Conjugate organocopper-mediated

One advantage of this method over organocopper-mediated conjugate addition is the availability of lithium alkynides and thermally unstable lithium carbenoids as Michael donors (Scheme 6.85). With alkynides, raising the reaction temperature after the Michael addition afforded cyclopropanation to give a single diastereomer. 

Conjugate addition [2] to Michael acceptors is the most important and useful reaction in organocopper chemistry, and the reaction is often used as the key step in the synthesis of numerous natural and unnatural products. Perhaps one of the most efficient methods for the synthesis of quaternary carbon centers is organo-copper-mediated conjugate addition to /I, yS-disubstituted enones. 

Similar to the addition reactions of acceptor-substituted dienes (Scheme 16), the outcome of the transformation depends on the regioselectivity of the nucleophilic attack of the organocopper reagent (1,4- vs. 1,6-addition) and of the electrophilic capture of the enolate formed. The allenyl enolate obtained by 1,6-addition can afford either a conjugated diene or an allene upon reaction with a soft electrophile, and thus opens up the possibility to create axial chirality. The first copper-mediated addition reactions to Michael acceptors of this type, for example, 3-alkynyl-2-cyclopentenone 75,... 

Many of the copper-mediated transformations summarized in the previous sections of this chapter can also be performed efficiently with catalytic amounts of copper salts or reagents. Indeed, some of the copper-catalyzed reactions have been discovered before the development of stoichiometric organocopper reagents. The focus of the last decade has been put on new copper-catalyzed transformations (e.g., conjugate reductions) and in particular on the discovery of chiral copper catalysts for highly enantioselective 1,4-addition and S -substitution reactions of prochiral substrates. 

Breit, B. Demel, P. Copper-mediated Diastereoselective Conjugate Addition and Allylic Substitution Reactions. In Modem Organocopper Chemistry, Krause, N., Ed. Wiley-VCH Weinheim, 2002 pp 188-223. 

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