3-Amino-6-methyluracil and its thio analogs were synthesized. From these thio analogs, 7-methyl-5H-1, 3, 4-thiadiazolo [3, 2-α] pyrimidin-5-one, its 2-amino and 2- or 5-thio derivatives were prepared. Reflux of thiadiazolopyrimidines with chloroacetic acid or hydrochloric acid led to the ring opening of the thiadiazole moiety to give unexpected 3-amino-6-methyluracil.
