o-Nitroaniline derivatives. Part 14.1,2 Cyclisations leading to benzimidazole N-oxides, N-hydroxybenzimidazolones and N-hydroxyquinoxaline-2,3-diones: a mechanistic borderline

Abstract

The base-induced cyclisations of N-(o-nitrophenyl)glycine derivatives (nitriles 9 or esters 13) bearing additional substituents at the other ortho-position are anomalous, resembling those involving N-(o-nitrophenyl)sarcosine analogues. The nitriles are converted into N-hydroxybenzimidazolones 10 and the esters into 1-hydroxyquinoxaline-2,3(1H,4H )diones 14 and 2,2′-diaminoazoxybenzene derivatives 15, instead of, or in addition to, the expected 2-substituted 1H-benzimidazole 3-oxides 11 and 16 or the 2-unsubstituted analogues, 17. The possibility that all these reactions proceed through a common 2,1,4-benzoxadiazine intermediate, 18, is explored.