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Favorskii rearrangement
The Favorskii rearrangement, named for the Russian chemist Alexei Yevgrafovich Favorskii, is most principally a rearrangement of cyclopropanones and α-halo ketones which leads to carboxylic acid derivatives. In the case of cyclic α-halo ketones, the Favorski rearrangement constitutes a ring contraction. This rearrangement takes place in the presence of a base, sometimes hydroxide, to yield a carboxylic acid but most of the time either an alkoxide base or an amine to yield an ester or an amide, respectively. α,α’-Dihaloketones eliminate HX under the reaction conditions to give α,β-unsaturated carbonyl compounds.〔Favorskii, A. E. ''J. Russ. Phys. Chem. Soc.'' 1894, ''26'', 590.〕〔Favorskii, A. E. ''J. Russ. Phys. Chem. Soc.'' 1905, ''37'', 643.〕〔Favorskii, A. E. ''J. Prakt. Chem.'' 1913, ''88'', 658.〕
==Reaction mechanism==
The reaction mechanism is thought to involve the formation of an enolate on the side of the ketone away from the chlorine atom. This enolate cyclizes to a cyclopropanone intermediate which is then attacked by the hydroxide nucleophile.
Usage of alkoxide anions such as sodium methoxide, instead of sodium hydroxide, yields the ring-contracted ester product.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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