Transformation of cyclopentane-1,3-diones into cyclohexane-1,4-diones - a novel ring enlargement process

Abstract 2-Alkyl-2-(2-oxopropyl)cyclopentane-1,3-diones are smoothly converted into 2-acetyl-3-alkylcyclohexane-1,4-diones (3-acetyl-2-alkylcyclohex-3-en-4-olones) by treatment with an equimolar amount of sodium hydroxide in water or sodium methoxide in methanol. This ring enlargement can be considered as the result of an intramolecular aldol reaction followed by a ring opening of the formed bicyclo[3.1.0]hexane system.