Cyclic condensations of 2‐amino‐1,3,4‐thiadiazole with 1,3‐dicarbonyl compounds

The reactions of 2‐amino‐1,3,4‐thiadiazole with 1,3‐dicarbonyl compounds are described. 2,4‐Pentanedione gave 2‐thiocyanato‐4,6‐dimethylpyrimidine while diethylmalonate and ethyl acetoacetate yielded 5‐hydroxy‐7 H ‐1,3,4‐thiadiazolo[3,2‐ a ]pyrimidin‐7‐one and 7‐methyl‐5 H ‐1,3,4‐thiadiazolo[3,2‐ a ]pyrimidin‐5‐one, respectively. The structure of the latter compound was confirmed by a synthesis of the alternative isomeric structure (5‐methyl‐7 H ‐1,3,4‐thiadiazolo[3,2‐ a ]pyrirnidin‐7‐one) from 2‐amino‐1,3,4‐thiadiazole and α‐bromocrotonic acid.