Nitrocyclohexadienones in aromatic nitration

Nitrocyclohexadienones have been identified as intermediates formed in a range of nitration reactions in recent years. The mechanisms of their subsequent reactions have been studied and discussed. published and other progress in these areas is reviewed. Some nitrocyclohexadienones containing electron-withdrawing substituents have been suggested as mild, selective and recyclable nitrating agents for phenols, naphthols and aromatic amines which do not involve problems of substrate oxidation. Studies of certain phenols involving the observation of chemically induced dynamic nuclear polarisation effects on reaction with N-15 labelled 2,3,5,6-tetrabromo-4-methyl-4-nitrocyclohexa-2,5-dien-1-one have established that nitro-products are formed by a radical. process. Bromination may be a concurrent and sometimes predominant process. These studies have been extended, including, for example, aniline as a substrate. With N,N-dimethylaniline, however, a main product is N-methyl-N-nitrosoaniline. Mechanisms for these processes are presented.