WAGNER-MEERWEIN REARRANGEMENT

1. WAGNER-MEERWEIN
REARRANGEMENT
PRESENTED BY- INDRAJIT SAMANTA
M.PHARMA, 1ST YEAR, 1ST SEM, DEPARTMENT
OF PHARMACEUTICAL CHEMISTRY,
SPER, JAMIA HAMDARD, NEW DELHI- 110062

2. CONTENTS
INTRODUCTION
REACTION
MECHANISM
SCOPE
APPLICATION
CONCLUSION
REFERENCE

3. INTRODUCTION
 In 1899, G. Wagner and W. Brickner reported the rearrangement of a pinene to bornyl chloride in the
presence of hydrogen chloride. The transformation baffled chemists at the time, since it contradicted the
classical structural theory that was based on the postulate of skeletal invariance.
 The Wagner-Meerwein rearrangement is an organic reaction used to convert an alcohol to an olefin
using an acid catalyst. The mechanism begins with protonation of the alcohol by the acid which is then
released as water to forms a carbocation. A 1,2-shift then occurs to form a more substituted and
stabilized carbo-cation. A final deprotonation with water produces the final olefin product and
regenerates the acid catalyst.

4. INTRODUCTION
 A Wagner–Meerwein rearrangement is a class of carbocation 1,2-rearrangement reactions in which a hydrogen, alkyl or aryl group
migrates from one carbon to a neighbouring carbon. They can be described as cationic [1,2]-sigma tropic rearrangements,
proceeding suprafacially and with stereochemical retention. As such, a Wagner–Meerwein shift is a thermally allowed pericyclic
process with the Woodward-Hoffmann symbol [ω0s + σ2s]. They are usually facile, and in many cases, they can take place at
temperatures as low as –120 °C.

5. CHARACTERISTICS
 Rearrangement of carbocation
 Change in carbon skeleton
 1-2 shift of alkyl, hydrogen and ring bond
 Observation in electrophilic addition, substitution and elimination reaction
 Alcohol, amines, alkyl halides general show W. M.
 Cyclic compounds under goes expansion or contraction
 It is sigmatropic rearrangement
 It is an intramolecular rearrangement,

6. GENERAL FEATURES OF THE WAGNER-
MEERWEIN REARRANGEMENT ARE:
 the generation of the initial carbocation can be achieved in a variety of ways (e.g., protonation of alkenes, alcohols, epoxides or
cyclopropanes, solvolysis of secondary and tertiary alkyl halides, or sulfonates in a polar protic solvent (semi pinacol
rearrangement), deamination of amines with nitrous acid (Tiffeneau-Demjanov rearrangement), treatment of an alkyl halide with
Lewis acid, etc.;
 the initial carbocation has a tendency to rearrange to a thermodynamically more stable structure, a change that may occur in
several different ways: e.g., [1,2]-alkyl, -aryl- or hydride shift to afford a more stable carbocation, ring expansion of strained
small rings such as cyclopropanes and cyclobutanes to give more stable five or six membered products, collapse by
fragmentation, etc..
 several consecutive [1.2]-shifts are possible if the substrate contains multiple structural elements that allow the formation of
gradually more stable structures;
 the various competing rearrangement pathways limit the synthetic utility of the Wagner-Meerwein rearrangement, since one
needs to install all the structural features that will drive the rearrangement in the desired direction;
 the final most stable carbocation's fate may be the loss of a proton to afford an alkene or capture by a nucleophile present in
the reaction mixture (solvent or conjugate base of the acid used to promote the rearrangement); and
 the stereochemistry of the migrating group is retained, which is in accordance of the Woodward-Hofmann rules

7. MECHANISM
STEP-1:
First step is in presence of H+ ions the X group (-OH or halide) takes the bonding pair of electrons
and leaves as HX forming carbonium ion.

8. MECHANISM
 STEP-2:
This carbonium ion undergoes rearrangement to produce more stable tertiary carbonium ion
by transfer of one of -R group to neighbouring carbon atom (or 1, 2 shift).

9. MECHANISM
 STEP-3:
Finally the nucleophile attacks on carbonium ion, there are two possibilities, if the attacking
nucleophile is same group which left in first step then rearranged product is obtained but if the molecule
gets deprotonated, the H+ ion from the neighbouring carbon leaves forming a double bond.

10. MECHANISM

11. SCOPE
 1. The deriving force of rearrangement reaction is formation of more stable
carbonium ion.
 2. The reaction is catalysed by Lewis acid like BF3, AlCl3, ZnCl2 or Conc. H2SO4
and more moist Ag2O (AgOH).
 3. In case of neopentyl alcohols if reaction is carried out with moist Ag2O it give
rearranged alcohol but if reaction is done with dehydrating agent like Conc.
H2SO4 alkene is obtained.
 4. In case of ring compound Wagner Meerwein Rearrangement takes place to
reduce the strain in the ring.

12. APPLICATION
 1. Hydrolysis of Neopentyl bromide:

13. APPLICATION
 2. Rearrangement of Neopentyl compounds:

14. APPLICATION
 3. Dehydration of Neopentyl alcohol:

15. APPLICATION
 4. Wagner Meerwein Rearrangement in ring
compounds

16. APPLICATION
 5. Wagner Meerwein Rearrangement in ring
compounds

17. APPLICATION
 5. Conversion of Bornyl Chloride to camphene

18. APPLICATION
 6. In cracking of petroleum products:

19. APPLICATION

20. APPLICATION

21. APPLICATION

22. APPLICATION

23. APPLICATION

24. APPLICATION

25. APPLICATION
 It is used for rearrangement of highly branched compounds like neopentyl
compounds.
 In ring compounds it is used to reduce the reduce the strain in ring.
 It is used in rearrangement of bicyclic terpene derivatives.

26. REFERENCE
 1. Wagner, G. J. Russ. Phys. Chem. Soc. 1899, 31, 690. Wagner first observed this rearrangement in
1899 and German chemist Hans Meerwein unveiled the mechanism in 1914.
 2. Hogeveen, H.; Van Kruchten, E. M. G. A. Top. Curr. Chem. 1979,80, 89-124. (Review).
 3. Kinugawa, M.; Nagamura, S.; Sakaguchi, A.; Masuda, Y.; Saito, H.; Ogasa, T.; Kasai, M. Org. Proc.
Res. Dev. 1998, 2, 344-350.
 4. Trost, B. M.; Yasukata, T. J. Am. Chem. Soc. 2001, 123, 7162 7163.
 5. Guizzardi, B.; Mella, M.; Fagnoni, M.; Albini, A. J. Org. Chem.2003, 68, 1067-1074.6028. 7. Guo, X.;
Paquette, L. A. J. Org. Chem. 2005, 70, 315-320.
 Hans Meerwein (1914). "Über den Reaktionsmechanismus der 7-9). 1 Umwandlung von Bomeol in
Camphen: [Dritte Mitteilung über Pinakolinumlagerungen.]" (https://zenodo.org/record/1427621).
Justus Liebig's Annalen der Chemie. 405 (2): 129-175. doi:10.1002/jlac.19144050202
(https://doi.org/10.1002/jlac.19