A facile and simple regioselective synthesis of uracils and their thio analogues has been achieved by cyclocondensation of a common precursor, diazadienium iodide 1, and isothiocyanates 2a,b. The key step in this synthetic process is the preparation of 4-methylsulfanylpyrimidine-2-thiones 3a,b, which after further elaboration gave the expected uracil analogues 4a,b-8a,b.