Electroreductive Homo-coupling of Quinolines for the Regioselective Synthesis of 1,2,3,4-Tetrahydro-2,3'-biquinolines

A simple and efficient electrochemical reductive homocoupling strategy for the synthesis of 1,2,3,4-tetrahydro-2,3'-biquinoline from commercially available quinolines has been developed. This method employs diethyl phosphite and water as hydrogen sources. Mechanistic studies indicate that the regioselective C2-C3 coupling in this reaction proceeds via enamine-iminium intermediates. This sustainable approach combines good regioselectivity with broad functional group tolerance under mild conditions, while the modular biquinoline products serve as versatile scaffolds for late-stage functionalization and synthetic diversification.