Stereoselective Synthesis of Cyclopropanes via Homoallylic Participation

A facile method for synthesizing trans-disubstituted cyclopropanes is described. γ,γ-Dimethyl homoallyl alcohols, upon conversion to the corresponding triflate, undergo smooth cyclization to give cyclopropanes in a stereoselective manner (trans) and in a stereospecific manner (inversion of configuration at the chiral center). Various functionalities could be introduced at the α-position of the newly formed cyclopropane ring by treating the cyclization mixture with hetero as well as carbon nucleophiles. Alternatively, treatment of the reaction mixture with triethylamine effects the clean elimination of a triflic acid to give high yields of the cyclopropanes with a 2-propenyl group, which are convertible to the corresponding cyclopropyl methyl ketones by ozonolysis in high yields. Also described is an application of the method to a short-step synthesis of a cyclopropane-containing eicosanoid, related to marine prostanoid biosynthesis.