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][4] 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.
[2] The benzylic methylene proton is acidic and deprotonation takes place to produce the benzylic ylide (1).
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).