Michael additions of benzotriazole-stabilized carbanions. A review

The 1,4-addition of benzotriazole-stabilized carbanions to Michael accepters is reviewed. The selectivity between 1,4- and 1,2-addition depends significantly on the electronic effect of the carbanion (usually lithium is the counterion), the type of the Michael acceptor, and steric effects. Steric hindrance of the benzotriazolyl group probably enhances the regioselectivity. Normally, 1,4-additions to alpha,beta-unsaturated ketone or ester are observed for carbanions stabilized by a benzotriazolyl group and an electron-withdrawing group (e.g. aryl, vinyl, carbonyl). For alpha,beta-unsaturated aldehydes as Michael accepters, 1,2-addition is more likely, except where electronic effects are very strong. A review with 39 references.