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.