Synthesis of vinylcyclopropanes by intramolecular epoxide ring opening: application for an enantioselective synthesis of dictyopterene A

Functionalized oxiranes react with omega-substituted allyl and alkynyl anions to form gamma,delta- and beta,gamma-unsaturated epoxides, respectively. With O-tosylated oxiranes and phenylthioallyls, the products take on a trans configuration around the double bond. The process involves opening of the epoxy ring and its reclosing on expulsion of the leaving group. A second deprotonation step opens up the ring again, which this time closes into a cyclopropyl ring. The sex pheromone dictyopterene A is thereby synthesized, after elaboration of the resulting vinylcyclopropane.