Organometallic reagents copper

House investigated the role of cuprous ions in the conjugate addition of organometallic reagents. He found that the catalytic effect can be explained by the intervention of a methyl copper derivative, which reacts rapidly with the carbon-carbon double bonds of the conjugated system. 

R Cu, or litliium or magnesium homocuprates RfCuM fM = Li, MgX), are fre-quently used, but a number of catalytic processes have also been developed. These processes nornnally utilize a catalytic amount of a copper salt CuY and a stoichiometric amount of an organometallic reagent R M IM = Li, MgX, ZnX, etc.). Hie leaving groups used include balides, esters, sulfonates, and epoxides, among others. 

Especially in the early steps of the synthesis of a complex molecule, there are plenty of examples in which epoxides are allowed to react with organometallic reagents. In particular, treatment of enantiomerically pure terminal epoxides with alkyl-, alkenyl-, or aryl-Grignard reagents in the presence of catalytic amounts of a copper salt, corresponding cuprates, or metal acetylides via alanate chemistry, provides a general route to optically active substituted alcohols useful as valuable building blocks in complex syntheses. 

Generally, organocopper compounds can be prepared by transmetallation between copper salts and organometallic reagents such as RLi, RMgX, and RZnX.53,53a,53b Copper alkynides can be obtained by reaction of terminal alkynes... 

The conjugate addition of organometallic reagents R M to an electron-deficient alkene under, for instance, copper catalysis conditions results in a stabilized car-banion that, upon protonation, affords the chiral yS-substituted product (Scheme 7.1, path a). Quenching of the anionic intermediate with an electrophile creates a disubstituted product with two new stereocenters (Scheme 1, path b). With a pro-chiral electrophile, such as an aldehyde, three new stereocenters can be formed in a tandem 1,4-addition-aldol process (Scheme 1, path c). 

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