Synthesis of Pyrimidines, Thienopyrimidines and Pyrazolopyrimidine

5‐Ethoxycarbonyl‐4‐methyl‐2‐phenylpyrimidin‐6(1H)‐thione ( 3 ), which was prepared from the reaction of ethyl β‐aminocrotonate 1 with benzoyl isothiocyanate ( 2 ) in refluxing acetone, was reacted with halo compounds to give S‐alkyl derivatives 4a‐h . Treatment of compounds 4a‐c with sod. ethoxide cyclized into thienopyrimidine 10a‐c . Hydrazinolysis of compound 3 gave hydroxypyrazolopyrimidine derivative 6 . Also the latter compound was obtained upon heating compound 4a with hydrazine hydrate under neat conditions, but when compound 4a refluxed with hydrazine hydrate in ethanol the corresponding carbohydrazide 5 was produced.