5.29 Ring-Closing Metathesis

Abstract

Ring-closing olefin metathesis (RCM) is one of the most general methods for the synthesis of cyclic molecules. This subject has not previously been covered in Comprehensive Organic Synthesis, because only very few synthetically useful RCM reactions were published before 1992. Since then, an enormous number of applications in organic synthesis have appeared. In this chapter the way leading to modern day RCM is highlighted first, followed by a brief discussion of some fundamental mechanistic aspects. Then representative examples for the synthesis of five- and six-membered carbo- and heterocycles are highlighted, with a focus on the specific aspects of the RCM step and on the implementation of RCM in a synthetic strategy. The following sections deal with the formation of medium-sized rings, the specifics of macrocyclizative RCM, metathesis-based syntheses of heterocycles with less common heteroatoms, and RCM reactions of heteroatom-substituted substrates. In the final sections, more general concepts of RCM, such as tethered RCM, relay RCM, regio- and stereoselective RCM, ring rearrangement metathesis, as well as sequential RCM–nonmetathesis transformations are introduced and their synthetic utility illustrated by selected applications.