REACTION OF LITHIUM DIALKYL- AND DIARYLCUPRATES WITH ORGANIC HALIDES

Lithium dialkyl- or diarylcuprates (R2CuLi) react with aryl iodides in ether solution by competing metal-halogen exchange and coupling reactions. Using appropriate reagents, high yields of the coupled product R-Ar can be obtained by allowing the metal-halogen exchange to proceed to completion in the presence of an excess of R2CuLi, and oxidizing the resulting mixture of organometallic species present in solution with nitrobenzene or oxygen. This reaction sequence works well with lithium di-n-alkyl- and diarylcuprates; it fails with di-sec-alkyl- and di-t-alkylcuprates. Although most alkyllithium reagents react with aryl iodides only by metal-halogen exchange, methyllithium, uncomplexed with copper, smoothly converts aryl iodides to arylmethanes. Coupling of lithium dialkyl- and diarylcuprates with alkyi halides appears to take place without significant metal-halogen exchange. The reaction of lithium diphenylcuprate with (–)-(R)-2-bromobutane occurs with the predominant inversion of configuration (84-92% stereoselectivity) expected of an SN2-like displacement. Coupling reactions involving an n-alkyl halide as one reaction partner proceed in high yield; those involving t-alky) halides fail. Lithium di-n-alkyl-,di-sec-alkyl-, and di-t-alkylcopper reagents all couple with n-alkyl halides. A number of preparations for representative copper(I) ate complexes are described, and the sensitivity of the coupling reactions to the method of preparation of the ate complex, to the nature of the solvent, and to the presence of lithium halides, trialkylphosphines, and dialkyl sulfides in solution are discussed. © 1969, American Chemical Society. All rights reserved.