Carbon nucleophile addition to sp(2)-unsaturated Fischer carbene complexes

The reactions of group 6 (alkoxy)(aryl)- and (alkoxy)(alkenyl)carbene compl exes with organolithium compounds, metal enolates, and enamines are summari zed. (Alkoxy)(aryl)carbene complexes underwent mainly nucleophilic addition to the carbene carbon atom, but either 1,4- or 1,6-addition products have been observed with derivatives bearing a bulky alkoxy group and phenyl- or alkyllithimns. The more widely studied (alkoxy)(alkenyl)carbene complexes r eact with carbon nucleophiles to give 1,2- or 1,4-addition products dependi ng on the steric surroundings of both the metal carbene complex and the nuc leophile as well as the nature of the latter. These reactions have been emp loyed for several useful carbon-carbon bond-forming processes taking place with high diastereoselectivity. (C) 2001 Elsevier Science B.V. All rights r eserved.