Electrochemical oxidation of 4-(piperazin-1-yl)phenols in the presence of indole derivatives: The unique regioselectivity in the synthesis of highly conjugated bisindolyl-p-quinone derivatives

The electrochemical oxidation of 4-(piperazin-1-yl)phenols have been studied in the presence of indole derivatives as nucleophiles in water/acetonitrile mixture by means of cyclic voltammetry and controlled-potential coulometry. The reaction mechanism is believed to be oxidation of 4-(piperazin-1-yl)phenols, Michael addition reaction, oxidation of the formed adduct, another Michael addition reaction, oxidation of new adduct and hydrolysis (ECECEC). The results revealed that bisindolyl-p-quinones were synthesized through the regioselective addition of indoles to electrochemically generated quinone imines in good yields at carbon electrode in a divided cell.