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Sommelet–Hauser rearrangement

From Wikipedia, the free encyclopedia

Sommelet–Hauser rearrangement
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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] Although the appearance is of one of the methyl groups migrating off the trimethylammonium group, the process is actually the a pericyclic reaction in which the nitrogen and its three methyl substituents migrate.

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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).[5]

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The Stevens rearrangement is a competing reaction.

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References

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