Regioselective electrosynthesis of pyrazolo[3,4-b]quinolin-5-one derivatives.

A highly efficient and regioselective method had been reported for the synthesis of pyrazoloquinoline derivatives. The current work studied the reaction of 3-indolylpyrazole, dimedone, and various aldehydes under electrochemical conditions. The various factors controlling electrochemical reactions were examined and optimized, including reaction time, temperature, current, solvent, type of electrodes, and supporting electrolytes. The scope of the reaction was investigated using different types of aldehydes. The reaction yielded exclusively pyrazolo[3,4-b]quinolin-5-ones in high yields and mild reaction conditions. The structure of the products was confirmed by 1H-NMR and 2D-NMR spectra. The reaction mechanism was followed up using cyclic voltammetry. Compared to the conventional heating method, the electrochemical method proved to be advantageous in terms of simple reaction conditions, short reaction time, higher yield, and eliminating the need for basic catalysis.