o-Nitroaniline derivatives. Part 10. 5- and 6-Amino-1H-benzimidazole 3-oxides

Abstract

Cyclisation of N-(4- or 5-acylamino-2-nitrophenyl)glycine esters in basic media gives alkyl 5- or 6-acylaminobenzimidazole-2-carboxylate N-oxides, e.g. (11a) or (11b). Acid hydrolysis of the latter, followed by reaction with ammonia, gives the title compounds (1b) and (1c), in acceptable yield. The corresponding reaction sequence with 4-acylamino-N-cyanomethyl-o-nitroanilines also gives (1b); where the acyl group is methylsulphonyl, however, the final product is 5-methanesulphonamidobenzimidazole N-oxide (9). Compound (1b) is also obtainable from ethyl 5-nitrobenzimidazole-2-carboxylate N-oxide by reduction followed by hydrolysis.

Attempts to cyclise N-(o-nitrophenyl)glycine derivatives containing a free amino group at the 5-position are unsuccessful. This failure is attributed to mesomeric deactivation of the nitro group by the amino lone pair.