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

A variety of pyrazolo[3,4-d]pyrimidine-6(7H)-thione derivatives were easily synthesized with a novel, simple, efficient, and regioselective method via three-component condensation reaction of 5-methyl-1H-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.