The Chemistry of Aryllead(IV) Tricarboxylates. Reaction with Aromatics to Give Biaryls

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Abstract
Aryllead(IV) tricarboxylates have been shown to react in trifluoroacetic acid with a range of aromatics to give biaryls. With aromatics more reactive than toluene the yields are generally good and the method provides a useful synthesis of unsymmetrical biaryls. A study of the mechanism of the reaction indicates an electrophilic substitution, although at least with the more reactive substrates this does not involve a free aryl cation. It is suggested that, for these compounds, the formation of a π-complex in which the aryl-lead bond is still intact is rate determining. For benzene and toluene, which give low yields in the above reaction, a marked improvement in the yield of the biaryl can be achieved by using AlCl3 in place of trifluoroacetic acid. Al(OCOCF3)3, Al(OCOCF2CF3)3 and Al(OCOCF2CF2CF3)3 have been shown to be equally effective in promoting the reaction, and, unlike AlCl3, do not suffer the disadvantage of causing alkyl and/or aryl group migrations.

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