Reaction of thiosemicarbazide with 1,5-diarylpent-1-yne-3,5-diones

Acetylenic diketones I were reacted with thiosemicarbazide to give either 6H- or 3H, 6H-pyrazolo-[1,5-c] pyrimidinethiones II and IV or III, depending on the nature of the substituents as well as the reaction conditions. The reaction of 2-aryl-5-phenyl-6H-pyrazolo [1,5-c] pyrimidine-7-thiones II with nitrous acid and benzenediazonium chloride gave the disulfide V and phenylazodisulfide VI derivatives, respectively. Reacting II with certain electrophiles gave the 3-substituted-7-thiones VII, VIII and IX; while oxidation with alkaline hydrogen peroxide afforded the respective pyrazolopyrimidinones X