Lactonisation par ouverture, en milieu acide, de cyclopropanes γ-carboxyliques

Abstract

The opening of cyclopropanes, bearing a carboxyl group, in formic acid leads to complex mixtures containing less than 30% lactones formed by an intramolecular nucleophilic process during the reaction. We show that the relative stereochemistry of the carboxyl group and the cyclopropyl group does not determine the proportion of lactone formed. On the other hand, when the opening is performed by a Lewis acid (BF3−etherate), lactonisation is the major route (84%) and although the mechanism of intramolecular cyclisation is not yet clear, this reaction provides a good route to lactones. [Journal translation]