o-Nitroaniline derivatives. Part 9. Benzimidazole N-oxides unsubstituted at N-1 and C-2
Since previous routes to the title compounds (1) have proved unsatisfactory as general methods, a simple new synthesis has been devised. N-Cyanomethyl-o-nitroanilines (5) are cyclised in basic media, giving 2-cyanobenzimidazole N-oxides (12) in good yield. Hydrolysis of these products with hydrochloric acid gives, directly, the title compounds as their hydrochloride salts (13), which may be isolated and purified, and which give the free N-oxides (1) by treatment with aqueous ammonia followed by evaporation.
o-Nitrophenylglycine esters (4) may satisfactorily replace the nitriles (5) in certain cases. A modification of this kind in the related nitropyridylglycine series leads to 3H-imidazol[4,5-b]pyridine 1-oxide (20).