Synthesis of some 2-(heteroarylamino)benzimidazoles and their cyclization with phosgene

2-(Benzimidazol-2-ylamino)pyridine (4a) , 2-(benzimidazol-2-ylamino)pyrazine (4b) , and 2-(benzimidazol-2-ylamino)thiazole (4c) underwent a ring-closure reaction on treatment with phosgene affording 6H-pyrimido-1′,2′:5,4]1,3,5]triazino1,2-a]benzimidazol-6-one (1a) , 6H-pyrazino1′,2′:5,4]1,3,5]triazino1,2-a]benzimidazol-6-one (1b) , and 5H-thiazolo2′,3′:4,5]1,3,5]triazino1,2-a]benzimidazol-5-one (1c) respectively. The structure of these hitherto unknown heterocyclic systems was confirmed by their ir and mass spectra.