Cleavage of 7- And 8-nitropyrido[1,2-a]benzimidazoles on treatment with dimethyl acetylenedicarboxylate

7-Nitropyrido[1,2-a]benzimidazole and 8-nitropyrido[1,2-a]benzimidazole undergo cleavage-recyclization under the action of an excess of dimethyl acetylenedicarboxylate.