Cation radical induced oxidative chemistry of hydrazones and oximes
Hoque, A. K. M. Mansurul
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Electron transfer reactions of cation radicals have drawn much interest (1). Shine and Sugiyama were the first to observe that alkyl radicals were formed by an initial electron transfer step in reactions of thianthrene cation radical with organomercurials (2). The possibility that thianthrene cation radical might efficiently trap the alkyl radicals led to attempts to generate alkyl radicals by the photolysis of azoalkanes in the presence of thianthrene cation radical at room temperature. It was found, however that the azoalkanes which were chosen reacted rapidly with thianthrene cation radical in the absence of light, leading to the reduction of the cation radical and formation of alkyl cation and radical products. This led to the study of the reactions of cation radicals with a number of azoalkanes (1). During the study of the reaction of thianthrene cation radical with azotoluene in acetonitrile, an interesting product, 1-benzyl-3-phenyl-5-methyl-1,2,4-triazole, was obtained as a major product along with alkyl cation and alkyl radical products (1, 3). It was found that the triazole was formed by a reaction in which the cation radical induced oxidative cycloaddition of benzaldehyde benzylhydrazone, a tautomer of azotoluene, to acetonitrile. This observation led to an interest in the study of reactions of cation radicals with arylhydrazones. The objective of studying the reactions of cation radicals with arylhydrazones was to explore the cation radical induced oxidative cycloaddition of hydrazones to nitrites to give trisubstituted 1,2,4-triazoles.