Syntheses of heterocyclic compounds. Part XXV. Action of acid on NN-disubstituted o-nitroanilines: benzimidazole N-oxide formation and nitro-group rearrangements

Abstract

A variety of NN-disubstituted o-nitroanilines are shown to give benzimidazole N-oxides, often in high yield, when heated in mineral acid solution. The product is accompanied by small amounts of the denitrated parent compound and p-nitro- and 2,4-dinitro-derivatives. Irradiation of acidic solutions of NN-disubstituted o-nitroanilines similarly yields either the corresponding benzimidazole N-oxide or the benzimidazole by different mechanisms and with no concomitant rearrangement of nitro-groups. Synthetic and mechanistic implications are discussed.