Benzofurazan N-oxides as synthetic precursors. Part 2. Conversion of benzofurazan N-oxides into 2H-benzimidazoles and some unusual reactions of 2H-benzimidazoles

Abstract

Benzofurazan N-oxides react with primary nitroalkanes to give 1-hydroxybenzimidazole 3-oxides; with secondary nitroalkanes, red 2,2-dialkyl-2H-benzimidazole 1,3-dioxides are formed. The 2H-benzimidazole oxides react as bis-1,3-dipolar nitrones with acetylenic dipolarophiles (methyl acetylenedicarboxylate and benzyne) but undergo a complex series of redox reactions with tetracyanoethylene giving purple quinonoid dicyanomethylene derivatives, also formed by the action of the malononitrile anion. O-Alkylation of the 2H-benzimidazole oxides occurs with methyl fluorosulphate, and irradiation results in rearrangement to O-2-nitrophenylhydroxylamine derivatives.