Carbon nucleophile addition to sp2-unsaturated Fischer carbene complexes

The reactions of group 6 (alkoxy)(aryl)- and (alkoxy)(alkenyl)carbene complexes with organolithium compounds, metal enolates, and enamines are summarized. (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 alkyllithiums. The more widely studied (alkoxy)(alkenyl)carbene complexes react with carbon nucleophiles to give 1,2- or 1,4-addition products depending on the steric surroundings of both the metal carbene complex and the nucleophile as well as the nature of the latter. These reactions have been employed for several useful carbon-carbon bond-forming processes taking place with high diastereoselectivity.