Synthesis of vinylcyclopropanes by intramolecular epoxide ring opening. Application for an enantioselective synthesis of dictyopterene A

Abstract

The reaction of functionalized oxiranes 1 with the sulfur- or silicon-stabilized anions 2 provides β-heteroatom-substituted γ,δ-unsaturated epoxides 5 with, for 5e,f, a trans C=C moiety. A cis compound 9 is obtained using acetylide anion 2c via 7 and subsequent partial hydrogenation of the C≡C bond in the intermediate oxirane 8. Regiospecific anion generation in 5,9is achieved by deprotonation, reductive desulfurization, and desilylation, respectively.The resulting anions 10 cyclize to 1-(hydroxyalkyl)-2-vinylcyclopropanes 11 by a stereochemically controlled S N i process.Starting from the optically active epoxide 1b,the approach allows synthesis of cyclopropane 11b with (1S,2R) configuration at the ring carbon atoms.This compound can be further elaborated to be algae sex pheromone dictyopterene A which is obtained along with the unnatural Z diastereomer