Synthetic methodology for the construction of structurally diverse cyclopropanes

Practical and efficient routes for the stereoselective conversion of homoal lylic alchols to diastereomerically pure cis-, trans-1,2-disubstituted, and 1,2,3-trisubstituted cyclopropanes have been developed. The routes are hig hlighted by olefin metathesis strategies and the stabilization of an interm ediate cyclopropylcarbinyl cation by the beta -silicon effect. The stereosp ecificity of the key cyclization step has been rationalized by transition-s tate models in which the important determinants include (i) a minimization of the steric interactions about the forming cyclopropane bond and (ii) an inversion of stereochemistry at the activated homoallylic alcohol position. The cyclopropane product chirality is ultimately controlled by the choice of homoallylic alcohol starting material. Through this method nonracemic, d iasteromerically pure homoallylic alcohols can be converted in two steps to nonracemic, diasteromerically pure cyclopropane structural units. The scop e and limitations of this versatile methodology have also been investigated .