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The Stevens rearrangement in organic chemistry is an organic reaction converting quaternary ammonium salts and sulfonium salts to the corresponding amines or sulfides in presence of a strong base in a 1,2-rearrangement.
Additional recommended knowledge
The original 1928 publication by T.S. Stevens  concerned the reaction of 1-phenyl-1- (N, N-dimethyl) ethanone with benzyl bromide to the ammonium salt followed by the rearrangement reaction with sodium hydroxide in water to the rearranged amine.
A 1932 publication  described the corresponding sulfur reaction.
Key in the reaction mechanism   for the Stevens rearrangement (explained for the nitrogen reaction) is the formation of an ylide after deprotonation of the ammonium salt by a strong base. Deprotonation is aided by electron-withdrawing properties of substituent R. Several reaction modes exist for the actual rearrangement reaction.
In an alternative reaction mechanism the N-C bond of the leaving group is homolytically cleaved to form a di-radical pair (3a). In order to explain the observed retention of configuration, the presence of a solvent cage is invoked. Another possibility is the formation of a cation-anion pair (3b), also in a solvent cage.
Competing reactions are the Sommelet reaction and the Hofmann elimination.
In one application a double-Stevens rearrangement expands a cyclophane ring . The ylide is prepared in situ by reaction of the diazo compound ethyl diazomalonate with a sulfide catalyzed by dirhodium tetraacetate in refluxing xylene.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Stevens_rearrangement". A list of authors is available in Wikipedia.|