A Systematic Study of Functionalized Oxiranes as Initiating Groups for Cationic Polycyclization Reactions

Three different methods have been developed that effectively utilize chiral oxiranes derived from Katsuki–Sharpless epoxidation of allylic alcohols as initiating groups for cationic cyclization of unsaturated substrates to form chiral polycycles. This type of transformation has previously been problematic. These employ either epoxy-methoximes, vinyl-substituted oxiranes, or hydroxymethyl oxiranes. All three approaches are described in detail. In addition, this research has led to possible explanations for previously encountered difficulties in this area and provided two new insights into the Lewis acid activation of oxiranes. The methodology described herein constitutes a valuable link between two powerful synthetic constructions, enantioselective Katsuki–Sharpless epoxidation and cationic polycyclization reactions.