One-Flask Synthesis of Pyrazolo[3,4-d]pyrimidines from 5-Aminopyrazoles and Mechanistic Study.

A novel one-flask synthetic method was developed in which 5-aminopyrazoles were reacted with -substituted amides in the presence of PBr₃. Hexamethyldisilazane was then added to perform heterocyclization to produce the corresponding pyrazolo[3,4-]pyrimidines in suitable yields. These one-flask reactions thus involved Vilsmeier amidination, imination reactions, and the sequential intermolecular heterocyclization.