o-Nitroaniline derivatives. Part 7. The synthesis of 2-alkoxybenzimidazole N-oxides (2-alkoxy-N-hydroxybenzimidazoles) from o-nitroanilines
N-Phenacyl-N-p-tolylsulphonyl-o-nitroanilines (8) are cyclised to 2-alkoxybenzimidazole N-oxides (⇌ 2-alkoxy-N-hydroxybenzimidazoles)(13)–(16) by sodium alkoxides in the appropriate alcohol. N-Phenacyl-o-nitroanilines themselves undergo cleavage, or at best give low yields of 2-benzoylbenzimidazole N-oxides, by reaction with alkoxides under similar conditions. N-Acetonyl-N-p-tolylsulphonyl-o-nitroanilines (9) are also cyclised to 2-alkoxybenzimidazole N-oxides by sodium alkoxides. When the ketonic functions of (8) and (9) are replaced by ester or cyano groups, however, cleavage occurs in alcoholic base in preference to cyclisation. N-Phenacyl-(8f) and N-acetonyl-N-p-tolylsulphonyl-6-methyl-2-nitroaniline (9f) are anomalous in that they are cyclised by alkoxides to 1-hydroxy-4-methylbenzimidazolone (21).