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The Favorskii rearrangement is the transformation of haloketones to branched-chain or ring-contracted carboxylic acid derivatives in the presence of a base, typically alkoxide or an amine. α,α’-Dihaloketones eliminate HX under the reaction conditions to give α,β-unsaturated carbonyl compounds.
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. See also | ||||||||
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