The Sommelet–Hauser rearrangement (named after M. Sommelet[1] and Charles R. Hauser[2]) is a rearrangement reaction of certain benzyl quaternary ammonium salts.[3] 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, [(C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>)N(CH<sub>3</sub>)<sub>3</sub>]I, rearranges in the presence of sodium amide to yield the o-methyl derivative of N,N-dimethylbenzylamine.
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).[4]
The Stevens rearrangement is a competing reaction.