Benzofurazan N-oxides as synthetic precursors. Part 3. Acid-catalysed cyclisation of NN-dialkyl-N′-(o-nitrophenyl)hydrazines

Abstract

Acid-catalysed cyclisation of the title hydrazines with constant-boiling hydrochloric acid or hot polyphosphoric acid causes cyclisation in three ways: (a) by the most common pathway, to give N-(alkylamino)benzimidazoles (4); (b) to give benzotriazoles (5) and their N-oxides (5a); and (c) to give 2-alkyl-1,2,4-benzotriazinium-6-olates (6). These synthetically useful reactions have been rationalised mechanistically and their scope and limitations examined.