Photolysis of flavone (4) with the electron-donating amines including triethylamine or 2-(N,N-dimethylamino)ethanol in acetonitrile, benzene or methylene dichloride can easily afford 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 molar ratios of substrate to amine, the kinds of amines, the solvents used and the irradiation sources. Higher yields were afforded 2,2¢-biflavanone(racemate) (5a), 2,2¢-biflavanone(meso) (5b) and flavanone (6) (30.0%, 20.9% and 15.8%, respectively) in the reaction condition of 1/2 molar ratio of flavone (4) to triethylamine in acetontrile with fourteen hours of irradiation.

6-Methoxyflavone (7) easily afforded two hydrodimers of rac-6,6²-dimethoxy-2,2²-biflavanone (8a) and meso-6,6²-dimethoxy-2,2²-biflavanone (8b) and one reductive product of 6-methoxyflavanone (9) by using photolysis with the electron-donating amines including triethylamine, 2-(N,N-dimethylamino)ethanol or N,N-dimethylaniline in solvents of acetonitrile, benzene or methylene dichloride. They were found to give higher yields of rac-6,6²-dimethoxy-2,2²-biflavanone (8a) and meso-6,6²-dimethoxy-2,2²-biflavanone (8b) (38.7% and 4.5%, 35.3% and 6.2%, respectively) in the reaction conditions of 1/10 molar ratio of 6-methoxyflavone (7) to triethylamine in a solvent of acetonitrile with irradiation of twenty-four hours by using 306 nm and 352 nm lamps.