5-amino-2-methylsulfanyl-thiazole-4-carboxylic acid ethyl ester 1 reacted with malononitrile, benzoylisothiocyanate, and 2-(methylsulfanyl-phenylaminomethylene) malononitrile to furnish the thiazolopyrimidine-2-one derivatives 2–4, respectively. 1 reacted with the