Epoxidation of allylic alcohols with peroxy-acids. Attempts to define transition state geometry

Abstract

In epoxidation of the conformationally biassed 5-t-butylcyclohex-2-enols by peroxybenzoic acid, higher cis-stereoselectivity and faster rate are found for the pseudo-equatorial than for the pseudo-axial alcohol. Cyclo-oct-2-en-1-ol is epoxidised with stereospecific introduction of the epoxy-group trans to hydroxy, and appropriate acyclic allylic alcohols show a preference for formation of the threo-epoxy-alcohol. A consistent interpretation of these results is advanced, based on the postulate that the preferred conformation of an allylic alcohol in the transition state for epoxidation is as in (XX).