o-Nitrobenzylidene compounds. Part 4. The cyanide-induced cyclisation of o-acetamido-N-(o-nitrobenzylidene)anilines: an improved route to quinoxalino[2,3-c]cinnolines

Abstract

Cyclisation of o-acetamido-N-(o-nitrobenzylidene)anilines (7) with potassium cyanide in methanol (preferably under nitrogen) leads in most cases to quinoxalino[2,3-c]cinnolines (6) of unambiguous substitution pattern. In some cases, cyclisation appears to be incomplete, and 2-amino-3-(o-nitrophenyl)quinoxalines (11) are obtained as by-products; in certain cases quinoxalino[2,3-c]cinnoline 5-oxides (10) are also detected. These by-products are assumed to result from oxidation of intermediates in the cyclisation process (7)→(6).