The general procedure for the synthesis of 2-(3,4-dimethoxyphenyl)-5,7-dihydroxy-6-methoxy-4H-benzopyran-4-one from 5,7-dihydroxy-3',4',6-trimethoxyflavone was as follows: 7-hydroxy-3',4',5,6-tetramethoxyflavone (4.44 g, 12.4 mmol) was suspended in 88 mL of acetonitrile. Aluminum trichloride (8.27 g, 5 eq.) was added to the suspension at room temperature and the reaction mixture was subsequently heated to reflux for 1.5 hours. After completion of the reaction, the solvent was removed by evaporation under reduced pressure. To the residue, 10% aqueous hydrochloric acid and chloroform were added and the mixed solution was heated to reflux until it became clear. After the solution was cooled to room temperature, the organic layer was separated, washed sequentially with water and brine, and then dried with anhydrous magnesium sulfate. The solvent of the organic layer was removed by evaporation under reduced pressure to obtain the crude product. The crude product was recrystallized in methanol to give 3.18 g of the target compound in 74% yield. The structure of the product was confirmed by NMR (CDCl3): δ 13.05 (s, 1H), 7.50 (dd, J = 8.6, 2.2 Hz, 1H), 7.31 (d, J = 2.1 Hz, 1H), 6.96 (d, J = 8.5 Hz, 1H), 6.59 (s, 1H), 6.56 (s, 1H), 6.48 (br s, 1H). 4.03 (s, 3H), 3.96 (s, 3H), 3.95 (s, 1H).
