Synthesis of 2,2′-biflavanones from flavone via electrolytic reductive coupling

Flavone (1) was easily reduced by using the electrochemical method to give two hydrodimers of 2,2'-biflavanone(racemate) (5a) and 2,2'-biflavanone(meso) (5b) and one reductive product of flavanone (6). Their yields were dependent on the nature of electrodes, the kinds of supporting electrolytes and the reaction temperature. They were found to afford higher yields of 2,2'-biflavanone(racemate) (5a) and 2,2'-biflavanone (meso) (5b) (32.4% and 24.8%, 35.8% and 13.4%, respectively,) in the reaction conditions of Pb(-)/C(+)H2SO4-7F/mol and C(-)/C(+)-H2SO4-5F/mol.