Palladium-catalyzed regioselective direct CH arylation of pyrazolo[3,4-d]pyrimidines

Nitrogenous bicycles are an apparently endless field of organic and biological research. In this study, we disclose an efficient pathway to the synthesis of the pyrazolo[3,4-d]pyrimidine scaffold in three steps from allopurinol. This key intermediate was engaged in the first example of regioselective CH arylation catalyzed by palladium to access a library of 3-substituted-1-methyl-4-phenyl-1H-pyrazolo[3,4-d]pyrimidines.