Specific Features of the Reduction of 7-Nitro-9-R-2,3-dihydroimidazo[1,2-a]benzimidazoles with SnCl2 in Hydrochloric Acid

The reduction of 7-nitro-N(9)-substituted 2,3-dihydroimidazo[1,2- a ]benzimidazoles with SnCl 2 in conc. HCl forms a mixture of the previously unknown 7-amino and 7-amino-6-chloro derivatives in a ratio depending on the nature of the substituent at position 9. This result gave grounds to assume that not the final heteroarylamine, but the intermediate heteroarylhydroxylamine formed by a mechanism similar to the acid-induced Bamberger rearrangement of arylhydroxylamines, is subjected to chlorination.