Arylation of arenes with diaroyl peroxides

The reaction is performed by heating the diaroyl peroxide in an excess of arene to be arylated as solvent in an oxygen atmosphere [104], or in the presence of nitrobenzene until the evolution of carbon dioxide ceased [105]. For example, the yield of biphenyl can be increased to almost 80% by the reaction of dibenzoyl peroxide in refluxing benzene, if nitrobenzene or similar oxidant is present. Nitrobenzene efficiently oxidizes transient arylcyclohexadienyl radicals to biaryls, thus preventing several side- 

When a monosubstituted benzene is attacked by aryl radical, a mixture of all three isomeric biphenyls is produced, as well as in the GBH reaction [105-107]. The nature of substituents apparently does not play any important role except those of bulky ort/jo-groups. The ortAo-substituted biaryl is always the main product followed by para- and meto-arylation product. The presence of a bulky ortho-tert-huXy group significantly decreases the amount of ort/io-arylation product, indicating the strong ort/io-steric effect. The typical isomer distribution and the yields of biaryls in the arylation of four mono-substituted benzenes with dibenzoyl peroxide are given in the Table 4. 

The trichloromethyl group causes the strong steric effect that results in a high chemoselective formation of meta-trichloromethylbiphenyls during the arylation of 

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