Copper salts dialkylcuprates

The second molar equivalent of the alkyllithium adds to the alkylcopper to give a neg atively charged dialkyl substituted derivative of copper(I) called a dialkylcuprate It is formed as its lithium salt a lithium dialkylcuprate... 

As stated above, intermolecular coupling reactions between carbon atoms are of limited use. In the classical Wurtz reaction two identical primary alkyl iodide molecules are reduced by sodium. n-Hectane (C100H202), for example, has been made by this method in 60% yield (G. Stallberg, 1956). The unsymmetrical coupling of two alkyl halides can be achieved via dialkylcuprates. The first halide, which may have a branched carbon chain, is lithiated and allowed to react with copper(I) salts. The resulting dialkylcuprate can then be coupled with alkyl or aryl iodides or bromides. Although the reaction probably involves radicals it is quite stereoselective and leads to inversion of chiral halides. For example, lithium diphenyl-cuprate reacts with (R)-2-bromobutane with 90% stereoselectivity to form (S)-2-phenylbutane (G.M. Whitesides, 1969). 

Lithium dialkylcuprates (Section 14.11) These reagents contain a negatively charged copper atom and are formed by the reaction of a copper(l) salt with two equivalents of an organolithium reagent. 

Lithium dialkylcuprates and diarylcuprates (R2CuLi and Ar2CuLi) are prepared by the reaction of a copper(I) salt with two equivalents of the corresponding organolithium reagent and undergo cross-coupling with primary alkyl halides and aryl and vinylic halides. 

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