REACTION OF PHENYLLITHIUM AND HALOTOLUENES . COMPETING ARYNE, DISPLACEMENT, AND HALOGEN-METAL EXCHANGE PROCESSES

The reaction of phenyllithium with the halotoluenes in benzene and benzene-ether has been studied in refluxing solvent and at 20°. The catalytic effect of piperidine and N,N,Nʹ,Nʹ-tetramethylethylenediamine (TMEDA) was also examined. Aryne formation was found to be the exclusive mechanism leading to biaryl generation for the fluoro, chloro, and bromo compounds while competition from an alternative process, apparently displacement, was observed for the iodotoluenes. Extensive halogen-metal exchange was observed only for the bromo and iodo compounds. Depletion of the concentration of the initial reagents by this process as well as the subsequent reaction of these exchange products prevents determination of an order of aryne-forming ability for the halide series. The relative rates of the various processes, as well as the over-all biaryl yield, were found to depend on the particular solvent-catalyst system employed. The possibility of synthetic application of dimethyl sulfate quenching of reaction mixtures was also examined. © 1969, American Chemical Society. All rights reserved.