Synthesis of [1, 2, 3] Thiadiazolo [5, 4-d] pyrimidines

Treatment of 4, 6-dimethyl-v-triazolo [4, 5-d] pyrimidine-5, 7 (4H, 6H)-dione (I) with phosphorus pentasulfide in pyridine afforded 5, 7-dimethyl [1, 2, 3] thiadiazolo [5, 4-d] pyrimidine-4 (5H)-one-6 (7H)-thione (II) through the v-triazole-thiadiazole rearrangement. The reaction of (II) with thionyl chloride gave 5, 7-dimethyl [1, 2, 3] thiadiazolo [5, 4-d]-pyrimidine-4, 6 (5H, 7H)-dione (III).