Sommelet–Hauser rearrangement

The Sommelet–Hauser rearrangement (named after M. Sommelet and Charles R. Hauser ) is a rearrangement reaction of certain benzyl quaternary ammonium salts. The reagent is sodium amide or another alkali metal amide and the reaction product a N,N-dialkylbenzylamine with a new alkyl group in the aromatic ortho position. For example, benzyltrimethylammonium iodide, [(C6H5CH2)N(CH3)3]I, rearranges in the presence of sodium amide to yield the o-methyl derivative of N,N-dimethylbenzylamine.


 * SommeletHauserReaction.svg

Mechanism
The benzylic methylene proton is acidic and deprotonation takes place to produce the benzylic ylide (1). This ylide is in equilibrium with a second ylide that is formed by deprotonation of one of the ammonium methyl groups (2). Though the second ylide is present in much smaller amounts, it undergoes a 2,3-sigmatropic rearrangement because it is more reactive than the first one and subsequent aromatization to form the final product (3).


 * Sommelet-Hauser Rearrangement Mechanism V.png

The Stevens rearrangement is a competing reaction.