A Green and Efficient Synthesis Method of Benzo[c]cinnolines: Electrochemical Reduction of 2,2'-Dinitrobiphenyl in the Presence of CO₂

Benzo[c]cinnolines are an essential framework material in medicinal chemistry owing to its promising anti-cancer and antioxidant activity, and good pharmacological properties. Accordingly, benzo[c]cinnolines are synthesized through electrochemical reduction of 2,2'-dinitrobiphenyl (DNBP) in aprotic solvents with CO2. Cyclic voltammetry (CV), cyclic voltabsorptometry (CVA), derivative cyclic voltabsorptometry (DCVA) techniques, and in-situ FT-IR spectroelectrochemistry are used to investigate the mechanism of electrochemical reduction of DNBP in the presence of CO2. It is a reversible 2-electron-transfer reaction in an aprotic solution of DMSO in the absence of CO2, while it turned into a completely irreversible 8-electron process in the presence of CO2. Benzo[c]cinnolines were finally obtained by potentiostatic electrolysis with conversion rate of 99 %, indicating the high selectivity of this reaction. Above all, DNBP can be electrochemically reduced into BC in the presence of CO2, providing a theoretical and practical path for electrochemical synthesis of bioactive benzo[c]cinnolines (BC).