Ring-closing metathesis as a construct for the synthesis of polycyclic alkaloids

Molybdenum and ruthenium alkylidene-catalyzed ring-closing metathesis (RCM) reactions have emerged as key constructs for the facile assembly of the polycyclic frameworks of a variety of natural products. Advances in catalyst development, particularly of highly reactive ruthenium species, have enabled facile ene-ene and ene-yne bond metatheses to create both carbocyclic and heterocyclic systems, sometimes possessing remarkable functional and structural complexity in a single operation. The operational simplicity, ease of handling, and generally high turnover numbers of the ruthenium-catalysts have brought RCM reactions to the forefront of practical carbon-carbon bond forming transformations. Some recent applications of RCM to the synthesis of alkaloid natural products are reviewed.