In the present work new and simple synthetic methods of 4-aryl-6-methyl-2-oxo-1,2,3,4 tetrahydropyrimidine-(5)- 1,3,4-thiadiazole-2-amine (3) and 4-aryl-6-methyl-2-oxo-1,2,3,4 tetrahydropyrimidine-(5)-1,3,4-oxadiazole-2- amine (3a) are described. Compound 1 is converted to Carbothiamide 2 by the reaction with ethyl ester followed by thiosemicarbazide. Compound 2 has acted as key intermediate for both the final compounds. In one pathway, 2 is converted to corresponding thiadiazloe 3 by treatment with conc.H2SO4 and NH3, and compound 3a by treatment with I2 followed by KI and NaOH to furnish the final compound. Structural elucidation is accomplished by IR, 1HNMR and Mass spectral data of the synthesized compounds.