Regioselective multi-component synthesis of 1H-pyrazolo[3,4-d]pyrimidine-6(7H)-thiones

A variety of pyrazolo[3,4- d ]pyrimidine-6(7 H )-thione derivatives were easily synthesized with a novel, simple, efficient, and regioselective method via three-component condensation reaction of 5-methyl-1 H -pyrazol-3-amine, arylisothiocyanates, and aldehydes in the presence of catalytic amount of p -toluenesulfonic acid ( p -TSA) in 1-butyl-3-methylimidazolium bromide ionic liquid with excellent yields and short reaction times.