Mechanism of the decarboxylative rearrangement of α-(carbonyl) cyclopropane carboxylic acids to 2-substituted-4,5-dihydrofurans

Abstract

Previously we described the thermal decarboxylation of 1- (cyclopropylcarbonyl) cyclopropane carboxylic acid at 120°C yielded 2-cyclopropyl-4,5-dihydrofuran instead of the expected dicyclopropyl ketone. The proposed mechanism proceeded through an initial ring opening of the 1,2-disubstitued cyclopropyl moiety leading to an α-allyl-β-keto acid system, specifically in this case α-(cyclopropylcarbonyl)-3-butenoic acid. In this paper we demonstrate that an α-(carbonyl)-3-butenoic acid when thermally decarboxylated rearranges to the substituted 4,5-dihydrofuran. Additionally, it was demonstrated that the decarboxylation and rearrangement are simultaneous and not a stepwise decarboxylation followed by rearrangement and ring closure. ©ARKAT USA, Inc.