“FORBIDDEN 1,2 CARBANION SHIFTS” MECHANISM AND APPLICATION … · 2010-11-30 · “FORBIDDEN...
Transcript of “FORBIDDEN 1,2 CARBANION SHIFTS” MECHANISM AND APPLICATION … · 2010-11-30 · “FORBIDDEN...
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“FORBIDDEN 1,2-CARBANION SHIFTS”
MECHANISM AND APPLICATION OF THE FRITSCH-
BUTTENBERG-WIECHELL REARRANGEMENT
Chun Ho Lam
17th November, 2010
1
Chun Ho Lam
17th November 2010
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Contents
Section 1:
Discovery of the Fritsch-Buttenberg-Wiechell (FBW) Rearrangement
Section 2:
Mechanistic Probing with Ring Expansion Model
The Woodward-Hoffmann Rules
Effect of different conditions on the mechanism
Investigation of the mechanism
Section 3:
A recent application of the FBW Rearrangement
2
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Section 1
3
Discovery of the
Fritsch-Buttenberg-Wiechell (FBW)
Rearrangement
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In 1894, discovered by the 3 scientists:
• Paul Ernst Moritz Fritsch
• Wilhelm Paul Buttenberg
• Heinrich G. Wiechell
Fritsch, P. Justus Liebigs Annalen der Chemie 1894, 3, 319.Buttenberg, W. P. Justus Liebig's Annalen der Chemie 1894, 3, 324
Wiechell, H. Justus Liebig's Annalen der Chemie 1894, 3, 337
Introduction of the FBW Rearrangement
4
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Possible Mechanisms for FBW
5
Fritsch, P. Justus Liebigs Annalen der Chemie 1894, 3, 319.Buttenberg, W. P. Justus Liebig's Annalen der Chemie 1894, 3, 324
Wiechell, H. Justus Liebig's Annalen der Chemie 1894, 3, 337
Route A
Route B
Route C
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Section 2 – Part A
6
Mechanistic Probing
with Ring Expansion Model
The Woodward Hoffmann Forbidden Transformation
Introduction to the Ring Expansion Model
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Mechanistic Probing Tool
Mechanism Probing:
Solvent
Halide group
Temperature
Substitute
7
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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Possible Routes
8
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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Elimination of Route A
9
“Diels-Alder Trap”
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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Elimination of Route C
Route C
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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The Only Way: Route B
However:
1. Anionic 1,2-sigmatropic rearrangement
11
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
2. Violates the Woodward-Hoffmann symmetry rule
3. This should be “impossible”
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The Woodward-Hoffmann Rule
An anionic sigmatropic rearrangement is a 4e- process
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Molecular Orbital Diagram
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The Woodward-Hoffmann Rule
Definition: Conversation of orbital symmetry in a (concerted) pericyclic reaction
Thermodynamically Allowed
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The “Forbidden” Examples
1,2-Wittig Rearrangement
Stevens rearrangement
15
Source: Strategic Application of Named Reaction in Organic Synthesis
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The “Allowed” Examples
Wagner-Meerwein Rearrangement
Beckmann Rearrangement
16
Source: Strategic Application of Named Reaction in Organic Synthesis
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Route B: The Forbidden Route
The only option left:
17
The important factors:
1. Vinyl Anion
2. Vinyl Group
3. Vinyl Anion Stabilizer (Bromine)
Erickson, K.L J. Org. Chem. 1973, 8, 1463.
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Importance of these factors?
No Double Bond
No Vinyl Anion
No Bromine
18
Erickson, K.L J. Org. Chem. 1973, 8, 1463.
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Polar vs. Non-Polar Solvent
In polar solvent:
In non-polar solvent:
19
Erickson, K.L J. Org. Chem. 1973, 8, 1463.
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Isomerization in Polar Solvent
Where does come from?
Polar solvent can stabilize the charges on the
resonance form thereby promotes side reaction.
Erickson, K.L J. Org. Chem. 1973, 8, 1463.
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Quick Summary
To trigger Route B, there must be:
Halogen
Vinyl Anion
Strong Base
Non-polar solvent
21
Route B: The Forbidden Route
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Section 2: Part B
22
~ Investigation of the FBW rearrangement ~
Mechanistic Probing
with Ring Expansion Model
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Possible Mechanism for Route B
Case 1
23
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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Possible Mechanism for Route B
Case 2:
Case 3
24
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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Elimination of Case 3
Case 3 is unlikely at low temperature because
The Diels-Alder trap shows Case 3 is not happening at
low temperature rearrangement.
25
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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The Remaining: Case 1 and Case 2
Case 1: Bromine attach to terminal carbon
Case 2: Bromine partially attach to vinyl group
26
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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Distinguish the 2 Cases with 13C
13C labeling reviews the reaction pathway depends
on the bromine position
Major Product
27
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
Cis
Trans
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The Overall Results
28
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
Trans
Cis
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The Overall Results Continued
29
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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Cis to Trans Isomerization
• ¾ reactions prefer Case 2, the migrating path.
• ¼ reaction prefers Case 1, the re-hybridization path.
30
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
Cis
Trans
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Isomerization Analysis
31
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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The Cis-Isomer Reaction
32
Isomerization
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
Rehybridization
Rotation of 13C Labeled Carbon
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Quick Summary
1. The trans migration pathway is strongly preferred.
2. Reaction happens in a stepwise rather than a
concerted mechanism.
W-H Rule Allow
W-H Rule Forbid
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The Role of Halogen in Reaction
% Yield A: B
F 40 1.52 : 1
Cl 32 2.80 : 1
Br 20 2.84 : 1
I 21 3.88 : 1
34
Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63 , 8880
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Trend Interpretation
35
Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63 , 8880
• Analysis with Newman Projection
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Trend Interpretation at Orbital Level
36
Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63 , 8880
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Trend Interpretation
% Yield A: B
F 40 1.52 : 1
Cl 32 2.80 : 1
Br 20 2.84 : 1
I 21 3.88 : 1
Single Mig.
Double Mig.
The Halogen dissociated
37
Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63 , 8880
BDE (kcal mol-1): F (117) > Cl (79) > Br (69) > I (51.7)
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Quick Summary
The size of Halogen is important to the mechanism
The 13C method system was “misleading”
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Stereo fate of the Migrating Group
1. Complete retention of stereogenic center
2. Double migration > Single migration
(Bromine is not on 13C)
3. High yield is due to tetra-substituted carbon
* ** *
39
Du Z.M.; Erickson K.L. J. Org. Chem. 2010, 75 , 7129
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1. Mechanism agrees with 13C study and Halogen study.
2. Double migration is preferred
Du Z.M.; Erickson K.L. J. Org. Chem. 2010, 75 , 7129
The Mechanism
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41
To Conclude the Findings
D.A. Trap
Ref. Study
Halogen Study
Du Z.M.; Erickson K.L. J. Org. Chem. 2010, 75 , 7129
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The MP2 6-31+G(d) Calculation
-37
-32
-27
-22
-17
-12
-7
-2
3
8
13
React TS Int 1 TS 2 Int2 TS 3 Prod
Fre
e E
ne
rgy
(k
ca
l m
ol-1
)
Reaction Coordinate
F
Cl
Br
HHal Li C
42
Pratt, L.M.; Nguyen N. V.; O. Kwon, Chem. Lett. 2009, 38, 574.
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Computational results vs. Ring Expansion model
Computational Results Ring Expansion Model
Carbene Carbene with Halogen
F, Cl, BrMakes no difference to
migration
F causes 50:50 Single : DoubleCl and Br causes mostly
Double.
Intermediate: the migrating group is in the vinyl system
Intermediate: the migrating Double Stepwise migration
43
Pratt, L.M.; Nguyen N. V.; O. Kwon, Chem. Lett. 2009, 38, 574.
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Reliability of the results
44
Reliable
Gas phase cond. resemble the non-polar solvent.
MP2 gives good estimation of the T.S. and Int
Results suggest other mechanism is possible.
Pratt, L.M.; Nguyen N. V.; O. Kwon, Chem. Lett. 2009, 38, 574.
However
The ring strain issue is not addressed
The spectator ion is different: Li vs. K
Migrating group is H, not alkyl group
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Summary
45
Mechanism bypasses WH Rule with a rehybridization
of the migrating group.
Mechanism is minor temp. dependent
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
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Summary Continued
46
Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem. 1998, 63 , 888046
Mechanism depends on:
Solvent polarity
Halide size
Temperature
Geometry of the reactant
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Combining the REM with FBW
47
According to the Ring Expansion Model:
Route A
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The Suggested FBW Rearrangement
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The Modified FBW Rearrangement
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Section 3
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Recent Application of Modified FBW
Rearrangement
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Introduction of Polyyne
What it is and what it does
Synthesis of Polyyne
with traditional Cu/Pd Coupling
with FBW rearrangement
Application of Modified FBW in Polyyne Synthesis
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Introduction of Polyyne
52
PolyyneSp-Hybridized
Carbyne
Sp2-Hybridized CarbonGraphite
Sp3-Hybridized CarbonDiamonds
Properties
1. Extremely Rigid
1. Thermal Conductor
2. Electrical Conductor
1. Electrical Conductor?
2. Optical Applications?
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Traditional Polyyne Synthesis
53
Homocoupling Reaction
Glaser Coupling
Eglinton Modification
Hay’s Modification
Source: Strategic Application of Named Reaction in Organic Synthesis
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Traditional Polyyne Synthesis
54
Hetercoupling Reaction:
Chodkiewitz-Cadiot
Sonogashira Cross Coupling
Source: Strategic Application of Named Reaction in Organic Synthesis
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Synthesis of Polyyne with Cu/Pd Coupling
55
Total Steps: 3
Overall Yield: 17%
Yamaguchi, M.; Park, H. J.; Hirama, M.; Torisu, K.; Nakamura, S.; Minami, T.; Nishihara, H.; Hiraoka, T. Bull. Chem. Soc. Jpn. 1994, 67, 1717.
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Total Steps: 4
Overall Yield: 56%
1 pot
Synthesis of Polyyne with RBW Rearrangement
Luu, T.; Morisaki Y.; Cunningham N.; Tykwinski R. R. J. Org. Chem., 2007, 72, 9622.
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Limitation of the FBW method
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Can FBW take over Cu coupling in Polyyne Synthesis?
Jahnke E.; Tywinski R.R.; Chem. Commum. 2010, 46 , 3235
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FBW vs. Copper Coupling
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1. FBW can be a 1-pot convenient method
2. Copper Chemistry is still an important coupling reaction
Jahnke E.; Tywinski R.R.; Chem. Commum. 2010, 46 , 3235
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Conclusion
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Bypass W-H Rule with “Rehybridizations”, Radical
rearrangement
Mechanism of FBW is most likely a double migration
process.
Computational study disagrees with the experiment
Methods with more similar condition should be
employed
FBW offers 1-pot synthesis of Polyyne
At low module of alkyne
Copper chemistry still has its importance.
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Acknowledgement
60
60
o Dr. Jackson
o Dr. Maleczka
o Dr. Huang
o Dr. Redko, Dr. Saumitra, Abby, Crystal,
Laura, Megan, Melisa, Meisam, San, Xin,
Zhe, members from Baker and Wulff’s group