Organolithium reagents, addition from alkyl halides

Addition of organolithium reagents to diphenylarsenoethene provides another route to a-arseno anions. This reaction is general to the second and third row elements (Si, P, S, Ge, As and Se) but does not occur with elements from the fourth and fifth rows (Sn, Sb, Te, Pb and Bi). Unlike their phosphorus analogs, triphenylarsonium salts cannot be prepared by reaction of triphenylarsine with an alkyl halide. Their preparation can be achieved by reaction of triphenylarsine with the more electrophilic alkyl tri-flates. It is also possible to alkylate arsonium ylides. ° ° ... 

Arylcopper intermediates can be generated from organolithium compounds, as in the preparation of cuprates.95 These compounds react with a second aryl halide to provide unsymmetrical biaryls in a reaction that is essentially a variant of the cuprate alkylation process discussed on p. 680. An alternative procedure involves generation of a mixed diarylcyanocuprate by sequential addition of two different aryllithium reagents to CuCN, which then undergo decomposition to biaryls on exposure to oxygen.96 The second addition must be carried out at very low temperature to prevent equilibration with the symmetrical diarylcyanocuprates. 

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