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Redox Neutral Reactions
Wang Chao2011.3.12
Redox Economy and Redox Neutral Reactions:
Angew. Chem. Int. Ed. 2009, 48, 2854 – 2867
R OMe
OLiAlH4
R OHDess-Martin
DIBAL R H
O
RRu cat
H2/CO R
O
H
R
NEt2
R NEt2
(Z)
(E)R NEt2
R NEt2
(S,E)
(Z,E)
(S)-BINAP-Rh(I)
(S)-BINAP-Rh(I)
(R)-BINAP-Rh(I)
Developed by Noyori;Employed by Takasago in total synthesis of Menthol
R OR R OR
R NR2 R NR2
OH
HR
O
R
Redox Isomerization:
R
Br
H
O N-heterocycliccarbene
nucleophileR
Nu
O
H
O
Nu
Osame
R
O
R
OH
H
O
Nu
Osame
R R
Ph
Br
H
O
Ph
Br
O
N N
N
Ph
Ph
Br
OH
N N
N
Ph
Ph
OH
N N
N
Ph
N N
N
Ph
base
Ph
O
N N
N
Ph
PhNH2
Ph NHPh
O
Scheidt: J. AM. CHEM. SOC. 2009, 131, 18028–18029
Ph OAr
NH OP
NNNR Ar1
NHC
OH
ArO
NN
N
R
Ar1
OH
NN
N
R
Ar1
H
H
O
NN
N
R
Ar1
Ph
NHP
ArO
O
Ph
NP
addition;H-migration
eliminationC-C bondformation
acylation
H
ArO
O
H Ph
NP
+ NHC
Ph OAr
NH OP
Hydride Shift Reactions: transition metals, lewis acids, organocatalysis
Akiyama:J. Am. Chem. Soc. 2011, 133, 2424–2426
R3
EWGGWE
R2R1
HH
R1 = alkyl,R2 = H, R3 = alkyl or H
R1 = H,R2 = alkyl, R3 = alkyl
[1,5]-H shift
[1,6]-H shift
H
H
GWE EWG
EWGEWG
R1R3
R2
R3
CHO
N
DPPindole (1 eq.)
N
NH
W, 150oC,15min
Seidel:J. Am. Chem. Soc. 2011, 133, 2100–2103
recent examples:
H
O
Ph
[Rh(dppe)]2(BF4)2
PhOH
PhO
O
Ph
M = Rh
Rh
O
Ph
H M
H
Ph
O
+ PhOH- M
R
R
+O
R
Ru-catalyst R
R
R
O
R
R
+OH
R
Ru-catalyst R
R
R
OH
R
OH
R
O
H
NC ArKOH
RAr
CNR
Ar
CN
[O]
[H][IrCp*Cl2]2
R
OH
+NH2
R'
cat[IrCp*Cl2]2
R NH
R'
Borrowing Hydrogen: reduction and oxidation coupled
Adv. Synth. Catal. 2007, 349, 1555 – 1575
Breit: J. Am. Chem. Soc. 2011, 133, 2386–2389
R1
H[(COD)RhCl]2 / L
R2COOHR1
O
R2
O O
PPh2 PPh2
LCH-OxidationAlkyne Reduction
[Rh]
R2COOHa [Rh] OHa
OR2
R1
Hb
Hc
Hc
Ha
R1
Hb
[Rh]O
OR2
R1 O
O
R2·R1
H Ha/c
Ha/c
R2COOHa
[Rh] OHa/b
OR2
R1
Ha/b
Ha/c
Ha/c
[Rh]O
OR2
R1
Ha/b
Ha/c
Ha/cOO
R2 major product
minor product
R R
RR
RR
++
LnM LnMH2
cata
cata
metathesiscata'
R OH R O
R NR'R NHR'
LnM LnMH2
cata
cata
H2NR'-H2O
Alkane Metathesis Amine Alkylation
Transition metal mediated dehydrogenative activation
Chem. Rev. 2010, 110, 681–703
ROH
dehydrogenation
- 2H22 R
O
H
+ ROH
H
RO
OHR
HB:
-H2OR
OR hydrogenation
+ 2H2 ROH
R
Mechanism of the Guerbet Reaction:
Guerbet alcohols
OHdehydrogenation
- H2O
H
MLn
oxidativeaddition
O
MLnH
migratorydeinsertion
MLn
CO
H
reductiveelimination H
+ MLnCO
deactivated complex
Decarbonylation as a Potential Inhibiting Pathway in Alcohol Activation:
N-Alkylation of Amines by Alcohols:
R OHoxidation
reduction
R O
R NR'
R'NH2
H2O
2H
R NHR'amine
Alkylation of Activated Nucleophiles by Alcohols:
R OHoxidation
reduction
R O
R Nuc
Nuc:
H2O
2H
R Nuc
CNPh PPh3
O
RO NO2R NC
O O
OR
O
RO
N
O
N
O
O
NH
NC
O
O NH
O
Representative Activated Nucleophiles Employed in Alcohol Activation Reactions
OHPh
·
5 mol% Ir cat
5 mol% Cs2CO3
DCE:EtOAc (1:1)75oC, 15h
+
(1eq.)
(4 eq.)
OHPh
90% yield
OHPh 5 mol%[RuHCl(CO)(PPh3)3]
5 mol% dppfTHF, 95oC, 15h
+
OHPh
81% yield1:1 dr
Ph
Ph
Krische: Angew. Chem. Int. Ed. 2009, 48, 34–46 J. Am. Chem. Soc. 2007, 129, 15134. Angew. Chem., Int. Ed. 2008, 47, 5220. J. Am. Chem. Soc. 2008, 130, 14891.
Transfer Hydrogenative C-C Coupling:
OH
+
OAc
Allylation:
2.5 mol% [Ir(cod)Cl]2
5 mol% ligand10 mol% m-NO2BzOH20 mol% Cs2CO3
THF, 100oC, 20h
OH
76% yield86% ee
PPh2
PPh2
Cl
MeO
MeO
Clligand
R OH
R
OH
RO
LnIr
R O
HR
OH
IrH
RO
LnIr
OAc
HOAc
IrLn
R OHRO
H
LnIr
Hydroacylation:
Coupling of Primary Alcohols and Terminal Olefins via Hydroacylation:
MeO
OH
Bu+
5 mol%[Rh(coe)Cl]2
20 mol% P-Ligand100% mol% aminoPy4,4'-dipyridyl,phenol, 150oC, 6h
MeO
O
Bu
92%
COOH
Ph2PP-Ligand
N
H2N
aminoPy
OHR1OR1
oxidation imine formationNR1
N
hydroacylation R2
NR1
NR2
hydrolysisR2 R1
O
2HR2
R2
OH [M] O
alkene reacts withelectrophiles
alkene reacts withnucleophiles
OH
Cyclohexanone (10 mol%)Al(OtBu)3 (10 mol%)CH2Cl2, 100oC, 24h
MeCH(CN)2 (1 eq.)KO-t-Bu (1 eq.)
O
Me
CNNCO
Me
CN
CN
OH
Me
CN
CN
-H2 + H2
E+ Nu
Dihydride Mechanism:
Monohydride Mechanism:
R1 R2
OMLnH
H
-hydride elim.
M-H insertion R1 R2
O+ MLnH2
R3 R4
OMLn
H
R1 R2
OH
H
R3 R4
OH
H
R1 R2
OMLn
H
protontransfer
-hydride elim.
M-H insertion R1 R2
O+ MLnH1
Mechanism of activation of alcohol: