The Baeyer-Villiger oxidation of a-substituted cyclic ketones

Abstract

The Baeyer-Villiger oxidation of 2-chlorocholestan-3-one and 2-bromo-cholestan-3-one gives the corresponding α-halo-lactones (VIIIa) and (VIIIc). The α-bromo-lactone is readily rearranged and converted into 2-methoxycarbonyl-3-oxa-5α-cholestane (Va) by boiling methanol but the α-choloro-lactone is unaffected by this treatment. Both the a-bromo-lactone and the or-chloro-lactone react with alkali to form 2-carboxy-3-oxa-5α-cholestane (Vb). α-Iodocholestan-3-one is unexpectedly converted into cholest-1-en-3-one in about 50% yield by trifluoro-peracetic acid.    2-Bromofriedelan-3-one did not undergo a Baeyer-Villiger reaction under the usual conditions, probably owing to the steric hindrance of the carbonyl group. The per-acid oxidation of 2β-hydroxyfriedelan-3-0110 yielded mainly the 2,3-seco-dicarboxylic acid and a smaller amount of the expected α-hydroxy-lactone. However 2β-acetoxyfriedelan-3-one underwent a Baeyer-Villiger oxidation in the expected fashion to give a high yield of the 2-acetoxy-lactone.