Synthesis of 5H-Benzimidazo[1,2-a][1,3,4]thiadiazolo[2,3-d][1,3,5]triazin-5-one and 12H-Benzimidazo [1,2-a]pyrimido[6,1-d][1,3,5]triazin-12-one. Two New Heterocyclic Ring Systems.