[OH:1][C:2]1[CH:7]=[C:6]([OH:8])[CH:5]=[CH:4][C:3]=1[C:9](=[O:18])[CH2:10][C:11]1[CH:16]=[CH:15][C:14]([OH:17])=[CH:13][CH:12]=1.B(F)(F)F.[CH3:23]COCC.CS(Cl)(=O)=O>CN(C=O)C>[OH:8][C:6]1[CH:7]=[C:2]2[C:3]([C:9](=[O:18])[C:10]([C:11]3[CH:16]=[CH:15][C:14]([OH:17])=[CH:13][CH:12]=3)=[CH:23][O:1]2)=[CH:4][CH:5]=1In a solution of 1-(2,4-dihydroxyphenyl)-2-(4-hydroxyphenyl)-ethanone (2 mmol) in DMF (6 mL), freshly destilled BF3.OEt2 (6.3 mL) was added under argon. The mixture was heated at 50° C., and a solution of methanesulphonyl chloride (1 mL) in dry DMF (1.5 mL) was added slowly. After reaction at 80° C. for 1 h, the mixture was cooled to rt and poured into a large volume of ice cold aq. sodium acetate (12 g/100 mL), then extracted with EtOAc, and the organic layer was dried and concentrated. The residue was purified by column chromatography on silica gel using a mixture of DCM and MeOH to give 7-hydroxy-3-(4-hydroxyphenyl)-chromen-4-one.
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