Arene oxidative nuclear substitution

The nitrosonium cation can serve effectively either as an oxidant or as an electrophile towards different aromatic substrates. Thus the electron-rich polynuclear arenes suffer electron transfer with NO+BF to afford stable arene cation radicals (Bandlish and Shine, 1977 Musker et al., 1978). Other activated aromatic compounds such as phenols, anilines and indoles undergo nuclear substitution with nitrosonium species that are usually generated in situ from the treatment of nitrites with acid. It is less well known, but nonetheless experimentally established (Hunziker et al., 1971 Brownstein et al., 1984), that NO+ forms intensely coloured charge-transfer complexes with a wide variety of common arenes (30). For example, benzene, toluene,... 

In a forthcoming paper we discuss the formation of arenes containing nuclear bromine in our oxidation system however, this involves a transition metal catalyst other than cobalt. The latter apparently results in little or no nuclear substitution by bromine. 

However, the outcome of the oxidation of alkyl-substituted arenes is not easy to predict owing to the competition between nuclear dimerization and dimerization through an Qf-carbon. For instance, a major product from oxidation of mesitylene in CH2CI2 is bimesityl [Eq. (46)], and from durene in CH2CI2-CF3SO3H, the heptamethyldiphenyl-methane [Eq. (47)] [104,105] no diphenylmethane is formed from mesitylene nor biphenyl from durene. 

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