2.10 Ring-Closing Metathesis

Abstract

AbstractRing-closing metathesis (RCM) has emerged as a powerful synthetic tool. Depending on the unsaturated functional groups involved, ring-closing-metathesis reactions are classified into three categories: diene ring-closing metathesis, enyne ring-closing metathesis, and diyne ring-closing metathesis. These are mediated/catalyzed by metal alkylidenes or alkylidynes to form cyclic alkenes or alkynes, with ring sizes ranging from small to large, and including both carbocycles and heterocycles. Mechanistically, diene and diyne ring-closing metathesis involves an exchange reaction between the participating alkenes or alkynes, whereas enyne ring-closing metathesis involves a formal addition reaction between an alkene and an alkyne. This chapter summarizes the distinctive features of these different ring-closing metathesis processes in terms of the advancement of mechanistic understanding and the development of effective catalyst systems and their application to natural product synthesis.