The Fritsch-Buttenberg-Wiechell rearrangement is a chemical reaction that transforms a 1,1-diaryl-2-bromo-alkene into a 1,2-diaryl-alkyne via a strong base, with detailed mechanisms discussed. Various pathways and their thermodynamic feasibility are analyzed, noting that the preferred reaction route is a stepwise trans migration process rather than concerted mechanisms. Applications of the modified rearrangement include the synthesis of novel polyynes and steroidal alkynes.

1. Fritsch–Buttenberg–
Wiechell
Rearrangement
Prof. Harish Chopra, SLIET, Longowal

2. Background
The Fritsch–Buttenberg–Wiechell (FBW) rearrangement,
named for Paul Ernst Moritz Fritsch (1859–1913), Wilhelm
Paul Buttenberg, and Heinrich G. Wiechell, is a chemical
reaction whereby a 1,1-diaryl-2-bromo-alkene rearranges
to a 1,2-diaryl-alkyne by reaction with a strong base such
as an alkoxide.
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3. Mechanism
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4. Mechanism
Mechanism Proof
Through
RING
EXPANSION
Model.
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5. Mechanism
Benzyne
Intermediate
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6. Mechanism
Benzyne
Intermediate
Traces at High temp.
Elimination of Possibility of Route A
As the Diels-Alder Adduct is formed only in traces at high
temperature, the formation of benzyne intermediate is ruled
out which eliminates the possibility of Route A mechanism
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7. Mechanism
Elimination of Possibility of Route C
If Route C mechanism is followed, the Grignard reaction will
also lead to similar ring cyclization through carbanion
intermediate formation, which never happens.
H2O
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8. Mechanism
Only Possibility of Route B
[through Anionic 1,2-Sigmatropic Rearrangement]
But, as per Woodward-Hoffmann symmetry rule, the anionic 1,2-
Sigmatropic rearrangement is 4-electron process and is
FORBIDDEN.
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9. Mechanism
Orbital Symmetry conversion in a pericyclic reaction
[Woodward-Hoffmann Rule]
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1,2-Sigmatropic
rearrangement may
be symmetrically
FORBIDDEN but
thermodynamically it
is a ALLOWED
process

10. Mechanism
Allowed Processes
10
Wagner-Meerwein Rearrangement
Beckmann Rearrangement
Forbidden Processes
1,2-Wittig Rearrangement
Stevens Rearrangement

11. Route B (Forbidden Route)
2014 2015
Vinyl anion
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Vinyl anion Stabilizer
(Bromine)Vinyl group

12. Route B (Forbidden Route)
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No Double Bond No Vinyl anion
No Bromine

13. Solvent Effects
Polar Solvents
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Non-Polar Solvents
Polar solvent can stabilize
the charges on the
resonance form thereby
promotes side reaction

14. 14
If reaction follows
Route B,
it must have:
Strong Base
Vinyl Anion
Halogen
Non-Polar Solvents
[A] Bromine attach to terminal carbon
Route B (Forbidden Route):
[B] Bromine partially attach to vinyl group
Mechanism

15. 15
Isotopic Labelling:
13C labeling reviews the reaction
pathway depends on the bromine
position
Mechanism
Un-Symmetrical
Substrates

16. 16
Isotopic Labelling:
13C labeling reviews the reaction
pathway depends on the bromine
position
Mechanism
Symmetrical
Substrates

17. 17
Cis-Trans IsomerizationMechanism
75% reactions prefer: Path [B], the migrating path
25% reactions prefer: Path [A], the re-hybridization path

18. 18
Isomerization analysisMechanism

19. 19
Isomerization analysisMechanism

20. 20
ConclusionMechanism
1. The trans migration pathwayis strongly preferred.
2. Reaction happens in a stepwise rather than a concerted mechanism.

21. 21
FBW RearrangementMechanism

22. 22
Modified FBW RearrangementMechanism

23. 23
Modified FBW RearrangementApplications
Synthesis of Novel Polyynes

24. 24
Modified FBW RearrangementApplications
Synthesis of Novel Polyynes

25. 25
Modified FBW RearrangementApplications
Synthesis of Steroidal Alkynes

26. 26
Modified FBW RearrangementApplications
Use of Lanthanum / I2

27. 27
Applications
Use of organolithium compounds
(CH2O)n, n-BuLi

28. 28
References
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
Du Z.M.; Haglund M. J.; Pratt L. A.; Erickson K.L. J. Org. Chem.1998,63,
8880
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429
Du Z.M.; Erickson K.L. J. Org. Chem. 2010, 75 , 7129
Erickson, K.L.; Niu, T.; Samuel S.P. J. Am. Chem. Soc. 1989, 111, 1429.
Erickson, K.L J. Org. Chem. 1973, 8, 1463
Jahnke E.; Tywinski R.R.; Chem. Commum. 2010, 46 , 3235

29. Thank You !
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