The reaction of thione 3 or its 2-methylthio derivative 4 with hydrazonoyl halides 5al, in the presence of triethylamine, yielded the corresponding triazolo(4,3-a)pyrimidin-5(1H)-ones 8al. The structure of compounds 8al was further conrmed by the reaction of 3 with the appropriate active chloromethylenes 11ac followed by coupling of the products with benzenediazonium chloride to aord the azo-coupling