Synthesis of pyrazolo[3,4-d]pyrimidine derivatives using ketene dithioacetals

The cyclization of 5-amino-3-methylthiopyrazole-4-carbonitriles or 4-carboxamides 3a-j , which were prepared by the reaction of ketene dithioacetals 1a,b 1a : bis(methylthiomethylenemalononitrile; 1b : bis(methylthio)methylenecyanoacetamide] with hydrazines (hydrazine hydrate, phenylhydrazine, p-chlorophenylhydrazine, p-nitrophenylhydrazine), with formamide or carbon disulfide proceeded to give the corresponding 4-amino- or 4-hydroxy-3-methylthiopyrazolo3,4-d]pyrimidines 6a-h in good yields. 3-Aminopyrazolo3,4-d]pyrimidine derivatives 6i-1 were also obtained by the application of the cyclization reaction of 3,5-diaminopyrazoles with formamide.