Non-conventional Aromatic Electrophilic Reactions Occurring via "ipso" Arenium Ion Intermediates

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Non-conventional reactions of benzenoid compounds which occur as a consequence of "ipso" attack of electrophiles have been investigated, with a special emphasis on the elucidation of the anomalies observed during the side-chain nitration of polysubstituted arenes; nitrooxylation with <HNO_3> / <CH_2> <Cl_2> and nitration with <HNO_3> / <(CH_3CO)_2> O. Based on the evidence obtained from product variations with substituents, electrochemical nitrodecarboxylation of arylacetates, and ESR examination of the initial stage of the side-chain reactions, a proposal is made that the side-chain substitution of polysubstituted arenes occurs via heterolytic path with <HNO_3> / <CH_2> <Cl_2> and via a homolytic path with <HNO_3> / <(CH_3CO)_2> O. The first isolation of a proposed methylenecyclohexadiene intermediate for the side-chain substitution of arenes under heterolytic conditions is also included.