Synthesis of Medium-Sized Rings by the Ring-Closing Metathesis Reaction

Conformational constraints are the keys for the efficient synthesis of medium-sized rings by ring-closing olefin metathesis (RCM). While the RCM reaction has already proved itself in the synthesis of the larger macrocycles, like that found in epothilone, only recently has this reaction been increasingly used in the construction of eight- to ten-membered carbo- and heterocycles. In the picture, a cyclopentane ring ensures the conformational constraints necessary for a successful cyclization.