One-Step Synthesis of Functionalized Pyrazolo[3,4- b ]pyridines via Ring Opening of the Pyrrolinium Ion.

Herein, we report a highly regioselective one-pot synthesis of pyrazolo[3,4- b ]pyridines via the reaction of 3-arylidene-1-pyrrolines with aminopyrazoles. The reaction proceeds through the sequential nucleophilic addition/electrophilic substitution/C-N bond cleavage and provides easy access to pyrazolo[3,4- b ]pyridine derivatives featuring a primary amino group. Moreover, the reaction can be terminated at the electrophilic substitution stage, thus providing convenient entry to the hardly accessible pyrazolopyrrolopyridine scaffold.