Conjugate Addition Reactions of Organocopper Reagents

Posner, Gary H.


Addition of an organometallic reagent to alpha,beta-usaturated carbonyl compounds occurs in one or both of two modes: attack at the carbonyl function produces a 1,2 adduct, whereas reaction with the entire system gives a 1,4 adduct. Organoalkali metal reagents derived from unstabilized carbanions generally add across the carbonyl group, where as enolate and other stabilized anions usually undergo a Michael addition, introducing a carboalkyl group at the beta carbon. Grignard reagents normally give 1,2 adducts. The wide scope of these reagents has made conjugate addition of alkyl and aryl groups a useful reaction in organic synthesis. Copper-promoted conjugate additions were generally effected by allowing an organomagnesium reagent and a alpha, beta- unsaturated carbonyl compound to react in the presence of a catalytic amount of copper salt. Studies since 1966 have shown that stoichiometric organocopper reagents in addition to their broad utility in coupling reactions with organic halides and in reaction with other substrates undergo unusually effective conjugate addition to a wide variety alpha,beta- unsaturated carbonyl substrates. Emphasis in this chapter is on stoichiometric organic copper reagents. Mechanism, scope, limitations, synthetic utility, and optimal conditions are considered.