General Ring-Closing Metathesis

Olefin metathesis catalyzed by transition-metal-carbene complexes is the most powerful and important carbon-carbon bond-forming reactions in modern synthetic organic chemistry. Metathesis transformations, including cross-metathesis (CM), ring-closing metathesis (RCM), enyne metathesis, alkyne metathesis, and ring-opening metathesis polymerization (ROMP), have gained prominence due to the high thermal stability, and excellent functional group compatibility of well-defined transition-metal alkylidene catalysts which have become available over the last two decades. The abundance of carbocyclic moieties in synthetic intermediates, as well as in many natural products, has led to numerous synthetic efforts employing RCM toward their formation. The formation of Si-heterocycles has been greatly facilitated by RCM. This chapter discusses some examples of ROM/RCM tandem processes and general RCM tandem processes. It describes several isomerization reactions relevant to ring-forming processes. Relay RCM (RRCM) is a substrate-controlled RCM reaction in which the substrate is designed/synthesized to dictate the mode of RCM to afford the desired product.