gives the 14-dication (142) but charge migration pro-vides the more stable 15-dication (143) Reaction of dication 143 withbenzene then gives the product46

There have been few reports of carbo-halonium dicationic species inthe literature In an attempt to prepare an adamantadiyl dication Olah andco-workers reported NMR evidence for the carbenium ion (144)

OH

CH3

Br

FSO3H-SbF5

SO2 minus60degC

CH3

BrSbF5

144

+

d+dminus

(48)

which possesses signiTHORNcant donor-acceptor interaction between thebromine atom and the Lewis acid (eq 48)12 This species is expected toalso exhibit modest superelectrophilic activation from the partial positivecharge on the bromine

723 Carboxonium-Centered Distonic Dication

A number of studies have reported the formation of carboxonium-centereddistonic dications These systems include diprotonated diketones diproto-nated dicarboxylic acids their derivatives and others A wide variety ofmixed dications have also been reported such as ammonium-carboxoniumdications oxonium-carboxonium dications acyl-carboxonium dicationsand other species Many of these carboxonium-centered dications exhibitproperties indicative of distonic superelectrophiles


724 Bis-carboxonium Dication

As described in the previous chapter a number of diketones have beendiprotonated in superacid to generate distonic superelectrophilic speciesSeveral types of 14-diketones yield the respective distonic superelec-trophiles (eq 49)47

146 147 149148a 148b

H3CCH3

OH

OH

+

+

OH

HO+

+ OH

HO+

+OH

HO

+

+ OH+

O

O

FSO3H-SbF5

SO2 minus 60degC

145

OH

HO

+

+

(49)

These distonic superelectrophiles (145147) have been characterized bylow-temperature 1H NMR (and 13C NMR in the case of 147) from FSO3HSbF5 solutionDication146was also studied by calorimetric studies to deter-mine the heat of diprotonation of 25-hexanedione48 It was found that theheat of diprotonation for the γ -diketones (like 25-hexanedione) is about5 kcalmol less than expected when compared to twice the heat of protona-tion of acetone or other monoketones The destabilization of dication 146by 5 kcalmol can be the result of electrostatic effects and it can be consid-ered evidence for the superelectrophilic character of such dications When26-admantanedione is reacted in FSO3HSbF5 solution the dication 148is formed as a persistent species observable by 1H and 13C NMR12 Thecarboxonium carbons of 148 are observed at δ13C 2477 while the mono-cationic species (149) has a carboxonium carbon at δ13C 2671 These 13CNMR data were interpreted as evidence for the increasing importance of thecarboxonium-type resonance structure (148a) due to electrostatic repulsiveeffects Some examples of aromatic diketones (ie diacetylbenzenes) havealso been reported to produce bis-carboxoniumdications in their protonationreactions in superacids47

A homologous series of aliphatic ketoacids were studied in FSO3HSbF5 solution by low-temperature NMR As discussed previously thegitonic superelectrophiles (150ab) have been generated but the distonicsuperelectrophiles (150c-e) were also observed49 Among the distonicsuperelectrophiles the two systems with the greatest distance betweencharge centers (150 de) undergo cleavage to the acyl-carboxonium dica-tions (151 de) at 0C by loss of water (eq 50) Diprotonated levulinic


acid (150c) however is found to be stable to dehydrative cleavage up totemperatures as high as 60C (eq 51)

150 a n = 0b n = 1

c n = 2d n = 3e n = 4

H3CC

(CH2)nC

OH

OH OH+ +

150de

FSO3H-SbF5

0degC minus H2O

151de

H3CC

(CH2)nC

OH

OH OH+ +

H3CC

(CH2)nC

OH O+ +

(50)

no reaction

150c

FSO3H-SbF5

0degC minus H2OH3CC

(CH2)2C

OH

OH OH+ +

(51)

The resistance to cleavage is an indication of the superelectrophilic char-acter of dication 150c Several aromatic compounds have likewise beenshown to produce dicationic species upon the protonation of carboxyl andcarbonyl functional groups Other bis-carboxonium dications have beendescribed involving protonation of carbonyl amide and other groups50

These distonic superelectrophiles (152153) have been shown to be usefulin condensation reactions (eqs 5253)

N

O

O

CH3CF3SO3H

C6H6

N

O

CH3

Ph

Ph 90152

N

HO

OH

CH3

+

+

(52)

N

O

O

OEt CF3SO3H

C6H6

N

O

OEt

Ph

Ph 97153

N

HO

OH

OEt

+

+

(53)

A number of bis-carboxonium distonic superelectrophiles have beengenerated from dicarboxylic acids and diesters Early studies of the pro-tonation of the aliphatic diacids were done by cryoscopic techniquesusing sulfuric acid media51 More recent work was also involved usinglow-temperature NMR methods The aliphatic dicarboxylic acids are con-verted to their diprotonated products (154a-f) in FSO3H-SbF5-SO2 solu-tion and the dications 154a-f have been characterized by 1H NMR52

Like the dications from the ketoacids discussed previously it was shownthat the bis-carboxonium dications may undergo dehydration to form acyl


cation center(s) This cleavage reaction is also shown to be sensitive tothe distance between the carboxonium charge centers (eq 54)

154 a n = 0b n = 1c n = 2

d n = 3e n = 4f n = 5

C(CH2)n

COH

OH OH+ +

HO

t12 = 1 hr

minus H2O

minus 20degC

154d-f

FSO3H-SbF5

minus 20degC minus H2O

155d-f

C(CH2)n

COH

OH OH+ +

HO

156d-f

C(CH2)n

CO O+ +

C(CH2)n

C

OH O+ +

HO (54)

Diprotonated pimelic adipic and glutaric acids (154 d-f) cleave to theacyl-carboxonium dications (155 d-f) at a rate that is similar to that ofmonoprotonated aliphatic carboxylic acids However succinic acid (154c)only cleaves to an extent of 50 in the FSO3HSbF5SO2 solution Lossof the second water molecule from 155 d-f occurs readily but even withincreased acidity the acyl-carboxonium dication 155c only cleaves to anextent of about 50 to the biacyl ion (156c) These data are consistent witha signiTHORNcant degree of superelectrophilic activation in the case of 154cand 155c although the results also show a diminishing superelectrophilicactivation in the charge separated species (154 d-f) and (155 d-f) Thereare also close parallels between these results and the formation of bis-acyldications from the aliphatic diacid chlorides (vide infra)

The dicationic species arising from phthalic acid and its esters havealso been studied Diprotonated phthalic acid (157) is observed by lowtemperature 1H and 13C NMR with its carboxonium carbons found atδ13C 181053a Warming the solution of 157 leads to the appearance ofa new set of signals that were assigned to the cleavage product theacyl-carboxonium dication 158 (eq 55)

CO2H

CO2H

FSO3H-SbF5 minusH2O

minus60degC minus30degC

+

OH

OH

OH

OH

OH

OH

O

O

OH

O

H

OH

OH

O

157 158 159

+ + +

++

+

+

(55)

NMR evidence also suggests the degenerate rearrangement via the anhy-dride derivative (159) A similar process was described for the chemistryof succinic and glutaric anhydrides in superacid The methyl ester of


OH

OMe

OH+OMe

160

OH

OMe

161

OH

OMe

162

OH

OMe

OH

OMe

163

OMHO OH

MeO

OH

MeO

OH

OMe

OH

OMe

164

OH

MeO

OH

MeO

165

(CO2MeH)6+

+ + +

+ + + + + +

+ + +

Scheme 4

phthalic acid was also shown to form the diprotonated species (160) inFSO3HSbF5SO2ClF at low temperature (Scheme 4) Other multiplyprotonated species (161165) are formed by the reactions of their respec-tive esters in superacid53b

Diprotonated aliphatic esters have been studied by low-temperatureNMR experiments and by calorimetric techniques4854 A series of diesters(166a-e) were studied in superacid by low-temperature NMR and in eachcase the diprotonated species (167a-e) could be observed as a persistentspecies at minus60C (eq 56)54

H3COC

(CH2)nC

OCH3

O O

166 a n = 0b n = 1c n = 2

d n = 3e n = 4

H3COC

(CH2)nC

OCH3

OH OH

167 a n = 0b n = 1c n = 2

d n = 3e n = 4

FSO3H-SbF5

+ +

(56)

In general the diprotonated diesters (167a-e) are more easily obtained thananalogous diprotonated diketones It has been suggested that this reszligectsthe effective charge delocalization or dispersal in the ester-based carbox-onium ions48 This is evident by the acid-strength required to form thediprotonated species with diketones requiring much stronger superacidsBased on the results from calorimetric studies of diester (di)protonation itwas observed that the effects of charge-charge repulsion is negligible withseparation of the two positive charges by three or more methylene units48

Thus 167c can be properly described as a distonic superelectrophile whilethe higher homologs 167 d-e have rapidly diminishing superelectrophilicactivation

Another interesting type of bis-carboxonium dications is the bis(13-dioxolanium) dication series (168170)

OO

O

OO

O

FSO3H O

O

O

O

minus2 CH3OH

168

+

+


OO

O O

O

O

O O

169 170

+ +

+

+

(57)

These ions were prepared from the appropriate 2-methoxyethyl esters(eq 57)55 Reaction in superacid leads to the formation of the 13-dioxolanium cation centers and the respective dicationic species Dica-tions 168170 were directly observed by NMR spectroscopy Their struc-tures energies and GIAODFT δ13C values were determined by ab initiocomputational methods There is generally good agreement between theobserved 13C NMR spectra and the calculated spectra Dication 168 givesa 13C NMR signal at δ13C 1822 for the carboxonium carbons in FSO3Hsolution while the calculated value (B3LYP6-311GB3LYP6-31Glevel) is at δ13C 1885 When the energies of the dications are comparedthe ortho-isomer (168) is found 150 kcalmol higher in energy then themeta and para isomers (169170) This increasing energy is thought tobe due to the steric effects of the ortho substituents as well as the electro-static repulsive effects of the two closely oriented cationic centers Clearlyspecies 168 should be considered a distonic superelectrophile due in partto energy considerations Using the same chemistry the tricationic species(171) is produced in superacid (eq 58)

O

O

O O

O

O

171

+

OO

O

OO

O

OOO

FSO3H

minus2 CH3OH

++

(58)

When comparing the 13C NMR data from the dications 168170 and thetrication 171 there is evidence for increasing superelectrophilic activationwith the trication For example themethylene carbons are found at δ13C775for dication 169 and δ13C 869 for trication 171 This increased deshieldingof the methylene carbons can be understood in terms of a greater delo-calization of the positive charges (in the trication) onto the ring oxygenatoms leading to deshielding of the methylene carbons The enhanced res-onance interaction with the oxygen atoms is thought to be the result of the


electrostatic repulsive effects of the three positive charges The optimizedgeometries also reveal a structural effect from the third positive charge Thebond length between the carboxonium carbon and the ipso-carbon increasesfrom 1453 ucircA in dication 169 to 1471 ucircA in the trication 171 This increasein bond length is due to coulombic repulsive effects

725 Onium-carboxonium dication

Among the reported distonic superelectrophiles a signiTHORNcant number ofammonium-carboxonium dications and related species have been stud-ied It has been shown that these electrophiles show enhanced reac-tivities compared with monocationic carboxonium ions For example4-piperidone (172) is diprotonated in superacidic CF3SO3H to give thedistonic superelectrophile (173) which condenses with benzene in highyield (eq 59)56 In contrast cyclohexanone forms the monocationic car-boxonium (174) ion but ion 174 is not sufTHORNciently electrophilic to reactwith benzene (eq 60)

NH

OCF3SO3H

C6H6

N

OH

H H172 173

NH

Ph Ph+

+ (59)

Ph PhO OH+

174

CF3SO3H

C6H6

(60)

The observed electrophilic reactivity is indicative of superelectrophilicactivation in the dication 173 Other ammonium-carboxonium dicationshave also been reported in the literature some of which have been shownto react with benzene or other weak nucleophiles (Table 4)142b57minus60

Besides ammonium-carboxonium dications (175179) a variety of N -heteroaromatic systems (180185) have been reported Several of thedicationic species have been directly observed by low-temperature NMRincluding 176 178180 183 and 185 Both acidic (175 180185) andnon-acidic carboxonium (176177) dicationic systems have been shownto possess superelectrophilic reactivity The quinonemethide-type dication(178) arises from the important biomolecule adrenaline upon reaction insuperacid (entry 4) The failure of dication 178 to react with aromaticcompounds (like benzene) suggests only a modest amount of superelec-trophilic activation An interesting study was done with aminobutyric acid


Table 4 Distonic superelectrophiles based on ammonium-carboxonium dicationsand related heterocyclic systems

NH3C

O

NH3C

OH

H

N O

O

N OOH

H

H3C N OCH3

H3C

OCH3

H3C N OCH3

H3C

H

HN CH3

HO

HO

OHN

CH3HO

HO

H H

H3C O

ONH3

H3C OH

OH

NH

O

HNH

OH

NOH O

H

HN

OH OH

H

N

SH3C

CH3

O

CH3 HN

SH3C

CH3

OH

CH3

NNPh

PhO

H

HNNPh

Ph H

N

H

O

H

OH

CH3

NCH3

Xminus

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

Entry Precursor Dication Entry Precursor Dication

175

176

177

178

179b

180

181

++

182

183

184

185

N

OH

NH

OH

+

+

+

+

++

+

+

+

+

+

+

+

+ +

+

+ NH3+

+

+

+

minus

+

HO

derivatives60 The series of diprotonated species (179a-c) were observedas persistent species in FSO3H-SbF5 solution at low temperature Thediprotonated α- and β-aminobutyric acids (179ab) were found to be sta-ble at temperatures as high as 45C but the diprotonated γ -aminobutyricacid was found to undergo cleavage to the amino-acylium dication(186 eq 61)

179b179a 179c

45degC

186

OH3N +OH

OHH3N

++H3C OH

OHNH3

+

+NH3

+H3C OH

OH

NH2+

+

(61)


As described in the previous chapter 179ab are thought to be stabletowards cleavage due to the close proximity of the charge centers Dipro-tonated 4-pyridinecarboxaldehyde (180) has been shown to react withnitrobenzene and saturated hydrocarbons demonstrating its superelec-trophilic character (eqs 6263)58a

N

CHOCF3SO3H

C6H5NO2

140degC N

NO2

NO2

53

(62)

N

CHO CF3SO3H

adamantane CO HNOH

H

H

O

ON

18060

++

+

(63)

Other diprotonated acyl-pyridines have likewise been studied61 In stud-ies of 5- 6- 7- and 8-hydroxyquinolines and 5-hydroxyisoquinolinedicationic intermediates like 185 (Table 4) were found to be involvedin superacid catalyzed reactions with benzene and cyclohexane59 Forexample 8-hydroxyquinoline (187) reacts in CF3SO3HSbF5 to generatedications (188 and 189) and undergoes ionic hydrogenation in the pres-ence of cyclohexane (eq 64) Compound 187 also reacts with benzene insuspensions of aluminum halides (eq 65)

NOH

CF3SO3H-SbF5

C6H12

C6H12 C6H12

NH

OHNH

OHN

187 188 189

++

++

(64)

ABr3 or AlCl3

C6H6N

OHNH

OH

Ph

N

OH

187

++ (65)

OH

190

+


Interestingly the comparable monocation (190) is not reactive towardsbenzene or cyclohexane This is an indication of the superelectrophiliccharacter of dication 188 The isomeric hydroxyquinolines and 5-hydroxy-isoquinoline react with 57 molar excess of aluminum chloride andcyclohexane at 90C to give ionic hydrogenation products and the corre-sponding distonic superelectrophiles (191193) are proposed asintermediates

191 193185 192 188

NH

OH+

+ NH

HO+

+ NH

HO+ + N

HOH

++

NH

OH+

+

When the reactions with benzene were compared it was found that thedistonic superelectrophiles 185 188 and 193 are the most reactive electro-philes59 Based on the results from computational studies (MNDO andDFT) the relative reactivities of the isomeric hydroxyquinolines and5-hydroxyisoquinoline can be correlated with the energies of the low-est unoccupied molecular orbital (εLUMO the square of the coefTHORNcients(c2) at the reactive carbon atoms and the NBO charges (q) on CHgroups For example 8-hydroxyquinoline (187) is found to be more reac-tive than 6-hydroxyquinoline in the superacid catalyzed reactions withbenzene and cyclohexane When the εLUMO for dication 188 is com-pared with the εLUMO for dication 191 dication 188 has a LUMO ofmuch lower energy It was proposed that lower εLUMO values correspondto increased electrophilic reactivities It is also noted that typical dica-tionic structures are found to have much lower εLUMO values (simminus12 eV)compared to analogous monocation εLUMO values (simminus7 eV) This studyalso showed evidence for the importance of atomic charge q at a reac-tion center in determining the reactivity from a kinetic point of viewGiven that the energy levels for the highest occupied molecular orbitals(HOMOs) for benzene (minus9782 eV) and cyclohexane (minus9109 eV) are con-siderably higher (less negative) than the εLUMO values for the dicationsthe superelectrophilic character of these species can be understood Tofurther characterize the intermediates involved in the conversions dica-tionic species 185 and 191193 were also studied by 1H and 13C NMRfrom 5-hydroxyquinoline 6-hydroxyquinoline 7-hydroxyquinoline and5-hydroxyisoquinoline respectively in CF3SO3H-SbF5 solutions Despitethe high acidity of the media however dications 191193 were found tobe in equilibrium with the monoprotonated species

In a related report 5-amino-1-naphthol (194) was shown to react withweak nucleophiles (cyclohexane and benzene) and the distonic super-electrophile 196 is proposed as the key intermediate (Figure 3)62 NMR


OH

NH2

Acid

OH

NH3

Acid

OH+

++

+

NH3

195 196

OH

eLUMO

q3

minus10979 eV minus7277 eV

3 3

+03 +025

190194

Figure 3 5-Amino-1-naphthol its protonated ions 195-196 and comparison to monoca-tion 190

studies indicate that the monocationic species 195 is formed in CF3CO2H(H0 minus27) and the dicationic species 196 from CF3SO3H (H0 minus141)or CF3SO3H-SbF5 (H 0 minus20) although with CF3SO3H both the mono-cation (195) and dicationic (196) are present in appreciable concentra-tions A dicationic species similar to 196 is also thought to arise fromsolutions with excess anhydrous AlCl3 or AlBr3 (eq 66) The superelec-trophilic reactivity of dication 196 is consistent withcomputation resultsthe energy level of the lowest unoccupied molecular orbital (εLUMO) andthe atomic charge of the reaction center (qi) In order to show the effectof a second charge center dication 196 is compared to the monocationic4-hydroxy-1-naphthalenonium ion 190 Dication 196 is found to have amuch lower εLUMO and a greater positive charge at carbon 3 when com-pared to the monocation 190 In reactions with excess (4 equivalents)AlCl3 or AlBr3 5-amino-1-naphthol undergoes ionic hydrogenation withcyclohexane while the reaction with benzene gives 5-amino-3- phenyl-1-tetralone (197) (eq 66)

OX+

+NH2X

ExcessAlCl3 or AlBr3

X= H or AlnCl3nminus or AlnBr3n

minus

1 C6H12

2 H2O

1 C6H6

2 H2O

O

NH2 O

NH2

70ndash80

15ndash40

OH

NH2

197

(66)

Since monocation 190 does not react with either benzene or cyclohexanethe results show that the protonated amino group signiTHORNcantly enhances the


electrophilicity of the carboxonium ion These results are also consistentwith the predictions based on εLUMO and qi

The activating effects of ammonium groups on carboxonium elec-trophiles has also been exploited in the Friedel-Crafts acylations withamides50 For example in comparing the superacid-catalyzed reactionsof acetanilide the monoprotonated species (198) is found to be unreac-tive towards benzene (eq 67) while the diprotonated superelectrophilicspecies (199) reacts with benzene to give the acyl transfer product inreasonably good yield (eq 68)

CF3SO3H

C6H6100degC

NH

CH3

O

NH

CH3

OH 98recovery ofacetanilide

198

+

(67)

NH

CH3

O

NH

CH3

OH

78NH2

NH3

CH3

O

199

C6H6CF3SO3H

C6H6100degC

+

+(68)

Other related distonic superelectrophiles (200201) were also shown toprovide acyl-transfer products with benzene and in the case of theaminopyridine derivative (202) intramolecular reaction produces theindanone (eq 69)

H3N

NH

OHH3N

NH

CH3

OH

200 201

++

+

+

N

NH

O

PhCF3SO3H C6H6

25degC

NH

NH

OH

Ph

O

Ph70

202

+

+

(69)

Although Friedel-Crafts acylation is well known with carboxylic acidsanhydrides and acid halides there are virtually no reports of Friedel-Craftsacylations being done with amides63 These results demonstrate the appli-cation of distonic superelectrophiles to accomplish such a difTHORNcult


synthetic goal as the Friedel-Crafts acylation of aromatic compounds withamides

The diprotonated benzoquinone monooximes have also been studiedUsing low temperature NMR dications such as 203 can be directlyobserved (eq 70)64 Little work has been done to study the electrophilicchemistry of these ionic species although Shudo and Okamato generateddication 204 in superacid and found it capable of reacting with phenol(eq 71)65

NOH

OFSO3H-SbF5

NOH

HOH

203

++ (70)

NOCF3SO3H

204

SO

OCH3 NHO S

O

OCH3C6H5OH

H

NHHO SO

OCH3

HO

+

+

(71)

Carbo-oxonium dications have also been described in the literature andsome of these may be considered distonic superelectrophiles An inter-esting example has been described by Sommer and co-workers in thecase of diprotonated p-anisaldehyde (206 Figure 4)66 The protonationequilibria of p-anisaldehyde in superacids were studied using dynamicNMR techniques It is known that O-protonated benzaldehydes and relatedcompounds exhibit signiTHORNcant rotational barriers (compared to the neu-tral benzaldehyde) due to π -delocalization (ie 205b) For monoproto-nated p-anisaldehyde (205) the rotational barrier was estimated to be186 kcalmol In strong superacid systems however the oxonium centeris formed producing the diprotonated p-anisaldehyde (206) This is foundto have a decreased rotational barrier of about 126 kcalmol The decreas-ing rotational barrier is the result of diminished neighboring aryl-groupstabilization of the carboxonium group Electron delocalization from thearyl group towards the carboxonium group is disfavored due to the interac-tion of the two positive charges (ie 206b) Other oxonium-carboxoniumdications have been reported such as the diprotonated products (207208)from hydroxycarboxylic acids67 but little is known about the electrophiliccharacter and superelectrophlic activation in such dications

HOO

OH H

H

207HO O

OHH

H

CH3

208

+

++

+


COH

OCH3

FSO3H

COH

OCH3

H

COH

OCH3

H

CO H

OCH3

H

FSO3H

SbF5

CO H

OCH3

H

H

CO H

OCH3

H

H

205a

205b

206a

206b

+ + +

+

+ +

+

Figure 4

726 Acyl-centered Distonic Dications

Monocationic acyl ions are readily prepared as persistent species in solu-tions of low nucleophile strength68 These acyl ions have been thoroughlycharacterized by IR and NMR spectroscopy and several acyl ion saltshave been characterized by X-ray crystallography The monocationic acylions are often prepared in situ from carboxylic acids esters or anhydridesby the action of a strong Broslashnsted acid or the ions can be prepared fromionization of an appropriate acid halide with a strong Lewis acid Bothmethods have been used to prepare acyl-centered dications some of whichcan be considered distonic superelectrophiles As described previouslydicarboxylic acids cleave to the bis-acyl ions in superacid (FSO3HSbF5)provided that the acyl cations are separated by at least three methyleneunits (eq 54)55 The THORNrst bis-acyl dications were reported by Olah andComisarow being prepared by the reactions of dicarboxylic acid szliguorideswith superacidic SbF5 (eq 72)69

FC

(CH2)nC

F

O O

209d-h

SbF5-SO2C

(CH2)nC

O O

210d-h

minus60degCF

C(CH2)n

CF

O O

209 c n = 2d n = 3e n = 4

f n = 5g n = 6h n = 7

+ +

2 SbF6minus (72)


Within the series of dicarboxylic acid szliguorides ionization provided thebis-acyl dications in all cases except with succinyl szliguoride It was sug-gested that the electrostatic repulsive effects inhibit formation of thebis-acyl dication from succinyl szliguoride (209c) Dications 210d-h werecharacterized by IR and 1H NMR in this study and they were also shown tobe reactive towards benzene to give the expected diketones Using calori-metric techniques to study the ionizations similar results were obtainedby Larson and Bouis49 It was found in these studies that systems withgreater than four methylene groups (ie 210f-g) exhibit similar heats ofreaction Thus bis-acyl dications (210f-h) may be considered onium dica-tions with separated acyl groups However based on heats of reaction itis estimated that dication 210e is ca 4 kcalmol less stable than 210fand consequently bis-acyl dications separated by four or less methylenegroups (210c-e) can be considered superelectrophilic

Bis-acyl dications have also been generated from terephthalic acidderivatives Ionization of terephthaloyl szliguorides (211a-c) with SbF5 hasbeen used to prepare bis-acyl cations (212a-c eq 73)69

CF

O

CF

O

X

X

X

X

211a X = Hb X = Clc X = Br

SbF5

CO

CO

X

X

X

X


+

+

(73)

X

X

X

X

213b X = Clc X = Br

+

+

which have been characterized by IR UV and 1H NMR spectroscopy70

The halogenated derivatives 212bc can also be generated from tetra-haloterephthalic acids with SO3 These bis-acyl dications have been stud-ied by mass spectroscopy being generated from the terephthaloylchlorides They fragment to the highly abundant C6X4

2+ ions (213bc)

727 Varied Distonic Superelectrophilic Systems

Besides the discussed distonic superelectrophiles there are a variety ofother dicationic systems that may be considered as such A signiTHORNcantnumber of sulfur-centered systems have been shown to form such per-sistent dicationic systems For example the dicationic carbosulfoniumspecies (215) was obtained by the oxidation of compound 214 (eq 74)71


SS

S 2 NO+BF4

minus

S

S+

+

SS

S

S

minus2 BF4

214 215

(74)

Many types of bis-sulfonium dications have been described in the litera-ture although little is known about the extent of superelectrophilic acti-vation in these species As an example the dithioniabicyclo[222]octanedication (217) is produced by reaction of the bicyclic dithioether dica-tion (216) with styrene derivatives (eq 75)72 Tertiary sulfonium dications(useful synthetic intermediates) have been prepared (eq 76)73

S

S2 CF3SO3

minusS

S

H

2 CF3SO3minus

45216 217

+

+

++

+

(75)

SS

(CH3O)2CH

SS CH3H3C

2BF4minus

218

+

+ +BF4minus (76)

The chemistry of dicationic sulfur-centered systems has been recentlyreviewed74 and is therefore not further discussed here

Due to the inherent stability of most ammonium ion centers struc-tures with two well-separated ammonium centers are considered oniumdications without superelectrophilic activation68 In rare cases howeverdistonic superelectrophiles are formed containing two ammonium cationiccenters One of the most important examples is the electrophilic szliguo-rinating agent called Selectszliguor (220) It is a very useful reagent toprepare varied szliguorinated products and its chemistry has been recentlyreviewed75 In a study comparing several types of electrophilic szliguori-nating agents Selectszliguor 220 was found to have a reduction poten-tial signiTHORNcantly more positive than the analogous monocationic salt 221(Table 5)76 Other than N -szliguorobis(triszliguoromethylsulfonyl)imide (219)220 has the most positive reduction potential Moreover it has beenshown that the electrophilic reactivity parallels the reduction potential

trade

trade


Table 5 Electrophilic szliguorinating agents and their electrochemical reductionpotentials (Ep)

F3C S N S CF3

F O

OO

O

NN

CH2Cl

F2 BF4

minus

NF

BF4minus

NF

CF3SO3minus

S

O

O

NF

H

S

O

O

NF

CH3H3C

Ep ReductionEp Reduction

+018

minus004

minus037

minus047

minus078

minus210

219

220

221

222

223

224

+

+

+

+

data 219 reacts with benzene to give szliguorobenzene However 220 doesnot react with benzene but szliguorinates anisole in good yield However inCF3SO3H medium 220 szliguorinates benzene chlorobenzene etc LikewiseN -szliguorobenzenesulfonimide (223) is incapable of szliguorinating anisole butdoes szliguorinate the more nucleophilic 13-dimethoxybenzene76 Based onthese results it is clear that the adjacent ammonium group enhances theelectrophilic reactivity of the N -szliguoro group in Selectszliguor and thus220 can be properly considered as a distonic superelectrophile

Phosphonium and arsonium dications have been studied and their chem-istry has also been recently reviewed74

There have been several distonic superelectrophiles described in the lit-erature that are oxonium-centered dications For example a series of diolswere solvated in FSO3H-SbF5-SO2 and the dicationic species were persis-tent at minus80C77 Upon warming to 25C the bis-oxonium ions undergorearrangement to the more stable carboxonium monocations (eq 77) Bar-ring a concerted mechanism the transformations are thought to involvethe carbo-oxonium dications (ie 225) and concomitant hydride shiftsInterestingly 25-hexanediol ionizes in superacid and with warming thecyclic oxonium ion (229) is formed (eq 78)

trade


HO O

HFSO3H-SbF5

minus80degC

HO O

H

H H25degC

minusH2O minusH+

~H

225 226

+ + HOH

H

H

H H

HH

++

OH

H

H

H HH

H+

(77)

H3CCH3

OH

OH

FSO3H-SbF5

minus60degCH3C

CH3

OH2

OH2minus30degC

minusH2OH3C

CH3O

HH

O CH3H3CHH

2+

O CH3H3C

H

228

229

227

+

+

+

+

+

(78)

In superacid it is possible to even generate gitonic superelectrophilessuch as diprotonated water (H4O2+)78 This suggests the possibility thatthe gitonic superelectrophile (228) may be involved in the cyclizationstep although it is unclear if it is a transition state in the conversion ora discrete high lying intermediate Some of the bis-oxonium ions lead tocleavage reactions (eq 79)

minus70degC

minusH2O

HO

HminusH+ minusH+OH OH

H

230

HO O

H

H H++ +

+

+ +

+ ++

(79)2334-Tetramethyl-24-pentanediol forms the oxonium dication 230 insuperacid and dehydration is followed by carbon- carbon bond cleavageAlthough such cleavage reactions can occur with monocationic oniumions in this case the cleavage reaction is likely an indication of the super-electrophilic nature of the dicationic intermediate(s)

Similar distonic superelectrophiles have been described as productsfrom the superacidic reactions of hydroxy ethers Olah and Sommer pre-pared and observed (by low temperature NMR) both 14- and 15-dioxo-nium dications (231234)79

H3CO

OH

H

H

231

+ +

232

H3CO O

H

CH3

HH

+ +

233

H3C OO

H

CH3 H

H

+

+

234

H3C OO

H

H

H

+

+


These species were prepared from the appropriate ethers in FSO3H-SbF5-SO2 solution at minus60C Like the protonated diols these oxonium dications(ie 235) were observed to undergo cleavage reactions leading to mono-cationic fragments or dehydration-rearrangement to give the oxonium ion236 (eq 80)

235

FSO3H-SbF5

minus60degC

H3CO

OH

CH3

minus10degC H3C CH3

OHCH3H3O

minus10degC

H3CO

H

CH3minusH+

236

~H

H3CO

OH

H

H CH3

+ ++

+

+H3C

OCH3

+

++

(80)Another interesting oxonium-based dication arises from p-methoxy-

benzene-diazonium ion in FSO3H-SbF5 solution (eq 81)80 Dication 237was observed by low-temperature 13C NMR spectroscopy Interestinglythe o-methoxybenzenediazonium ion does not form the oxonium dication238 (eq 82)

NN

O

CH3

FSO3H-SbF5

SO2ClF

minus75degC

237

+

NN

O

CH3

H

+

+2 X

minusXminus (81)

NN

OH3C

FSO3H-SbF5

SO2ClF

minus75degC

NN

OH3C H

238

+

+

+

2 Xminus

Xminus

(82)

presumably due to the proximity of the developing charge on the oxoniumand diazonium groups This may be an indication that oxonium-baseddications like 237 should be considered distonic superelectrophiles

A number of distonic halonium-based dications are also known andtheir properties are often superelectrophilic81 The chemistry of haloniumions was thoroughly reviewed thus only a few aspects are describedhere Alkylation of dihaloalkanes with methyl and ethyl szliguoroantimonate(CH3F-SbF5-SO2 and CH3CH2F-SbF5-SO2) gives the monoalkylatedhalonium ions andor the dialkylated dihalonium ions depending on thereaction conditions Iodine shows an unusual ability to stabilize positive


charge as seen in the formation of dialkyl alkylene diiodonium ions (239eq 83) Remarkably the dihalonium ion 239a has been prepared withonly a single methylene group separating the iodonium centers formallya gitonic superelectrophile However in the case of dibromoalkanes thedihalonium ion 240 is formed with three methylene groups separating thehalonium centers (eq 84)

I-(CH2)n-Iminus78degC

excessCH3F-SbF5

CH3-I-(CH2)n-I-CH3

239 a n = 1b n = 2c n = 3

d n = 4e n = 5f n = 6

+ +

(83)

Br Brminus78degC

excessCH3F-SbF5

Br BrCH3H3C

240+ + (84)

In contrast the 12-dibromoalkanes only give the monohalonium ions andcleavage products Dialkyl alkylenedichloronium ions were not observedIn the case of dialkyl alkylenedibromonium ions it is clear that charge-charge repulsive effects lead to a signiTHORNcant destabilization of the sys-tems having only two methylene groups between the bromonium groupswhen compared to the charge separated species 240 This may indicatethe superelectrophilic character of 240 and other related species Thedialkyl phenylenedihalonium ions exhibit similar trends81 For exampleall isomeric diiodobenzenes give the dihalonium ions 241243 and eventhe triiodonium ions (244) can be prepared p-Dibromobenzene can bedialkylated to give the dibromonium ion 245 however the reactions ofm- or o-dibromobenzene with excess alkylating agent only provides themonoalkylation products (246247)

241 242 243 244

I

I

CH3

H3C

IICH3H3C

I

I

CH3

CH3

IICH3H3C

ICH3

Br

Br

BrBr Br

Br

CH3CH3CH3

H3C

Br

I

CH3

H3C

245 246 247 248

+

+

+ + +

+

+ +

+

+ + +

+

+


Coloumbic repulsive effects are thought to destabilize the o- or m-dibro-monium ions Mixed dihalonium ions (248) have also been preparedAlkylarylchloronium ions however could not be prepared under theseconditions due to facile aromatic ring alkylation

In a related study bromoanisoles were reacted with excess CH3F-SbF5and the dicationic product 250 was only formed with p-bromoanisole82

NMR studies indicated that the dication is in equilibrium with the oxoniummonocation 249 (eq 85)

O

Br

CH3minus78degC

excessCH3F-SbF5

O

Br

CH3

CH3

H3C

O

Br

CH3

CH3

249 250

(10) (44)Ratio

+

+

+

(85)The isomeric o- or m-bromoanisole give only the oxonium monocationsPresumably dialkylation is inhibited by unfavorable charge-charge repul-sive effects in the m- or o-isomers

Interesting dihalonium ions have also been prepared from 14-dihalo-cubanes (251 eq 86)83 Both diiodo and dibromocubanes were dimethy-lated in excess CH3F-SbF5 to give the dihalonium ions (252ab) whichwere stable at minus70C 14-Dichlorocubane (251c) did not give the dihalo-nium ion 252c When the halocubanes (253a-c) were reacted with CH3F-SbF5 the corresponding halonium cubanes (254a-c) could not be obtainedas stable species (eq 87)

X

X

excessCH3F-SbF5

minus70degC

X

X

CH3

H3C251 a X = I

b X = Brc X = Cl

252 ab

+

+

(86)

XCH3F-SbF5

minus70degC

X CH3

253a X = Ib X = Brc X = Cl

254a-c

+

(87)

This unusual observation is explained with consideration of the super-electrophilic nature of the dihalonium ions (252ab) It is thought that thecubyl framework is stabilized by the pair of electron-withdrawing halo-nium groups while in the case of the monohalonium cubanes (254a-c)

REFERENCES 277

the cubyl framework does not have this stabilization In this same studycubyl diacyl and dicarboxonium dications were also prepared as well asa novel tetracarbocationic species

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(41) (a) J R Brooks D N Harcourt R D Waigh J Chem Soc Perkin Trans1 1973 2588 (b) H Takayama T Suzuki T Nomoto Chem Lett 1978865 (c) K R Gee P Barmettler M R Rhodes R N McBurney N LReddy L-Y Hu R E Cotter P N Hamilton E Weber J F W KeanaJ Med Chem 1993 36 1938 (d) D N Brooks D N Harcourt J ChemSoc (C) 1969 626

(42) (a) Y Zhang D A Klumpp Tetrahedron Lett 2002 43 6841 (b) D AKlumpp P J Kindelin A Li Tetrahedron Lett 2005 46 2931


(44) D A Klumpp A Li D J DeSchepper Abstract of Papers 232nd NationalMeeting of the American Chemical Society San Francisco CA September2006 American Chemical Society Washington DC 2006 Abstract ORGN561

(45) A Kleemann J Engel B Kutscher D Reichert Pharmaceutical Sub-stances 4th Ed Thieme Stuttgart 2001 p 308

(46) Y Zhang S A Aguirre D A Klumpp Tetrahedron Lett 2002 43 6837

(47) G A Olah M Calin J Am Chem Soc 1968 90 4672

(48) J W Larsen P A Bouis J Am Chem Soc 1975 97 6094



(51) A Wiles J Chem Soc 1953 996


(53) (a) D Bruck M Rabinovitz J Am Chem Soc 1977 99 240 (b) D BruckM Rabinovitz J Am Chem Soc 1976 98 1599

(54) G A Olah P W Westerman J Org Chem 1973 38 1986

(55) V Prakas Reddy G Rasul G K S Prakash G A Olah J Org Chem 2003 68 3507

(56) D A Klumpp M Garza A Jones S Mendoza J Org Chem 1999 646702


(57) (a) D A Klumpp G V Sanchez Jr Y Zhang S L Aguirre S de LeonJ Org Chem 2002 67 5028 (b) D A Klumpp S L Aguirre G VSanchez Jr S J de Leon Org Lett 2001 3 2781

(58) (a) D A Klumpp Y Zhang P J Kindelin S Lau Tetrahedron 2006 625915 (b) D A Klumpp A Jones S Lau S DeLeon M Garza Synthesis 2000 1117

(59) K Y Koltunov G K S Prakash G Rasul G A Olah J Org Chem 2002 67 4330

(60) G A Olah D L Brydon R D Porter J Org Chem 1970 35 317


(62) K Y Koltunov G K S Prakash G Rasul G A Olah Tetrahedron 200258 5423

(63) H Heaney in Comprehensive Organic Synthesis B M TrostI Fleming Eds Pergamon Press Oxford 1991 Vol 2 pp 733-750(a) G A Olah Friedel-Crafts and Related Reactions Wiley-InterscienceNew York 1964Vol 3 pp 1636

(64) G A Olah D J Donovan J Org Chem 1978 43 1743

(65) K Shudo Y Orihara T Ohta T Okamato J Am Chem Soc 1981 103943

(66) J Sommer P Rimmelin T Drakenberg J Am Chem Soc 1976 98 943

(67) G A Olah A T Ku J Org Chem 1970 35 3913


(69) G A Olah M B Comisarow J Am Chem Soc 1966 88 3313

(70) (a) Reference 69 (b) J O Knobloch F Ramirez J Org Chem 1970 401101

(71) R L Blankespoor M P Doyle D M Hedstrand W H TamblynD A V Dyke J Am Chem Soc 1981 103 3313

(72) V G Nenajdenko N E Shevchenko E S Balenkova J Org Chem 199863 2168

(73) V Boekelheide P H Anderson T A Hylton J Am Chem Soc 1974 961558


(75) (a) G S Lal G P Pez R G Syvret Chem Rev 1996 96 1737(b) P T Nyffeler S G Duron M D Burkart S P Vincent C-H WongAngew Chem Int Ed 2005 44 192 (c) T Shamma H Buchholz G KS Prakash G A Olah Isr J Chem 1999 39 1029

(76) A G Gilincinski G P Pez R G Syvret G S Lal J Fluorine Chem1992 59 157

(77) G A Olah J Sommer J Am Chem Soc 1968 90 927

REFERENCES 281


(79) G A Olah J Sommer J Am Chem Soc 1968 90 4323(80) K Laali G A Olah J Org Chem 1985 50 3006(81) G A Olah Y K Mo E G Melby H C Lin J Org Chem 1973 38

367(82) G A Olah E G Melby J Am Chem Soc 1973 95 4971(83) N J Head G Rasul A Mitra A Bashir-Heshemi G K S Praksh G A

Olah J Am Chem Soc 1995 117 12107

8SIGNIFICANCE AND OUTLOOK

The concept of superelectrophilic activation was THORNrst developed based onthe increasing trend of electrophilic reactivities observed in superacidicmedia1 Varied electrophiles showed signiTHORNcantly enhanced reactivitiesin superacids and were capable of reacting with extremely weak nucle-ophiles Many of the reported superelectrophiles have been generated instrong and superacidic media2 The need for a highly acidic media can beunderstood in terms of their low nucleophilicity and ability to protonate(or coordinate) available electron pair donor site(s) of the electrophilesdecreasing neighboring group participation with the electrophilic centerThis interaction with the acidic media leads to doubly electron-deTHORNcientactivated species or superelectrophiles Fully formed cationic specieshowever are the limiting case and superelectrophilic activation moreoften involves only partial proton transfer or weak coordination withLewis acids ie electrophilic solvation

Although superelectrophilic activation has been most often observedin superacid media examples have also been reported involving reactionsoccurring in less acidic environments including enzyme systems zeolitesetc as well as in the gas phase It has also been shown that onium chargecenters (ammonium phosphonium etc) can be involved in superelec-trophilic activation These considerations suggest that superelectrophilicactivation is a rather general phenomenon Berkessel and Thauer suggested


283

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284 SIGNIFICANCE AND OUTLOOK

for example that locally highly electron deTHORNcient environments could bepresent at enzyme active sites3 Moreover properly positioned acidicfunctional groups and Lewis acid sites may be able to participate in mul-tidentate interaction with substrates producing doubly electron-deTHORNcientsuperelectrophilic species Besides superelectrophilic activation in biolog-ical systems multidentate interaction may also be important in solid acidcatalyzed reactions involving for example NaTHORNon-H and H-ZSM-5 andtheir analogs4 Some solid acids are known to possess acidic sites clusteredtogether in close proximity In order to explain how these acids can some-times display remarkable activities for example allowing the catalytictransformations of extremely low nucleophilicity alkanes (even methane)it has been suggested by Olah that bi- and multidentate interactions canlead to superelectrophiles4 In other types of zeolites Corma noted thatcationic charges in the zeolite framework produce very high electrostaticTHORNelds (φFN) and THORNeld gradients (φFQ) in the channels and cavities5 Thismay also contribute to observed superelectrophilic activation

There is now considerable experimental and theoretical evidence tosupport the concept of superelectrophilic activation discussed throughoutour book Several types of superelectrophilic dicationic species have beenobserved in the condensed phase using spectroscopic techniques such aslow-temperature NMR Other superelectrophiles have been observed in thegas phase using mass spectrometric methods Kinetic studies have likewiseprovided evidence for various superelectrophiles in superacid-catalyzedreactions Superelectrophilic activation is also conTHORNrmed by varied obser-vations as trends of reactivity vs acidity electrophilic chemistry involv-ing extremely weak nucleophiles product studies isotopic exchange andstructure-activity relationships Calorimetric and kinetic studies have alsoprovided thermodynamic data by which superelectrophiles can be studiedTheoretical calculations have been particularly useful Many superelec-trophiles were shown to be kinetically stable gas-phase species often hav-ing considerable barriers to deprotonation or fragmentation reactions Bycomparing usual electrophiles with the corresponding superelectrophilescalculations have been able to correlate reactivity trends with molec-ular orbital energy levels and charge densities of the involved super-electrophiles Moreover thermodynamic activation parameters obtainedfrom ab initio calculations have been compared with kinetically deter-mined experimental values Good agreement between the calculated andexperimental data has been considered evidence for the involvementof superelectrophiles Theoretical calculations have also provided use-ful structural and spectral data allowing comparison with experimentallydetermined data

SIGNIFICANCE AND OUTLOOK 285

Superelectrophilic reactions have been shown to be particularly use-ful in various synthetic conversions particularly of unactivated σ andπ -bonds such as in alkanes and electron deTHORNcient arenes Superelec-trophiles have also been used in the synthesis of natural products andbiologically active compounds Superelectrophilic chemistry has alsofound varied applications in macromolecular chemistry and materialscience1317

Experimental and theoretical studies of superelectrophiles have revealedmany interesting structure-activity relationships Superelectrophilic acti-vation was shown to be a consequence of decreasing neighboring groupparticipation into electron deTHORNcient reactive cationic centers of the elec-trophilic reagent Decreasing neighboring group participation often leadsto enhanced reactivities as a consequence of the inductive electrostaticandor resonance effects of electron withdrawing substituents in the dou-bly electron-deTHORNcient species For de facto dicationic superelectrophiles(and higher polycations) coulombic repulsion has been shown to signif-icantly inszliguence the chemistry of these species Charge-charge separa-tion is an important driving force for such superelectrophilic reactionsOnium (ammonium pyridinium phosphonium etc) substituents particu-larly enhance the reactivities of adjacent electrophilic sites Similar acti-vating effects have been demonstrated in organometallic and catalyticsystems

SigniTHORNcant structure-activity relationships in superelectrophiles relateto the distance between charge centers To an approximation superelec-trophilic activation decreases with increasing separation of charge centersThis leads to the distinction between gitonic and distonic superelectro-philes the latter being characterized by three or more atoms separatingthe charge centers It was shown however that superelectrophilic acti-vation may also occur by suitable geometrical arrangement forcing thecharge centers into close proximity It has been suggested that superelec-trophilic activation in enzymatic systems may be accomplished by closelyoriented cationic charges6

Since the concept of superelectrophilic activation was proposed 30years ago there have been many varied superelectrophiles reported both inexperimental and theoretical studies Superelectrophiles can be involvedin both gas and condensed phase reactions ranging from interstellar spacedown to the active sites of certain enzymes Moreover synthetic conver-sions involving superelectrophiles are increasingly used in the synthesisof valuable products Superelectrophilic activation has also been useful inthe development of a number of new catalytic processes It is our beliefthat superelectrophilic chemistry will continue to play an increasing rolein both synthetic and mechanistic chemistry


REFERENCES

(1) G A Olah A Germain H C Lin D Forsyth J Am Chem Soc 197597 2928 G A Olah G K S Prakash M Barzaghi K LammertsmaP R Schleyer J Am Chem Soc 1986 108 1062 G A Olah G K SPrakash M Marcelli K Lammertsma J Phys Chem 1988 92 878G A Olah G K S Prakash K Lammertsma Res Chem Intermed 198912 14

(2) G A Olah D A Klumpp Acc Chem Res 2004 37 211(3) A Berkessel R K Thauer Angew Chem Int Ed Engl 1995 34 2247(4) G A Olah Angew Chem Int Ed Engl 1993 32 767(5) A Corma Chem Rev 1995 95 559(6) D A Klumpp R Rendy Y Zhang A Gomez A McElrea Org Lett 2004

6 1789

INDEX

ab initio calculationsestimated activation energies for

superelectrophilicelectrocyclizations 4748

of superelectrophilesenergies of LUMOs 49estimation of electronic chemical

potential 4950estimation of electrophilicity indexes

4950estimation of chemical hardness

4950estimation of NBO charges 49estimation of NMR chemical shifts

5052superelectrophilic isodesmic reactions

4849Aceanthrenequinone

condensation with deactivated arenes141142

diprotonated in superacid 141142superelectrophilic in polymer synthesis

142


Acenapthenequinonecondensation with benzene 141diprotonated in superacid 141

Acetic aciddiprotonated calculated NMR chemical

shifts 5152diprotonated calculated structure and

stability 212Acetoacetamide

condensation with benzene 199diprotonation 199200

Acetoacetic acid diprotonation and NMRstudy 199200

Acetone diprotonated 8688 157 seealso carboxonium ions

N-Acetonylpyridinium saltscondensation with benzene 205protonation in CF3SO3H 205

Acetyl cationelectrophilic solvation 154superelectrophilic

from AlCl3 154reactions with arenes 155

287

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288 INDEX

Acetylene dication (CHCH2+) structureand stability 132

N-Acetyl-4-piperidone diprotonation258

Acyl cationslong-lived 5monocationic 269superelectrophilic 153155

acetyl cation 153155from AlCl3 90from HF-BF3 86studied by theoretical methods

58pivaloyl cation from AlCl3 154propenoyl cation 219propionyl cation 249

N-Acyliminium salts superelectrophiliccalculated structures stabilities and

reactions 207208evidence for 207208in AlCl3 205206in CF3SO3H 207208reactions with weak nucleophiles

205208Acyl-transfer from amides 267Adamanta-13-diyl dication

attempted preparation 188calculated structure and relative

stability 18926-Adamantanedione diprotonation

25726-Adamantanediyl dication


stability 189Adipic acid 259Adrenaline formation of dication

224225Aliphatic 13-carbodication deprotonation

13Aliphatic diesters diprotonated

calorimetric studies 260NMR studies 260

Aliphatic glycolsdiprotonation in superacid 213superelectrophilic pinacolone

rearrangement 213Alkenyl N-heterocycles diprotonated

250251

Alkoxy alcoholsdiprotonated 214superelectrophilic pinacolone

rearrangement 214Alkylthioalkylation reaction with

deactivated arenes 1920Aminoacetals

forming ammonium-carbeniumdications 204 225226

forming 13-carboxonium-ammoniumdications 204

reactions with benzene 204α-Aminoacids

diprotonation in superacid 204triprotonation in superacid 204

Aminoalcoholsformation of dications in superacid 37

224observation of dications in

FSO3H-SbF5 37 224225reactions with arenes in CF3SO3H 37

224Aminobutyric acids diprotonation

cleavage to acyl-ammonium dications262263

NMR studies 2622635-Amino-1-naphthol diprotonation

calculated structures stabilities andproperties266

NMR studies 266reactions with weak nucleophiles 266

Ammoniaborene dication (NH3BH2+)structure and stability 129generation using charge stripping mass

spectroscopy 128129Ammonium group

activation of adjacent carboxoniumions 262268

activation of adjacent carbocations224

Ammonium-carbenium dicationsfrom aminoacetals 225from aminoalcohols 224from heterocycles 225

Aniline N-oxidesformation of geminal dications

111113reactions in superacid 111113

INDEX 289

p-Anisaldehyde diprotonationdecreased neighboring group

participation 268269NMR studies 268269

Aprotic superacids 9091Aromatic dications 12Aromatic diesters diprotonation 260Arsonium dications 272Aryldiazonium dications 1733-Arylindenones diprotonated in triszligic

acid 85Aspartic acid triprotonated 204Atomic charge (qi) 266Aza-polycyclic aromatic compounds

255Azonium ions long-lived 5

Benzaldehyde diprotonatedcalculated structures and stabilities


158160Benzene elimination 255Benzophenone cyanohydrin 226Benzopinacol reaction in superacid

134135Benzoquinone monooxime 268Benzoyl cation superelctrophilic

reactions with arenes 155Bicyclic hydrazinium ions

methods of preparation 169170structures 169

14-Bicyclo[222]octadiyl dication235236

Bi-dentate interactionwith hydrogen bonding catalysts 9394with solid acids 93

11prime-Binaphthalene-22prime-diyl dications241

Biological systems 9394 14815011prime-Biphenyl-22prime-diyl dications 24118-Bis(diarylmethyl)naphthalene dications

effects of charge-charge separation239240

preparation and study 239240Bis(13-dioxolanium) dications

calculated structures and stabilities261

NMR studies 260261

Bis(szliguroenyl) dication 1213Bis-acyl dications

observation by NMR 269270reactions with arenes 269270

11prime-Bisadamanta-33prime-diyl dication237

Bis-carboxonium ions diprotonated123-indanetrione 19913-indanedione 19924-pentanedione 198199

Bis-sulfonium dications 271Boron and aluminum-centered systems

128131Boron-based ions superelectrophilic

studied by theoretical methods71

p-Bromoanisole dialkylated 27623-Butanedione

condensation with benzene 140141diprotonation in CF3SO3H 140141monooxime diprotonation in CF3SO3H

143

Calorimetric studiesbis-acyl dications 270protonation of diesters 260protonation of diketones 257

Camphor 245β-Carbenium-acyl dications


generation in superacid 21813-Carbenium-cabonium dications

192Carbenium ions superelectrophilic


Carbenium-nitrilium dications226

13-Carbenium-oxonium dications213215

Carbocationscrystalline 78historical background 1long-lived 5

Carbon dioxideprotosolvated 163superelectrophilic from AlAlCl3

91

290 INDEX

Carbonic acid diprotonated 163Carbonium ions superelectrophilic


Carbonyl groupelectrophilic and protosolvation 5electrophilic strength 45LUMO 5protonation 4inductive effects of triszliguoro and

trichloromethyl groups 22see also carboxonium ions

α-Carbonyl nitromethanessuperelectrophilic reactions withbenzene 223224

Carbonylation of dimethyl ether 116Carborane anions 78Carboxonium ions

activating adjacent electrophilic sites247

long-lived 5silylated 8superelectrophiles 156164superelectrophilic

diprotonated acetaldehyde 157diprotonated acetone 157from FSO3H-SbF5 8687from HF-BF3 8688generated in triszligic acid 8283hydride abstraction 157observation of by NMR 3738piperidones 205 262pivaldehyde 8 214215promoting rearrangments 160163studied by theoretical methods

5358Carboxonium-carbenium 13-dications

194198Carboxonium-vinyl dication 197198Carboxylation

of alkyl groups 243244superelectrophilic with CO2 from

AlCl3 91Carboxylic acids diprotonated 8889

211212CCl22+

reaction with Cl2 45structure and stability 109

CF22+

gas phase reactions 45 109structure and stability 109

CF32+ ion gas phase formation andreactions 167168

C-H σ -bond protonation from HF-SbF589

CH2XH2+ (X = F Cl Br I) dications167

Chalcone diprotonation in superacid195

Charge-charge separationeffect on amino acid ionization 204effecting heats of protonation 257effecting pKR+ values 238239effecting relative stabilities 251253in 18-Bis(diarylmethyl)naphthalene

dications 238239in charge migration reactions

aza-polycyclic aromatic compounds254255

butorphanol 254structural effects 254255

in the Nazarov reaction transition state106

in oxyfunctionalizations 245246in remote functionalization 244in retropinacol rearrangements 161isomerization of 14-dialkyl-1

4-cyclohexyl dications 234isomerization of 15-manxyl dication

234235Chiral dications


from 2-oxazolines 224from aminoalcohols 224redox behavior 241

N-Chlorosuccinimide diprotonated fromH2O-BF3 9192

Cinnamic acidsdiprotonation observation by NMR


Cobalt-stabilized propargyl cationselectrophilicities 2

Coulombic explosion 43Coulombic repulsive effects

alkylation of bromoanisole 276

INDEX 291

alkylation of dihaloalkanes anddihaloarenes 275

ionization of dicarboxylic acid szliguorides270

protonation of o-methoxybenzene-diazonium ion 274

tris(13-dioxolanium) trication262

Cryoscopic experiments 222 258Cyclizations superelectrophilic


cyclodehydration 2526 15715812-ethylenedications

ab initio calculations cyclizationenergetics 137

cyclization kinetics andthermodynamics 136

cyclizations to szliguorene products134139

cyclizations to phenanthreneproducts 134139

Grewe cyclization 249259Houben-Hoesch reaction 2627

8283 146indanones 195196Nazarov reaction 25 48 106 157158Pictet-Spengler reaction 2829 8283

147tetralones 246248

Cyclodehydration of13-diphenyl-1-propanone

kinetic studies 2526pKBH+ 26activation parameters 158evidence for superelectrophiles

157158use of CF3SO3H 2526

14-Cyclohexanedione diprotonation257

Cyclohexenonediprotonated in HF-SbF5 194isomerization in superacid 194

Cyclopropyl-stabilized 13-carbodicationcalculated and experimental NMR data

189190method of preparation 189

13-Dehydro-57-adamantane dication1213

Diacetylbenzenes diprotonation 257Diadamanta-49-diyl dication 237Dialkylhalonium ions

formation of geminal superelectrophiles119121

superelectrophilicevidence for 120in the alkylation of arenes 119structures and stabilities 120

22-Diaryl-13-indanedionessuperelectrophilic rearrangement162163

Diazenes dialkylation 170Diazenium dications methods of

preparation 171Diazoles dialkylation 170Diazomethane

diprotonation 172formation of methyldiazonium dication

172Diazonium dications


diprotonated diazomethane 172diprotonated dinitrogen (N2H2

2+) 172Dibromonium dications 27512-Dicarbonyl compounds formation of

superelectrophiles 140143Dicarboxylic acid szliguorides reactions to

bis-acyl dications 269270Dicarboxylic acids diprotonation

cleavage to acyl cations 258259cryoscopic studies 258NMR studies 258259

Dicationic carbon dioxide (CO22+)

formed in the gas phase 163reactions with H2 164

24-Dichloro-24-dimethylpentaneionization in superacid 188

14-Dihalocubanes formation ofdihalonium ions 276

Dihalogen dications (HXXH2+ X = ClBr) 178

Dihydro[5]helicene dication 242Diiodonium dications 275Diketones diprotonation 140143 257Dimethyl oxonium ion

carbonylation 116superelectrophilic 115116

292 INDEX

Dimethylbromonium ion protosolvationstructures and stabilities 121 167

Dimethylperoxidealkylation 175176formation of a vicinal dication

calculated structure and stability176

DimethylsulfoxideNMR studies from superacid 177178protonation and diprotonation


GIAO-MP2 NMR data 177178Diols diprotonated 27227313-Dioxane superacidic ring opening

213Diprotonated

acetaldehyde 157acetone 157ammonia (NH5

2+)analogous gold complex 111calculated structure and stability

110111from gas phase reaction 110111

butane (C4H122+) calculated structures

and stabilities 242243formaldehyde (CH2OH2

2+)calculated structure and stability 157observation in gas phase 157reaction with isoalkanes 157

hydrogen sulTHORNde (H4S2+)analogous gold complex 118calculated structure and stability 117evidence for its formation 117

iminesevidence for 147superelectrophilic cyclizations

147148methane (CH6

2+)analogous gold complex 108calculated structure and stability 108

methyl halides calculated structures andstabilities 121

nitriles 145propane (C3H10

2+) calculatedstructures and stabilities 192193

αβ-unsaturated ketones 194195water (H4O2+)

analogous gold complex 114115

calculated NBO charges 105106calculated NMR chemical shifts

5152evidence for its formation 113114calculated structure and stability

114Distonic superelectrophiles

14-carbodications 233234acyl-carbenium dications 248249acyl-carbonium dications 248249ammonium-carboxonium dications

262268aryl-stabilzed carbodications 237238bis-carbonium dications 242243bis-carboxonium dications 257262bis-oxonium dications 272274carbenium-carbonium dications 243carbo-ammonium dications 249256carbodicationic systems 232243carbo-halonium dications 256carbo-phosphonium dications 256carboxonium-carbenium dications 244

246247carboxonium-carbonium dications 244cyclopropyl-stabilzed 233234dihalonium dications 274276structural requirements 231232sulfur-based dications 270271

Disulfonium dicationsmethods of preparation 176177reactions 176177

Dithiocarbenium ions electrophilicities 2

Electrocyclizationα-(methoxycarbonyl)diarylmethanol

NMR observation ofsuperelectrophiles 4041

kinetic studies 136137effects of acidity 3031

Electron transfer involving HCX2+ ions(X = F Cl Br I) 109

Electrophile strength 25Electrophiles historical background 1Electrophilic activation involving

phosphonium 208Electrophilic solvation 11 283Electrophilicity 23Enones

Superelectrophilic

INDEX 293

3-arylindenones diprotonated intriszligic acid 85 194

chalcone 195cyclohexenone 194from AlCl3 91from HUSY zeolite 92mestityl oxide 194

Ester cleavageAac1 209superelectrophilic

evidence for superelectrophiles209210

need for low temperatures 99NMR studies 209210

Esters diprotonatedcalculated structures and stabilities

210reactions with arenes 211

Ethane dication (CH3CH32+) structure

and stability 132Ethylacetoacetate diprotonation and NMR

study 199200Ethylene dication (CH2CH2

2+)formation in gas phase 131132halogenated derivatives 132hyperconjugation 126calculated structure and stability

13113212-Ethylenedications




cyclizations to phenanthrene products135139

evidence for in szliguorene cyclization139

observation by NMR 136Ethylene glycol diprotonated 214Ethyleniminium protonated calculated

structures and stabilities 146147Ethynyl pyridines diprotonated 250251

Fluorooxonium dications (FOH32+ and

F2OH22+) 114

Fluorosulfonic acid (FSO3H) use informing superelectrophiles 85

Formic acid diprotonated calculatedstructure and stability 212

Formyl cationGatterman-Koch formylation 151superelectrophilic


evidence for 151153from HF-BF3 88from CF3SO3H 84reaction with adamantane 23reactions with isoalkanes 22 151

Freidel-Crafts acylationreactions of deactivated arenes 21superelectrophilic acetyl and benzoyl

ions 33involvement of diprotonated esters

211use of amide derivatives 267

Gatterman reactionevidence for superelectrophiles 145pKBH+ of hydrogen cyanide 32use of CF3SO3H-SbF5 8283use of superacids 32

Gitionic superelectrophiles13-carbodications 187193carbon-carbon vicinal systems 131144carbon-halogen vicinal systems

164168carbon-nitrogen vicinal systems

145151carbon-oxygen vicinal systems

151164carboxonium-centered 13-dications

193212geminal

azodications 110113carbodications 108110delocalization of charge 105106halodications 119121oxo and sulfodications 113119structural considerations 105107

halogen-centered vicinal-dications178179

nitrogen-centered vicinal systems168175

noble gas-centered vicinal systems179180

294 INDEX

Gitionic superelectrophiles (contd)oxygen and sulfur-centered vicinal

dications 175178vicinal structural considerations

125128Glutamic acid triprotonated 204Glutaric acid 259Grewe cyclization 249250Guanidinium ion protonated dication

148

H2O-BF3 use in formingsuperelectrophiles 9192

H4Se2+ dication analogous gold complex118

H4Te2+ dication 118H5S3+

calculatedNBO charges 106structure and stability 119

analogous gold complexes 119Halocarbonyl cations superelectrophilic

155156Halogenation superelectrophilic

N-halosuccinimides 201Halonium ions superelectrophilic

(H3X2+) calculated structures andstabilities 120121

Halonium ionslong-lived 5superelectrophilic studied by theoretical

methods 7274N-Halosuccinimides

superelectrophiliccalculated structures stabilitiesand

reactions 201203reactions with deactivated arenes

201203Hammett acidity scale 6Hammett equation 2HCX2+ ions (X = F Cl Br I)

gas phase reactions 108109calculated structures and stabilities

108109Heliomethonium dication (CH4He2+) 180Helium dimer dication He2

2+ 12N-Heteroaromatic compounds

diprotonation 20520625-Hexanedione diprotonation 257

HF-BF3 use in formingsuperelectrophiles 8688

HF-SbF5 use in formingsuperelectrophiles 8889

Houben-Hoesch reactioninvolving diprotonated nitriles 146superelectrophilic

kinetic studies 2627use of CF3SO3H-SbF5 8283

HUSY zeolite use in formingsuperelectrophiles 9293

Hydrazinium dicationsmethods of generation 168170inductive effects 126127

Hydrazoic acid diprotonated (H2N3H2+)172

Hydride transfer from alkanes orcycloalkanes

to diprotonated naphthols 9192to superelectrophilic

acetyl ion 89carboxonium ions 8687 157trihalomethyl cations 164166

Hydrogen peroxide studies of protonatedproducts 175

Hydroxyalkylation222-triszliguoroacetophenone 5acetophenone 5superelectrophilic

N-acetonylpyridinium salts 205N-acetyl-4-piperidone 25823-butanedione 31carboxonium ions 38diprotonated acetoacetamide 199isatin 20parabanic acid 20 2034-piperidones 205 262phosphonium-substituted ketones 208reactions involving deactivated

arenes 2021use of low temperature 98with chloral 2122

Hydroxyanilinesformation of geminal dications


Hydroxycarboxylic acids diprotonation268

Hydroxyethers diprotonation 273274

INDEX 295

Hydroxyquinolinesdiprotonation

calculated structures stabilities andproperties 264266

ionic hydrogenation 264265LUMO energies 264265reactions with arenes 264265

superelectrophiles from AlCl3 264Hyperconjugation ethylene dication 126Hypercoordinate ions superelectrophilic

studied by theoretical methods 63

Imines diprotonatedfrom CF3SO3H 8283reactions of 2829

Iminium ions electrophilicities 2Indenones diprotonated 85 194195Inductive effects szliguorine-substitution 5Infrared and Ramen spectroscopy use in

the study of superelectrophiles4142

Iodination of alkanes and cycloalkanes atlow temperature 9697

Ionic hydrogenationhydroxyquinolines 3839 2642651-naphthol 2485-Amino-1-naphthol 266carbonic acid 163methanol 116

Isatin superelectrophiliccondensation with arenes 142143polymer formation 142143

Isoformyl cation 151Isopentenoyl cation protonation

calculated structures and properties219

Isopropyleniminium protonatedcalculated structures and stabilities147

Isoxazolidines formation of dications216

Ketoacidsdiprotonation

cleavage to acyl-carboxoniumdications 257258

NMR studies 257258α-ketoacids

condensation with benzene 140141

diprotonated 140α-Ketoesters diprotonated 140Kinetic studies

estimating nucleophilicities andelectrophilicities 23

use of NMR 40cyclodehydration 157158Nazarov reaction 157158Houben-Hoesch reactions 146Pictet-Spengler reaction 2728 147stereomutation role of

superelectrophile 27Koch-Haaf carbonylation

superelectrophilic effect oftemperature 9798

Lactic aciddiprotonation 213formation of lactide in superacid 213

β-Lactone ring opening viasuperelectrophile 210

Lewis acids electrophilic solvation 90Linear free-energy relationships 23Lysine triprotonated 204

Magic acid (FSO3H-SbF5)

use in stable ion conditions for NMR86

acidity range 6Malonic acid diprotonation and NMR

study 201Malonyl szliguoride

preparation of the diacyl dication 217reaction with SbF5 217

Mass-spectroscopycharge stripping 42electron ionization 42electrospray ionization 43photoionization 42observation of protoacetyl dication 44

155observation of protoformyl dication 153observation of protonitonium dication

4344Mesityl oxide

diprotonatedobservation by NMR 194reaction with cyclohexane 194

296 INDEX

Mesityl oxide (contd)superelectrophile AlCl3 electrophilic

solvation 194Metal-free dehydrogenase enzyme 9394

model studies related to 148150Metallocene catalysts 7Methane

dicationic ions from mass spectrometry108

diprotonation 108triprotonation 108

Methanolreactions in superacid 115116self-condensation 116117

Methionine triprotonated 204Methyl acetate

protonation and reaction in superacid209210

synthesis from dimethyl ether 1189-Methyl-9-szliguorenyl cation protonation

191Methyl halides diprotonation

calculated structures and stabilities 121167

NBO charges 167Methyl oxonium ion (CH3OH2

2+)formation of geminal superelectrophile

115superelectrophilic

alkylation of arenes 115reaction with hydrogen 115

Methyleniminium ion protonatedcalculated structures and stabilities

146observation in gas phase 146

Multi-dentate interactionwith hydrogen bonding catalysts 9394with solid acids 93

Multiply-charged ions fragmentation andrearrangements 1213

NaTHORNon-H use in formingsuperelectrophiles 92

Naphtholsdiprotonated

from AlCl3 9192from HF-SbF5 89reactions with weak nucleophiles 248

2-Naphthol

protonation and electrophilicsolvation 195

superelectrophilic ionichydrogenation 195

Naphthyl ethers diprotonation 195Nazarov reaction

in superacid 157158superelectrophilic

ab initio calculations 48delocalization of charge 106kinetic studies 25 157158use of low temperature 98

use of CF3SO3H 25Neighboring group participation

decreasingin superelectrophilic activation 4 10

283in enzymatic activation 24shown by NMR 238inszliguencing rotational barriers 268

NH32+ dication structure and stability111

Ninhydrincondensation with arenes 162163superelectrophilic rearrangement

162163Nitration

reactivities with deactivated arenes1819 173174

superelectrophilic reactions 173174superelectrophilic use of low

temperature 98Nitriles diprotonated 2627Nitrilium ions protonation to form

superelectrophiles 145Nitroethylene

diprotonatedevidence for 220reaction with benzene 220

reaction in CF3SO3H 35Nitrogen-based ions superelectrophilic


Nitronic acidsdiprotonation 223reactions with arenes 223

Nitronium ionprotosolvation 174

INDEX 297


superelectrophilic17O NMR study 175calculated structures and stability

175electrophillic solvation with AlCl3

173174formation in superacids 173174from szliguorosulfonic acid 85from triszligatoboric acid 84from CF3SO3H 8283study by infrared and Ramen

spectroscopy 41with AlCl3 90

long-lived 5reactions with alkanes 9

2-Nitropropene diprotonated reactionwith benzene 220

Nitrosobenzene formation of geminaldication 113

β-Nitrostyrene reaction in CF3SO3H3536

Nitro-substituted benzenes diprotonationNMR studies 222223reactions with benzene 222223

Nitro-substituted naphthalenesdiprotonation in superacid NMR

studies 3536reaction in CF3SO3H 3536

Nitro-substituted oleTHORNnsdiprotonation in superacid NMR

studies 3536 222reactions with benzene 220222superelectrophiles from CF3SO3H

8283NMR

necessity of low temperature for studiesof superelectrophiles 99101

use in the study of superelectrophiles3440

Noble gas clusters 44 179Nucleophiles

historical background 1strength 25

Nucleophilicity 23

OleTHORNnic aminesdiprotonated 250

reactions with arenes 250Oleum (H2SO4-SO3) use in forming

superelectrophiles 82Organosulfurane (IV) dications

118Oxalic acid diprotonated 140Oxalyl chloride

attempted preparation of the oxalyldication 216217

reaction with SbF5 216217Oxalyl dication (+OCCO+) calculated

structure and stability 216217Oxamide dication 142Oxazolines

diprotonation 215reaction with arenes 215ring opening to distonic

superelectrophiles 215Oxonium ions

long-lived 5superelectrophilic

from FSO3H-SbF5 8687from HF-BF3 88from HF-SbF5 8889from triszligatoboric acid 8485studied by theoretical methods

5859see also diprotonated water

trialkyloxonium salts (Meerwein saltsR3O+Xminus)

formation of geminalsuperelectrophiles 115

superelectrophilic alkylation ofarenes 115

Oxyfunctionalization 245246Ozone reactions in superacid 176

246

Pagodane dication 1213Parabanic acid superacid promoted

reactions with arenes 203Phenalenone 190Phenylenediyl dications pKR+ values

23922prime-p-Phenylene-di-2-propanol ionization

to superelectrophile 2383-Phenylpropynoic acid diprotonation

197198Phosphonium dications 272

298 INDEX

Phosphonium ions superelectrophilicstudied by theoretical methods 69

Phosphonium-carboxonium dications 208Phthalic acid 259Pictet-Spengler reaction kinetic study and

role of superelectrophiles 27Pimelic acid 259Pinacolone rearrangement 213Piperidones

condensation with benzene 205diprotonated 2054-piperidone 262

Pivaldehydediprotonated 88superelectrophilic rearrangement


conditions 214215Pivaloyl cation superelectrophilic from

AlCl3 154pKR+ value deTHORNnition 3p-Methoxybenzene-diazonium ion

protonation 274Pnictogenocarbenium ions (CH2XH2+

X = P As Sb)calculated isodesmic reactions of

superelectrophiles 151protonation 150151

Polycyclic aromatic hydrocarbonssuperelectrophilic gas phase route4546

Polymer catalysts 78Polymer polycarbonate and bisphenols 4Polymer synthesis 28513-Propanediol

diprotonation NMR studies 272273diprotonation rearrangement to

propanal 272273Propenoyl cation protonation calculated

structures and properties 219Propionyl cation

evidence for acyl-carbonium dication249

protosolvated calculated structures andstabilities 249

Protio-adamantyl dications (C10H162+)


Proto-tert-butyl cation

evidence for 144NBO charges 125126

Protoacetyl dication (CH3COH2+)calculated NMR chemical shifts 5152from HF-BF3 153154gas phase observation 44 155generation in the gas phase 155isodesmic reaction 4849reaction isobutane 153154

Protoformyl dication (HCOH2+)generation in the gas phase 153

Protonated iminium dications 146147Protonitronium dication (HONO2+)

calculated NMR chemical shifts 5152calculated structure and stability 175gas phase observation 4344generation in the gas phase 175

Protosolvatedalkylcarbenium ions 143144alkylcarbenium ions leading to

13-carbodications 191192tert-butyl cation 1442-propyl cation 144

Protosolvationacetyl cation 810 153154activated complex 128nitronium salts 910

Pyruvic acidcleavage to acetyl cation in superacid

218diprotonated 218

Quantum mechanical Coulmobic repulsionenergy 106

2-Quinolinol superelectrophilic ionichydrogenation 197

Rare gas clusters 4344Retropinacol rearrangement

calculated energetics 161promoted by superacids 160161reactions in CF3SO3H 2930superelectrophillic 2930

Selectszliguor 271272Silicenium ions 8Solid acids use in forming

superelectrophiles 9293

trade

INDEX 299

Stannyl cation 78Stereomutation kinetic study and role of

superelectrophile 27Steroid chemistry 245Succinic acid 259Succinic anhydride diprotonation

equilibrium with acyl-carboxoniumdication 201

NMR study 201Sulfonium ions long-lived 5Sulfonium ions

superelectrophilicfrom FSO3H-SbF5 8687studied by theoretical methods

6971Sulfuric acid use in forming

superelectrophiles 82Superacidic media 56 283Superacids

Broslashnsted deTHORNnition 6CF3SO3H-SbF5 acidity range 6FSO3H-SbF5 acidity range 6HF-BF3 acidity range 6HF-SbF5 acidity range 6H2SO4-SO3 acidity range 6nucleophilicity of 56properties 56

Superelectrophilic activationeffect on LUMO 93historical background 8in acyl-transfer 267

Superelectrophilescalculational methods and studies

4674chemical hardness 4950classes and categories 1011effecting equilibria 128electronic chemical potential 4950electrophilicity index 4950enzyme system 2324 148150experiments requiring of low

temperatures 95100from reactions with Lewis acids 9092gas-phase studies 4246in situ generation 81kinetic studies 2433necessity for elevated temperatures

9596partial protonation 107

reactions in the gas phase 4446reactivities

with alkanes or alkyl groups 2223with deactivated arenes 1819with hydrogen 2324proTHORNles 1824

spectroscopic studies 3342Wheland intermediates 190

Terephthaloyl szliguorides reactions tobis-acyl dications 270

Terpene chemistry 244245tert-Butyl cation protosolvation from

HF-SbF5 89Tetraaryl-12-ethylene dications

charge delocalization 125126chiral derivatives 132134NMR study 34X-ray crystallography 34

Tetrahydropyridinesdiprotonation 225reactions with arenes 225 250

Tetrakis(dimethylamino)ethylene dicationmethods of preparation 143structure 143

Tetrakis-(p-dimethylaminophenyl)-ethylenedication

methods of preparation 134structure 134

Tetralones 246248Tetramethylammonium ion

calculated structures and stabilities ofprotonated dications 168

protosolvation in superacid 168Tetramethylhexathiaadamantane 235Tetramethylhydrazine formation of the

hydrazinium dication 1692334-Tetramethyl-24-pentanediol

ionization in superacid 188Tetranisylethylene dication

chemistry of 133methods of preparation 13213313C NMR 134

Tetraphenylethylene dicationcyclization 134135methods of generation 134135reaction in superacid 134135

Theoretical calculations kinetic stabilityof superelectrophiles 11

300 INDEX

Thioalkylcarbenium ionsuperelectrophilic reactions 1920superelectrophilic from AlCl3 91

Thiourea diprotonated study by infraredand Ramen spectroscopy 42

Tri(p-nitrophenylmethyl)cation pKR+value 3

Trialkyloxonium salts (Meerwein saltsR3O+Xminus)


superelectrophilic alkylation of arenes115

Trialkylselenonium salts (R3Se+Xminus)

alkylation of arenes 118formation of geminal superelectrophiles

118Trialkylsulfonium salts (R3S+Xminus)


118Trialkyltelluronium salts (R3Te+Xminus)


118Trications one-carbon 110Triszligatoboric acid (2 CF3SO3H-B

(O3SCF3)3) use in formingsuperelectrophiles 8485 115

Triszligic acid (CF3SO3H)use in forming superelectrophiles

8283with CF3CO2H use in kinetic studies

85with SbF5 use in forming

superelectrophiles 8284Triszligic anhydride use with triszligic acid

82Triszliguoroacetic acid

protosolvated 211diprotonated


cleavage reactions 211212Trihalomethyl cations

protosolvation from HF-SbF5 89superelectrophilic


effect of temperature 9697evidence for 164166from AlCl3 and AlBr3 91isodesmic reactions 166reactions with alkanes and alkyl

groups 164166Trihydrobromonium ion (H3Br2+)

formation in superacid 121Trimethylene methane dication 190Triphenylmethyl cation

historical background 1pKR+ value 3reaction with superelectrophilic

nitronium ion 19Triprotonated hydrogen sulTHORNde (H5S3+)

analogous gold complex 119structure and stabibility 119

Triprotonated methane (CH73+)


Triprotonated water (H5O3+) 119Tris(13-dioxolanium) trication 261262Trivalent dicationic nitrogen species

(R3N2+) in superacid reactions111113

Tscherniac amidomethylationsuperelectrophilic 207

Two-electron three center bonding 108

Unsaturated amidesdiprotonated

from HUSY zeolite 92from NaTHORNon-H 92reactions with arenes 197

superelectrophilic from AlCl3 91Unsaturated carboxylic acids

diprotonation 246247reactions with arenes 246247see also cinnamic acid

Unstable 13-carbodications 188UV-visible spectroscopy use in the study

of superelectrophiles 4041

Varying degree of protonation ofsuperelectrophiles 27 127

Vicinal superelectrophiles seesuperelectrophiles

Vinyl dications 250251

INDEX 301

Wallach rearrangement involvement ofaryldiazonium dications 172173

Weakly coordinating anions 78

Xenon diszliguoride 179X-ray crystal structure

tetraarylethylene dications 3418-Bis(diarylmethyl)naphthalene

dications 238239

tetrakis(dimethylamino)ethylenedication 143

Zeolites electrostatic THORNelds 284Zucker-Hammett Hypothesis applied to


Cover Page

Title SUPERELECTROPHILES AND THEIR CHEMISTRY

ISBN 0470049618

CONTENTS

Preface

1 General Aspects

2 Study of Superelectrophiles

3 Generating Superelectrophiles

4 Gitonic Geminal Superelectrophiles

5 Gitonic Vicinal Superelectrophiles

6 Gitonic 13-Superelectrophiles

7 Distonic Superelectrophiles

8 Significance and Outlook

Index



GEORGE A OLAH

DOUGLAS A KLUMPP

WILEY-INTERSCIENCE













QD27135E54043 2007547prime2dc22

2007019597


10 9 8 7 6 5 4 3 2 1

CONTENTS

Preface vii

1 General Aspects 1








Index 287

v

PREFACE



vii

viii PREFACE



1GENERAL ASPECTS




1

copy

2 GENERAL ASPECTS



OH

OX

1




log k(20C) = s(N + E) (2)


GENERAL ASPECTS 3

MeO

CO2Me

CO2Me

Me2N

CN

CN

(OC)3Fe

MeOOMe

minus25

minus20

minus15

minus10

minus5

0

5

10

N O

tBu

tBu

E

252015minus10 minus5 0 5 10

Me MeO

Me

Me

Me NO2

OSiMe3N

O

O

OSiMe3MeMe

N




Me3C+

+

+

+

+

minusminus






4 GENERAL ASPECTS


H3CC

CH3

O

CH3Li +CH3

C CH3

OLi

H3C

dminus

d+ (3)

H3CC

CH3

O

CH3OH +

CH3

C OCH3

OH

H3C

H+

+ (4)


PhCHO+2

N(CH3)2

N(CH3)2

N(CH3)2

HCl

H

leucomalachitegreen

(5)

OH2

H3C+ C

CH3

O H2SO4

H3C CH3

OHHO


bisphenol A(6)


GENERAL ASPECTS 5


O

CH3

CF3SO3H

C6H6


2

OH

CH3

+

(7)

O

CF3

CF3SO3H

C6H6

OH

CF3 F3C

C6H5

C6H5

C6H5minusH2O

3

C6H6 C6H6

+

(8)



6 GENERAL ASPECTS

H3CC

CH3 +minus

F CH3SbF5

H3CC

CH3

CH3

SbF6(9)

CH3

OH FSO3H-SbF5CH3

+

minus[FSO3-(SbF5)n]

(10)





H2SO4

SO3(50)

HSO3FSbF5

(50)

Magic Acid(90)

CF3SO3HSbF5

(10)

HF (7)BF3

HFSbF5

(2)(50)

10 15 20 25 30

10 15 20 25 30(minusH0)

(minusH0)


GENERAL ASPECTS 7







8 GENERAL ASPECTS


CH2Cl2minus30degC

minusCH4


Sn Snn-Bu

n-Bun-Bu

n-Bun-Bu

n-Bu+


[CB11(CH3)12]minus

(12)

ArSi

ArAr

Ar = mesityl


ArSi

Ar

Ar

[CHB11(CH3)5Br6]

+

minus

(13)

PhC

CH3

+ minusO

(CH3CH2)3SiH

(C6H5)3C B(C6F5)4

minus78degC

PhC

CH3

OSi(CH2CH3)3

B(C6F5)4

(C6H5)3CH

4

+

minus+ (14)



GENERAL ASPECTS 9

CO

H3C OHC

CH3

CH3CH3HC

O

CH3

H+

COH

CH3

CCH3

CH3CH3H

COH

H3CC

H3C

CH3

CH3H

NO REACTION

ISOBUTANE

HFBF3CO

CH3

5

COH

H3CC

CH3

CH3CH3

H

2+

6


CO

CH3

CO

CH3

CO

CH3

H Ad+

COH

CH3

57

+

+

+

+

+

+

+

+ +

+

+




+BF4minus or NO2

+PF6




8

CH4 + NO2H2+ CH

HH

NO2H

H2+

8minusH+ CH3NO2H+

+ + + +

(15)


10 GENERAL ASPECTS







N

HO

CH3

OH

OH

OH

Ph

OON

N

F

CH2Cl+

+

++

+

+

++

H CCH3

CH3

CH3

OH2+

+

O

OH2

Ph

PhO OH

H3C Br CH3

H

2+

N+ +

+

+

GENERAL ASPECTS 11




O OH+ +

+

OH2

9

H+H+

(16)

12 GENERAL ASPECTS

N

O

HH+ H+

HN

O

H

10

+ HN

OH

H+

+

(17)






Ph

PhPh

Ph

2+

11

2+

12

2+

13




GENERAL ASPECTS 13


Dications

2+

CH3

CH3H3C

H3C

H3C CCH3

2+2+

2+

16

18

14 15

19

17

Higher Cations

Ph Ph

Ph

PhPh Ph

Ph

Ph

20

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

21

R

R R

R

R

R

22 23

+ ++

+

+

+

+

+

++

+ ++

+

+ +


ClCl

SbF5

SO2ClFminus78degC

+

+

24

(18)

27

Cl + ++

Cl

25 26

SbF5

SO2ClFminus78degC

(19)

OHOH ++

HO

28

SbF5

HSO3F

SO2ClFminus78degC

+

(20)

14 GENERAL ASPECTS


REFERENCES










REFERENCES 15


















16 GENERAL ASPECTS









21 INTRODUCTION



17

copy






+PF6minus) in




NO2O2N

+ NO2BF4

FSO3HNO2O2N

NO2

150degC

62

(1)


F

+ HNO3


F

25degC

89

FF

FF

F

F

F(2)




Ph

PhNO2

2) H2O

BF4minus

OH

H2OndashBF3

Et3SiH

Ph

PhNO2

H

64

+ (3)


NO O NO O NO OHH A

31 2

d++ + + +





SR1

R2

R3

SR1

R2

R3

AlCl3

SR1

R2

R3

AlCl3

4

dminus

d++ ++ (4)

Cl SCH3


SCH3

87(5)


N

N

O

O

OH

H CF3SO3H

C6H5Cl

65

N

NO

OH

H

Cl

Cl

(6)

N

O

O

H

CF3SO3H

C6H5Cl

NO

H

ClCl

99

(7)




N O

H

CF3SO3H

C6H5NO2N OH

H

H N

HNO2

O2N10

5

+ +(8)

CH3

O

CF3SO3H

C6H6


6

CH3

OH+

(9)

NCH3

O

CF3SO3H

C6H6

NCH3

OHHN

CH3

Ph Ph

93

7

++

(10)

OCH3

O

CF3SO3H

C6H5NO2OCH3

OH

H

O

NO2

8

82

+

+

(11)




CCF3

O

CF3SO3H

C6H6

CCF3

OH

CF3

Ph Ph+

(12)

HC

CCl3

O H2SO4

CCCl3H

C6H5Cl

Cl Cl

HC

CCl3

OH+

(13)



CCH3

CH3CH3H

CO

H

COH

HC

CH3

CH3CH3

H

HFBF3

CO

H9

COH+

H 2+

CCH3

CH3CH3

COH

HminusH+

minusH+

minusH+

H+

C

CH3

CH3CH3

COH2

HC

H3C CH3CH3

COH2

HCH3C

CH3

CH3

COH

HCH3C

CH3

CH3

CO

H

10

91

+ +

+

+

+

+

+

++

Scheme 1



H


H E

2) H2O

+

E+ = HCO+ or HCOH2+

CHO

minus2H+

(14)



11 12

HN

NH

N

NHs

O

H2N

CH3

CH3

H

Hr

H2

ENZYMEHN

NH

N

NH

O

H2N

CH3

CH3

H

H

A

+

++ H+

(15)

CH3

H3C CH3H2

CH3

H3C CH3

HH

13CH3

H3C CH3

H

H

++

+

+ +

(16)


H2

NN

N

H

14

H+

+N

NN

+ +(17)



23 KINETIC STUDIES


N

NH

ring

ring

H3C R

HH

Protonation

N

NH

ring

ring

H3C R

HH

H

11

H2

N

N H

ringring

H3CR

HH

++


KINETIC STUDIES 25


Ph

O

Ph

O

Ph

5 hrs 0degC

91

15

18

16minus2 H

CF3SO3H CF3SO3H

OH2

Ph

OH2

Ph

17

2+

Ph

OH

Ph

+ +

+

+

(18)




Ph Ph

O

Ph

19

22

H+

Ph Ph

OH

21

Ph Ph

OH2

OH2

PhH

slow orno reaction

rate-determining

80degC Ph Ph

OH22+

72

20

CF3SO3H

+ +

+

+

+




CF3SO3HCF3CO2H

CNH+

O

23 24 25

CN

H +

C

NHH+

+

(19)


KINETIC STUDIES 27




OCH3

OCH3

FSO3HSbF5

minus60degC

hn

minusH+H+

26 26a 26b

2727

k1

OCH3

+

OCH3+

OCH3

H

++OCH3

H

+

+

Δ




N

RprimeR

H+

NH

RprimeR

(20)


N


NH50degC 1 h

7628a

(21)

N

CF3SO3H

NH

69

28b

150degC

(22)

N

Ph

28c

NH

Ph 90

29 30

CF3SO3H

150degC

31

N

Ph

H+

N

Ph

HH

++


KINETIC STUDIES 29

28a28c28d28e

minusH0

log

k

minus55

minus5

minus45

minus4

minus35

105 11 115 12 125

28a

28c

N

N

28d

28e

N

N

Cl

CH3





PhPh

PhPh

OCF3SO3H

PhPh

minus2 H+

minusH2O

32 34

36

99

33 35

PhPh

Ph

H2OPh

+

+

PhPh

PhPh

OH2

+

+PhPh

PhPh

OH+



Acid System

Acidity (H0)

(CF3SO3H-CF3CO2H

ww

)Product

Ratio (3236)




ACID

O

OCH3

minus40degC

YIELD

minus27

0

minus118

20

minus132

94

H037 38

O

OCH3

HOOH

OCH3

+

+

(24)

KINETIC STUDIES 31




H3CCH3

O

OCF3SO3H

C6H65 min

H3CCH3

O

OHH

H3CCH3

O

94

39

42 41

++

40

H3CCH3

OH

OH+

+

H3CCH3

OH+

+

Scheme 6



acidC

NH2

H

H2OC

O

HNaCN orTMS-CN

+

(25)

H+

H C NH+

H+

H C N H+ ++

H C NH

H

NaCN orTMS-CN

4443 45

(26)













Acid H0 Yielda





H3C C O H3C C OH

46

C O C OH

47

H+H++ + + + + +








XXCF3SO3H

48a X = OH 49

(27)

SbF5

RR

R R

SO2ClF

minus78degC

RR

R R

50R = H NMe2 OCH3

Heat

minus2H+

RR

R R

+ +

(28)





NO

O

CF3SO3H

C6H6

0degC

NOH

OH

N OH

51 96

++

(29)

53

NO

O

H3C

CH3

52

13C NMR Data (ppm)

NOH

OH

H3C

CH3

266 1999 1303

296

CF3SO3H

NOH

OH

H3C

CH3

++

+ +

C6H6

minus5degC

(30)



NO

O

CF3SO3H NOH

OH

NOH2

OHNOH

C6H6


54

C6H6

C6H6

+minus N

OH

OH+

+ + +

++

Scheme 7

NO2

C6H60degC

NH2

Ph

NH2

Ph

NH2

Ph

Ph

NHO OH

NHO OH

55

CF3SO3H+ +

+

+

++

Scheme 8




CH3

HOPh

Ph

CF3SO3H

C6H6

CH3

Ph

Ph

Aqueous

Workup

Ph

Ph+ (31)

PhNH2

OH

CH3

Ph

PhNH2

CH3

PhPh

CF3SO3H

C6H6

PhNH3

CH3

Ph

80

56 57

C6H6+

+ (32)



200 180

57Ph

d 6-A

ceto

ne

d 6-A

ceto

ne

++Ph

CH3

H3N

160 140 120 100 80 60 40 20 ppm




CH3

N

O

H3CCH3

N

OH

H3C H3C

NOH

CH3

PhPh

75

HO HHO

58

CF3SO3H

C6H6

+

+

(33)

N

O

O

CH3 N

HO

OH

CH3 N

O

CH3

Ph

Ph

59

CF3SO3H

C6H6

75

+

+

(34)

CF3SO3H

C6H6

99 PhP

PhPh

CH3

Ph

Ph

Cl

Ph P OH

PhPh

Ph P O+ + ++

minus

minusPh

PhCH3

Br

60

CH3(35)

N

H

O N

H

HN+ +

H

OH

61

C6H3Cl2

C6H3Cl2CF3SO3H

o-C6H4Cl

87

(36)

CF3SO3H

C6H6

74ndash99

NN

Rprime

R

O

H

NN

Rprime

R

HO

H

+

+

H NN

Rprime

RH

PhPh

62

(37)






(1)

(2)

(3)

(4)

(5)

(6)

(7)


NOH

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

HF-SbF5

minus30degC

HF-SbF5

minus30degC

ACID

minus30degC

NOH H

H H

OH OHH H

OHH H

HH

78 22

OH OHH H

HH

33 67Cl

Cl

Cl

HF-SbF5

OHH H

80 20Cl

Cl

OHH

H

Cl

OHH

HH

H

FSO3H-SbF5

0 100

OH

N

OH

N

OHH H

H

N

OH

N

OH

H H H

OH

NH2

OH

NH3H H

+ +

+

++

+

+

+

+

+

+ +

+

+

+

H+

+

H+

H+



CF3SO3H

minus20degC

O

OCH3OH

OCH3

65 R = minusOCH3

O

OCH3

HO


R

R

R

R

R

R63 R = H

+

+

(38)











HF6-31G MP26-31GHF6-31G MP26-31G

ω I ω I

O = +N = O 2760 190 2526 1717

2660 1773 2415 191426 3 1246 21006 540 884 408682 0 553 21630 50 541 51

O = +N = OH 2654 919 2566 62

1682 0 1302 0750 5 601 3
























3+



CS3+ CS23+ CSe2

3+

Diatomics B23+ S2

3+ CI23+ Br23+ I23+


2+







2+species (eq 43)43




NbC5H62+ + NbC6H6

2+












C6H5CH3

minus2eminus

C7H62+

HC CH

+ C9H62+C9H7

2+ (44)



C

CC C

CCC

HH

H

H

HH

2+

HC CH


C

CC C

CCC

HHH

H

HH

C C HH 2+

C

CC

C

CC

CC

CH H

H

HH

H

H

H2+

Erel = minus144 eV

C

CC

C

CC

CC

CH

H

HH

H

H

H2+

Erel = minus126 eV

C

CC

C

CC

CC

CH

H

HH

H

H2+

minusHminusH2

+

Scheme 9







OHacid

+ +

+O

69

CF3SO3H +

+OH

70

O+

OO

71

69 72(45)






O

78

+OH

+OH2OH

O

73

+OH +OH2

+

+OH2

+ + + +

ΔE = 1827 kcalmol

ΔE = 616 kcalmol

ΔE = 1827 kcalmol

OH

74 7975

+OH2

ΔE = 1237 kcalmol

80


Scheme 10



H3CC

OH

H3CC

OH

HCH4


CH3

46 83 84

++

+

+

++

(46)



N

OH

CF3SO3H-SbF5

NH

OH85 86

++ (47)

NH

HO

88

N

87

HOCF3SO3H-SbF5

+

+(48)



ω = μ22η



















CH3CO2H 13C1 1719 13C2 207 13C1 1769 13C2 20817O1 1943 17O2 4134 17O12 2510

CH3C(OH)2+13C1 2020 13C2 217 13C1 203717O1 2283 17O2 2312 17O 1930


89 17O1 1482 17O2 2942

CH3CO+ 13C1 1557 13C2 63 13C1 150317O 3438 17O 2995


46 17O 1946

HNO315N 3668 15N 3770

NO+2

15N 2683 15N 25101


3

H3O+ 17O 300 17O 1021H 72 1H 95-106


90 1H 136






HC

OH2

H

+

+

MP26-31GMP26-31G


48505152

H3CC

OH2

H

+

+

MP26-31GMP26-31G


4850

H3CC

OH2

CH3

+

+

MP26-31GMP26-31G


4850

HC

OH

OH2

+

+

MP26-31GMP26-31G


4850

H3CC

OH

OH2

++

MP26-31GMP26-31G


4850

HOC

OH

OH2

+

+

MP26-31GMP26-31G


485053

H+O=C=+

OH MP26-31GMP26-31G


4850



54





H3NC

OH

OH+

+



55

F3CC

OH2

OH+

+ MP26-31GMP2(fu)6-31G


56

FC

OH2

OH+



57

H3CC

O

OH

H

CH3+


Geometry energy 58

H3CC

O

O

CH3

CH3

H3C +

+


Geometry energy 58

H3CC

O

O

H

CH3

H3C

+


Geometry energy 58

OH

HO

HO

OH

+

+



59





NH

OH+



35c

NH

OH++



35c

NH

OH

+



35c

NH

OH

+



35c

HN

H

OH+


Geometry energy 60

O

OOO

+



61

OO

O

OO

O+

+

+



61





CCH

H

H

OH

+


62

CCH

H

OH

OH

+


62

CCHO

OH

OH

OH

+

+ MP26-31GMP26-31G


63

CCHO

NH2

OH

NH2

+

+ MP26-31GMP26-31G


63

CCH3CO

OCH3

OCH3

OCH3+

+


63

OH

OH

HO

HO

+

+


63

H3NC

NH2

OH+

+ MP4(SDTQ)6-311GMP26-311G


64

H3NC

NH3

OH+

+

+



64





HN OHHO



65

HN OHHO



65

N OHHO

Cl+ +



66

N OHHO

ClH+ + + B3LYP6-31G



OH2

+



18

OH2

+



18

OH2

CH3+



18

H3CC

CO

H

CH3

CH3

HH

+

+


Geometry energy 14b

CC

CO

H

H

H

H

H

H+

+

HF6-31GHF4-31G


24





HOC

COH

OH

OH

+ + MP26-31GHF6-31G


67


H3Cminus+C=+



425270


CC

CO

H HH

H+

+ MP26-311+GMP26-311+G


69

CC

CO

H HH3C

CH3++ MP4(SDTQ)

6-311+GMP26-311+G


69

CO

CO+



59

Hminus +C=

+OminusH MP26-31G



50

Fminus +C=

+OminusH MP4(SDTQ)

6-31GMP26-31G


57





O H

H

HH

2+MP4(STDQ)6-311++GMP26-311G


48507071

O H

H

HF



72

O H

H

FF



72

O H

H

CH3

H3C2+

MP26-31GMP26-31G


4850

O CH3

H

CH3

H3C2+



4850

H3CC

COH2

HCH3

CH2 ++


Geometry energy 14b

H3CO

OCH3

CH3

CH3

+

+

MP26-31GMP26-31G


73





C C OH

HH H

+

+


Geometry energy 68

C CO

HHH H

CH H

++


Geometry energy 68

C CO

HHH H

CH CH3

++


Geometry energy 68

C

CO

HHH

HC

CH3

CH3+

+


Geometry energy 68

CH3C

CH3H3C

H

CO

H

H+

+


Geometry energy 14b

C NH

HH H

H

HH

+

+


C NNH

HH H

+

+


C NH

HH H

CH

H

H+

+

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75





C CH

HH H

N

H

H

H

+

+MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

CN

H

CH3

H

CHH

H

H++

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

H3CN

C

C

H HH

H

H H

++

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

C FH

HH H

H+

+



7677

C ClH

HH H

H+

+



7677

C BrH

HH H

H+

+



7677

C IH

HH H

H+

+



7677

Si CH

HH H

H

H

+

+



78

Si S iH

HH H

H

H

+

+



78





CH53+ MP26-31G


charges79




80




81

C C

H

H

H H HH

HH +

+



80

HC

CC

HH H

H HH H++



80

HC

CC

CH

HH

H H

HH

H H

HH

+

+ MP4(SDTQ)6-311GMP26-311G


80

HC

CC

HH CH3

H HH H++



80

C C

H

H

H HH

H+

+



78

C C

H

H

H H H

CH3+

+

MP46-31GMP26-31G

Geometry energy 82

C C

H

H

H H H

CH

HH

+

+MP46-31GMP26-31G

Geometry energy 82





C OH

HHH

H H

+

+

MP26-31GMP26-31G



48507477

C SH

HHH

H H

+

+

MP26-31GHF6-31G



5077

C OCH3

+CH3H

HH H+

MP4(STDQ)6-311++GMP26-311G

Geometry energy 75




83

BH52+ and BH6



79a

NH52+ and NH6



718485

PH52+ and PH6



7185

AsH63+ and AsH3+



7185

CH3N

CH3

CH3

CH

HH

H+ +


Geometry energy 84





HC

CCH3

CH3

H H++


Geometry energy 86

H

+

+



87


C CH

H

H

H++

MP36-31GHF6-31G


88

C CF

F

F

F++

MP26-31GHF6-31G


67

HC

CC

CH

H

H

H H

H H

+

+



89

+ +



90

OH

CH3

+ +



25





OH

OCH3

+ +



25

OH

H

+ +



25

+

+


Geometry energy 87

+

+

+



91

CH3

H3C +

+



91


89

CH2

CH3

CH3H3C

H2C++ B3LYP6-311G



92





HN

+



35c

HN +



35c

NH

SCH3

+

+


Geometry energy 93

NH

SCH3H

+

+


Geometry energy 93


H2NN

NH2

NHH

+



94

N3N

N3

NN

N+

+



94

+

+H2N

CNH3

NHH MP4(SDTQ)6-31G



94





H3NC

NH3

NHH

+ +



95

H2NC

N

NHH

H H

CH3+

+ B3LYP 6-311+GB3LYP6-311+G


96

H2NC

N

NHH

H H

BH4+

+ B3LYP6-311+GB3LYP 6-311+G


96

H2NC

N

NHH

H H

AlCl4+

+ B3LYP6-311+GB3LYP6-311+G


96

O=+N=+



3741

O=+N=+




97



97





Hminus +Nequiv+



98

Hminus +Nequiv+



98

Nequiv+Nminus+



98

C N NH

H

H



98

C C NH

HH

++

HF6-31GHF4-31G


62

H3C CNH3

H

++ MP4(SDTQ)6-31G


C CNH3H

H HH

+

+


Geometry energy 99

H3C CNH3

CH3

++



99

HC

HN

H

HH

++

MP26-31GMP26-31G


51





HONH2

OH

NH2+

+ MP26-31GMP26-31G


67

H2NNH2

OH

OH+

+ MP26-31GMP26-31G


67

H2NNH2

NH2

NH2+

+ MP2 6-31GMP26-31G


67

NN

+

+

HF6-31GHF6-31G


100

Phosphonium Systems

HC

PH

HH

H+ +

MP26-31GMP26-31G


51

HC

PH

H

HH

2+

MP26-31GMP26-31G


51


S2+8 and S2+

n (n = 37) B3PW916-311+G(3 df)B3PW916-311+G


101





2+

HS

H

HH



50102

2+

CH3

SH3C H

H MP26-31GHF6-31G


50

2+

CH3

SH3C CH3

H MP26-31GHF6-31G


50

2+

CH3

SH3C CH3

CH3 MP26-31GHF6-31G


50

2+

CH3

SH3C OH



103

2+

H3CS

H3CO

H



103

2+

H3CS

H3CO

H



103

2+

H3CS

H3CO

CH3



103

H2NC

NH3

SH+



38





H3NC

NH3

SH+

+

+



38

H2NC

NH3

SH2+

+

+



38

HSC

SH

SH 2+ (P)MP4(SDTQ)



104

2+

CH3

SH3C H

H MP26-31GHF6-31G


50

HSC

CSH

SH

SH

++

MP26-31GHF6-31G


67

Boron-Based Systems

HN

BH

HH

++ MP46-311G(dp)



105




Halonium Systems

H

H



76106

H

H



76106

H

H



76106

H

H



76106

CH3

CH3



76

Cl 2+

CH3

CH3



76

Br 2+

CH3

CH3



76

I 2+

CH3

CH3



76




Halonium Systems

HC

F

H

H+ +MP26-31GMP26-31G


51

HC

Cl

H+ + H

MP26-31GMP26-31G


51107

+

+F

CF

F



107

+Cl

CCl

ClH

+



107

+Br

CBr

BrH

+



107

+I

CI

IH

+



107

+ +Cl

CCl

ClHH +



107

+ +Br

CBr

BrHH +



107




Halonium Systems

+ +I

CI

IHH +



107

+

+

++Cl

CCl

Cl

HH



107

BrC

Br

Br

HH

H

++

+



107

IC

I

I

HH

H

++

+



107

ClC

Cl

H

H++MP26-31GMP26-31G


107

ClC

Cl

H

HH +

+ +

MP26-31GMP26-31G


107


REFERENCES 75

REFERENCES
















2312















J Am Chem Soc 1997 117 4345

REFERENCES 77






































REFERENCES 79
































81

copy








Ph Ph

O

Ph Ph

OH2

Ph Ph

O

Ph Ph

OH2

H3CCH3

O

O

H3CCH3

OH

OH

N

Ph

N

Ph

H

H

(1)

(2)

(3)

(4)

(5)

(10)

(11)

(7)

Ph OH

O

Ph OH

OH

(12)

(13)

NO

Ph

RN

PhR

OH

H

(15)

ROH

O

O

ROH

OH

OH

(6)

Ph NHPh

O

Ph NHPh

OH

NO

OBF4

NOH

O2 X

Ph CH3

O

Ph CH3

OH

N

O

R

O

N

OH

R

OH

(8)

(9)

(14)

(16)

(17)

R2N

O

O

NOH

OH

NO2 NHO OH

R1

R3

R2

R1

R3

Ph

OH

O

Ph

OH

OH

(18)


Ph OCH3

O

Ph OCH3

OH

H

N

R

O

O

N

R

OH

OH

(19)

Ph

OH2

PhPh

O

CH3

Ph

OPhPh

Ph Ph

OH2PhPh

Ph

O

O

Ar

Ar

OH2

O

Ar

Ar

+

minus

+minus

++

++

+

+

+

+

+

+

++

+

+

+ +

++

minus

+

+

+

+

+

+

+

+

++

++

+

+

+

+

+

+

+

+


H C NH+ +

H

NaCN orTMS-CN

5SbF595CF3SO3H

1

(1)


CN

CH3

TfOminusC6H6

CN

CH3

H C

O

2 3

5SbF595CF3SO3H

+

++

(2)

OHO

OMe

OMe

MeO

SbF5CF3SO3H

OH

OMe

OMe

MeO4 5

+ + (3)


HNO2

2 CF3SO3HB(O3SCF3)3

minusH2OO N O

H+

O N O H

6

+ + +(4)

2 CF3SO3HB(O3SCF3)3

O

+ 2+

CH3

CH3

H3CO

CH3

CH3

H3CH

7 8

(5)

CO H CO+


SbF5CF3SO3H

H CO H

9

+ + (6)


CH3OHH+

CH3OH2 CH3OH2

HA

HA

CH3OH3

2+++

(7)


N

Ph

H

H

N+

PhH

CF3SO3H -CF3CO2H

10

++

(8)

11

Ph

OH2

PhPh

OH

PhCF3SO3H -CF3CO3H

+

+

+

(9)

Ph Ph

OH2

12Ph Ph


+ (10)

CN

H


NH H

13

+ +

+(11)




O

Ph

FSO3H

orCF3SO3H

OH

Ph

14

+

+

OH

OHN

HO

OH

CH3

15 16

+

+

+

+

(12)






OCH3

OCH3

OCH3

OCH3

H H

HH

OCH3 O

CH3

H

OCH3

H

H3C OCH3

O

H3C OCH3

OH

H

H2N NH2

O

H2N NH3

OH

(1)

(2)

(3)

(4)

XCH3H3C

CH3

+

X = O S Se Te

FSO3HSbF5

FSO3HSbF5

XCH3H3C

CH3

H2+

2+

SDH

HS DH

H

D

(5)

(6)


17

18

19

20

21

22

FSO3HSbF5

FSO3HSbF5

FSO3HSbF5

+

+

+

+

+ +

++

+

+

+

+FSO3HSbF5



C

O

H3C OHC

O

CH3

H

C

OH

CH3

HFBF3C

O

CH3

23 24

+

+

+

+ (13)

C

O

R CH3

R = H CH3

HFBF3or HFSbF

C

OH

R CH3

H+

C

OH2

R CH3

25 26

C

OH2

R CH3

2++ +

+(14)

CH3

C

O

CH3

CH3H

HFBF3

CH3

C

OH2

CH3

CH3H

2+

CH3

C

OH2

CH3

CH3H

27

+

+

(15)

CH3OCH3 CH3OCH3

HCH3OCH3

H minusminus

H 2++HF-BF3

BF4 2 BF4

28

(16)




O

H

D

D

O

H

H

D

minusD+O

H+ +

D

D

HHF-SbF5

29

2+

(17)

F3CC

OH

OHFSbF5

F3CC

OH

OHH

F3C F3CC

OH2

OH minus H2O

C

OH++

++

++ (18)


OH

Cl

HF-SbF5

OH+

+

Cl

(19)

OH

HF-SbF5

OH

OH OH+

+

(20)

DF-SbF5

31

minus78degC

H3C H3C H3CC

CH3

CH3

CC

CH3

HH

H

D

CCH2D

CH3

minusH+

30

++

+

+

(21)

CCl4HF-SbF5 Cl

CCl

Cl

H+ Cl+ ++

CCl

Cl32

H (22)








AlCl3

Al2Cl7

33

+minus (23)


C

O

H3C Cl AlCl3

AlCl3C

Od+

d+

dminus

dminus

dminus

H3C

AlCl3

CH3COCl bull 2AlCl3

34

AlCl3

Al2Cl7+

+minus (24)



CBr4 bull 2 AlBr3Br

CBr+

minusd+

minus

+

Br

BrC

Br

Br

35

AlBr3

AlBr3

Al2Br7

Al2Br7

(25)

Cl SCH3

SCH3 S

CH3

AlCl3

2 AlCl3

Al2Cl7

Al2Cl7

AlCl3 +minus

minus

+

dminus

d+

(26)

ClAl

ClCl

OC

O

AlCl3

ClAl

ClCl

OC

O

AlCl3 ClAl

ClCl

OC

O

AlCl3

AlCl3AlCl3

2 AlCl3+

++minus minus minus

d+

d+

d+

(27)


H3C CH3

CH3 O 13 equivAlCl3

H3C CH3

CH2 OAlCl3

+

+minus

(28)

R NRprime2

O

R NRprime2

O

H H

X


minus

5 equivAlCl3

+

+

(29)


OH OH H

HH

X3 equivAlCl3


minus

+

+

(30)

OH

HO

OX

HH

HH

OH

X3 equivAlCl3

+

+

+


minus

(31)

N

O

O

ClBF3-H2O

N

OH

O

Cl N

OH

OH

Cl N

OH

OH

Cl

HH+H+

+ +

+

+

+

+

(32)


Ph NEt2

O HUSY

C6H6130degC

Ph NEt2

OX

Ph NEt2

OPh97+

+

(33)

Ph CH3

O HUSY

Ph CH3

OX

Ph CH3

O70

C6H6130degC

+

+

(34)

NH

O

Ph

Nafion-H

NH

OH

Ph

H

NH

O

Ph

70

36

C6H6130degC

+

+

(35)





HN

NH

N

N+

+ +

HO

H2N

CH3

CH3

H

42 43

HN

NH

N

NHs

O

H2N

CH3

CH3

H

Hr

H2


dehydrogenaseH+

(36)


Ph H

O

H3C CH3

O

NH

O

NH

OH

Ph

Ph

20 mol

minus25degC Ph CH3

OOH

51 yield 83 ee

N

O

N

O

Ph

Ph

CH3

PhH

OH

H

d

37

38

N

O

O

CH3

PhH

O

H 39Ph Ph

OH2 OH2

H

40 41

+

+

d+

+

+

+

+

+

Scheme 1









(1) N

O

O

ClNO2

NO2

Cl

105degC 69

(2)

N

O

Ph

HHUSY

CF3SO3H

130degC

25degC


OH

Ph

H N

O

Ph

H(3) 90

90

85

OH

NH2

AlCl3 110degC

OH

NH2

70

NH2

O

(4)

(5)


65degC

FF

FNO2

O N OH

FF

FNO2

O2N96

N

O

H

(6)

CF3SO3H 130degCNO2

HN

OH

H10

N

NO2

NO2

(7)

N

O

CH3

OH

CF3SO3H 80degCCl

ClN

OH

CH3N

O

CH3

ClCl

60

Ph Ph

O

CF3SO3H 80degCPh Ph

OH2 Ph 84

(8)N



phenyl

phenyl

phenyl

phenyl

phenyl


CH2

H2OndashBF3 N

OH

OHCl

H

+

+

+

+

+

+

+

+ +

+

+

+

+

+

+

++




CCl4-AlI3 I2

minus20degC

I

70

CXX

X

MXn

44

+

d+dminus

(37)


CH3CH2CH3+ CO


minus30degC

minus10degC

Temp

CH3OH COCH3O

CHCH3H3C

Yield

50

28

Scheme 2

CCH3H3C

CH3

i-PrOH i-PrOHCO CO

CH3CH2CHCH3

CO O CH(CH3)2 C

O O CH(CH3)2

C(CH3)3

minus20degC

0degC

Temp

525 100

129 100

Product Ratio

CH3CH2CH2CH3+ CO

+CH3CH2CHCH3


+

Scheme 3



80HNO3 minus78degC

(CF3SO2)2ONO2

(38)O N O

HA

O N OH

6

+

d+

+ +

NO2

94

(CF3SO2)2O


NO2NO2

+ BF4minus

CF3SO3H0degC

64

+ + (40)


H3CCH3

O

O CF3SO3H

C6H6 0degC5 min

H3CCH3

OH

OHH3C

CH3

O

PhPh95

45

+

+ (41)

Ph

O O

Ph

91

Ph

OH2

CF3SO3H

+

+0degC

(42)


PhO

PhHO

OCH3

CF3SO3H

minus40degC PhOH

Ph

OCH3

O

OCH3

9446

+ +

(43)





H3C

O CH3

O CH3

BF4

CD3SO3FSbF5

minus30degC

47

H3C

O CH3

O CH3

48

D3C

(NuCH3)+

H3C

O CD3

O CH3

Nu+

+

+

minus

+





DFSbF5

50

minus78degC

H3CC

C

H

HH

H

D

H3CC

CH2D

H

minusH+

H3CC

CH2

H+ H+

H3CC

CH3

H

49

+ +

+

+

Scheme 4

OCH3

OCH3FSO3HSbF5

minus60degCOCH3

hn

ΔOCH3

OCH3

HOCH3

H

minusH+ H+

51a 51b

5252

k1

+

+

+

+ ++

Scheme 5


REFERENCES 101


REFERENCES











1997 62 6666




















REFERENCES 103



















58 5423











105

copy


HO

H

HH

+070

+070

+070

+070

minus080

Td

2+

HO

H+0458

+0458

minus0916

C2v

HS

HH

+049

+056

+056

+056

+035

3+

Cs

+049HH

1 2




CH3

OCF3SO3H

25degC

CH3

OH

CH3

OH H

O HH

CH3

O

CH3

+

97

3

CH3

OH H

4a 4b

2+

5

++

+

+

+

CH3

OH H

4c

+

+

Scheme 1







H3CO

CH3

CH3 H3CO

CH3

CH3

H Ad+ dminus

H3CO

CH3

CH3

H

2+

6 7

++



42 GEMINAL SYSTEMS










HC

HH

H

H H 2+

8

CAuPPh3

AuPPh3Ph3PAu

Ph3PAu

AuPPh3

AuPPh3

2+

2 X minus

9

HC

HH

H

H H3+

10

H



2+ CH3bull2+CH2


GEMINAL SYSTEMS 109


H C F2+

H C Cl2+

H C Br2+

H C I2+

11a 11b 11c 11d









CClCl

Cl

SbF5CClCl

Cl

SbF5or H+

12

Cl C Cl2+

13a

FCCl3SbF5 RH

HCCl3 bull SbF5

HCCl2

minus SbClF5minus

RHCH2Cl2

RHCl C Cl

13b

+ +dminusd+

++ +

Scheme 2





2+CS2

2+ CF2+ CS22+

COS3+ CS23+ CSe2

3+ CS3+









GEMINAL SYSTEMS 111



N

H

H H

H

H2+

C4v

14

NLAuLAu

AuL

AuL

AuL

2+

2 BF4minus

15L = P(C6H5)3

NH32+ + H2


16 14(1)






NOH

H

C6H6

acid NH

NH2

Ph

18 19

CF3CO2H


56 9 para8 ortho

17

+

Scheme 3



NOH

H

H+ NO

HH

H

minus H2O

NH

NH

NH

HSn-2-like

C6H6

minusH+

19

17 20

21 22

NO

H

H

H

C6H6

+

+

+

+

+

Scheme 4

NOH

H

2H+ NO

HH

H

minusH2O NH

17 23

C6H6

HN

H

24a

2+H

H

NH

H

H

HN

H

H

H

Hminus2H+NH2

Ph

19 26 25

24b

+ + +

+

+

++

+

+

Scheme 5

GEMINAL SYSTEMS 113


N

CH3

minusO

CH3CF3SO3H N

CH3

CH3

28b27

NCH3

CH3

28a

2+ ++

+ (2)

NOH

H

30b

NO

NOH

H

30a

2+

29

CF3SO3H

+

+ (3)

N

O

CF3SO3H

31H3CO

NH3CO

H3CO

NH3CO

H3CO

H3CO

NH3CO

H3CO

2+

minusH2O

32

minus

+ +

+

(4)




OH

DD

OH

DO

HH

DO

H

HO

HH

H



HD

DO

HH

D(b) O

HD

DH

2+O

HH

DH

2+O

HH

H

++












GEMINAL SYSTEMS 115

OAuPAr3

AuPAr3

Ar3PAu

Ar3PAu


33

2+



OH3C

CH3

CH3


CH3

CH3

H2+

C6H5CH3 OH3C

H

CH3++

34

+




H+ HA

H

3635 37

H O CH3

HO CH3

H

HO CH3

H

A

H O CH3

H

H

+

δminus

δ+

+

2+ (6)

2 CH3OH CH3OCH3

minusH2O

CH3OCH3

H

HAH+

CH3OCH3

H

H

38 39

+ 2+

(7)




minusH2CH4 (8)






CH3OCH3 CH3OCH3

H

+CH3OCH3

H

H 2+HF-BF3

CO

BF4minus

O

C

minus2HF

CH3CO BF3OCH3

minusBF3

CH3CO2CH3

382BF4

minus

+ minus



GEMINAL SYSTEMS 117

CH3OHH+

HO

CH

HH

HH O

CH

HH

HH2+

3537

minusH3O+

CH

HH

OC

HHHH

H

minusH+

C

HHH

OC

HHHH

hydrocarbons

+

+ +

+

+

Scheme 7


SH

D

D

SH

H

D


SH

D

D

H SH

H

D

H SH

H

H(10)


minusSiH4 and PH4


OH

HH

H2+ 2++ +

SH

HH

SH

HH

HOH

HH


+ +(11)




S SBF3bullOEt2

XeF2

40

SN

N

F

FCH3

CH3

CH3

CH3

42

2+

[S(NP(CH3)4]2+

2Clminus

41

2 BF4minus

2+

2 SbF6minus




Se

H

H

H

H

44

43

45

Te

H

H

H

HAu Au

Au

Au

S

2ClO4minus

PhPh3

Ph3P

Ph3P

Ph3P2+

2+ 2+



X

+2+

H3C

CH3

CH3

FSO3HndashSbF5XH3C

CH3

CH3

HC6H5CH3

X = S SeTe

Xylenes(12)

GEMINAL SYSTEMS 119




S

H

H H

H H3+

2

Cs

SH33+ + H2 SH5


2 (13)






3+and SH6

4+ respectively





2H3CndashBrSbF5

SO2ClFH3C Br CH3

minus

+

X46

(14)

H3C Br CH3+ 2+

H3C Br CH3

X

HX

H X

H3C Br CH3

H 2 X46 47 48

+





H3C Br CH3+

minusSbF646

Nu

H3C Br + H3C Nu

CD3F SbF5H3C Br CH3

49

CD3

2+

H3C Br CD3

50

+

Scheme 8

GEMINAL SYSTEMS 121

BrC CH

H

HH

H

H

H


2+

BrC CH

HH

H

H

H


2+H

51 52

Figure 3








REFERENCES

















REFERENCES 123





















481







125

copy


C CH

H

H

HC C

H

H+

H+

H

1

CC

CH3

CH3


3

2++

+ +

1432 Aring

etc

NBO charges+052

+027

H3CC

CH3

CH3

tert-butyl cation

2

+058

+014

HH

H

H

+094

D2h


OCH3

OCH3

OCH3

H3CO

SbF5 SO2ClF

minus78degC

OCH3

OCH3

OCH3

H3CO

OCH3

OCH3

OCH3

H3CO

etc

1583 ppm 1753 ppm

4 5 5

++

+

+

Scheme 1



N

N

KCN

CNHH

N

N

CN

H

minusHCN

N

N

HNC

+

+

minus

+

minus

(1)


CNCF3SO3H

CF3CO2H

CN

H

H+ C

NH H

O

6 7 8

++

+

(2)

Ph Ph

O

Ph Ph

OH

Ph Ph

OH2

80degC

9 10 11

H+CF3SO3H

Ph+

+

+

(3)




H

OACID

C6H6

H

OHH

OH

H

HOH2

HH OH2

C6H6

H+

minusH+Products

15

16

H

OH2

12 + C6H6

H

O

CF3SO3H

C6H6

or H

OH

H

Hplus otherproducts

12 13

14

+

+

+

+

+

+

+ +

+

Scheme 2



52 VICINAL SYSTEMS




VICINAL SYSTEMS 129




2+ (18)

B NH

H H

HH B N

H

H

H

2+2+

17 18

C2v

C3v








CCl++ d+ dminus

d+ dminusd+ dminus

Cl

Cl

SbF5CClCl

Cl

SbF5B ClCl

Cl

AlCl3

19 20

Cl C Cl2+

2+ +

22 23

Cl B Cl+ +

H C H25 26

H B H

24

Cl Al Cl

CHH

H H

2+

27

BHH

H H

+

28

H3C +

+

+

CH3C

CH

H

H H

3

H3C

++

BH3C

CH

H

H H

29

Al ClCl

Cl

AlCl3

21

OH2

CHO OH

30

+OH2

BHO OH

31

HCHH

HH H 2+

32

HBHH

HH H +

33







VICINAL SYSTEMS 131







H3CCH3

O

O

CF3SO3H

H3CCH3

+OH

+OH

35a 35b34

H3CCH3

OH

OH

++

(5)






1 36

H CC H2+

Dinfinh

37

C C

H

H

H

H

HH

Cs

38

2+2+

C C

H

H

HH

C2

H

H

H

H

C CH

H H

H+ +



O

OO

O

SbCl5

25degC

5150

O

OO

O

+

+

(6)


VICINAL SYSTEMS 133


Ar Ar

ArAr

Ar Ar

Ar Ar

PhPh

Ph Ph

CH2CH3Ar

CH3CH2 Ar

OHPh

Ph Ph

OHPh

Ph OCH3

OHAr

Ar OCH3

OHPh

Ph OH

SbCl5 Br2 or I2

SbCl5 or AgNO3

SbF5


CF3SO3H

Ag (I) CF3SO3H

CF3SO3H-SbF5

CF3SO3H


40

42

44

45

46

47

48


HO OH


Ar Ar

ArAr

Ar Ar

Ar Ar

PhPh

Ph Ph

CH2CH3Ar

CH3CH2 Ar

OPh

Ph Ph

OPh

Ph OCH3

OAr

Ar OCH3

OPh

Ph OH

HO

Cl

HO

HO





4 5

39

43

Ar Ar

O O


41

+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +



NMe2

NMe2

NMe2

Me2N

NMe2

NMe2

NMe2

Me2N

39 40

SbCl5

NMe2

NMe2

NMe2

Me2N+

+

+

+

(7)



VICINAL SYSTEMS 135

42

SbF5 SO2ClF

ndash78degC

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph

CF3SO3H

OHHO

Ph

Ph Ph

PhO

PhPh

O

PhPh

CF3SO3H

CF3SO3H

52

ndash2 H+

H H

Ph

Ph Ph

PhH2O+

++ +

++

Scheme 3



CH2CH3Ar

CH3CH2 Ar+

44

CH2CH3Ar

CH3CH2 Ar

+

OCH3

OCH3

+

2+ + CH2CH3Ar

CH3CH2 Ar

43 54

(8)


PhO

Ph

Ph

HO CF3SO3H

Ph OH

8

55 5645 45

PhOH

Ph

Ph

++

Ph OHPh

Ph

+ + +

O

Ph

74

(9)


PhO

Ph

OR

HO CF3SO3H

O

OR

R = CH3 46R = H 48

R = CH3 59 81R = H 60 65

ndash45degC

R = CH3 57R = H 58

OH

OCH3

OCH3

H3CO

47

+ +

Ph OH

Ph

OR

+ +

(10)


ArO

Ar

Ar

HO

Ar = p-methylphenyl

CF3SO3H-SbF5

ndash30˚C

61

O

Ar

Ar OH

70 14

0degCAr

OHAr

Ar

+ + +

(11)

ArO

Ar

OH

HO


O

OH

82

CF3SO3H

ndash20degC30 min

ArOH

Ar

OH

+ +(12)



VICINAL SYSTEMS 137

PhO

Ph

OCH3

HO

O OCH3

5957

ACID

ndash40degC YIELD


0 20 94

Scheme 4



HO OCH3


57

46

2 H+

Ph OH

Ph

OCH3

+ +

+ ++

+(13)




HO CH3



63 64

2 H+

PhO

PhHO

CH3

O CH3

63 65

H+

CH3

PhO

PhHO

63

PhO

PhHO

CH3

CF3SO3H

ndash40degC

OCH3

70

Ph OH

Ph

CH3

+ +

PhO

Ph

CH3

+

+

+

+

++

++

Scheme 5

66 67

67a 67b 67c


+0594 +0635 +1063


+

OH

H

H

+OH

H

H

+

+ OH

H

H

+

++

O

H

H

+ OH

H

H

+

+

Figure 2


VICINAL SYSTEMS 139



Ph

Ph

O

OCH3Cl

Ag+

CF3SO3H

H2O

Ph

Ph

O

OCH3HO

5996

68 69

46

57

Ph

Ph

O

OCH3+

(14)



Ph Ph

OHO CF3SO3H

Ph Ph

OH

Ph Ph

OH

OH

11

70 70

+ +

+

+ (15)

7171

Ph Ph Ph Ph Ph Ph


+ +

+ + (16)



OC C

H

H O

H

H

HC C

H OH

O H

72 73


+ + + +



HO OH

OHHO OHHO

HO OH Ph OH

OHHO OCH3HO

Ph OH

HO OCH3

OH

HO OCH3

OH

H3C H3C

74 74 75 76

77 77

+

+

+ + + + + +

+ + +

+



VICINAL SYSTEMS 141

H3CCH3

O

O

CF3SO3H

C6H65 min 0degC

H3CCH3

OH+

+

+

++

O

H3CCH3

OH

OH

H3CCH3

OH

OHH3C

CH3

O

Ph Ph

95

357834(17)

H3COH

O

OCF3SO3H

C6H6H3C

OH

OH

OH

H3COH

OH

OH

H3COH

OH

Ph PhPh

Ph

79

+ CO + H2O

+

++

+

+

(18)


Ph OH

OH

OH

Ph OH

OH

OH

80 80

HO OH

OH

OH

OH

HO OH

OH

OH

OH

81 81

HOOH

OH

OHHO

OH

OH

OH

82 82

OHOH

OHHO OHHO

83 83

+

+

+ ++ +

+

+

+ +

+

+ +

++ +

+

++

+




O O

O

CF3SO3H

C6H5Cl

94

HO OH

Cl

Cl

HO O+ + +

+ +HO OH

84 84

(19)



H2NNH2

O

O

FSO3H-SbF5

minus78degC H2NNH2

OH

OHH2N

NH2

OH

OH

H2NNH2

OH

OH

85 85 85

+

+

+

+

+

+

(20)



VICINAL SYSTEMS 143


N

O

O

H

CF3SO3H

86

N

OH

OH

H

+

+

86

N

OH

OH

H

+

+(21)

H3CCH3

N

O

HO

CF3SO3H-SbF5

87

H3CCH3

N

OH

HO H+

+

87

H3CCH3

N

OH

HO H

+ + (22)



N

NN

N N N N N N N

Cl2

88 88 88

NN+ +

NN+

+NN

+ +

2 Clminus

(23)




DFSbF5

3

minus78degC

H3CC

CH2D

CH3

minusH+

H3CC

CH2

CH3

2

H3CC

CH3

CH3

+ H3CC

C

CH3

HH

H

D

+

+

+

+ H+

Scheme 6




DFSbF5

90

minus78degC

H3CC

C

H

HH

H

D

H3CC

CH2D

H

H3CC

CH3

D

89

++minusH++

+H3C

CCH3

H

+

(24)


VICINAL SYSTEMS 145


(CH3)3SiCN

acid 20degCCl Cl

H2OCHO

+CHO

Cl




30 min

10 min

2

93

(25)


H+

H C NH+ H+

NaCN orTMS-CN

9291

H C N H+

H C NH

H

+ +

(26)



C6H6

ACID

C

O

93 94

H2OC N CH3

CF3SO3

+

minusC

N

CH3

H

++

(27)




CN CF3SO3H

CN

H

H

O

6

8

CN

H

slow

fast

H2O

H2O

+

++

(28)



95 96 97

NHC

H

H

H+ N

HCH

H

H H

++

NHC

H

H

H H+

+



H3CC

NH

H

H

98


99

+

H+

CC

NH

H

HH

H

HH

+

+H3C

CN

H

H

HH

++

(29)

VICINAL SYSTEMS 147

H3CC

NH

CH3

H

100

+

H+

H3CC

NH

CH3

HH

++

(30)

H3CN

CH

CH3

H

H+

101

+

CN

CH

CH3

H

H

HH

H+

+

(31)



N

Ph

H3C

CH3

acid




2 h

26 h

94

50

104

N

Ph

H3C

CH3

HN

Ph

H3C

CH3

H

HN

H

PhCH3

H3C

temperature

60degC

72degC

102 103

++

+

(32)



105

23degC

CF3SO3D

108

N



NHHD

107

NH

H D

N 106

109

NH

D

H

NH

D

+ + +

+

+ ++

+

Figure 3


110

FSO3HSbF5

minus40degC

111

H2NC

NH2

NH2

+

H2NC

NH3

NH2

+

+(33)



114

H2

112 113

HN

NH

N

NH

O

H2N

CH3

CH3

H

H

AH

HN

NH

N

NH

O

H2N

CH3

CH3

H

AH

+

HN

NH

N

NH

O

H2N

CH3

CH3

H

A

H+ +

(34)


VICINAL SYSTEMS 149


N

NtBu

tBu

H

1 atm H2 DMAP

N

N

tBu

tBu

H

H

Clminus

+ (35)



149

33

minus57

4

minus87


115

NN

H

116

NN

HH

118


H2

H2+ H

117

244

H2

H2O

H2

NH3

115

115

116

116

117 + H3O

118 + H3O

117 + NH4

118 + NH4

HH H

H2

H2O

H2

NH3

+

+

+

+

+

+

+

+




C PH

H

H

HC As

H

H

H

HC

H

H

H

H

119 120 121

122

2+

C PH

H

H

HH

C PH

H

H

HH

2+

125

123

2+

C AsH

H

H

HH

C AsH

H

H

HH

2+

126

124

2+

CH

H

H

HH

C Sb

Sb

Sb

H

H

H

HH

2+

127

+++

Figure 4

VICINAL SYSTEMS 151


C

H

H

H+H

H

H

HHC

H

H

H H

119ndash121

X = P As SbH

H

H

HC X C X

+

++ (36)

2+ +

+C CX X

H

H

H

HH C

H

H

H+H

H

H

HHHC

H

H

H H+

125ndash127

X= P AsSb

(37)





CCH2

CH2CH3CH2CH3H

HFBF3

128 129

CO

2+

CH3CCH2CH3

CH2CH3

C

O

H

130

C

O

H

H

C

OH

HC

CH3

CH2CH3

CH2CH3

H

CCH3CH2

CH2CH3

CH3

C

O

H

+

minusH+

C

CH3

CH2CH3

CH2CH3

C

OH

H

+

H+

C

O

H

++

+

131




C

O

H

128 129 132


133

+

C

O

H

H

+

+C

O

H

H Ad+ dminus

C

O

H

BF3

d+ dminus

+BF4

minus+


VICINAL SYSTEMS 153






C

O

H HH

H


C

O

H H

H

1232 (6-31G) 1102 (6-31G)1120 (MP3 6-31G)

132

CH HHCinfinv

CH HCHCinfinv

2+



2+

Cinfinv

2+

132135 134

1087 (6-31G)

128

O OO

+

C

O

H Cinfinv

+

C

O

H

H

Cinfinv

+

+



C

O

H3C OHC+O

CH3

HFBF2C

O+

CH3

136 137

HFBF3

minusH2OC+O

CH3

H F BF3d+ dminus

C+OH

CH3

+




m

138 139

C+

O

H3C AlCl4

AlCl3d+ dminus

minusC

O

H3C Cl AlCl3

AlCl3

d++

dminus

dminus



CCO

ClCH3

H3CH3C

2 AlCl3C

CO

CH3

H3CH3C

AlCl4minus

CC

O

CH3

H3CH3C

AlCl4minus

AlCl3

(CH3)3CHH C(CH3)3

CCO

HCH3

H3CH3C

AlCl3

140

+ +

+ +minusminus

(38)


VICINAL SYSTEMS 155




C OH+ minus2H++ + +

C O H

141

ClOH

HCl

O

Cl

+

+

(39)






C OBr

H-Aor SbF5

C OBr H A+ d+

d+

+

dminus

dminus

+CH3CH2CH3

SbF5 CO

Br2 (---SbF5)

H3CC CH3H

C HBrO

HA

minusHBrminusHA

+

H3C C CH3H

CO

142

Scheme 11




RprimeC

Rprime

OH

RprimeC

Rprime

O+

++

H

RprimeC

Rprime

OH H

H+


(40)


CRR

RRprimeC

RprimeH

RprimeCR

R

RRprimeC

Rprime

RprimeH+ ++ + (41)

VICINAL SYSTEMS 157

CO

R CH3

143a R = H 143b R = CH3

CCH3

CH3CH3H

HFSbF5or HFBF3

COH

R CH3

H+

COH2

R CH3C

CH3

CH3CH3H

COH2

RCH3

CH3C

CH3

CH3H

144 ab 145 ab

NO REACTION

ISOBUTANECOH3

R CH3

2+

+

+ +

+

+

+








OCF3

acid




5 h

5 h

99

43

temperature

0degC

0degC

OHCF3 OH2

CF3 O

CF3

146

+ +

+

Scheme 13



O

acid

OH

F3C F3C

OH2

F3C F3C

product yieldtime

20 min

20 min

68

2

temperature

80degC

80degC

147 148

+ +

+



acid system

Scheme 14

VICINAL SYSTEMS 159


CF3SO3H

C6H6

O

H

OH

+150

149

151

152

153

100 CF3CO2H





100 CF3SO3H

minus27

minus90

minus10

minus12

minus13

minus14

0

4

15

40

77

83

Acid Acidity H0

Total YieldProducts

150+151+152+153



OH+

+ + + +

++++

2+ +

+H H+

OH2

H

OH2

H

14 12 12

OH

H

13

OH

H

154

OH

H

156

OH

H

155

HH

H

H

H

HH

(42)




VICINAL SYSTEMS 161

PhPh

O

PhPh

CF3SO3H

PhPh

OH

PhPh

PhPh

OH2

PhPh Ph

PhPh

Ph

H2OPh Ph

157 158 159 16052

+ +

++

+

(43)



C CH3

CH3

CH3

HCO

HFminusBF3

C CH3

CH3

CH3

C

H

HO

C CH3

CH3

CH3

C

H

OH

H

CCH3

CH3

CHO

HH

H3C

CCH3

CH3

CHHO

H3C

H+

minusH+CCH3

CH3

CHO

H3C

HCCH3

CH3

CO

H3C

H CCH3

CH3

C

H3C

OH

HH

161 162

163164166 165

minusH+

+ +

+

+

+

+

+

+

+

Scheme 15









VICINAL SYSTEMS 163

Ph

Ph

O

O

OH

OH

O

O

PhOH

OPh

PhOH2

OPh C

PhOH2

O

Ph

O

O

PhPh

C

Ph

OH2

O

Ph

C

Ph

OH2

O

Ph

C

Ph

OH

O

Ph

O

OH

PhPh

C6H6

H2SO4

C6H6

CF3SO3HO

O

PhPh

Ph

Ph

O

O

CF3SO3H

C6H6

CF3SO3H

minusH+

H+

167 168

169

170170

minusH+

+ +

+

+

+

+

+

+

+

+

+

Scheme 16

OCH3

OCH3 FSO3HSbF5 H+hn

Δminus60degCOCH3

OCH3 OCH3H

171 172 173 174

+

+ ++

(44)



HOC

OH

OH HOC

OH2

OHHO C OH CH4

175 176

H+ 4H2

minus2H3O+

H+

H3O+

30

+

+

+ + +

(45)









CCl4ndashSbF5


+ (46)

CCl4ndashSbF5


+(47)

H3C NCH3

CH3

O

HH3C N

CH3

CH3

OH

H


H3C NCH3

CH3

O

H

F

80


minus30degC

+

+

(48)


VICINAL SYSTEMS 165

XC

X

X XC

X

X

SbF5

HFndashSbF5

XC

X

X

SbF5

X = Cl Br I

XC

X

XH

179

178177 177

++

+d+

+

+

dminus






ClC

Cl

ClCl

ClC

Cl

Cl

ClC

Cl

ClH+

++ + +

+++

+ +

ClC

ClH

ClH

HClC

ClH

ClH



1766 1648 183916061603

17791575

1732

NA 695 274 43NA

184183182181180








(1)+



(2)+



(3)+


CH3CHCH3 minus39181

(4)2+


HCCl3 H++


(5)3+


HCCl3H2 ++


(6)4+


HCCl3H3 ++


VICINAL SYSTEMS 167








BrC CH

HH

H

H

H


2+

BrC CH

HH

H

H

H


2+H

188 189

BrC CH

HH

H

H

H

187

HXC H

H

H

H

2+

H

190 Cs

X = F Cl Br I

+

Figure 6












DF-SbF5

20degC

NCH3CH3

H3C

CH3D2+

2+

+

N CH3CH3

H3C

D

not formed191

N CCH3

H3C

CH3

N CH3CH3

H3C

CH3

DH

HH N CH2D

CH3

H3C

CH3

minusCH3+

minusH+

192

+

+

Scheme 19

VICINAL SYSTEMS 169


H3CN

NCH3

CH3

CH3

CH3SO3F

CH3SO3F

H3CN

NCH3

CH3

CH3H3C

No Reaction

70 H2SO4

H3CN

NCH3

CH3

CH3H3C

H

193

+ ++

(49)


N

N minuseminus

+ +

+minuseminus

N

N

N

N


194 195 196

(50)


N

N

Br OH

40 HBF4

N

N

197

2BF4minus

+

+(51)


BrBr +

CH3

13C

H3C

NN

CH3

CH3

CH3AgBF4

HBF4N

NH3C

CH3

CH3

CH3

CH3

198

2BF4minus

+

+

(52)




N

NCH2CH3BF4

minus

(CH3)3O BF4+N

NCH2CH32 BF4

minus

CH3

++

+

+

minus (53)

N N

S

N N N N

S

H3C CH3

S

H3C CH3

1992 BF4

minus2 BF4minus

(CH3)3O BF4++

+

+

+ +

minus

(54)


VICINAL SYSTEMS 171

N+ +

+N Cl

2 Clminus

H2O

N N O

Clminus

+ 2 HCl

200

(55)

N

NCH3

CF3SO3H

N

NCH3H

H

H+

N

NH

HHH N

NCH3H

HHH

201

+

+ +

++

+

CH3

++



Ph N N PhCF3SO3CH3

Ph N NPh

CH3CF3SO3

minus+

(57)

N Nminus2eminus

NaClO4

N N

2 ClO4minus

++

(58)

NN

2NO+ PF6minus

CH3CN N

N

202 203

81

2PF6minus

+

+

(59)





204 205 206 207

N N NH

HH

+ +N N N

H

H

H+ +

CN H

H

NH

H+

+N N HH

++

CN H

H

N FSO3H-SbF5

minus120degC


++

++

minus

N2minusH+

CN H

H

NH

H

208

(60)




VICINAL SYSTEMS 173

NN

OHF-SbF5

SO2

minus78degC

NN

OH

NN

OH

H

minusH2O

211

N NN NH2ON

NHO

209 210

+++

++

++

Scheme 20





NO O NO O NO OHH A

213 214212

+ + δ++ +


215


H

NO2

216


+ BF4minus (61)


NO2Cl ++ d

+

dminus

minusNO O

AlCl3

Al2Cl7217

3 AlCl3(62)


CH

HH

NO2H

H2+

CH3NO2H+ + H+

214

218

B(O3SCF3)3NO2

+CF3SO3H

NO2H2+ CH4

(63)




VICINAL SYSTEMS 175






H2O2

HF-SbF5

minus25degC HO

OH

H

XminusH

OO

H

H

2 XminusH219+

+

+(64)


H3CO

OCH3

CF3F-SbF5-SO2

minus50degC H3CO

OCH3

CH3

220

H3CO

OCH3

CH3

221

CH3

+

++ (65)



S

S

S

S

2 CF3SO3

2 (CF3SO2)2O

+

+

minus(66)

S

S

2 CF3CO2

S

S

O

CF3CO2H +

+ minus

(67)




VICINAL SYSTEMS 177

S

S

S

S

2 Xminus

2 Xminus

OHX

S

SHO

S

SO

H

H

222 223 224

225

minusH2O

Xminus

HX+

++

+

+

Scheme 22


S

S

2 CF3SO3

225

OH

OHSSminusH+

+

+

++

minus

(68)




H3CS

CH3

OH

H3CS

CH3

O

HH3C

SCH3

OH

H3CS

CH3

O

H

2+ 2+HH

226 227 228 229


+ +





Cl ClAlCl3

Cl Cl AlCl3AlCl3

Cl Cl AlCl3AlCl3

HA

230

231

Cl ClH

A

HACl ClH

A

H

A

d+

d+

dminus

dminus

dminus

d+

d+

dminus

dminus

d+

d+

dminus

(69)


2+ etc)116


VICINAL SYSTEMS 179


X OH+

X O HH+

X OH

HX O Hor

H232 233

+ + + + +IIII (70)

H ClH+ H+

HO Cl

H

HO Cl

HH

234

+ + +O (71)


HO ClH+ H+ H+

O

O

O HO Cl

O

O

OH HO Cl

O

OH

OH HO Cl

OH

OH

OH

235 236

+ ++

+

++ (72)






F FSbF5

F F SbF5

SbF5F Xe F SbF5SbF5

237

Xe Xed+

dminus

dminus

dminus

d++

(73)




HC

H

H

H

He

2+

238



2+ and He

REFERENCES










REFERENCES 181






































REFERENCES 183










































REFERENCES 185























489 209









187

copy



(CH3)3C-Xsuperacid

CCH3

CH3

H3C

1

(1)

OHHO

FSO3HSbF5

2

OH

4 5

minus78degC

3

+++

++

(2)



ClCl

6 8

minus78degC

SbF5

7

minusH+

+ + +(3)

Ph Ph

Ph PhOHHO

9Ph

Ph Ph

Ph

FSO3HSbF5

minus130degC

FSO3HSbF5

minus78degCPh CH3

Ph

Ph Ph

OH

++

+

+(4)

FF SbF5 Fexcess

SbF5

10 11 12

+ + +d+

dminus

(5)






12 13 14

Rel Energy(kcalmol)

00 04 33 15

HH

HH+ + +

+++

++


OHOH

FSO3H-SbF5

SO2ClF minus78degC

d13C

16 17

262

+ +

(6)CH3

274

18

d13C

+




Ph

Ph

Ph

Ph

PhPh

OH OHFSO3H-SbF5

SO2ClF minus78degC

Ph

Ph

Ph

Ph

PhPh

or

Ph

Ph

Ph

Ph

PhPh

2+

19 20

+ +

(7)


Ph

Ph

Ph

O O HA

or

O OH

Ph

PhH

NO2 Ph

PhH

NO2 etc

21 22 23

minusH+

N+

++ +

+ d+

+ + ++

N

(8)



O

HNO3

70 H2SO4

OH OHO2N H

minus2H+

O

NO2

24

++ +

(9)





2+

2828

CH3

CH3

CH3

H3C

H3CC

CH3

CH3

CH3

CH3

H3C

H3CC

CH3

29 29

2+

CH3

CH3

CH3H3C

30

N

NO

N

N

CH3

CH3

H3C

H3C

31

O OH

CH3H

H

O OH

CH3H

H

32 32

+

++ +

+ +

+ +++++




HO CH3DSO3F

SO2ClFminus78degC

CH3 CH3

H

D

H

D

D+

minusH+D+

minusH+

CH2D

H

D

CH2D

D

CD3

DD

DD

25 26 27

+ + + +

+++ +



DFSbF5

33

minus78degC

H3CC

CH3

CH3

H3CC

C

CH3

HH

H

D

H3CC

CH2D

CH3

minusH+

1

+ +

+

+

(10)


CH2CH3

34 35

CH3CH2 CC

CH2CH3

HH

H

H

C

HH

36

CH3CH2 CC

CH3CH2

CH3H

H

H

++ + + +

+

(11)







37 38 39

CC

C

H H

HH

HH

H

H

H

H

+ +C

CC

H H

H

H

HHH

HH

H

++ C

CC

H CH3

HH

HH

H

H

H

H

+ +





H3CC

CC

CH3

O CH3

HHH3C

CC

CCH3

O CH3

HH

40a 40b

HH

+ +

+

+




H3CC

CC

CH3

O CH3

H

H+ H+

41

H3CC

CC

CH3

OH CH3

H

H3CC

CC

CH3

OH2 CH3

H

H3CC

CC

CH3

OH CH3

H

H+

HH3C

CC

CCH3

OH CH3

HH

42

40b 40a

H3CC

CC

CH3

O CH3

HH

43

Cl3Al

+ +

+

++

+

++

+minus

(12)


O

HF-SbF5

OH OH OH

CH3

O

CH344 44

+

+ +

+

+

+(13)

O

R

Rprime

CF3SO3H

OH

R

Rprime

45

OH

R

Rprime

45

+

+

+

+

(14)



Ph CH3

OH

Ph Ph

OH2

46 47

+

+ +

+


OH 3 equivAlCl3

C6H12

OX

H H

H

H

OC6H12


minus

+

+(15)

OCH3

Ph

HF-SbF5OCH3

Ph

49

SO2ClFminus30degC

OCH3

Ph

49

+

++

+ (16)





OH

O

Ph

50

CF3SO3H

C6H6

O

Ph

51

(17)

OH

OH

Ph OH

OH

Ph OH

OH

Ph

Ph

53

OH

OH

Ph

52 53 5554

OH

OH2

Ph

+

+

+

++ +

+ +


O

Ph PhOH

OH

Ph

57

Ph

OH

O

Ph

56

CF3SO3H

C6H6

Ph

OH

OH

Ph

58

PhPhC6H6

+

+ +

(18)

CH3Ph

59

Ph

Ph

CF3SO3H

C6H6

PhNo Reaction

C6H6

+ (19)




Ph NH2

OCF3SO3H

C6H6 Ph NH2

OHC6H6

Ph NH2

OPh

60 61

+

+

(20)


C6H12

N OH AlCl3N O

H

X

62 63

H

H

N O

H


80

90degC

+

+

(21)

64

N O

H

X

H AH

H

d+

+

dminus




CO2H

O

Ph Ph

65

99

CF3SO3H

C6H6Ph

HOOH

H

66C6H6

58

Ph

HOOH

H

66

OH

OH

Ph

57

Ph

Ph +

+

++

+

+(22)

CPh

67

C6H6

Acid

Ph NH

O

Ph

H

HN

H

O

Ph68

NHPh

O+

+

(23)


P

Ph

Ph

PhN

H

Ph

Ph

69 70

NNN

H

71

+ +

++

+

+


H3C CH3

O O FSO3H-SbF5-SO2

minus60degC H3C CH3

OH OH

H3C CH3

OH OH

73a 73b

+ +

+ +(24)





HO OHCH3

HO OH

90 91

OH

OH

OH

OH

OH92 93

++

+ +

+

++



H3C NH2

O O

H3C NH2

OH OHCF3SO3H

78 79

C6H6

H3C NH2

O

95

PhPh

99

H3C NH2

Ph OH

94

+ + +

+

(25)



HO OH

O O

HO OH

OH OH

O OO O OHHO

XN OHHO

XN OO

H3C CH3

O O

H3C CH3

OH OH

H3C OH

O O

H3C OH

OH OH

H3C OCH3

O O

H3C OCH3

OH OH

H3C NH2

O O

H3C NH2

OH OH

N N

OO

O

HH N N

OHO

OH

HH


(1)

(2)

(3)

(4)

(5)

(6)a

(7)

(8)

72 73

74 75

76 77

78 79

80 81

82 83

84 85

86 87

OH

OH

OH

OH88 89

(9)

X = H Cl Br I

CF3SO3H

CF3SO3H

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

HF-SbF5

CF3SO3H

FSO3H-SbF5

BF3-H2O


+ +

+ +

+ +

+ +

+

+ +

+ +

+

+

+

+

+




O OHHO

83

OC OH

OH

COHO

OH

96 96

+

+ + + +

+ (26)




NO2

F N OO

XBF3-H2O

NO2

F

X = Cl Br I84

X

819592

X Yield

ClBrI

97

+ (27)




N OO

Cl

N OOCl+

N OO

Cl

N OHOCl+

H

N OO

Cl

N OHHOCl+

H

H

N OO

Cl HN OHHO

Cl+H H

H

ΔH kcalmol

3244

1922

702

minus1020

98

+

++

+

++

+

+

+

minus

+

+

+

+


H

Cl

N OO

Dagger

N OO

Cl

H Cl

N OO

ΔG1Dagger

d+ _

_

+

(28)


ΔG1Dagger ΔG2

ΔG2δ+

Daggergt

H

Cl

N OO

H H

H

DaggerN OO

Cl

H H

H

H Cl

NH

OHHO

Dagger

+ ++

++

+

+

+ +

(29)



N N

OO

O

HH N N

OHO

OH

HH

86 87

CF3SO3H

C6H6

2 C6H6

N N

O

O

HH

Ph

Ph

+

+

(30)






H3NO

O

CH3FSO3H-SbF5-SO2

minus60degC H3NOH

OH

CH3

H3NO

CH3

99 100

minusH2O

+ ++ +

+minus (31)

H3N OH

OH

minusH2O H3N

O

101 102

+

+

++

(32)


Ph OH

NHTs

OCF3SO3H Ph OH

N

OH

SH

H Ar

O

O

103

+

+ (33)


H2NOCH3

OCH3

CF3SO3H

C6H6

H3NOCH3

H3NOCH3

H3NPh

C6H6 minusCH3OH

H2NPh

Ph95

104 105 105

106107

++

+

+

+

+

(34)




N

O CF3SO3H

N

OH

H

N

OH

H

+

+

+

+(35)


NO

CH3

X

CF3SO3H

C6H6

N

CH3

X

PhPh

92

+ +

minusminus

(36)





N

O

H

N

OH

H

H

N

S O

CH3 N

S OH

CH3

H

NH

O

NH

OHH

NO

CH3

Xminus

NOH

CH3

N

OH

N

OH H

N

OH

N

OH

X

CF3SO3H

CF3SO3H

CF3SO3H

CF3SO3H

CF3SO3H-SbF5

HBr-AlBr3

X = H or AlnBr3n

108

109

110

111

112

113

(1)

(2)

(3)

(4)

(5)

(6)


+

+

+

+

+

+

++

+

+

+

+

+

minus

NH

O

Cl

14-20 equivAlCl3

m-C6H4C12

N

OAlCl3

H

AlCl3 NHO

Cl

Cl80

116114 115

N

O

H+ +

d+

dminus

(37)



N

O

O

OH CF3SO3HN

OH

O

OH2N

OH

O

CH2 N

O

OCH2

N

OH

O

CH2N

OH

O

CH2

H

117 118

117 117

N

OH

O

CH2

117

N

O

O

OH CF3SO3H

C6H6

N

O

O

++

+

+

+

+

++

+

+

++

Scheme 2



N

O

OH

CH3

CF3SO3H

p-C6H4Cl2

N

O

CH3

Cl

66

80degC Cl

N CH3

O

120

N CH3

OH

121119 122

+

+

+

(38)

123

N

O

OH

CH3

CF3CO2HN

O

CH3

OCH3

67

80degC H3CO

N CH3

O

120119

p-C6H4(OCH3)2

+

(39)


PhP

O

PhPh

CH3

PhP

PhPh

CH3

Ph

Ph

X

88CF3SO3H

C6H6

PhP

OH

PhPh

CH3

124

+ + +

minus

(40)



N CH3

O

++

N CH3

OH

HH

+

TheoryLevel




+126

N CH3

OH

+

+

+

N CH3

OH

HH

2+




120

121

TheoryLevel





H3C OCH3

O

H3C OCH3

OH

H3C OCH3

O

HH3C

O

+acid

CH3OHAac1

125 126

+

+ +

(41)


H3C OCH3

O

H3C OCH3

OHFSO3HSbF5

SO2minus78degC

H+

H3C OCH3

OH

127H

H3C

O

+ CH3OH2

125

+++

++

(42)




H3CO CH3

O CH3

BF4

CD3FSbF5SO2

minus30degC

128

H3CO CH3

O CH3

129

D3C

H3CO CD3

O CH3

130

(NuCH3)+Nu

++

+

+

minus(43)

O

H3CCH3

O

HF-BF3

O

H3CCH3

HOOH

H3CCH3

HO OH2

OC

CH3H3C

131 132 133

++++

+ (44)




OCH3

O

CF3SO3H

C6H5NO2

O

NO2

82

(45)

OCH3

OH

H

OCH3

OH2

134 135

+

+

+

+



F3CC

OH

OFSO3HSbF5

F3CC

OH

OHH

F3CC

OH2

OH minusH2O

F3CC

OHCF4

136 137 138

minusSbF5

minusCOH+

CF3

139

+ ++

+

+

+

SbF6minus

+

(46)








HC

O

O

141

H

H

H

H3CC

O

O

140

H

H

H



2+2+




H3CO O

CH3

CH3 CH3 O OHH

142 143

++

++


O HF-SbF5

SO2

O OOH

HO O

HO O

H

HO O

H H

H144

145

146

+ +

+

+

+

+ +

(47)


HOCH3

OH

OFSO3HSbF5

SO2minus80degC

HOCH3

OH2

OH

minus30degC

minus2 H3O+ O

O

CH3

CH3

OH

HOHO

CH3

OH2

OH

147 147 148

+

+

+

+

+

+

(48)


HO

CH2CH2

OH

FSO3H SbF5

SO2minus80degC

O

CH2CH2

O

H

H

H

H

minusH2O

O

CH2C

H

H

H

H

~H

minusH+ HC

CH3

OH

149 150 152

O O

H

H

H

H

151

C C

H H

HH

2+

+ + +

+ +

+ d+

d+

(49)

O

CH2CH2

O

H

H

H

HminusH2O

149

O

CH2C

H

H

H HC

CH3

OH

152

+ +

+ +

minusH+ (50)



CH3O

CH2 CH2

OH

FSO3H SbF5

SO2

minus80degCO

CH2 CH2

O

H

H3C

H

H

minusH2O

HC

CH3

O

153 154

H3C

+ +

+

(51)




C

CH3

CH3

CH3

C

OH

H C

CH3

CH3

CH3

CH C

H3C CH3

CH3

C

H

CH3CCH3

CH3

C

O

H

C

CH3

CH3

CH3

C

O

HH+ H+

minusH+

C

H

CH3

CH3

CH3CC

H3C CH3

CH3

C

OH

HCH3C

CH3

CH3

C

H

155 156 157

158159160

+

OH+

OH2

+OH2

+

OH2

+

+

+

++




O

NH3C

Ph

H3CN

O

H

Ph

Ph

CF3SO3H

O

NH3C

Ph

CF3SO3H

H H

H

H3CN

OH

H Ph

C6H6O

NH3C

Ph161

162163

C6H6

+ +

+

+

+

(52)



NO

S

PhPh

2 equiv AlCl3

C6H6 NO

S

PhPh Ph N

Ph

AlCl3

AlCl3S

AlCl3

OAlCl3Ph N

PhS

OH

Ph

76

164 167165 166

+

+minus

minus

+

+

minus

minus

(53)


624 Acyl-dications


RC

O

RC

O

168a 168b

HR

COH

169

+

+ +

++




ClC

CCl

O

O

SbF5 SO2ClF

minus80degC ClC

C

O

O

SbF5

ClC

C

O

OSb F5

minusCOCl

CO

C

C

O

O

170 171 172 172

173 174

+ ClC

O+

+

+

+

+

dminus

d+




FC

CC

F

O O

HH

SbF5 SO2ClF

minus80degCC

CC

F

O O

HHSbF5

CC

CO O

HH

CC

CO O

HH

175 176 177

+ + +

++

FC

CH2C

F

O O

178n

SbF5C

CH2C

O O

nn ge 3 2 SbF6

+ +minus

d+

dminus

(54)




H3C CC

OH

O

OFSO3H

H3C CC

OH

OH

O

H3CC

COH

OH

OH

H3C C CO

OH

H3CC

CO

OH

H3CC

O

179

180

181

SbF5 +

+

+

+

+

+

+ +

(55)


HF-SbF5H2C C

OH3C

CO

H3C CO

CO

185184182 183

186

Cl CO+

+

+ +

+

+ +

(56)


HF-SbF5

187

H3C CO

188

CH3

H3C CO

189

H3C CO

CH3

H3C CO

productsCl CO

CH3

++

+ +

+ +

++

+ +

CC

CO

H

HH H

CC

CO

H

H

H

H

190 191 192

CC

COH

H

H

H+

+ + +

+

+ (57)




CC

CO

CH3

H3CH H

CC

COH

CH3

H3C

HC

CC

OC

H3C

H

193 188 194

HH

H

HC

CC

OH

CH CH3

195

H

HH

CC

CH3

H3CH H

196

H

H

++ + +

+

++ + + +





NO

O

CF3SO3H

C6H6

0degC

NOH

OH

NOH

197

96

NOH

OH

197

++

+

+

(58)

NO

O

CF3SO3HN

OH

OH

199

H3C

CH3

H3C

CH3

198

+ +

(59)

NOH

OH

2+ +

197

H

H

H

N

N N

H H

H

H

H

H

200



Ph

NO

OCF3SO3H

C6H6N

OH

OH

PhN

OH

CH3CH3 CH3

OH

CH3OH

minus40degC

Ph NOHCH3

OHOCH3CH3OH

OCH3

CH3

OCH3

C6H6

H2OPh

CH3

O

85

201 202 203

+ + + +minus

Scheme 5


NO

OCF3SO3H

2) H2O

minus40degC

1) CH3OH

2 hr72

Ph

O+

minusC6H6

(60)


NO2

NO2

CF3SO3H

minus20degC

CF3SO3H

minus20degC

209 211

NOH

OH

210

21

+

+ (61)


NO

O

CF3SO3H

C6H6

40degC4 hr204

NOH

OH

C6H6

NOH

OH

205 206

NH

OHN

O

208

NH

OH

207a207b

minus2H+

minusH2O

+

+

+

+ +

+

++

H+

minus

Scheme 6



CF3SO3H

C6H6

Ph

NH2NO2 50N

OH

OH

N

OH

OH

212

213

214

+

+

+ +

(62)




NO2

CF3SO3H

215

N

216

OHHON

216

OHHO+

+ +

+ (63)

NOH

H

CF3SO3H NH

H2+ 2+ 2+

++

NH

H

NH

H

minusH2O

(64)



H3C NONa

OHF

C6H6

H3C NOH

OH

H3C NOH

OH2

H3C NOH

OH2

Ph N

CH3

OH

C6H6217

+

+ +

+

+

+

minus

(65)

EtONO2

O CF3SO3H

C6H6 EtON

OH

OH

OH

EtON

OH

OH2

OH

C6H6

EtON

O OH

Ph219218

+

+++

+

(66)


PhNO2

O

PhN

OH

OH

OH

PhN

OH

OH2

OH

C6H6

PhN

O OH

Ph22 0 221

CF3SO3H

C6H6++

+

+

+

(67)




PhNH2

CH3

OHPh

PhNH3

CH3

Ph

PhNH2

CH3

PhPh

222 223 80

CF3SO3H

C6H6+

+ (68)

PhC CH3

Ph

59

+


HN

CH3

OH

OH

HO

224

FSO3H-SbF5

225b225a

NCH3

OH

HO

H H

++

NCH3

OH

HO

H H+

+

(69)


N

CH3

CH3

CF3SO3H

C6H6 N

CH3

CH3HN

CH3

CH3

Ph

87

226 227

+

+(70)

NHN

CH3N

CH3

Ph

228

CF3SO3H

C6H6

+ +

(71)


NOCH2CH3

OCH2CH3

CF3SO3H

o-C6H4Cl2

N Cl

Cl

Cl

Cl

CH3CH2

CH3CH2N

OCH2CH3CH3CH2

CH3CH2

H N

CH3CH2

CH3CH2

H Cl

Cl

CH3CH2

CH3CH2

229 230

231

+

+ + +

(72)




PhC

CN

OHPh FSO3H-SbF5

PhC C

PhN

PhC C

PhN H

232 233 234

orPh

C CPh

N

235

H Ad+ dminus+ + + +

(73)

PhC

CN

OHPh CF3SO3H

236

C6H6 PhC CN

PhPh

237

74 (74)


REFERENCES





REFERENCES 227





































REFERENCES 229

















7036









N

H3C

OCF3SO3H

C6H6 N

H3C

Ph Ph

Reactive to C6H6

1

N

H3C

OH

H

+

+ (1)


231

copy


Unreactive to C6H6

NH

HO

CH3

2

+ +



3a 3c3b

H3C CH3

OH OH+ +

H3C CH3

OH OH+

+ H3C CH3

OH OH

+ + (2)

4 5

N O

CH3

PhPh

H H+

H3C NPh

OH

H Ph

+

++

(3)


72 DISTONIC SYSTEMS





H3CCH3

CH3

CH3

Cl

Cl

SbF5

SO2ClFndash78degC

6

H3CCH3

CH3

CH3

++

(4)



H3C

CH3

OH

H3C

CH3HO

H

H

FSO3H

SbF5SO2ClF

87

H3C CH3

CH3 CH3

+ (5)

FSO3H


9

OH

HO

H

H

10

H

H

+

+(6)

CH3

OHHO

H3C

11 12

CH3

H3C

++

(7)




CH3

OH

H3C

HO

FSO3H

SbF5SO2ClF

13 14 15

CH3

H3C

H +

CH3

H3C not formed+

+

(8)

FSO3H

SbF5SO2ClF

OH

HO

16 17 18

+

++

+

(9)

H

H

H

H

HO

OH SbF5SO2ClF

ndash78degC++ (10)


19 20CH3

H3CFSO3H

SbF5SO2ClF


+

+ +

+ (11)

21

+ +



S SS

SS S

CH3

CH3

H3C

H3C

CF3SO3H

22

S SS

SS

CH3

CH3

H3C

H3C +

+

(12)



Cl

Cl

SbF5

SO2ClFndash80degC

23 24 25Cl

+ +

+(13)



2527261

4


28

+ +

+

Figure 1




HOH

HO

H

FSO3H-SbF5

ndash80degC

29 30 31

HOH2

H2O

H

++

H

H

+

+

(14)


CH3

OH

HO

CH3

FSO3H-SbF5

ndash80degC

32 33 34

CH3

H2O

CH3

+

+CH3

H3C

+

+

(15)



37

CH3

CH3

H3CCH3

OH

OH

SbF5

SO2ClF

38

3635

+ + CH3

CH3

H3C CH3+

++

+

(16)






PhPh

Ph

Ph

2224

PhPh

Ph

Ph

PhPh 2479

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

2451

2523

2456

2209

39

40

41

42

43

44

+

+

+

+

+

+

+

+

+

+

+

+



CCH3C CH3

CH3

CH3

CH3H3C

45 46

C


1379

+ + +

14912408

471minusCH3C+

CipsoCring

142414072557

339minusCH3C+

CipsoCortho





47 48 49


Ph

Ph

Ph

Ph+ +

Ph

Ph

Ph

Ph

+

+Ph

PhPh

Ph

+ +


OPhPh

PhPh

(CH3)3Si-O3SCF3

[(CH3)3Si]2O

2 eminusPh

Ph

Ph

Ph

50 512 Xminus

Ph Ph PhPh+ +

(17)

BBPh Ph PhPh

52





(H3C)2N

CH3

CH3

(H3C)2N

CH3

CH3

N(CH3)2

H3C

H3C95

50 X = ClO4minus

(18)




53

2eminus

OCH3H3CO

H3CO OCH3

54

OCH3H3CO





ArAr

ArAr

HO

OHAr = p-MeOC6H4

55

HBF4

56

ArAr

ArAr

Mg

57

ArAr

ArAr

+

+2 (p-BrC6H4)3N

SbCl6

+

minus

(20)



OR

ROS

S

HBF4

S

S

Zn

SS

58 59 60

2 (p-BrC6H4)3N

SbCl6minus

++

+

(21)



iodine (eq 22)23

ArAr

ArAr

Ar = p-(Me2N)C6H4

61

I2

ArAr

ArAr

62

H H

2 I3minus

+ +

(22)




HC

CC

CHH

H

H H

H H

H H

HH

2+ 2+

HC

CC

CHH

H

H H

H HHH

H

H

63 (C2) 64 (C1)




minusH+ minusCH3+

HC

CC

CHH

H

H H

H H

H H

H H2+

63


CC

HH

H

HH

H

HH

+

HC

CC

C

H

HH

H

H HH

HH H

+



H3C

CH3 HH

H

H H3C

CH3

CH3

H

H H

65 66

++

+ +





H3C CH3

O HF-SbF5

CO 20C

H2O

H3C CH3

O CO2H

+ H3CCH3

O

CO2H

H3C CH3

OH

H3C CH3

OHHH

H

H

H+

H3C CH3

OH

H3C CH3

OH CO H2OCO

67 68

67

H2

H

H3C

CH3OH H

HH

CH4

~HH3C

CH3

OHCO

H3CCH3

OH

CO

H2O

68

69 70 71 72

73 74 75

+

+

+

++

+ +

+

+

++

+

+

+ +

Scheme 1



H3CCH3

O

CH3

HF-SbF5

CO minus20degC

H2O

H3C

CH3O

CH3

CO2H

60

(24)



CH3

CH3

O HF-SbF5

CH3

CH3

OH H+CH3

CH3

OH

H

H

H

H2

CH3

CH3

OHOH+CH3

CH3

OCH3

CH3

76 77 78

7980

+ + +

+ + +

(25)



H3C NCH3

O

H CH3

CCl4 HF-SbF5

minus30degCH3C N

CH3

OH

H CH3


H3C NCH3

O

H CH3

F

81 82

+

+






O FSO3H-SbF5

O3 minus78degC

O O

60(27)

CCH2CH2CH2CH3

H

OFSO3H-SbF3

O3 minus78degCC

CH2CH2

H

HO C CH3

H O O OH

HminusH2O2

CCH2CH2

H

HO CCH3

OH

HCH3

O

O 80

83 84

+

+

++

(28)

CCH2CH2CH3

H

OFSO3H-SbF5

O3 minus78degCC

CH2

H

HO C CH3

H O O OH

HminusH2O2

CCH2

H

HO CCH3

OH

not formed85

+

+

++




CO2HCF3SO3H

C6H6

O

CH38586 87

orH3COH

OH+ +

CH3 O

+

+

(30)


Ph CO2HCF3SO3H

C6H6

O

Ph9888 89

orPhOH

OH+ +

PhO

+

+

(31)

H

H

Ph

HOOH

CF3SO3H

Ph

OH

OH

90 88

++

+ Ph

OH

OH+ +

(32)


HO OH

OO

O

CF3SO3H

C6H6

C6H6

HOPh

OH

Ph

minus2H2O

minusCO HO Ph

OH

Ph

Ph

O

Ph Ph8991

+

+

+

(33)

CH3Ph

Ph

92

+




OH

ACID

OH

C6H6

O

Ph O

cyclohexane

93

+

+

(34)



O

NH3CPh

Ph

H3CN

O

H

PhPh

61

ClCl

CF3SO3H

o-C6H4Cl2

(86 de)94 95

H3CN

OH

H

PhPh

H

+

+





Cl CO

HF-SbF5 H3CC

OH3C

CO

96 97

H2CC

O+

+

+ + ++

(36)

C OHF-SbF5

98 99

H

HC O

H

H

H+ + +

(37)

DF-SbF5

100 101

C OCH2DCH2minusH+

25 D

20degC12 days

C OCH3CH2

+C OCH2CH2

D H

+

+

+

(38)





NR

OH

NR

OCH3

H3PO4

102

N

R

OCH3

H

+

+


NH

CF3SO3H

o-C6H4Cl2

Cl

Cl

42 NH

103

N

H

H +

+

(40)

N Ph CF3SO3H

C6H6

N Ph

Ph

99

104 105

N PhH +

+ (41)

107106 108 109 110

NPhH Ph

+

+ Ph

NPh

CH3H

H

+

+

NH3+

+Ph NCH3

HH

+ +CH3

H3N

+

+





N+

+

+

+

+

+

+

+

HN

N H

CH3N+

+

+N

Ph

OH

N+

N+ +

Ph

OH

PhN+ +NPh

OHOH

N

S

CH3

N

S

CH3

CH3

H

NNPh

NPh

PhCH3

CH3

N

PhCH3

CH3

H

N

O PhPhPh

H3C

N

O PhPhPh

H3C H


111

112

113

114

115

116

117

118

NN

CH3

CH3

Ph

119

N

O Ph

H3C

120

N

++




122

N

S

PhH

123

N

S

PhH

HCH3 CH3

N

S

Ph

CH3 CF3SO3H

minusH2OOH

12125degC

N

S

Ph

CH3

PhN

S

Ph

CH3

Ph56 26


+

C6H6 C6H6

+ ++

Figure 2



Ph

Ph

Ph2H+

NH

+

125 126


HF3-21G

HF6-31G (d)

HF6-311G (d)

PBE16-311G (d)

MP26-311g (d)

MPW16-311G (d)PCMsp

00

00

00

00

00

177

171

179

100

103

7400

124

++

Ph

Ph

NH

+

+

PhN




14-dication

15-dication

127

19-dication

110-dication

129

130

HN

HH

CH3+ +

128

HN

HH

CH3+

+ HN CH3

HH

+ +

HN CH3

HH

+

+



H2N

HO

H3CO

HCl ether

H3N

H2O

H3CO

H3N

H3CO H3CO

H3N

H3CO

H2NN

OH

H3CO

Butorphanol

131 132

+

+ +

++

+

Scheme 2



NH3C

OH

Ph

NH3C

Ph

Ph

H 98

CF3SO3H

134

C6H6

133

NH3C

Ph

H+

+

NH3C

Ph

H

H

++

(42)

N

PhOH

N

Ph

Ph 97Ph

Ph

CF3SO3H

C6H6

135

N

Ph

Ph

H136

N

Ph

Ph

H+

+

+

+

(43)



NNPh

Ph

Ph

HO

NNPh

86

CF3SO3H (44)

O

ON N

Ph NN

Ph

60

OHPhO

OCF3SO3H (45)



N

H

N

PhPh

CH3

CH3CH3

CH3

CH3

OH2

H

CF3SO3H

N

Ph

HNNH

H

minus H2O

138 139

93

CH3

N

Ph

OH

Ph

137

+

+

N

PhPh

H

CH3

+

+

+

+

+

N

PhPh

H

CH3

+

+

+

minusC3H6

minusH+




PhP

PhPh

CH3

CH3Br

CF3SO3H

C6H6Ph

P

PhPh

CH3

CH32 X

PhP

PhPh

CH3H3C

140 92

+ + + +

minus 2 Xminusminus

(46)

PhP

PhPh

Br

CF3SO3H

C6H6Ph

P

PhPh

2 X

141

CH3

CH3 PhP

PhPh

2 X

CH3 PhP

PhPh

2 X

CH3

142 143

99

++

minus minus minus

+ + +

minus

+



OH

CH3

Br

FSO3H-SbF5

SO2 minus60degC

CH3

BrSbF5

144

+

d+dminus

(48)







146 147 149148a 148b

H3CCH3

OH

OH

+

+

OH

HO+

+ OH

HO+

+OH

HO

+

+ OH+

O

O

FSO3H-SbF5

SO2 minus 60degC

145

OH

HO

+

+

(49)





150 a n = 0b n = 1

c n = 2d n = 3e n = 4

H3CC

(CH2)nC

OH

OH OH+ +

150de

FSO3H-SbF5

0degC minus H2O

151de

H3CC

(CH2)nC

OH

OH OH+ +

H3CC

(CH2)nC

OH O+ +

(50)

no reaction

150c

FSO3H-SbF5

0degC minus H2OH3CC

(CH2)2C

OH

OH OH+ +

(51)



N

O

O

CH3CF3SO3H

C6H6

N

O

CH3

Ph

Ph 90152

N

HO

OH

CH3

+

+

(52)

N

O

O

OEt CF3SO3H

C6H6

N

O

OEt

Ph

Ph 97153

N

HO

OH

OEt

+

+

(53)





154 a n = 0b n = 1c n = 2

d n = 3e n = 4f n = 5

C(CH2)n

COH

OH OH+ +

HO

t12 = 1 hr

minus H2O

minus 20degC

154d-f

FSO3H-SbF5


155d-f

C(CH2)n

COH

OH OH+ +

HO

156d-f

C(CH2)n

CO O+ +

C(CH2)n

C

OH O+ +

HO (54)



CO2H

CO2H

FSO3H-SbF5 minusH2O


+

OH

OH

OH

OH

OH

OH

O

O

OH

O

H

OH

OH

O

157 158 159

+ + +

++

+

+

(55)



OH

OMe

OH+OMe

160

OH

OMe

161

OH

OMe

162

OH

OMe

OH

OMe

163

OMHO OH

MeO

OH

MeO

OH

OMe

OH

OMe

164

OH

MeO

OH

MeO

165

(CO2MeH)6+

+ + +

+ + + + + +

+ + +

Scheme 4



H3COC

(CH2)nC

OCH3

O O

166 a n = 0b n = 1c n = 2

d n = 3e n = 4

H3COC

(CH2)nC

OCH3

OH OH

167 a n = 0b n = 1c n = 2

d n = 3e n = 4

FSO3H-SbF5

+ +

(56)




OO

O

OO

O

FSO3H O

O

O

O

minus2 CH3OH

168

+

+


OO

O O

O

O

O O

169 170

+ +

+

+

(57)


O

O

O O

O

O

171

+

OO

O

OO

O

OOO

FSO3H

minus2 CH3OH

++

(58)






NH

OCF3SO3H

C6H6

N

OH

H H172 173

NH

Ph Ph+

+ (59)

Ph PhO OH+

174

CF3SO3H

C6H6

(60)





NH3C

O

NH3C

OH

H

N O

O

N OOH

H

H3C N OCH3

H3C

OCH3

H3C N OCH3

H3C

H

HN CH3

HO

HO

OHN

CH3HO

HO

H H

H3C O

ONH3

H3C OH

OH

NH

O

HNH

OH

NOH O

H

HN

OH OH

H

N

SH3C

CH3

O

CH3 HN

SH3C

CH3

OH

CH3

NNPh

PhO

H

HNNPh

Ph H

N

H

O

H

OH

CH3

NCH3

Xminus

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)


175

176

177

178

179b

180

181

++

182

183

184

185

N

OH

NH

OH

+

+

+

+

++

+

+

+

+

+

+

+

+ +

+

+ NH3+

+

+

+

minus

+

HO


179b179a 179c

45degC

186

OH3N +OH

OHH3N

++H3C OH

OHNH3

+

+NH3

+H3C OH

OH

NH2+

+

(61)



N

CHOCF3SO3H

C6H5NO2

140degC N

NO2

NO2

53

(62)

N

CHO CF3SO3H

adamantane CO HNOH

H

H

O

ON

18060

++

+

(63)


NOH

CF3SO3H-SbF5

C6H12

C6H12 C6H12

NH

OHNH

OHN

187 188 189

++

++

(64)

ABr3 or AlCl3

C6H6N

OHNH

OH

Ph

N

OH

187

++ (65)

OH

190

+



191 193185 192 188

NH

OH+

+ NH

HO+

+ NH

HO+ + N

HOH

++

NH

OH+

+




OH

NH2

Acid

OH

NH3

Acid

OH+

++

+

NH3

195 196

OH

eLUMO

q3


3 3

+03 +025

190194



OX+

+NH2X



minus

1 C6H12

2 H2O

1 C6H6

2 H2O

O

NH2 O

NH2

70ndash80

15ndash40

OH

NH2

197

(66)





CF3SO3H

C6H6100degC

NH

CH3

O

NH

CH3


198

+

(67)

NH

CH3

O

NH

CH3

OH

78NH2

NH3

CH3

O

199

C6H6CF3SO3H

C6H6100degC

+

+(68)


H3N

NH

OHH3N

NH

CH3

OH

200 201

++

+

+

N

NH

O

PhCF3SO3H C6H6

25degC

NH

NH

OH

Ph

O

Ph70

202

+

+

(69)





NOH

OFSO3H-SbF5

NOH

HOH

203

++ (70)

NOCF3SO3H

204

SO

OCH3 NHO S

O

OCH3C6H5OH

H

NHHO SO

OCH3

HO

+

+

(71)


HOO

OH H

H

207HO O

OHH

H

CH3

208

+

++

+


COH

OCH3

FSO3H

COH

OCH3

H

COH

OCH3

H

CO H

OCH3

H

FSO3H

SbF5

CO H

OCH3

H

H

CO H

OCH3

H

H

205a

205b

206a

206b

+ + +

+

+ +

+

Figure 4



FC

(CH2)nC

F

O O

209d-h

SbF5-SO2C

(CH2)nC

O O

210d-h

minus60degCF

C(CH2)n

CF

O O

209 c n = 2d n = 3e n = 4

f n = 5g n = 6h n = 7

+ +

2 SbF6minus (72)




CF

O

CF

O

X

X

X

X


SbF5

CO

CO

X

X

X

X


+

+

(73)

X

X

X

X

213b X = Clc X = Br

+

+



2+ ions (213bc)




SS

S 2 NO+BF4

minus

S

S+

+

SS

S

S

minus2 BF4

214 215

(74)


S

S2 CF3SO3

minusS

S

H

2 CF3SO3minus

45216 217

+

+

++

+

(75)

SS

(CH3O)2CH

SS CH3H3C

2BF4minus

218

+

+ +BF4minus (76)



trade

trade



F3C S N S CF3

F O

OO

O

NN

CH2Cl

F2 BF4

minus

NF

BF4minus

NF

CF3SO3minus

S

O

O

NF

H

S

O

O

NF

CH3H3C


+018

minus004

minus037

minus047

minus078

minus210

219

220

221

222

223

224

+

+

+

+




trade


HO O

HFSO3H-SbF5

minus80degC

HO O

H

H H25degC

minusH2O minusH+

~H

225 226

+ + HOH

H

H

H H

HH

++

OH

H

H

H HH

H+

(77)

H3CCH3

OH

OH

FSO3H-SbF5

minus60degCH3C

CH3

OH2

OH2minus30degC

minusH2OH3C

CH3O

HH

O CH3H3CHH

2+

O CH3H3C

H

228

229

227

+

+

+

+

+

(78)


minus70degC

minusH2O

HO


H

230

HO O

H

H H++ +

+

+ +

+ ++



H3CO

OH

H

H

231

+ +

232

H3CO O

H

CH3

HH

+ +

233

H3C OO

H

CH3 H

H

+

+

234

H3C OO

H

H

H

+

+



235

FSO3H-SbF5

minus60degC

H3CO

OH

CH3

minus10degC H3C CH3

OHCH3H3O

minus10degC

H3CO

H

CH3minusH+

236

~H

H3CO

OH

H

H CH3

+ ++

+

+H3C

OCH3

+

++



NN

O

CH3

FSO3H-SbF5

SO2ClF

minus75degC

237

+

NN

O

CH3

H

+

+2 X

minusXminus (81)

NN

OH3C

FSO3H-SbF5

SO2ClF

minus75degC

NN

OH3C H

238

+

+

+

2 Xminus

Xminus

(82)






excessCH3F-SbF5

CH3-I-(CH2)n-I-CH3

239 a n = 1b n = 2c n = 3

d n = 4e n = 5f n = 6

+ +

(83)

Br Brminus78degC

excessCH3F-SbF5

Br BrCH3H3C

240+ + (84)


241 242 243 244

I

I

CH3

H3C

IICH3H3C

I

I

CH3

CH3

IICH3H3C

ICH3

Br

Br

BrBr Br

Br

CH3CH3CH3

H3C

Br

I

CH3

H3C

245 246 247 248

+

+

+ + +

+

+ +

+

+ + +

+

+





O

Br

CH3minus78degC

excessCH3F-SbF5

O

Br

CH3

CH3

H3C

O

Br

CH3

CH3

249 250

(10) (44)Ratio

+

+

+



X

X

excessCH3F-SbF5

minus70degC

X

X

CH3

H3C251 a X = I

b X = Brc X = Cl

252 ab

+

+

(86)

XCH3F-SbF5

minus70degC

X CH3


254a-c

+

(87)


REFERENCES 277


REFERENCES



































REFERENCES 279













































REFERENCES 281









283

copy










REFERENCES



6 1789

INDEX











142












287

copy

288 INDEX



















250251























INDEX 289



















NMR studies 260261










143











91

290 INDEX














211212CCl22+


CF22+






















INDEX 291












































292 INDEX







213Diprotonated









147148methane (CH6





















Superelectrophilic

INDEX 293





















F2OH22+) 114














193212geminal





294 INDEX




148




































INDEX 295



































4344Mesityl oxide


296 INDEX























2-Naphthol











162163Nitration










INDEX 297















8283NMR





Nucleophilicity 23

















246






298 INDEX































218diprotonated 218







trade

INDEX 299

































300 INDEX














































INDEX 301





dications 238239




Cover Page


ISBN 0470049618

CONTENTS

Preface

1 General Aspects








Index












QD27135E54043 2007547prime2dc22

2007019597


10 9 8 7 6 5 4 3 2 1

CONTENTS

Preface vii

1 General Aspects 1








Index 287

v

PREFACE



vii

viii PREFACE



1GENERAL ASPECTS




1

copy

2 GENERAL ASPECTS



OH

OX

1




log k(20C) = s(N + E) (2)


GENERAL ASPECTS 3

MeO

CO2Me

CO2Me

Me2N

CN

CN

(OC)3Fe

MeOOMe

minus25

minus20

minus15

minus10

minus5

0

5

10

N O

tBu

tBu

E

252015minus10 minus5 0 5 10

Me MeO

Me

Me

Me NO2

OSiMe3N

O

O

OSiMe3MeMe

N




Me3C+

+

+

+

+

minusminus






4 GENERAL ASPECTS


H3CC

CH3

O

CH3Li +CH3

C CH3

OLi

H3C

dminus

d+ (3)

H3CC

CH3

O

CH3OH +

CH3

C OCH3

OH

H3C

H+

+ (4)


PhCHO+2

N(CH3)2

N(CH3)2

N(CH3)2

HCl

H

leucomalachitegreen

(5)

OH2

H3C+ C

CH3

O H2SO4

H3C CH3

OHHO


bisphenol A(6)


GENERAL ASPECTS 5


O

CH3

CF3SO3H

C6H6


2

OH

CH3

+

(7)

O

CF3

CF3SO3H

C6H6

OH

CF3 F3C

C6H5

C6H5

C6H5minusH2O

3

C6H6 C6H6

+

(8)



6 GENERAL ASPECTS

H3CC

CH3 +minus

F CH3SbF5

H3CC

CH3

CH3

SbF6(9)

CH3

OH FSO3H-SbF5CH3

+

minus[FSO3-(SbF5)n]

(10)





H2SO4

SO3(50)

HSO3FSbF5

(50)

Magic Acid(90)

CF3SO3HSbF5

(10)

HF (7)BF3

HFSbF5

(2)(50)

10 15 20 25 30

10 15 20 25 30(minusH0)

(minusH0)


GENERAL ASPECTS 7







8 GENERAL ASPECTS


CH2Cl2minus30degC

minusCH4


Sn Snn-Bu

n-Bun-Bu

n-Bun-Bu

n-Bu+


[CB11(CH3)12]minus

(12)

ArSi

ArAr

Ar = mesityl


ArSi

Ar

Ar

[CHB11(CH3)5Br6]

+

minus

(13)

PhC

CH3

+ minusO

(CH3CH2)3SiH

(C6H5)3C B(C6F5)4

minus78degC

PhC

CH3

OSi(CH2CH3)3

B(C6F5)4

(C6H5)3CH

4

+

minus+ (14)



GENERAL ASPECTS 9

CO

H3C OHC

CH3

CH3CH3HC

O

CH3

H+

COH

CH3

CCH3

CH3CH3H

COH

H3CC

H3C

CH3

CH3H

NO REACTION

ISOBUTANE

HFBF3CO

CH3

5

COH

H3CC

CH3

CH3CH3

H

2+

6


CO

CH3

CO

CH3

CO

CH3

H Ad+

COH

CH3

57

+

+

+

+

+

+

+

+ +

+

+




+BF4minus or NO2

+PF6




8

CH4 + NO2H2+ CH

HH

NO2H

H2+

8minusH+ CH3NO2H+

+ + + +

(15)


10 GENERAL ASPECTS







N

HO

CH3

OH

OH

OH

Ph

OON

N

F

CH2Cl+

+

++

+

+

++

H CCH3

CH3

CH3

OH2+

+

O

OH2

Ph

PhO OH

H3C Br CH3

H

2+

N+ +

+

+

GENERAL ASPECTS 11




O OH+ +

+

OH2

9

H+H+

(16)

12 GENERAL ASPECTS

N

O

HH+ H+

HN

O

H

10

+ HN

OH

H+

+

(17)






Ph

PhPh

Ph

2+

11

2+

12

2+

13




GENERAL ASPECTS 13


Dications

2+

CH3

CH3H3C

H3C

H3C CCH3

2+2+

2+

16

18

14 15

19

17

Higher Cations

Ph Ph

Ph

PhPh Ph

Ph

Ph

20

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

21

R

R R

R

R

R

22 23

+ ++

+

+

+

+

+

++

+ ++

+

+ +


ClCl

SbF5

SO2ClFminus78degC

+

+

24

(18)

27

Cl + ++

Cl

25 26

SbF5

SO2ClFminus78degC

(19)

OHOH ++

HO

28

SbF5

HSO3F

SO2ClFminus78degC

+

(20)

14 GENERAL ASPECTS


REFERENCES










REFERENCES 15


















16 GENERAL ASPECTS









21 INTRODUCTION



17

copy






+PF6minus) in




NO2O2N

+ NO2BF4

FSO3HNO2O2N

NO2

150degC

62

(1)


F

+ HNO3


F

25degC

89

FF

FF

F

F

F(2)




Ph

PhNO2

2) H2O

BF4minus

OH

H2OndashBF3

Et3SiH

Ph

PhNO2

H

64

+ (3)


NO O NO O NO OHH A

31 2

d++ + + +





SR1

R2

R3

SR1

R2

R3

AlCl3

SR1

R2

R3

AlCl3

4

dminus

d++ ++ (4)

Cl SCH3


SCH3

87(5)


N

N

O

O

OH

H CF3SO3H

C6H5Cl

65

N

NO

OH

H

Cl

Cl

(6)

N

O

O

H

CF3SO3H

C6H5Cl

NO

H

ClCl

99

(7)




N O

H

CF3SO3H

C6H5NO2N OH

H

H N

HNO2

O2N10

5

+ +(8)

CH3

O

CF3SO3H

C6H6


6

CH3

OH+

(9)

NCH3

O

CF3SO3H

C6H6

NCH3

OHHN

CH3

Ph Ph

93

7

++

(10)

OCH3

O

CF3SO3H

C6H5NO2OCH3

OH

H

O

NO2

8

82

+

+

(11)




CCF3

O

CF3SO3H

C6H6

CCF3

OH

CF3

Ph Ph+

(12)

HC

CCl3

O H2SO4

CCCl3H

C6H5Cl

Cl Cl

HC

CCl3

OH+

(13)



CCH3

CH3CH3H

CO

H

COH

HC

CH3

CH3CH3

H

HFBF3

CO

H9

COH+

H 2+

CCH3

CH3CH3

COH

HminusH+

minusH+

minusH+

H+

C

CH3

CH3CH3

COH2

HC

H3C CH3CH3

COH2

HCH3C

CH3

CH3

COH

HCH3C

CH3

CH3

CO

H

10

91

+ +

+

+

+

+

+

++

Scheme 1



H


H E

2) H2O

+

E+ = HCO+ or HCOH2+

CHO

minus2H+

(14)



11 12

HN

NH

N

NHs

O

H2N

CH3

CH3

H

Hr

H2

ENZYMEHN

NH

N

NH

O

H2N

CH3

CH3

H

H

A

+

++ H+

(15)

CH3

H3C CH3H2

CH3

H3C CH3

HH

13CH3

H3C CH3

H

H

++

+

+ +

(16)


H2

NN

N

H

14

H+

+N

NN

+ +(17)



23 KINETIC STUDIES


N

NH

ring

ring

H3C R

HH

Protonation

N

NH

ring

ring

H3C R

HH

H

11

H2

N

N H

ringring

H3CR

HH

++


KINETIC STUDIES 25


Ph

O

Ph

O

Ph

5 hrs 0degC

91

15

18

16minus2 H

CF3SO3H CF3SO3H

OH2

Ph

OH2

Ph

17

2+

Ph

OH

Ph

+ +

+

+

(18)




Ph Ph

O

Ph

19

22

H+

Ph Ph

OH

21

Ph Ph

OH2

OH2

PhH

slow orno reaction

rate-determining

80degC Ph Ph

OH22+

72

20

CF3SO3H

+ +

+

+

+




CF3SO3HCF3CO2H

CNH+

O

23 24 25

CN

H +

C

NHH+

+

(19)


KINETIC STUDIES 27




OCH3

OCH3

FSO3HSbF5

minus60degC

hn

minusH+H+

26 26a 26b

2727

k1

OCH3

+

OCH3+

OCH3

H

++OCH3

H

+

+

Δ




N

RprimeR

H+

NH

RprimeR

(20)


N


NH50degC 1 h

7628a

(21)

N

CF3SO3H

NH

69

28b

150degC

(22)

N

Ph

28c

NH

Ph 90

29 30

CF3SO3H

150degC

31

N

Ph

H+

N

Ph

HH

++


KINETIC STUDIES 29

28a28c28d28e

minusH0

log

k

minus55

minus5

minus45

minus4

minus35

105 11 115 12 125

28a

28c

N

N

28d

28e

N

N

Cl

CH3





PhPh

PhPh

OCF3SO3H

PhPh

minus2 H+

minusH2O

32 34

36

99

33 35

PhPh

Ph

H2OPh

+

+

PhPh

PhPh

OH2

+

+PhPh

PhPh

OH+



Acid System

Acidity (H0)

(CF3SO3H-CF3CO2H

ww

)Product

Ratio (3236)




ACID

O

OCH3

minus40degC

YIELD

minus27

0

minus118

20

minus132

94

H037 38

O

OCH3

HOOH

OCH3

+

+

(24)

KINETIC STUDIES 31




H3CCH3

O

OCF3SO3H

C6H65 min

H3CCH3

O

OHH

H3CCH3

O

94

39

42 41

++

40

H3CCH3

OH

OH+

+

H3CCH3

OH+

+

Scheme 6



acidC

NH2

H

H2OC

O

HNaCN orTMS-CN

+

(25)

H+

H C NH+

H+

H C N H+ ++

H C NH

H

NaCN orTMS-CN

4443 45

(26)













Acid H0 Yielda





H3C C O H3C C OH

46

C O C OH

47

H+H++ + + + + +








XXCF3SO3H

48a X = OH 49

(27)

SbF5

RR

R R

SO2ClF

minus78degC

RR

R R

50R = H NMe2 OCH3

Heat

minus2H+

RR

R R

+ +

(28)





NO

O

CF3SO3H

C6H6

0degC

NOH

OH

N OH

51 96

++

(29)

53

NO

O

H3C

CH3

52

13C NMR Data (ppm)

NOH

OH

H3C

CH3

266 1999 1303

296

CF3SO3H

NOH

OH

H3C

CH3

++

+ +

C6H6

minus5degC

(30)



NO

O

CF3SO3H NOH

OH

NOH2

OHNOH

C6H6


54

C6H6

C6H6

+minus N

OH

OH+

+ + +

++

Scheme 7

NO2

C6H60degC

NH2

Ph

NH2

Ph

NH2

Ph

Ph

NHO OH

NHO OH

55

CF3SO3H+ +

+

+

++

Scheme 8




CH3

HOPh

Ph

CF3SO3H

C6H6

CH3

Ph

Ph

Aqueous

Workup

Ph

Ph+ (31)

PhNH2

OH

CH3

Ph

PhNH2

CH3

PhPh

CF3SO3H

C6H6

PhNH3

CH3

Ph

80

56 57

C6H6+

+ (32)



200 180

57Ph

d 6-A

ceto

ne

d 6-A

ceto

ne

++Ph

CH3

H3N

160 140 120 100 80 60 40 20 ppm




CH3

N

O

H3CCH3

N

OH

H3C H3C

NOH

CH3

PhPh

75

HO HHO

58

CF3SO3H

C6H6

+

+

(33)

N

O

O

CH3 N

HO

OH

CH3 N

O

CH3

Ph

Ph

59

CF3SO3H

C6H6

75

+

+

(34)

CF3SO3H

C6H6

99 PhP

PhPh

CH3

Ph

Ph

Cl

Ph P OH

PhPh

Ph P O+ + ++

minus

minusPh

PhCH3

Br

60

CH3(35)

N

H

O N

H

HN+ +

H

OH

61

C6H3Cl2

C6H3Cl2CF3SO3H

o-C6H4Cl

87

(36)

CF3SO3H

C6H6

74ndash99

NN

Rprime

R

O

H

NN

Rprime

R

HO

H

+

+

H NN

Rprime

RH

PhPh

62

(37)






(1)

(2)

(3)

(4)

(5)

(6)

(7)


NOH

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

CF3SO3H-SbF5

minus30degC

HF-SbF5

minus30degC

HF-SbF5

minus30degC

ACID

minus30degC

NOH H

H H

OH OHH H

OHH H

HH

78 22

OH OHH H

HH

33 67Cl

Cl

Cl

HF-SbF5

OHH H

80 20Cl

Cl

OHH

H

Cl

OHH

HH

H

FSO3H-SbF5

0 100

OH

N

OH

N

OHH H

H

N

OH

N

OH

H H H

OH

NH2

OH

NH3H H

+ +

+

++

+

+

+

+

+

+ +

+

+

+

H+

+

H+

H+



CF3SO3H

minus20degC

O

OCH3OH

OCH3

65 R = minusOCH3

O

OCH3

HO


R

R

R

R

R

R63 R = H

+

+

(38)











HF6-31G MP26-31GHF6-31G MP26-31G

ω I ω I

O = +N = O 2760 190 2526 1717

2660 1773 2415 191426 3 1246 21006 540 884 408682 0 553 21630 50 541 51

O = +N = OH 2654 919 2566 62

1682 0 1302 0750 5 601 3
























3+



CS3+ CS23+ CSe2

3+

Diatomics B23+ S2

3+ CI23+ Br23+ I23+


2+







2+species (eq 43)43




NbC5H62+ + NbC6H6

2+












C6H5CH3

minus2eminus

C7H62+

HC CH

+ C9H62+C9H7

2+ (44)



C

CC C

CCC

HH

H

H

HH

2+

HC CH


C

CC C

CCC

HHH

H

HH

C C HH 2+

C

CC

C

CC

CC

CH H

H

HH

H

H

H2+

Erel = minus144 eV

C

CC

C

CC

CC

CH

H

HH

H

H

H2+

Erel = minus126 eV

C

CC

C

CC

CC

CH

H

HH

H

H2+

minusHminusH2

+

Scheme 9







OHacid

+ +

+O

69

CF3SO3H +

+OH

70

O+

OO

71

69 72(45)






O

78

+OH

+OH2OH

O

73

+OH +OH2

+

+OH2

+ + + +

ΔE = 1827 kcalmol

ΔE = 616 kcalmol

ΔE = 1827 kcalmol

OH

74 7975

+OH2

ΔE = 1237 kcalmol

80


Scheme 10



H3CC

OH

H3CC

OH

HCH4


CH3

46 83 84

++

+

+

++

(46)



N

OH

CF3SO3H-SbF5

NH

OH85 86

++ (47)

NH

HO

88

N

87

HOCF3SO3H-SbF5

+

+(48)



ω = μ22η



















CH3CO2H 13C1 1719 13C2 207 13C1 1769 13C2 20817O1 1943 17O2 4134 17O12 2510

CH3C(OH)2+13C1 2020 13C2 217 13C1 203717O1 2283 17O2 2312 17O 1930


89 17O1 1482 17O2 2942

CH3CO+ 13C1 1557 13C2 63 13C1 150317O 3438 17O 2995


46 17O 1946

HNO315N 3668 15N 3770

NO+2

15N 2683 15N 25101


3

H3O+ 17O 300 17O 1021H 72 1H 95-106


90 1H 136






HC

OH2

H

+

+

MP26-31GMP26-31G


48505152

H3CC

OH2

H

+

+

MP26-31GMP26-31G


4850

H3CC

OH2

CH3

+

+

MP26-31GMP26-31G


4850

HC

OH

OH2

+

+

MP26-31GMP26-31G


4850

H3CC

OH

OH2

++

MP26-31GMP26-31G


4850

HOC

OH

OH2

+

+

MP26-31GMP26-31G


485053

H+O=C=+

OH MP26-31GMP26-31G


4850



54





H3NC

OH

OH+

+



55

F3CC

OH2

OH+

+ MP26-31GMP2(fu)6-31G


56

FC

OH2

OH+



57

H3CC

O

OH

H

CH3+


Geometry energy 58

H3CC

O

O

CH3

CH3

H3C +

+


Geometry energy 58

H3CC

O

O

H

CH3

H3C

+


Geometry energy 58

OH

HO

HO

OH

+

+



59





NH

OH+



35c

NH

OH++



35c

NH

OH

+



35c

NH

OH

+



35c

HN

H

OH+


Geometry energy 60

O

OOO

+



61

OO

O

OO

O+

+

+



61





CCH

H

H

OH

+


62

CCH

H

OH

OH

+


62

CCHO

OH

OH

OH

+

+ MP26-31GMP26-31G


63

CCHO

NH2

OH

NH2

+

+ MP26-31GMP26-31G


63

CCH3CO

OCH3

OCH3

OCH3+

+


63

OH

OH

HO

HO

+

+


63

H3NC

NH2

OH+

+ MP4(SDTQ)6-311GMP26-311G


64

H3NC

NH3

OH+

+

+



64





HN OHHO



65

HN OHHO



65

N OHHO

Cl+ +



66

N OHHO

ClH+ + + B3LYP6-31G



OH2

+



18

OH2

+



18

OH2

CH3+



18

H3CC

CO

H

CH3

CH3

HH

+

+


Geometry energy 14b

CC

CO

H

H

H

H

H

H+

+

HF6-31GHF4-31G


24





HOC

COH

OH

OH

+ + MP26-31GHF6-31G


67


H3Cminus+C=+



425270


CC

CO

H HH

H+

+ MP26-311+GMP26-311+G


69

CC

CO

H HH3C

CH3++ MP4(SDTQ)

6-311+GMP26-311+G


69

CO

CO+



59

Hminus +C=

+OminusH MP26-31G



50

Fminus +C=

+OminusH MP4(SDTQ)

6-31GMP26-31G


57





O H

H

HH

2+MP4(STDQ)6-311++GMP26-311G


48507071

O H

H

HF



72

O H

H

FF



72

O H

H

CH3

H3C2+

MP26-31GMP26-31G


4850

O CH3

H

CH3

H3C2+



4850

H3CC

COH2

HCH3

CH2 ++


Geometry energy 14b

H3CO

OCH3

CH3

CH3

+

+

MP26-31GMP26-31G


73





C C OH

HH H

+

+


Geometry energy 68

C CO

HHH H

CH H

++


Geometry energy 68

C CO

HHH H

CH CH3

++


Geometry energy 68

C

CO

HHH

HC

CH3

CH3+

+


Geometry energy 68

CH3C

CH3H3C

H

CO

H

H+

+


Geometry energy 14b

C NH

HH H

H

HH

+

+


C NNH

HH H

+

+


C NH

HH H

CH

H

H+

+

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75





C CH

HH H

N

H

H

H

+

+MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

CN

H

CH3

H

CHH

H

H++

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

H3CN

C

C

H HH

H

H H

++

MP4(SDTQ)6-311+GMP26-311+G

Geometry energy 75

C FH

HH H

H+

+



7677

C ClH

HH H

H+

+



7677

C BrH

HH H

H+

+



7677

C IH

HH H

H+

+



7677

Si CH

HH H

H

H

+

+



78

Si S iH

HH H

H

H

+

+



78





CH53+ MP26-31G


charges79




80




81

C C

H

H

H H HH

HH +

+



80

HC

CC

HH H

H HH H++



80

HC

CC

CH

HH

H H

HH

H H

HH

+

+ MP4(SDTQ)6-311GMP26-311G


80

HC

CC

HH CH3

H HH H++



80

C C

H

H

H HH

H+

+



78

C C

H

H

H H H

CH3+

+

MP46-31GMP26-31G

Geometry energy 82

C C

H

H

H H H

CH

HH

+

+MP46-31GMP26-31G

Geometry energy 82





C OH

HHH

H H

+

+

MP26-31GMP26-31G



48507477

C SH

HHH

H H

+

+

MP26-31GHF6-31G



5077

C OCH3

+CH3H

HH H+

MP4(STDQ)6-311++GMP26-311G

Geometry energy 75




83

BH52+ and BH6



79a

NH52+ and NH6



718485

PH52+ and PH6



7185

AsH63+ and AsH3+



7185

CH3N

CH3

CH3

CH

HH

H+ +


Geometry energy 84





HC

CCH3

CH3

H H++


Geometry energy 86

H

+

+



87


C CH

H

H

H++

MP36-31GHF6-31G


88

C CF

F

F

F++

MP26-31GHF6-31G


67

HC

CC

CH

H

H

H H

H H

+

+



89

+ +



90

OH

CH3

+ +



25





OH

OCH3

+ +



25

OH

H

+ +



25

+

+


Geometry energy 87

+

+

+



91

CH3

H3C +

+



91


89

CH2

CH3

CH3H3C

H2C++ B3LYP6-311G



92





HN

+



35c

HN +



35c

NH

SCH3

+

+


Geometry energy 93

NH

SCH3H

+

+


Geometry energy 93


H2NN

NH2

NHH

+



94

N3N

N3

NN

N+

+



94

+

+H2N

CNH3

NHH MP4(SDTQ)6-31G



94





H3NC

NH3

NHH

+ +



95

H2NC

N

NHH

H H

CH3+

+ B3LYP 6-311+GB3LYP6-311+G


96

H2NC

N

NHH

H H

BH4+

+ B3LYP6-311+GB3LYP 6-311+G


96

H2NC

N

NHH

H H

AlCl4+

+ B3LYP6-311+GB3LYP6-311+G


96

O=+N=+



3741

O=+N=+




97



97





Hminus +Nequiv+



98

Hminus +Nequiv+



98

Nequiv+Nminus+



98

C N NH

H

H



98

C C NH

HH

++

HF6-31GHF4-31G


62

H3C CNH3

H

++ MP4(SDTQ)6-31G


C CNH3H

H HH

+

+


Geometry energy 99

H3C CNH3

CH3

++



99

HC

HN

H

HH

++

MP26-31GMP26-31G


51





HONH2

OH

NH2+

+ MP26-31GMP26-31G


67

H2NNH2

OH

OH+

+ MP26-31GMP26-31G


67

H2NNH2

NH2

NH2+

+ MP2 6-31GMP26-31G


67

NN

+

+

HF6-31GHF6-31G


100

Phosphonium Systems

HC

PH

HH

H+ +

MP26-31GMP26-31G


51

HC

PH

H

HH

2+

MP26-31GMP26-31G


51


S2+8 and S2+

n (n = 37) B3PW916-311+G(3 df)B3PW916-311+G


101





2+

HS

H

HH



50102

2+

CH3

SH3C H

H MP26-31GHF6-31G


50

2+

CH3

SH3C CH3

H MP26-31GHF6-31G


50

2+

CH3

SH3C CH3

CH3 MP26-31GHF6-31G


50

2+

CH3

SH3C OH



103

2+

H3CS

H3CO

H



103

2+

H3CS

H3CO

H



103

2+

H3CS

H3CO

CH3



103

H2NC

NH3

SH+



38





H3NC

NH3

SH+

+

+



38

H2NC

NH3

SH2+

+

+



38

HSC

SH

SH 2+ (P)MP4(SDTQ)



104

2+

CH3

SH3C H

H MP26-31GHF6-31G


50

HSC

CSH

SH

SH

++

MP26-31GHF6-31G


67

Boron-Based Systems

HN

BH

HH

++ MP46-311G(dp)



105




Halonium Systems

H

H



76106

H

H



76106

H

H



76106

H

H



76106

CH3

CH3



76

Cl 2+

CH3

CH3



76

Br 2+

CH3

CH3



76

I 2+

CH3

CH3



76




Halonium Systems

HC

F

H

H+ +MP26-31GMP26-31G


51

HC

Cl

H+ + H

MP26-31GMP26-31G


51107

+

+F

CF

F



107

+Cl

CCl

ClH

+



107

+Br

CBr

BrH

+



107

+I

CI

IH

+



107

+ +Cl

CCl

ClHH +



107

+ +Br

CBr

BrHH +



107




Halonium Systems

+ +I

CI

IHH +



107

+

+

++Cl

CCl

Cl

HH



107

BrC

Br

Br

HH

H

++

+



107

IC

I

I

HH

H

++

+



107

ClC

Cl

H

H++MP26-31GMP26-31G


107

ClC

Cl

H

HH +

+ +

MP26-31GMP26-31G


107


REFERENCES 75

REFERENCES
















2312















J Am Chem Soc 1997 117 4345

REFERENCES 77






































REFERENCES 79
































81

copy








Ph Ph

O

Ph Ph

OH2

Ph Ph

O

Ph Ph

OH2

H3CCH3

O

O

H3CCH3

OH

OH

N

Ph

N

Ph

H

H

(1)

(2)

(3)

(4)

(5)

(10)

(11)

(7)

Ph OH

O

Ph OH

OH

(12)

(13)

NO

Ph

RN

PhR

OH

H

(15)

ROH

O

O

ROH

OH

OH

(6)

Ph NHPh

O

Ph NHPh

OH

NO

OBF4

NOH

O2 X

Ph CH3

O

Ph CH3

OH

N

O

R

O

N

OH

R

OH

(8)

(9)

(14)

(16)

(17)

R2N

O

O

NOH

OH

NO2 NHO OH

R1

R3

R2

R1

R3

Ph

OH

O

Ph

OH

OH

(18)


Ph OCH3

O

Ph OCH3

OH

H

N

R

O

O

N

R

OH

OH

(19)

Ph

OH2

PhPh

O

CH3

Ph

OPhPh

Ph Ph

OH2PhPh

Ph

O

O

Ar

Ar

OH2

O

Ar

Ar

+

minus

+minus

++

++

+

+

+

+

+

+

++

+

+

+ +

++

minus

+

+

+

+

+

+

+

+

++

++

+

+

+

+

+

+

+

+


H C NH+ +

H

NaCN orTMS-CN

5SbF595CF3SO3H

1

(1)


CN

CH3

TfOminusC6H6

CN

CH3

H C

O

2 3

5SbF595CF3SO3H

+

++

(2)

OHO

OMe

OMe

MeO

SbF5CF3SO3H

OH

OMe

OMe

MeO4 5

+ + (3)


HNO2

2 CF3SO3HB(O3SCF3)3

minusH2OO N O

H+

O N O H

6

+ + +(4)

2 CF3SO3HB(O3SCF3)3

O

+ 2+

CH3

CH3

H3CO

CH3

CH3

H3CH

7 8

(5)

CO H CO+


SbF5CF3SO3H

H CO H

9

+ + (6)


CH3OHH+

CH3OH2 CH3OH2

HA

HA

CH3OH3

2+++

(7)


N

Ph

H

H

N+

PhH

CF3SO3H -CF3CO2H

10

++

(8)

11

Ph

OH2

PhPh

OH

PhCF3SO3H -CF3CO3H

+

+

+

(9)

Ph Ph

OH2

12Ph Ph


+ (10)

CN

H


NH H

13

+ +

+(11)




O

Ph

FSO3H

orCF3SO3H

OH

Ph

14

+

+

OH

OHN

HO

OH

CH3

15 16

+

+

+

+

(12)






OCH3

OCH3

OCH3

OCH3

H H

HH

OCH3 O

CH3

H

OCH3

H

H3C OCH3

O

H3C OCH3

OH

H

H2N NH2

O

H2N NH3

OH

(1)

(2)

(3)

(4)

XCH3H3C

CH3

+

X = O S Se Te

FSO3HSbF5

FSO3HSbF5

XCH3H3C

CH3

H2+

2+

SDH

HS DH

H

D

(5)

(6)


17

18

19

20

21

22

FSO3HSbF5

FSO3HSbF5

FSO3HSbF5

+

+

+

+

+ +

++

+

+

+

+FSO3HSbF5



C

O

H3C OHC

O

CH3

H

C

OH

CH3

HFBF3C

O

CH3

23 24

+

+

+

+ (13)

C

O

R CH3

R = H CH3

HFBF3or HFSbF

C

OH

R CH3

H+

C

OH2

R CH3

25 26

C

OH2

R CH3

2++ +

+(14)

CH3

C

O

CH3

CH3H

HFBF3

CH3

C

OH2

CH3

CH3H

2+

CH3

C

OH2

CH3

CH3H

27

+

+

(15)

CH3OCH3 CH3OCH3

HCH3OCH3

H minusminus

H 2++HF-BF3

BF4 2 BF4

28

(16)




O

H

D

D

O

H

H

D

minusD+O

H+ +

D

D

HHF-SbF5

29

2+

(17)

F3CC

OH

OHFSbF5

F3CC

OH

OHH

F3C F3CC

OH2

OH minus H2O

C

OH++

++

++ (18)


OH

Cl

HF-SbF5

OH+

+

Cl

(19)

OH

HF-SbF5

OH

OH OH+

+

(20)

DF-SbF5

31

minus78degC

H3C H3C H3CC

CH3

CH3

CC

CH3

HH

H

D

CCH2D

CH3

minusH+

30

++

+

+

(21)

CCl4HF-SbF5 Cl

CCl

Cl

H+ Cl+ ++

CCl

Cl32

H (22)








AlCl3

Al2Cl7

33

+minus (23)


C

O

H3C Cl AlCl3

AlCl3C

Od+

d+

dminus

dminus

dminus

H3C

AlCl3

CH3COCl bull 2AlCl3

34

AlCl3

Al2Cl7+

+minus (24)



CBr4 bull 2 AlBr3Br

CBr+

minusd+

minus

+

Br

BrC

Br

Br

35

AlBr3

AlBr3

Al2Br7

Al2Br7

(25)

Cl SCH3

SCH3 S

CH3

AlCl3

2 AlCl3

Al2Cl7

Al2Cl7

AlCl3 +minus

minus

+

dminus

d+

(26)

ClAl

ClCl

OC

O

AlCl3

ClAl

ClCl

OC

O

AlCl3 ClAl

ClCl

OC

O

AlCl3

AlCl3AlCl3

2 AlCl3+

++minus minus minus

d+

d+

d+

(27)


H3C CH3

CH3 O 13 equivAlCl3

H3C CH3

CH2 OAlCl3

+

+minus

(28)

R NRprime2

O

R NRprime2

O

H H

X


minus

5 equivAlCl3

+

+

(29)


OH OH H

HH

X3 equivAlCl3


minus

+

+

(30)

OH

HO

OX

HH

HH

OH

X3 equivAlCl3

+

+

+


minus

(31)

N

O

O

ClBF3-H2O

N

OH

O

Cl N

OH

OH

Cl N

OH

OH

Cl

HH+H+

+ +

+

+

+

+

(32)


Ph NEt2

O HUSY

C6H6130degC

Ph NEt2

OX

Ph NEt2

OPh97+

+

(33)

Ph CH3

O HUSY

Ph CH3

OX

Ph CH3

O70

C6H6130degC

+

+

(34)

NH

O

Ph

Nafion-H

NH

OH

Ph

H

NH

O

Ph

70

36

C6H6130degC

+

+

(35)





HN

NH

N

N+

+ +

HO

H2N

CH3

CH3

H

42 43

HN

NH

N

NHs

O

H2N

CH3

CH3

H

Hr

H2


dehydrogenaseH+

(36)


Ph H

O

H3C CH3

O

NH

O

NH

OH

Ph

Ph

20 mol

minus25degC Ph CH3

OOH

51 yield 83 ee

N

O

N

O

Ph

Ph

CH3

PhH

OH

H

d

37

38

N

O

O

CH3

PhH

O

H 39Ph Ph

OH2 OH2

H

40 41

+

+

d+

+

+

+

+

+

Scheme 1









(1) N

O

O

ClNO2

NO2

Cl

105degC 69

(2)

N

O

Ph

HHUSY

CF3SO3H

130degC

25degC


OH

Ph

H N

O

Ph

H(3) 90

90

85

OH

NH2

AlCl3 110degC

OH

NH2

70

NH2

O

(4)

(5)


65degC

FF

FNO2

O N OH

FF

FNO2

O2N96

N

O

H

(6)

CF3SO3H 130degCNO2

HN

OH

H10

N

NO2

NO2

(7)

N

O

CH3

OH

CF3SO3H 80degCCl

ClN

OH

CH3N

O

CH3

ClCl

60

Ph Ph

O

CF3SO3H 80degCPh Ph

OH2 Ph 84

(8)N



phenyl

phenyl

phenyl

phenyl

phenyl


CH2

H2OndashBF3 N

OH

OHCl

H

+

+

+

+

+

+

+

+ +

+

+

+

+

+

+

++




CCl4-AlI3 I2

minus20degC

I

70

CXX

X

MXn

44

+

d+dminus

(37)


CH3CH2CH3+ CO


minus30degC

minus10degC

Temp

CH3OH COCH3O

CHCH3H3C

Yield

50

28

Scheme 2

CCH3H3C

CH3

i-PrOH i-PrOHCO CO

CH3CH2CHCH3

CO O CH(CH3)2 C

O O CH(CH3)2

C(CH3)3

minus20degC

0degC

Temp

525 100

129 100

Product Ratio

CH3CH2CH2CH3+ CO

+CH3CH2CHCH3


+

Scheme 3



80HNO3 minus78degC

(CF3SO2)2ONO2

(38)O N O

HA

O N OH

6

+

d+

+ +

NO2

94

(CF3SO2)2O


NO2NO2

+ BF4minus

CF3SO3H0degC

64

+ + (40)


H3CCH3

O

O CF3SO3H

C6H6 0degC5 min

H3CCH3

OH

OHH3C

CH3

O

PhPh95

45

+

+ (41)

Ph

O O

Ph

91

Ph

OH2

CF3SO3H

+

+0degC

(42)


PhO

PhHO

OCH3

CF3SO3H

minus40degC PhOH

Ph

OCH3

O

OCH3

9446

+ +

(43)





H3C

O CH3

O CH3

BF4

CD3SO3FSbF5

minus30degC

47

H3C

O CH3

O CH3

48

D3C

(NuCH3)+

H3C

O CD3

O CH3

Nu+

+

+

minus

+





DFSbF5

50

minus78degC

H3CC

C

H

HH

H

D

H3CC

CH2D

H

minusH+

H3CC

CH2

H+ H+

H3CC

CH3

H

49

+ +

+

+

Scheme 4

OCH3

OCH3FSO3HSbF5

minus60degCOCH3

hn

ΔOCH3

OCH3

HOCH3

H

minusH+ H+

51a 51b

5252

k1

+

+

+

+ ++

Scheme 5


REFERENCES 101


REFERENCES











1997 62 6666




















REFERENCES 103



















58 5423











105

copy


HO

H

HH

+070

+070

+070

+070

minus080

Td

2+

HO

H+0458

+0458

minus0916

C2v

HS

HH

+049

+056

+056

+056

+035

3+

Cs

+049HH

1 2




CH3

OCF3SO3H

25degC

CH3

OH

CH3

OH H

O HH

CH3

O

CH3

+

97

3

CH3

OH H

4a 4b

2+

5

++

+

+

+

CH3

OH H

4c

+

+

Scheme 1







H3CO

CH3

CH3 H3CO

CH3

CH3

H Ad+ dminus

H3CO

CH3

CH3

H

2+

6 7

++



42 GEMINAL SYSTEMS










HC

HH

H

H H 2+

8

CAuPPh3

AuPPh3Ph3PAu

Ph3PAu

AuPPh3

AuPPh3

2+

2 X minus

9

HC

HH

H

H H3+

10

H



2+ CH3bull2+CH2


GEMINAL SYSTEMS 109


H C F2+

H C Cl2+

H C Br2+

H C I2+

11a 11b 11c 11d









CClCl

Cl

SbF5CClCl

Cl

SbF5or H+

12

Cl C Cl2+

13a

FCCl3SbF5 RH

HCCl3 bull SbF5

HCCl2

minus SbClF5minus

RHCH2Cl2

RHCl C Cl

13b

+ +dminusd+

++ +

Scheme 2





2+CS2

2+ CF2+ CS22+

COS3+ CS23+ CSe2

3+ CS3+









GEMINAL SYSTEMS 111



N

H

H H

H

H2+

C4v

14

NLAuLAu

AuL

AuL

AuL

2+

2 BF4minus

15L = P(C6H5)3

NH32+ + H2


16 14(1)






NOH

H

C6H6

acid NH

NH2

Ph

18 19

CF3CO2H


56 9 para8 ortho

17

+

Scheme 3



NOH

H

H+ NO

HH

H

minus H2O

NH

NH

NH

HSn-2-like

C6H6

minusH+

19

17 20

21 22

NO

H

H

H

C6H6

+

+

+

+

+

Scheme 4

NOH

H

2H+ NO

HH

H

minusH2O NH

17 23

C6H6

HN

H

24a

2+H

H

NH

H

H

HN

H

H

H

Hminus2H+NH2

Ph

19 26 25

24b

+ + +

+

+

++

+

+

Scheme 5

GEMINAL SYSTEMS 113


N

CH3

minusO

CH3CF3SO3H N

CH3

CH3

28b27

NCH3

CH3

28a

2+ ++

+ (2)

NOH

H

30b

NO

NOH

H

30a

2+

29

CF3SO3H

+

+ (3)

N

O

CF3SO3H

31H3CO

NH3CO

H3CO

NH3CO

H3CO

H3CO

NH3CO

H3CO

2+

minusH2O

32

minus

+ +

+

(4)




OH

DD

OH

DO

HH

DO

H

HO

HH

H



HD

DO

HH

D(b) O

HD

DH

2+O

HH

DH

2+O

HH

H

++












GEMINAL SYSTEMS 115

OAuPAr3

AuPAr3

Ar3PAu

Ar3PAu


33

2+



OH3C

CH3

CH3


CH3

CH3

H2+

C6H5CH3 OH3C

H

CH3++

34

+




H+ HA

H

3635 37

H O CH3

HO CH3

H

HO CH3

H

A

H O CH3

H

H

+

δminus

δ+

+

2+ (6)

2 CH3OH CH3OCH3

minusH2O

CH3OCH3

H

HAH+

CH3OCH3

H

H

38 39

+ 2+

(7)




minusH2CH4 (8)






CH3OCH3 CH3OCH3

H

+CH3OCH3

H

H 2+HF-BF3

CO

BF4minus

O

C

minus2HF

CH3CO BF3OCH3

minusBF3

CH3CO2CH3

382BF4

minus

+ minus



GEMINAL SYSTEMS 117

CH3OHH+

HO

CH

HH

HH O

CH

HH

HH2+

3537

minusH3O+

CH

HH

OC

HHHH

H

minusH+

C

HHH

OC

HHHH

hydrocarbons

+

+ +

+

+

Scheme 7


SH

D

D

SH

H

D


SH

D

D

H SH

H

D

H SH

H

H(10)


minusSiH4 and PH4


OH

HH

H2+ 2++ +

SH

HH

SH

HH

HOH

HH


+ +(11)




S SBF3bullOEt2

XeF2

40

SN

N

F

FCH3

CH3

CH3

CH3

42

2+

[S(NP(CH3)4]2+

2Clminus

41

2 BF4minus

2+

2 SbF6minus




Se

H

H

H

H

44

43

45

Te

H

H

H

HAu Au

Au

Au

S

2ClO4minus

PhPh3

Ph3P

Ph3P

Ph3P2+

2+ 2+



X

+2+

H3C

CH3

CH3

FSO3HndashSbF5XH3C

CH3

CH3

HC6H5CH3

X = S SeTe

Xylenes(12)

GEMINAL SYSTEMS 119




S

H

H H

H H3+

2

Cs

SH33+ + H2 SH5


2 (13)






3+and SH6

4+ respectively





2H3CndashBrSbF5

SO2ClFH3C Br CH3

minus

+

X46

(14)

H3C Br CH3+ 2+

H3C Br CH3

X

HX

H X

H3C Br CH3

H 2 X46 47 48

+





H3C Br CH3+

minusSbF646

Nu

H3C Br + H3C Nu

CD3F SbF5H3C Br CH3

49

CD3

2+

H3C Br CD3

50

+

Scheme 8

GEMINAL SYSTEMS 121

BrC CH

H

HH

H

H

H


2+

BrC CH

HH

H

H

H


2+H

51 52

Figure 3








REFERENCES

















REFERENCES 123





















481







125

copy


C CH

H

H

HC C

H

H+

H+

H

1

CC

CH3

CH3


3

2++

+ +

1432 Aring

etc

NBO charges+052

+027

H3CC

CH3

CH3

tert-butyl cation

2

+058

+014

HH

H

H

+094

D2h


OCH3

OCH3

OCH3

H3CO

SbF5 SO2ClF

minus78degC

OCH3

OCH3

OCH3

H3CO

OCH3

OCH3

OCH3

H3CO

etc

1583 ppm 1753 ppm

4 5 5

++

+

+

Scheme 1



N

N

KCN

CNHH

N

N

CN

H

minusHCN

N

N

HNC

+

+

minus

+

minus

(1)


CNCF3SO3H

CF3CO2H

CN

H

H+ C

NH H

O

6 7 8

++

+

(2)

Ph Ph

O

Ph Ph

OH

Ph Ph

OH2

80degC

9 10 11

H+CF3SO3H

Ph+

+

+

(3)




H

OACID

C6H6

H

OHH

OH

H

HOH2

HH OH2

C6H6

H+

minusH+Products

15

16

H

OH2

12 + C6H6

H

O

CF3SO3H

C6H6

or H

OH

H

Hplus otherproducts

12 13

14

+

+

+

+

+

+

+ +

+

Scheme 2



52 VICINAL SYSTEMS




VICINAL SYSTEMS 129




2+ (18)

B NH

H H

HH B N

H

H

H

2+2+

17 18

C2v

C3v








CCl++ d+ dminus

d+ dminusd+ dminus

Cl

Cl

SbF5CClCl

Cl

SbF5B ClCl

Cl

AlCl3

19 20

Cl C Cl2+

2+ +

22 23

Cl B Cl+ +

H C H25 26

H B H

24

Cl Al Cl

CHH

H H

2+

27

BHH

H H

+

28

H3C +

+

+

CH3C

CH

H

H H

3

H3C

++

BH3C

CH

H

H H

29

Al ClCl

Cl

AlCl3

21

OH2

CHO OH

30

+OH2

BHO OH

31

HCHH

HH H 2+

32

HBHH

HH H +

33







VICINAL SYSTEMS 131







H3CCH3

O

O

CF3SO3H

H3CCH3

+OH

+OH

35a 35b34

H3CCH3

OH

OH

++

(5)






1 36

H CC H2+

Dinfinh

37

C C

H

H

H

H

HH

Cs

38

2+2+

C C

H

H

HH

C2

H

H

H

H

C CH

H H

H+ +



O

OO

O

SbCl5

25degC

5150

O

OO

O

+

+

(6)


VICINAL SYSTEMS 133


Ar Ar

ArAr

Ar Ar

Ar Ar

PhPh

Ph Ph

CH2CH3Ar

CH3CH2 Ar

OHPh

Ph Ph

OHPh

Ph OCH3

OHAr

Ar OCH3

OHPh

Ph OH

SbCl5 Br2 or I2

SbCl5 or AgNO3

SbF5


CF3SO3H

Ag (I) CF3SO3H

CF3SO3H-SbF5

CF3SO3H


40

42

44

45

46

47

48


HO OH


Ar Ar

ArAr

Ar Ar

Ar Ar

PhPh

Ph Ph

CH2CH3Ar

CH3CH2 Ar

OPh

Ph Ph

OPh

Ph OCH3

OAr

Ar OCH3

OPh

Ph OH

HO

Cl

HO

HO





4 5

39

43

Ar Ar

O O


41

+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +



NMe2

NMe2

NMe2

Me2N

NMe2

NMe2

NMe2

Me2N

39 40

SbCl5

NMe2

NMe2

NMe2

Me2N+

+

+

+

(7)



VICINAL SYSTEMS 135

42

SbF5 SO2ClF

ndash78degC

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph

CF3SO3H

OHHO

Ph

Ph Ph

PhO

PhPh

O

PhPh

CF3SO3H

CF3SO3H

52

ndash2 H+

H H

Ph

Ph Ph

PhH2O+

++ +

++

Scheme 3



CH2CH3Ar

CH3CH2 Ar+

44

CH2CH3Ar

CH3CH2 Ar

+

OCH3

OCH3

+

2+ + CH2CH3Ar

CH3CH2 Ar

43 54

(8)


PhO

Ph

Ph

HO CF3SO3H

Ph OH

8

55 5645 45

PhOH

Ph

Ph

++

Ph OHPh

Ph

+ + +

O

Ph

74

(9)


PhO

Ph

OR

HO CF3SO3H

O

OR

R = CH3 46R = H 48

R = CH3 59 81R = H 60 65

ndash45degC

R = CH3 57R = H 58

OH

OCH3

OCH3

H3CO

47

+ +

Ph OH

Ph

OR

+ +

(10)


ArO

Ar

Ar

HO

Ar = p-methylphenyl

CF3SO3H-SbF5

ndash30˚C

61

O

Ar

Ar OH

70 14

0degCAr

OHAr

Ar

+ + +

(11)

ArO

Ar

OH

HO


O

OH

82

CF3SO3H

ndash20degC30 min

ArOH

Ar

OH

+ +(12)



VICINAL SYSTEMS 137

PhO

Ph

OCH3

HO

O OCH3

5957

ACID

ndash40degC YIELD


0 20 94

Scheme 4



HO OCH3


57

46

2 H+

Ph OH

Ph

OCH3

+ +

+ ++

+(13)




HO CH3



63 64

2 H+

PhO

PhHO

CH3

O CH3

63 65

H+

CH3

PhO

PhHO

63

PhO

PhHO

CH3

CF3SO3H

ndash40degC

OCH3

70

Ph OH

Ph

CH3

+ +

PhO

Ph

CH3

+

+

+

+

++

++

Scheme 5

66 67

67a 67b 67c


+0594 +0635 +1063


+

OH

H

H

+OH

H

H

+

+ OH

H

H

+

++

O

H

H

+ OH

H

H

+

+

Figure 2


VICINAL SYSTEMS 139



Ph

Ph

O

OCH3Cl

Ag+

CF3SO3H

H2O

Ph

Ph

O

OCH3HO

5996

68 69

46

57

Ph

Ph

O

OCH3+

(14)



Ph Ph

OHO CF3SO3H

Ph Ph

OH

Ph Ph

OH

OH

11

70 70

+ +

+

+ (15)

7171

Ph Ph Ph Ph Ph Ph


+ +

+ + (16)



OC C

H

H O

H

H

HC C

H OH

O H

72 73


+ + + +



HO OH

OHHO OHHO

HO OH Ph OH

OHHO OCH3HO

Ph OH

HO OCH3

OH

HO OCH3

OH

H3C H3C

74 74 75 76

77 77

+

+

+ + + + + +

+ + +

+



VICINAL SYSTEMS 141

H3CCH3

O

O

CF3SO3H

C6H65 min 0degC

H3CCH3

OH+

+

+

++

O

H3CCH3

OH

OH

H3CCH3

OH

OHH3C

CH3

O

Ph Ph

95

357834(17)

H3COH

O

OCF3SO3H

C6H6H3C

OH

OH

OH

H3COH

OH

OH

H3COH

OH

Ph PhPh

Ph

79

+ CO + H2O

+

++

+

+

(18)


Ph OH

OH

OH

Ph OH

OH

OH

80 80

HO OH

OH

OH

OH

HO OH

OH

OH

OH

81 81

HOOH

OH

OHHO

OH

OH

OH

82 82

OHOH

OHHO OHHO

83 83

+

+

+ ++ +

+

+

+ +

+

+ +

++ +

+

++

+




O O

O

CF3SO3H

C6H5Cl

94

HO OH

Cl

Cl

HO O+ + +

+ +HO OH

84 84

(19)



H2NNH2

O

O

FSO3H-SbF5

minus78degC H2NNH2

OH

OHH2N

NH2

OH

OH

H2NNH2

OH

OH

85 85 85

+

+

+

+

+

+

(20)



VICINAL SYSTEMS 143


N

O

O

H

CF3SO3H

86

N

OH

OH

H

+

+

86

N

OH

OH

H

+

+(21)

H3CCH3

N

O

HO

CF3SO3H-SbF5

87

H3CCH3

N

OH

HO H+

+

87

H3CCH3

N

OH

HO H

+ + (22)



N

NN

N N N N N N N

Cl2

88 88 88

NN+ +

NN+

+NN

+ +

2 Clminus

(23)




DFSbF5

3

minus78degC

H3CC

CH2D

CH3

minusH+

H3CC

CH2

CH3

2

H3CC

CH3

CH3

+ H3CC

C

CH3

HH

H

D

+

+

+

+ H+

Scheme 6




DFSbF5

90

minus78degC

H3CC

C

H

HH

H

D

H3CC

CH2D

H

H3CC

CH3

D

89

++minusH++

+H3C

CCH3

H

+

(24)


VICINAL SYSTEMS 145


(CH3)3SiCN

acid 20degCCl Cl

H2OCHO

+CHO

Cl




30 min

10 min

2

93

(25)


H+

H C NH+ H+

NaCN orTMS-CN

9291

H C N H+

H C NH

H

+ +

(26)



C6H6

ACID

C

O

93 94

H2OC N CH3

CF3SO3

+

minusC

N

CH3

H

++

(27)




CN CF3SO3H

CN

H

H

O

6

8

CN

H

slow

fast

H2O

H2O

+

++

(28)



95 96 97

NHC

H

H

H+ N

HCH

H

H H

++

NHC

H

H

H H+

+



H3CC

NH

H

H

98


99

+

H+

CC

NH

H

HH

H

HH

+

+H3C

CN

H

H

HH

++

(29)

VICINAL SYSTEMS 147

H3CC

NH

CH3

H

100

+

H+

H3CC

NH

CH3

HH

++

(30)

H3CN

CH

CH3

H

H+

101

+

CN

CH

CH3

H

H

HH

H+

+

(31)



N

Ph

H3C

CH3

acid




2 h

26 h

94

50

104

N

Ph

H3C

CH3

HN

Ph

H3C

CH3

H

HN

H

PhCH3

H3C

temperature

60degC

72degC

102 103

++

+

(32)



105

23degC

CF3SO3D

108

N



NHHD

107

NH

H D

N 106

109

NH

D

H

NH

D

+ + +

+

+ ++

+

Figure 3


110

FSO3HSbF5

minus40degC

111

H2NC

NH2

NH2

+

H2NC

NH3

NH2

+

+(33)



114

H2

112 113

HN

NH

N

NH

O

H2N

CH3

CH3

H

H

AH

HN

NH

N

NH

O

H2N

CH3

CH3

H

AH

+

HN

NH

N

NH

O

H2N

CH3

CH3

H

A

H+ +

(34)


VICINAL SYSTEMS 149


N

NtBu

tBu

H

1 atm H2 DMAP

N

N

tBu

tBu

H

H

Clminus

+ (35)



149

33

minus57

4

minus87


115

NN

H

116

NN

HH

118


H2

H2+ H

117

244

H2

H2O

H2

NH3

115

115

116

116

117 + H3O

118 + H3O

117 + NH4

118 + NH4

HH H

H2

H2O

H2

NH3

+

+

+

+

+

+

+

+




C PH

H

H

HC As

H

H

H

HC

H

H

H

H

119 120 121

122

2+

C PH

H

H

HH

C PH

H

H

HH

2+

125

123

2+

C AsH

H

H

HH

C AsH

H

H

HH

2+

126

124

2+

CH

H

H

HH

C Sb

Sb

Sb

H

H

H

HH

2+

127

+++

Figure 4

VICINAL SYSTEMS 151


C

H

H

H+H

H

H

HHC

H

H

H H

119ndash121

X = P As SbH

H

H

HC X C X

+

++ (36)

2+ +

+C CX X

H

H

H

HH C

H

H

H+H

H

H

HHHC

H

H

H H+

125ndash127

X= P AsSb

(37)





CCH2

CH2CH3CH2CH3H

HFBF3

128 129

CO

2+

CH3CCH2CH3

CH2CH3

C

O

H

130

C

O

H

H

C

OH

HC

CH3

CH2CH3

CH2CH3

H

CCH3CH2

CH2CH3

CH3

C

O

H

+

minusH+

C

CH3

CH2CH3

CH2CH3

C

OH

H

+

H+

C

O

H

++

+

131




C

O

H

128 129 132


133

+

C

O

H

H

+

+C

O

H

H Ad+ dminus

C

O

H

BF3

d+ dminus

+BF4

minus+


VICINAL SYSTEMS 153






C

O

H HH

H


C

O

H H

H

1232 (6-31G) 1102 (6-31G)1120 (MP3 6-31G)

132

CH HHCinfinv

CH HCHCinfinv

2+



2+

Cinfinv

2+

132135 134

1087 (6-31G)

128

O OO

+

C

O

H Cinfinv

+

C

O

H

H

Cinfinv

+

+



C

O

H3C OHC+O

CH3

HFBF2C

O+

CH3

136 137

HFBF3

minusH2OC+O

CH3

H F BF3d+ dminus

C+OH

CH3

+




m

138 139

C+

O

H3C AlCl4

AlCl3d+ dminus

minusC

O

H3C Cl AlCl3

AlCl3

d++

dminus

dminus



CCO

ClCH3

H3CH3C

2 AlCl3C

CO

CH3

H3CH3C

AlCl4minus

CC

O

CH3

H3CH3C

AlCl4minus

AlCl3

(CH3)3CHH C(CH3)3

CCO

HCH3

H3CH3C

AlCl3

140

+ +

+ +minusminus

(38)


VICINAL SYSTEMS 155




C OH+ minus2H++ + +

C O H

141

ClOH

HCl

O

Cl

+

+

(39)






C OBr

H-Aor SbF5

C OBr H A+ d+

d+

+

dminus

dminus

+CH3CH2CH3

SbF5 CO

Br2 (---SbF5)

H3CC CH3H

C HBrO

HA

minusHBrminusHA

+

H3C C CH3H

CO

142

Scheme 11




RprimeC

Rprime

OH

RprimeC

Rprime

O+

++

H

RprimeC

Rprime

OH H

H+


(40)


CRR

RRprimeC

RprimeH

RprimeCR

R

RRprimeC

Rprime

RprimeH+ ++ + (41)

VICINAL SYSTEMS 157

CO

R CH3

143a R = H 143b R = CH3

CCH3

CH3CH3H

HFSbF5or HFBF3

COH

R CH3

H+

COH2

R CH3C

CH3

CH3CH3H

COH2

RCH3

CH3C

CH3

CH3H

144 ab 145 ab

NO REACTION

ISOBUTANECOH3

R CH3

2+

+

+ +

+

+

+








OCF3

acid




5 h

5 h

99

43

temperature

0degC

0degC

OHCF3 OH2

CF3 O

CF3

146

+ +

+

Scheme 13



O

acid

OH

F3C F3C

OH2

F3C F3C

product yieldtime

20 min

20 min

68

2

temperature

80degC

80degC

147 148

+ +

+



acid system

Scheme 14

VICINAL SYSTEMS 159


CF3SO3H

C6H6

O

H

OH

+150

149

151

152

153

100 CF3CO2H





100 CF3SO3H

minus27

minus90

minus10

minus12

minus13

minus14

0

4

15

40

77

83

Acid Acidity H0

Total YieldProducts

150+151+152+153



OH+

+ + + +

++++

2+ +

+H H+

OH2

H

OH2

H

14 12 12

OH

H

13

OH

H

154

OH

H

156

OH

H

155

HH

H

H

H

HH

(42)




VICINAL SYSTEMS 161

PhPh

O

PhPh

CF3SO3H

PhPh

OH

PhPh

PhPh

OH2

PhPh Ph

PhPh

Ph

H2OPh Ph

157 158 159 16052

+ +

++

+

(43)



C CH3

CH3

CH3

HCO

HFminusBF3

C CH3

CH3

CH3

C

H

HO

C CH3

CH3

CH3

C

H

OH

H

CCH3

CH3

CHO

HH

H3C

CCH3

CH3

CHHO

H3C

H+

minusH+CCH3

CH3

CHO

H3C

HCCH3

CH3

CO

H3C

H CCH3

CH3

C

H3C

OH

HH

161 162

163164166 165

minusH+

+ +

+

+

+

+

+

+

+

Scheme 15









VICINAL SYSTEMS 163

Ph

Ph

O

O

OH

OH

O

O

PhOH

OPh

PhOH2

OPh C

PhOH2

O

Ph

O

O

PhPh

C

Ph

OH2

O

Ph

C

Ph

OH2

O

Ph

C

Ph

OH

O

Ph

O

OH

PhPh

C6H6

H2SO4

C6H6

CF3SO3HO

O

PhPh

Ph

Ph

O

O

CF3SO3H

C6H6

CF3SO3H

minusH+

H+

167 168

169

170170

minusH+

+ +

+

+

+

+

+

+

+

+

+

Scheme 16

OCH3

OCH3 FSO3HSbF5 H+hn

Δminus60degCOCH3

OCH3 OCH3H

171 172 173 174

+

+ ++

(44)



HOC

OH

OH HOC

OH2

OHHO C OH CH4

175 176

H+ 4H2

minus2H3O+

H+

H3O+

30

+

+

+ + +

(45)









CCl4ndashSbF5


+ (46)

CCl4ndashSbF5


+(47)

H3C NCH3

CH3

O

HH3C N

CH3

CH3

OH

H


H3C NCH3

CH3

O

H

F

80


minus30degC

+

+

(48)


VICINAL SYSTEMS 165

XC

X

X XC

X

X

SbF5

HFndashSbF5

XC

X

X

SbF5

X = Cl Br I

XC

X

XH

179

178177 177

++

+d+

+

+

dminus






ClC

Cl

ClCl

ClC

Cl

Cl

ClC

Cl

ClH+

++ + +

+++

+ +

ClC

ClH

ClH

HClC

ClH

ClH



1766 1648 183916061603

17791575

1732

NA 695 274 43NA

184183182181180








(1)+



(2)+



(3)+


CH3CHCH3 minus39181

(4)2+


HCCl3 H++


(5)3+


HCCl3H2 ++


(6)4+


HCCl3H3 ++


VICINAL SYSTEMS 167








BrC CH

HH

H

H

H


2+

BrC CH

HH

H

H

H


2+H

188 189

BrC CH

HH

H

H

H

187

HXC H

H

H

H

2+

H

190 Cs

X = F Cl Br I

+

Figure 6












DF-SbF5

20degC

NCH3CH3

H3C

CH3D2+

2+

+

N CH3CH3

H3C

D

not formed191

N CCH3

H3C

CH3

N CH3CH3

H3C

CH3

DH

HH N CH2D

CH3

H3C

CH3

minusCH3+

minusH+

192

+

+

Scheme 19

VICINAL SYSTEMS 169


H3CN

NCH3

CH3

CH3

CH3SO3F

CH3SO3F

H3CN

NCH3

CH3

CH3H3C

No Reaction

70 H2SO4

H3CN

NCH3

CH3

CH3H3C

H

193

+ ++

(49)


N

N minuseminus

+ +

+minuseminus

N

N

N

N


194 195 196

(50)


N

N

Br OH

40 HBF4

N

N

197

2BF4minus

+

+(51)


BrBr +

CH3

13C

H3C

NN

CH3

CH3

CH3AgBF4

HBF4N

NH3C

CH3

CH3

CH3

CH3

198

2BF4minus

+

+

(52)




N

NCH2CH3BF4

minus

(CH3)3O BF4+N

NCH2CH32 BF4

minus

CH3

++

+

+

minus (53)

N N

S

N N N N

S

H3C CH3

S

H3C CH3

1992 BF4

minus2 BF4minus

(CH3)3O BF4++

+

+

+ +

minus

(54)


VICINAL SYSTEMS 171

N+ +

+N Cl

2 Clminus

H2O

N N O

Clminus

+ 2 HCl

200

(55)

N

NCH3

CF3SO3H

N

NCH3H

H

H+

N

NH

HHH N

NCH3H

HHH

201

+

+ +

++

+

CH3

++



Ph N N PhCF3SO3CH3

Ph N NPh

CH3CF3SO3

minus+

(57)

N Nminus2eminus

NaClO4

N N

2 ClO4minus

++

(58)

NN

2NO+ PF6minus

CH3CN N

N

202 203

81

2PF6minus

+

+

(59)





204 205 206 207

N N NH

HH

+ +N N N

H

H

H+ +

CN H

H

NH

H+

+N N HH

++

CN H

H

N FSO3H-SbF5

minus120degC


++

++

minus

N2minusH+

CN H

H

NH

H

208

(60)




VICINAL SYSTEMS 173

NN

OHF-SbF5

SO2

minus78degC

NN

OH

NN

OH

H

minusH2O

211

N NN NH2ON

NHO

209 210

+++

++

++

Scheme 20





NO O NO O NO OHH A

213 214212

+ + δ++ +


215


H

NO2

216


+ BF4minus (61)


NO2Cl ++ d

+

dminus

minusNO O

AlCl3

Al2Cl7217

3 AlCl3(62)


CH

HH

NO2H

H2+

CH3NO2H+ + H+

214

218

B(O3SCF3)3NO2

+CF3SO3H

NO2H2+ CH4

(63)




VICINAL SYSTEMS 175






H2O2

HF-SbF5

minus25degC HO

OH

H

XminusH

OO

H

H

2 XminusH219+

+

+(64)


H3CO

OCH3

CF3F-SbF5-SO2

minus50degC H3CO

OCH3

CH3

220

H3CO

OCH3

CH3

221

CH3

+

++ (65)



S

S

S

S

2 CF3SO3

2 (CF3SO2)2O

+

+

minus(66)

S

S

2 CF3CO2

S

S

O

CF3CO2H +

+ minus

(67)




VICINAL SYSTEMS 177

S

S

S

S

2 Xminus

2 Xminus

OHX

S

SHO

S

SO

H

H

222 223 224

225

minusH2O

Xminus

HX+

++

+

+

Scheme 22


S

S

2 CF3SO3

225

OH

OHSSminusH+

+

+

++

minus

(68)




H3CS

CH3

OH

H3CS

CH3

O

HH3C

SCH3

OH

H3CS

CH3

O

H

2+ 2+HH

226 227 228 229


+ +





Cl ClAlCl3

Cl Cl AlCl3AlCl3

Cl Cl AlCl3AlCl3

HA

230

231

Cl ClH

A

HACl ClH

A

H

A

d+

d+

dminus

dminus

dminus

d+

d+

dminus

dminus

d+

d+

dminus

(69)


2+ etc)116


VICINAL SYSTEMS 179


X OH+

X O HH+

X OH

HX O Hor

H232 233

+ + + + +IIII (70)

H ClH+ H+

HO Cl

H

HO Cl

HH

234

+ + +O (71)


HO ClH+ H+ H+

O

O

O HO Cl

O

O

OH HO Cl

O

OH

OH HO Cl

OH

OH

OH

235 236

+ ++

+

++ (72)






F FSbF5

F F SbF5

SbF5F Xe F SbF5SbF5

237

Xe Xed+

dminus

dminus

dminus

d++

(73)




HC

H

H

H

He

2+

238



2+ and He

REFERENCES










REFERENCES 181






































REFERENCES 183










































REFERENCES 185























489 209









187

copy



(CH3)3C-Xsuperacid

CCH3

CH3

H3C

1

(1)

OHHO

FSO3HSbF5

2

OH

4 5

minus78degC

3

+++

++

(2)



ClCl

6 8

minus78degC

SbF5

7

minusH+

+ + +(3)

Ph Ph

Ph PhOHHO

9Ph

Ph Ph

Ph

FSO3HSbF5

minus130degC

FSO3HSbF5

minus78degCPh CH3

Ph

Ph Ph

OH

++

+

+(4)

FF SbF5 Fexcess

SbF5

10 11 12

+ + +d+

dminus

(5)






12 13 14

Rel Energy(kcalmol)

00 04 33 15

HH

HH+ + +

+++

++


OHOH

FSO3H-SbF5

SO2ClF minus78degC

d13C

16 17

262

+ +

(6)CH3

274

18

d13C

+




Ph

Ph

Ph

Ph

PhPh

OH OHFSO3H-SbF5

SO2ClF minus78degC

Ph

Ph

Ph

Ph

PhPh

or

Ph

Ph

Ph

Ph

PhPh

2+

19 20

+ +

(7)


Ph

Ph

Ph

O O HA

or

O OH

Ph

PhH

NO2 Ph

PhH

NO2 etc

21 22 23

minusH+

N+

++ +

+ d+

+ + ++

N

(8)



O

HNO3

70 H2SO4

OH OHO2N H

minus2H+

O

NO2

24

++ +

(9)





2+

2828

CH3

CH3

CH3

H3C

H3CC

CH3

CH3

CH3

CH3

H3C

H3CC

CH3

29 29

2+

CH3

CH3

CH3H3C

30

N

NO

N

N

CH3

CH3

H3C

H3C

31

O OH

CH3H

H

O OH

CH3H

H

32 32

+

++ +

+ +

+ +++++




HO CH3DSO3F

SO2ClFminus78degC

CH3 CH3

H

D

H

D

D+

minusH+D+

minusH+

CH2D

H

D

CH2D

D

CD3

DD

DD

25 26 27

+ + + +

+++ +



DFSbF5

33

minus78degC

H3CC

CH3

CH3

H3CC

C

CH3

HH

H

D

H3CC

CH2D

CH3

minusH+

1

+ +

+

+

(10)


CH2CH3

34 35

CH3CH2 CC

CH2CH3

HH

H

H

C

HH

36

CH3CH2 CC

CH3CH2

CH3H

H

H

++ + + +

+

(11)







37 38 39

CC

C

H H

HH

HH

H

H

H

H

+ +C

CC

H H

H

H

HHH

HH

H

++ C

CC

H CH3

HH

HH

H

H

H

H

+ +





H3CC

CC

CH3

O CH3

HHH3C

CC

CCH3

O CH3

HH

40a 40b

HH

+ +

+

+




H3CC

CC

CH3

O CH3

H

H+ H+

41

H3CC

CC

CH3

OH CH3

H

H3CC

CC

CH3

OH2 CH3

H

H3CC

CC

CH3

OH CH3

H

H+

HH3C

CC

CCH3

OH CH3

HH

42

40b 40a

H3CC

CC

CH3

O CH3

HH

43

Cl3Al

+ +

+

++

+

++

+minus

(12)


O

HF-SbF5

OH OH OH

CH3

O

CH344 44

+

+ +

+

+

+(13)

O

R

Rprime

CF3SO3H

OH

R

Rprime

45

OH

R

Rprime

45

+

+

+

+

(14)



Ph CH3

OH

Ph Ph

OH2

46 47

+

+ +

+


OH 3 equivAlCl3

C6H12

OX

H H

H

H

OC6H12


minus

+

+(15)

OCH3

Ph

HF-SbF5OCH3

Ph

49

SO2ClFminus30degC

OCH3

Ph

49

+

++

+ (16)





OH

O

Ph

50

CF3SO3H

C6H6

O

Ph

51

(17)

OH

OH

Ph OH

OH

Ph OH

OH

Ph

Ph

53

OH

OH

Ph

52 53 5554

OH

OH2

Ph

+

+

+

++ +

+ +


O

Ph PhOH

OH

Ph

57

Ph

OH

O

Ph

56

CF3SO3H

C6H6

Ph

OH

OH

Ph

58

PhPhC6H6

+

+ +

(18)

CH3Ph

59

Ph

Ph

CF3SO3H

C6H6

PhNo Reaction

C6H6

+ (19)




Ph NH2

OCF3SO3H

C6H6 Ph NH2

OHC6H6

Ph NH2

OPh

60 61

+

+

(20)


C6H12

N OH AlCl3N O

H

X

62 63

H

H

N O

H


80

90degC

+

+

(21)

64

N O

H

X

H AH

H

d+

+

dminus




CO2H

O

Ph Ph

65

99

CF3SO3H

C6H6Ph

HOOH

H

66C6H6

58

Ph

HOOH

H

66

OH

OH

Ph

57

Ph

Ph +

+

++

+

+(22)

CPh

67

C6H6

Acid

Ph NH

O

Ph

H

HN

H

O

Ph68

NHPh

O+

+

(23)


P

Ph

Ph

PhN

H

Ph

Ph

69 70

NNN

H

71

+ +

++

+

+


H3C CH3

O O FSO3H-SbF5-SO2

minus60degC H3C CH3

OH OH

H3C CH3

OH OH

73a 73b

+ +

+ +(24)





HO OHCH3

HO OH

90 91

OH

OH

OH

OH

OH92 93

++

+ +

+

++



H3C NH2

O O

H3C NH2

OH OHCF3SO3H

78 79

C6H6

H3C NH2

O

95

PhPh

99

H3C NH2

Ph OH

94

+ + +

+

(25)



HO OH

O O

HO OH

OH OH

O OO O OHHO

XN OHHO

XN OO

H3C CH3

O O

H3C CH3

OH OH

H3C OH

O O

H3C OH

OH OH

H3C OCH3

O O

H3C OCH3

OH OH

H3C NH2

O O

H3C NH2

OH OH

N N

OO

O

HH N N

OHO

OH

HH


(1)

(2)

(3)

(4)

(5)

(6)a

(7)

(8)

72 73

74 75

76 77

78 79

80 81

82 83

84 85

86 87

OH

OH

OH

OH88 89

(9)

X = H Cl Br I

CF3SO3H

CF3SO3H

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

FSO3H-SbF5

HF-SbF5

CF3SO3H

FSO3H-SbF5

BF3-H2O


+ +

+ +

+ +

+ +

+

+ +

+ +

+

+

+

+

+




O OHHO

83

OC OH

OH

COHO

OH

96 96

+

+ + + +

+ (26)




NO2

F N OO

XBF3-H2O

NO2

F

X = Cl Br I84

X

819592

X Yield

ClBrI

97

+ (27)




N OO

Cl

N OOCl+

N OO

Cl

N OHOCl+

H

N OO

Cl

N OHHOCl+

H

H

N OO

Cl HN OHHO

Cl+H H

H

ΔH kcalmol

3244

1922

702

minus1020

98

+

++

+

++

+

+

+

minus

+

+

+

+


H

Cl

N OO

Dagger

N OO

Cl

H Cl

N OO

ΔG1Dagger

d+ _

_

+

(28)


ΔG1Dagger ΔG2

ΔG2δ+

Daggergt

H

Cl

N OO

H H

H

DaggerN OO

Cl

H H

H

H Cl

NH

OHHO

Dagger

+ ++

++

+

+

+ +

(29)



N N

OO

O

HH N N

OHO

OH

HH

86 87

CF3SO3H

C6H6

2 C6H6

N N

O

O

HH

Ph

Ph

+

+

(30)






H3NO

O

CH3FSO3H-SbF5-SO2

minus60degC H3NOH

OH

CH3

H3NO

CH3

99 100

minusH2O

+ ++ +

+minus (31)

H3N OH

OH

minusH2O H3N

O

101 102

+

+

++

(32)


Ph OH

NHTs

OCF3SO3H Ph OH

N

OH

SH

H Ar

O

O

103

+

+ (33)


H2NOCH3

OCH3

CF3SO3H

C6H6

H3NOCH3

H3NOCH3

H3NPh

C6H6 minusCH3OH

H2NPh

Ph95

104 105 105

106107

++

+

+

+

+

(34)




N

O CF3SO3H

N

OH

H

N

OH

H

+

+

+

+(35)


NO

CH3

X

CF3SO3H

C6H6

N

CH3

X

PhPh

92

+ +

minusminus

(36)





N

O

H

N

OH

H

H

N

S O

CH3 N

S OH

CH3

H

NH

O

NH

OHH

NO

CH3

Xminus

NOH

CH3

N

OH

N

OH H

N

OH

N

OH

X

CF3SO3H

CF3SO3H

CF3SO3H

CF3SO3H

CF3SO3H-SbF5

HBr-AlBr3

X = H or AlnBr3n

108

109

110

111

112

113

(1)

(2)

(3)

(4)

(5)

(6)


+

+

+

+

+

+

++

+

+

+

+

+

minus

NH

O

Cl

14-20 equivAlCl3

m-C6H4C12

N

OAlCl3

H

AlCl3 NHO

Cl

Cl80

116114 115

N

O

H+ +

d+

dminus

(37)



N

O

O

OH CF3SO3HN

OH

O

OH2N

OH

O

CH2 N

O

OCH2

N

OH

O

CH2N

OH

O

CH2

H

117 118

117 117

N

OH

O

CH2

117

N

O

O

OH CF3SO3H

C6H6

N

O

O

++

+

+

+

+

++

+

+

++

Scheme 2



N

O

OH

CH3

CF3SO3H

p-C6H4Cl2

N

O

CH3

Cl

66

80degC Cl

N CH3

O

120

N CH3

OH

121119 122

+

+

+

(38)

123

N

O

OH

CH3

CF3CO2HN

O

CH3

OCH3

67

80degC H3CO

N CH3

O

120119

p-C6H4(OCH3)2

+

(39)


PhP

O

PhPh

CH3

PhP

PhPh

CH3

Ph

Ph

X

88CF3SO3H

C6H6

PhP

OH

PhPh

CH3

124

+ + +

minus

(40)



N CH3

O

++

N CH3

OH

HH

+

TheoryLevel




+126

N CH3

OH

+

+

+

N CH3

OH

HH

2+




120

121

TheoryLevel





H3C OCH3

O

H3C OCH3

OH

H3C OCH3

O

HH3C

O

+acid

CH3OHAac1

125 126

+

+ +

(41)


H3C OCH3

O

H3C OCH3

OHFSO3HSbF5

SO2minus78degC

H+

H3C OCH3

OH

127H

H3C

O

+ CH3OH2

125

+++

++

(42)




H3CO CH3

O CH3

BF4

CD3FSbF5SO2

minus30degC

128

H3CO CH3

O CH3

129

D3C

H3CO CD3

O CH3

130

(NuCH3)+Nu

++

+

+

minus(43)

O

H3CCH3

O

HF-BF3

O

H3CCH3

HOOH

H3CCH3

HO OH2

OC

CH3H3C

131 132 133

++++

+ (44)




OCH3

O

CF3SO3H

C6H5NO2

O

NO2

82

(45)

OCH3

OH

H

OCH3

OH2

134 135

+

+

+

+



F3CC

OH

OFSO3HSbF5

F3CC

OH

OHH

F3CC

OH2

OH minusH2O

F3CC

OHCF4

136 137 138

minusSbF5

minusCOH+

CF3

139

+ ++

+

+

+

SbF6minus

+

(46)








HC

O

O

141

H

H

H

H3CC

O

O

140

H

H

H



2+2+




H3CO O

CH3

CH3 CH3 O OHH

142 143

++

++


O HF-SbF5

SO2

O OOH

HO O

HO O

H

HO O

H H

H144

145

146

+ +

+

+

+

+ +

(47)


HOCH3

OH

OFSO3HSbF5

SO2minus80degC

HOCH3

OH2

OH

minus30degC

minus2 H3O+ O

O

CH3

CH3

OH

HOHO

CH3

OH2

OH

147 147 148

+

+

+

+

+

+

(48)


HO

CH2CH2

OH

FSO3H SbF5

SO2minus80degC

O

CH2CH2

O

H

H

H

H

minusH2O

O

CH2C

H

H

H

H

~H

minusH+ HC

CH3

OH

149 150 152

O O

H

H

H

H

151

C C

H H

HH

2+

+ + +

+ +

+ d+

d+

(49)

O

CH2CH2

O

H

H

H

HminusH2O

149

O

CH2C

H

H

H HC

CH3

OH

152

+ +

+ +

minusH+ (50)



CH3O

CH2 CH2

OH

FSO3H SbF5

SO2

minus80degCO

CH2 CH2

O

H

H3C

H

H

minusH2O

HC

CH3

O

153 154

H3C

+ +

+

(51)




C

CH3

CH3

CH3

C

OH

H C

CH3

CH3

CH3

CH C

H3C CH3

CH3

C

H

CH3CCH3

CH3

C

O

H

C

CH3

CH3

CH3

C

O

HH+ H+

minusH+

C

H

CH3

CH3

CH3CC

H3C CH3

CH3

C

OH

HCH3C

CH3

CH3

C

H

155 156 157

158159160

+

OH+

OH2

+OH2

+

OH2

+

+

+

++




O

NH3C

Ph

H3CN

O

H

Ph

Ph

CF3SO3H

O

NH3C

Ph

CF3SO3H

H H

H

H3CN

OH

H Ph

C6H6O

NH3C

Ph161

162163

C6H6

+ +

+

+

+

(52)



NO

S

PhPh

2 equiv AlCl3

C6H6 NO

S

PhPh Ph N

Ph

AlCl3

AlCl3S

AlCl3

OAlCl3Ph N

PhS

OH

Ph

76

164 167165 166

+

+minus

minus

+

+

minus

minus

(53)


624 Acyl-dications


RC

O

RC

O

168a 168b

HR

COH

169

+

+ +

++




ClC

CCl

O

O

SbF5 SO2ClF

minus80degC ClC

C

O

O

SbF5

ClC

C

O

OSb F5

minusCOCl

CO

C

C

O

O

170 171 172 172

173 174

+ ClC

O+

+

+

+

+

dminus

d+




FC

CC

F

O O

HH

SbF5 SO2ClF

minus80degCC

CC

F

O O

HHSbF5

CC

CO O

HH

CC

CO O

HH

175 176 177

+ + +

++

FC

CH2C

F

O O

178n

SbF5C

CH2C

O O

nn ge 3 2 SbF6

+ +minus

d+

dminus

(54)




H3C CC

OH

O

OFSO3H

H3C CC

OH

OH

O

H3CC

COH

OH

OH

H3C C CO

OH

H3CC

CO

OH

H3CC

O

179

180

181

SbF5 +

+

+

+

+

+

+ +

(55)


HF-SbF5H2C C

OH3C

CO

H3C CO

CO

185184182 183

186

Cl CO+

+

+ +

+

+ +

(56)


HF-SbF5

187

H3C CO

188

CH3

H3C CO

189

H3C CO

CH3

H3C CO

productsCl CO

CH3

++

+ +

+ +

++

+ +

CC

CO

H

HH H

CC

CO

H

H

H

H

190 191 192

CC

COH

H

H

H+

+ + +

+

+ (57)




CC

CO

CH3

H3CH H

CC

COH

CH3

H3C

HC

CC

OC

H3C

H

193 188 194

HH

H

HC

CC

OH

CH CH3

195

H

HH

CC

CH3

H3CH H

196

H

H

++ + +

+

++ + + +





NO

O

CF3SO3H

C6H6

0degC

NOH

OH

NOH

197

96

NOH

OH

197

++

+

+

(58)

NO

O

CF3SO3HN

OH

OH

199

H3C

CH3

H3C

CH3

198

+ +

(59)

NOH

OH

2+ +

197

H

H

H

N

N N

H H

H

H

H

H

200



Ph

NO

OCF3SO3H

C6H6N

OH

OH

PhN

OH

CH3CH3 CH3

OH

CH3OH

minus40degC

Ph NOHCH3

OHOCH3CH3OH

OCH3

CH3

OCH3

C6H6

H2OPh

CH3

O

85

201 202 203

+ + + +minus

Scheme 5


NO

OCF3SO3H

2) H2O

minus40degC

1) CH3OH

2 hr72

Ph

O+

minusC6H6

(60)


NO2

NO2

CF3SO3H

minus20degC

CF3SO3H

minus20degC

209 211

NOH

OH

210

21

+

+ (61)


NO

O

CF3SO3H

C6H6

40degC4 hr204

NOH

OH

C6H6

NOH

OH

205 206

NH

OHN

O

208

NH

OH

207a207b

minus2H+

minusH2O

+

+

+

+ +

+

++

H+

minus

Scheme 6



CF3SO3H

C6H6

Ph

NH2NO2 50N

OH

OH

N

OH

OH

212

213

214

+

+

+ +

(62)




NO2

CF3SO3H

215

N

216

OHHON

216

OHHO+

+ +

+ (63)

NOH

H

CF3SO3H NH

H2+ 2+ 2+

++

NH

H

NH

H

minusH2O

(64)



H3C NONa

OHF

C6H6

H3C NOH

OH

H3C NOH

OH2

H3C NOH

OH2

Ph N

CH3

OH

C6H6217

+

+ +

+

+

+

minus

(65)

EtONO2

O CF3SO3H

C6H6 EtON

OH

OH

OH

EtON

OH

OH2

OH

C6H6

EtON

O OH

Ph219218

+

+++

+

(66)


PhNO2

O

PhN

OH

OH

OH

PhN

OH

OH2

OH

C6H6

PhN

O OH

Ph22 0 221

CF3SO3H

C6H6++

+

+

+

(67)




PhNH2

CH3

OHPh

PhNH3

CH3

Ph

PhNH2

CH3

PhPh

222 223 80

CF3SO3H

C6H6+

+ (68)

PhC CH3

Ph

59

+


HN

CH3

OH

OH

HO

224

FSO3H-SbF5

225b225a

NCH3

OH

HO

H H

++

NCH3

OH

HO

H H+

+

(69)


N

CH3

CH3

CF3SO3H

C6H6 N

CH3

CH3HN

CH3

CH3

Ph

87

226 227

+

+(70)

NHN

CH3N

CH3

Ph

228

CF3SO3H

C6H6

+ +

(71)


NOCH2CH3

OCH2CH3

CF3SO3H

o-C6H4Cl2

N Cl

Cl

Cl

Cl

CH3CH2

CH3CH2N

OCH2CH3CH3CH2

CH3CH2

H N

CH3CH2

CH3CH2

H Cl

Cl

CH3CH2

CH3CH2

229 230

231

+

+ + +

(72)




PhC

CN

OHPh FSO3H-SbF5

PhC C

PhN

PhC C

PhN H

232 233 234

orPh

C CPh

N

235

H Ad+ dminus+ + + +

(73)

PhC

CN

OHPh CF3SO3H

236

C6H6 PhC CN

PhPh

237

74 (74)


REFERENCES





REFERENCES 227





































REFERENCES 229

















7036









N

H3C

OCF3SO3H

C6H6 N

H3C

Ph Ph

Reactive to C6H6

1

N

H3C

OH

H

+

+ (1)


231

copy


Unreactive to C6H6

NH

HO

CH3

2

+ +



3a 3c3b

H3C CH3

OH OH+ +

H3C CH3

OH OH+

+ H3C CH3

OH OH

+ + (2)

4 5

N O

CH3

PhPh

H H+

H3C NPh

OH

H Ph

+

++

(3)


72 DISTONIC SYSTEMS





H3CCH3

CH3

CH3

Cl

Cl

SbF5

SO2ClFndash78degC

6

H3CCH3

CH3

CH3

++

(4)



H3C

CH3

OH

H3C

CH3HO

H

H

FSO3H

SbF5SO2ClF

87

H3C CH3

CH3 CH3

+ (5)

FSO3H


9

OH

HO

H

H

10

H

H

+

+(6)

CH3

OHHO

H3C

11 12

CH3

H3C

++

(7)




CH3

OH

H3C

HO

FSO3H

SbF5SO2ClF

13 14 15

CH3

H3C

H +

CH3

H3C not formed+

+

(8)

FSO3H

SbF5SO2ClF

OH

HO

16 17 18

+

++

+

(9)

H

H

H

H

HO

OH SbF5SO2ClF

ndash78degC++ (10)


19 20CH3

H3CFSO3H

SbF5SO2ClF


+

+ +

+ (11)

21

+ +



S SS

SS S

CH3

CH3

H3C

H3C

CF3SO3H

22

S SS

SS

CH3

CH3

H3C

H3C +

+

(12)



Cl

Cl

SbF5

SO2ClFndash80degC

23 24 25Cl

+ +

+(13)



2527261

4


28

+ +

+

Figure 1




HOH

HO

H

FSO3H-SbF5

ndash80degC

29 30 31

HOH2

H2O

H

++

H

H

+

+

(14)


CH3

OH

HO

CH3

FSO3H-SbF5

ndash80degC

32 33 34

CH3

H2O

CH3

+

+CH3

H3C

+

+

(15)



37

CH3

CH3

H3CCH3

OH

OH

SbF5

SO2ClF

38

3635

+ + CH3

CH3

H3C CH3+

++

+

(16)






PhPh

Ph

Ph

2224

PhPh

Ph

Ph

PhPh 2479

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

2451

2523

2456

2209

39

40

41

42

43

44

+

+

+

+

+

+

+

+

+

+

+

+



CCH3C CH3

CH3

CH3

CH3H3C

45 46

C


1379

+ + +

14912408

471minusCH3C+

CipsoCring

142414072557

339minusCH3C+

CipsoCortho





47 48 49


Ph

Ph

Ph

Ph+ +

Ph

Ph

Ph

Ph

+

+Ph

PhPh

Ph

+ +


OPhPh

PhPh

(CH3)3Si-O3SCF3

[(CH3)3Si]2O

2 eminusPh

Ph

Ph

Ph

50 512 Xminus

Ph Ph PhPh+ +

(17)

BBPh Ph PhPh

52





(H3C)2N

CH3

CH3

(H3C)2N

CH3

CH3

N(CH3)2

H3C

H3C95

50 X = ClO4minus

(18)




53

2eminus

OCH3H3CO

H3CO OCH3

54

OCH3H3CO





ArAr

ArAr

HO

OHAr = p-MeOC6H4

55

HBF4

56

ArAr

ArAr

Mg

57

ArAr

ArAr

+

+2 (p-BrC6H4)3N

SbCl6

+

minus

(20)



OR

ROS

S

HBF4

S

S

Zn

SS

58 59 60

2 (p-BrC6H4)3N

SbCl6minus

++

+

(21)



iodine (eq 22)23

ArAr

ArAr

Ar = p-(Me2N)C6H4

61

I2

ArAr

ArAr

62

H H

2 I3minus

+ +

(22)




HC

CC

CHH

H

H H

H H

H H

HH

2+ 2+

HC

CC

CHH

H

H H

H HHH

H

H

63 (C2) 64 (C1)




minusH+ minusCH3+

HC

CC

CHH

H

H H

H H

H H

H H2+

63


CC

HH

H

HH

H

HH

+

HC

CC

C

H

HH

H

H HH

HH H

+



H3C

CH3 HH

H

H H3C

CH3

CH3

H

H H

65 66

++

+ +





H3C CH3

O HF-SbF5

CO 20C

H2O

H3C CH3

O CO2H

+ H3CCH3

O

CO2H

H3C CH3

OH

H3C CH3

OHHH

H

H

H+

H3C CH3

OH

H3C CH3

OH CO H2OCO

67 68

67

H2

H

H3C

CH3OH H

HH

CH4

~HH3C

CH3

OHCO

H3CCH3

OH

CO

H2O

68

69 70 71 72

73 74 75

+

+

+

++

+ +

+

+

++

+

+

+ +

Scheme 1



H3CCH3

O

CH3

HF-SbF5

CO minus20degC

H2O

H3C

CH3O

CH3

CO2H

60

(24)



CH3

CH3

O HF-SbF5

CH3

CH3

OH H+CH3

CH3

OH

H

H

H

H2

CH3

CH3

OHOH+CH3

CH3

OCH3

CH3

76 77 78

7980

+ + +

+ + +

(25)



H3C NCH3

O

H CH3

CCl4 HF-SbF5

minus30degCH3C N

CH3

OH

H CH3


H3C NCH3

O

H CH3

F

81 82

+

+






O FSO3H-SbF5

O3 minus78degC

O O

60(27)

CCH2CH2CH2CH3

H

OFSO3H-SbF3

O3 minus78degCC

CH2CH2

H

HO C CH3

H O O OH

HminusH2O2

CCH2CH2

H

HO CCH3

OH

HCH3

O

O 80

83 84

+

+

++

(28)

CCH2CH2CH3

H

OFSO3H-SbF5

O3 minus78degCC

CH2

H

HO C CH3

H O O OH

HminusH2O2

CCH2

H

HO CCH3

OH

not formed85

+

+

++




CO2HCF3SO3H

C6H6

O

CH38586 87

orH3COH

OH+ +

CH3 O

+

+

(30)


Ph CO2HCF3SO3H

C6H6

O

Ph9888 89

orPhOH

OH+ +

PhO

+

+

(31)

H

H

Ph

HOOH

CF3SO3H

Ph

OH

OH

90 88

++

+ Ph

OH

OH+ +

(32)


HO OH

OO

O

CF3SO3H

C6H6

C6H6

HOPh

OH

Ph

minus2H2O

minusCO HO Ph

OH

Ph

Ph

O

Ph Ph8991

+

+

+

(33)

CH3Ph

Ph

92

+




OH

ACID

OH

C6H6

O

Ph O

cyclohexane

93

+

+

(34)



O

NH3CPh

Ph

H3CN

O

H

PhPh

61

ClCl

CF3SO3H

o-C6H4Cl2

(86 de)94 95

H3CN

OH

H

PhPh

H

+

+





Cl CO

HF-SbF5 H3CC

OH3C

CO

96 97

H2CC

O+

+

+ + ++

(36)

C OHF-SbF5

98 99

H

HC O

H

H

H+ + +

(37)

DF-SbF5

100 101

C OCH2DCH2minusH+

25 D

20degC12 days

C OCH3CH2

+C OCH2CH2

D H

+

+

+

(38)





NR

OH

NR

OCH3

H3PO4

102

N

R

OCH3

H

+

+


NH

CF3SO3H

o-C6H4Cl2

Cl

Cl

42 NH

103

N

H

H +

+

(40)

N Ph CF3SO3H

C6H6

N Ph

Ph

99

104 105

N PhH +

+ (41)

107106 108 109 110

NPhH Ph

+

+ Ph

NPh

CH3H

H

+

+

NH3+

+Ph NCH3

HH

+ +CH3

H3N

+

+





N+

+

+

+

+

+

+

+

HN

N H

CH3N+

+

+N

Ph

OH

N+

N+ +

Ph

OH

PhN+ +NPh

OHOH

N

S

CH3

N

S

CH3

CH3

H

NNPh

NPh

PhCH3

CH3

N

PhCH3

CH3

H

N

O PhPhPh

H3C

N

O PhPhPh

H3C H


111

112

113

114

115

116

117

118

NN

CH3

CH3

Ph

119

N

O Ph

H3C

120

N

++




122

N

S

PhH

123

N

S

PhH

HCH3 CH3

N

S

Ph

CH3 CF3SO3H

minusH2OOH

12125degC

N

S

Ph

CH3

PhN

S

Ph

CH3

Ph56 26


+

C6H6 C6H6

+ ++

Figure 2



Ph

Ph

Ph2H+

NH

+

125 126


HF3-21G

HF6-31G (d)

HF6-311G (d)

PBE16-311G (d)

MP26-311g (d)

MPW16-311G (d)PCMsp

00

00

00

00

00

177

171

179

100

103

7400

124

++

Ph

Ph

NH

+

+

PhN




14-dication

15-dication

127

19-dication

110-dication

129

130

HN

HH

CH3+ +

128

HN

HH

CH3+

+ HN CH3

HH

+ +

HN CH3

HH

+

+



H2N

HO

H3CO

HCl ether

H3N

H2O

H3CO

H3N

H3CO H3CO

H3N

H3CO

H2NN

OH

H3CO

Butorphanol

131 132

+

+ +

++

+

Scheme 2



NH3C

OH

Ph

NH3C

Ph

Ph

H 98

CF3SO3H

134

C6H6

133

NH3C

Ph

H+

+

NH3C

Ph

H

H

++

(42)

N

PhOH

N

Ph

Ph 97Ph

Ph

CF3SO3H

C6H6

135

N

Ph

Ph

H136

N

Ph

Ph

H+

+

+

+

(43)



NNPh

Ph

Ph

HO

NNPh

86

CF3SO3H (44)

O

ON N

Ph NN

Ph

60

OHPhO

OCF3SO3H (45)



N

H

N

PhPh

CH3

CH3CH3

CH3

CH3

OH2

H

CF3SO3H

N

Ph

HNNH

H

minus H2O

138 139

93

CH3

N

Ph

OH

Ph

137

+

+

N

PhPh

H

CH3

+

+

+

+

+

N

PhPh

H

CH3

+

+

+

minusC3H6

minusH+




PhP

PhPh

CH3

CH3Br

CF3SO3H

C6H6Ph

P

PhPh

CH3

CH32 X

PhP

PhPh

CH3H3C

140 92

+ + + +

minus 2 Xminusminus

(46)

PhP

PhPh

Br

CF3SO3H

C6H6Ph

P

PhPh

2 X

141

CH3

CH3 PhP

PhPh

2 X

CH3 PhP

PhPh

2 X

CH3

142 143

99

++

minus minus minus

+ + +

minus

+



OH

CH3

Br

FSO3H-SbF5

SO2 minus60degC

CH3

BrSbF5

144

+

d+dminus

(48)







146 147 149148a 148b

H3CCH3

OH

OH

+

+

OH

HO+

+ OH

HO+

+OH

HO

+

+ OH+

O

O

FSO3H-SbF5

SO2 minus 60degC

145

OH

HO

+

+

(49)





150 a n = 0b n = 1

c n = 2d n = 3e n = 4

H3CC

(CH2)nC

OH

OH OH+ +

150de

FSO3H-SbF5

0degC minus H2O

151de

H3CC

(CH2)nC

OH

OH OH+ +

H3CC

(CH2)nC

OH O+ +

(50)

no reaction

150c

FSO3H-SbF5

0degC minus H2OH3CC

(CH2)2C

OH

OH OH+ +

(51)



N

O

O

CH3CF3SO3H

C6H6

N

O

CH3

Ph

Ph 90152

N

HO

OH

CH3

+

+

(52)

N

O

O

OEt CF3SO3H

C6H6

N

O

OEt

Ph

Ph 97153

N

HO

OH

OEt

+

+

(53)





154 a n = 0b n = 1c n = 2

d n = 3e n = 4f n = 5

C(CH2)n

COH

OH OH+ +

HO

t12 = 1 hr

minus H2O

minus 20degC

154d-f

FSO3H-SbF5


155d-f

C(CH2)n

COH

OH OH+ +

HO

156d-f

C(CH2)n

CO O+ +

C(CH2)n

C

OH O+ +

HO (54)



CO2H

CO2H

FSO3H-SbF5 minusH2O


+

OH

OH

OH

OH

OH

OH

O

O

OH

O

H

OH

OH

O

157 158 159

+ + +

++

+

+

(55)



OH

OMe

OH+OMe

160

OH

OMe

161

OH

OMe

162

OH

OMe

OH

OMe

163

OMHO OH

MeO

OH

MeO

OH

OMe

OH

OMe

164

OH

MeO

OH

MeO

165

(CO2MeH)6+

+ + +

+ + + + + +

+ + +

Scheme 4



H3COC

(CH2)nC

OCH3

O O

166 a n = 0b n = 1c n = 2

d n = 3e n = 4

H3COC

(CH2)nC

OCH3

OH OH

167 a n = 0b n = 1c n = 2

d n = 3e n = 4

FSO3H-SbF5

+ +

(56)




OO

O

OO

O

FSO3H O

O

O

O

minus2 CH3OH

168

+

+


OO

O O

O

O

O O

169 170

+ +

+

+

(57)


O

O

O O

O

O

171

+

OO

O

OO

O

OOO

FSO3H

minus2 CH3OH

++

(58)






NH

OCF3SO3H

C6H6

N

OH

H H172 173

NH

Ph Ph+

+ (59)

Ph PhO OH+

174

CF3SO3H

C6H6

(60)





NH3C

O

NH3C

OH

H

N O

O

N OOH

H

H3C N OCH3

H3C

OCH3

H3C N OCH3

H3C

H

HN CH3

HO

HO

OHN

CH3HO

HO

H H

H3C O

ONH3

H3C OH

OH

NH

O

HNH

OH

NOH O

H

HN

OH OH

H

N

SH3C

CH3

O

CH3 HN

SH3C

CH3

OH

CH3

NNPh

PhO

H

HNNPh

Ph H

N

H

O

H

OH

CH3

NCH3

Xminus

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)


175

176

177

178

179b

180

181

++

182

183

184

185

N

OH

NH

OH

+

+

+

+

++

+

+

+

+

+

+

+

+ +

+

+ NH3+

+

+

+

minus

+

HO


179b179a 179c

45degC

186

OH3N +OH

OHH3N

++H3C OH

OHNH3

+

+NH3

+H3C OH

OH

NH2+

+

(61)



N

CHOCF3SO3H

C6H5NO2

140degC N

NO2

NO2

53

(62)

N

CHO CF3SO3H

adamantane CO HNOH

H

H

O

ON

18060

++

+

(63)


NOH

CF3SO3H-SbF5

C6H12

C6H12 C6H12

NH

OHNH

OHN

187 188 189

++

++

(64)

ABr3 or AlCl3

C6H6N

OHNH

OH

Ph

N

OH

187

++ (65)

OH

190

+



191 193185 192 188

NH

OH+

+ NH

HO+

+ NH

HO+ + N

HOH

++

NH

OH+

+




OH

NH2

Acid

OH

NH3

Acid

OH+

++

+

NH3

195 196

OH

eLUMO

q3


3 3

+03 +025

190194



OX+

+NH2X



minus

1 C6H12

2 H2O

1 C6H6

2 H2O

O

NH2 O

NH2

70ndash80

15ndash40

OH

NH2

197

(66)





CF3SO3H

C6H6100degC

NH

CH3

O

NH

CH3


198

+

(67)

NH

CH3

O

NH

CH3

OH

78NH2

NH3

CH3

O

199

C6H6CF3SO3H

C6H6100degC

+

+(68)


H3N

NH

OHH3N

NH

CH3

OH

200 201

++

+

+

N

NH

O

PhCF3SO3H C6H6

25degC

NH

NH

OH

Ph

O

Ph70

202

+

+

(69)





NOH

OFSO3H-SbF5

NOH

HOH

203

++ (70)

NOCF3SO3H

204

SO

OCH3 NHO S

O

OCH3C6H5OH

H

NHHO SO

OCH3

HO

+

+

(71)


HOO

OH H

H

207HO O

OHH

H

CH3

208

+

++

+


COH

OCH3

FSO3H

COH

OCH3

H

COH

OCH3

H

CO H

OCH3

H

FSO3H

SbF5

CO H

OCH3

H

H

CO H

OCH3

H

H

205a

205b

206a

206b

+ + +

+

+ +

+

Figure 4



FC

(CH2)nC

F

O O

209d-h

SbF5-SO2C

(CH2)nC

O O

210d-h

minus60degCF

C(CH2)n

CF

O O

209 c n = 2d n = 3e n = 4

f n = 5g n = 6h n = 7

+ +

2 SbF6minus (72)




CF

O

CF

O

X

X

X

X


SbF5

CO

CO

X

X

X

X


+

+

(73)

X

X

X

X

213b X = Clc X = Br

+

+



2+ ions (213bc)




SS

S 2 NO+BF4

minus

S

S+

+

SS

S

S

minus2 BF4

214 215

(74)


S

S2 CF3SO3

minusS

S

H

2 CF3SO3minus

45216 217

+

+

++

+

(75)

SS

(CH3O)2CH

SS CH3H3C

2BF4minus

218

+

+ +BF4minus (76)



trade

trade



F3C S N S CF3

F O

OO

O

NN

CH2Cl

F2 BF4

minus

NF

BF4minus

NF

CF3SO3minus

S

O

O

NF

H

S

O

O

NF

CH3H3C


+018

minus004

minus037

minus047

minus078

minus210

219

220

221

222

223

224

+

+

+

+




trade


HO O

HFSO3H-SbF5

minus80degC

HO O

H

H H25degC

minusH2O minusH+

~H

225 226

+ + HOH

H

H

H H

HH

++

OH

H

H

H HH

H+

(77)

H3CCH3

OH

OH

FSO3H-SbF5

minus60degCH3C

CH3

OH2

OH2minus30degC

minusH2OH3C

CH3O

HH

O CH3H3CHH

2+

O CH3H3C

H

228

229

227

+

+

+

+

+

(78)


minus70degC

minusH2O

HO


H

230

HO O

H

H H++ +

+

+ +

+ ++



H3CO

OH

H

H

231

+ +

232

H3CO O

H

CH3

HH

+ +

233

H3C OO

H

CH3 H

H

+

+

234

H3C OO

H

H

H

+

+



235

FSO3H-SbF5

minus60degC

H3CO

OH

CH3

minus10degC H3C CH3

OHCH3H3O

minus10degC

H3CO

H

CH3minusH+

236

~H

H3CO

OH

H

H CH3

+ ++

+

+H3C

OCH3

+

++



NN

O

CH3

FSO3H-SbF5

SO2ClF

minus75degC

237

+

NN

O

CH3

H

+

+2 X

minusXminus (81)

NN

OH3C

FSO3H-SbF5

SO2ClF

minus75degC

NN

OH3C H

238

+

+

+

2 Xminus

Xminus

(82)






excessCH3F-SbF5

CH3-I-(CH2)n-I-CH3

239 a n = 1b n = 2c n = 3

d n = 4e n = 5f n = 6

+ +

(83)

Br Brminus78degC

excessCH3F-SbF5

Br BrCH3H3C

240+ + (84)


241 242 243 244

I

I

CH3

H3C

IICH3H3C

I

I

CH3

CH3

IICH3H3C

ICH3

Br

Br

BrBr Br

Br

CH3CH3CH3

H3C

Br

I

CH3

H3C

245 246 247 248

+

+

+ + +

+

+ +

+

+ + +

+

+





O

Br

CH3minus78degC

excessCH3F-SbF5

O

Br

CH3

CH3

H3C

O

Br

CH3

CH3

249 250

(10) (44)Ratio

+

+

+



X

X

excessCH3F-SbF5

minus70degC

X

X

CH3

H3C251 a X = I

b X = Brc X = Cl

252 ab

+

+

(86)

XCH3F-SbF5

minus70degC

X CH3


254a-c

+

(87)


REFERENCES 277


REFERENCES



































REFERENCES 279













































REFERENCES 281









283

copy










REFERENCES



6 1789

INDEX











142












287

copy

288 INDEX



















250251























INDEX 289



















NMR studies 260261










143











91

290 INDEX














211212CCl22+


CF22+






















INDEX 291












































292 INDEX







213Diprotonated









147148methane (CH6





















Superelectrophilic

INDEX 293





















F2OH22+) 114














193212geminal





294 INDEX




148




































INDEX 295



































4344Mesityl oxide


296 INDEX























2-Naphthol











162163Nitration










INDEX 297















8283NMR





Nucleophilicity 23

















246






298 INDEX































218diprotonated 218







trade

INDEX 299

































300 INDEX














































INDEX 301





dications 238239




Cover Page


ISBN 0470049618

CONTENTS

Preface

1 General Aspects








Index

Superelectrophiles and Their...

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Transcript of Superelectrophiles and Their...