TheFavorskiĭ Rearrangement of Haloketones

Abstract The Favorskii rearrangement is the skeletal rearrangement of a alpha‐halogenated ketones in the presence of certain nucleophilic bases, such as hydroxides, alkoxides, or amines to give carboxylic acid salts, esters or amides, respectively. Monohaloketones undergo the reaction to yield derivatives of saturated acids having the same number of carbon atoms. In a similar manner, suitable dihaloketiones produce unsaturated carboxylic acids. Analogous rearrangements of trihaloketones can give rise to unsaturated halo acids. The Favorskii reaction has found application for the preparation of highly branched acyclic carboxylic acids. It is a preferred route to various 1‐cycloalkanecarboxylic acids and provides a direct method for ring contraction in simple alicyclic systems and in steroids.