[F:1][C:2]1[CH:11]=[CH:10][C:9]([F:12])=[C:8]2[C:3]=1[CH:4]=[CH:5][CH2:6][O:7]2.C1C=C(Cl)C=C(C(OO)=[O:21])C=1.[O-]S([O-])(=S)=O.[Na+].[Na+]>C(Cl)Cl.O>[F:1][C:2]1[CH:11]=[CH:10][C:9]([F:12])=[C:8]2[C:3]=1[CH:4]1[O:21][CH:5]1[CH2:6][O:7]25,8-Difluoro-2H-chromene (35 g, 0.21 mole) was dissolved in 500 ml DCM and MCPBA (77%, 93 g, 0.42 mole) was added. The reaction was stirred at room temperature for 30 minutes. 50 g Na2S2O3 in 500 ml water was added to quench the reaction. The organic layer washed with 2N NaOH solution (2×500 ml), brine (200 ml), dried over Na2SO4 and concentrated. The residue was recrystallized from EtOAc/Hexane solution to give rise to 21.6 g pure product. The residue from mother liquor was purified by column chromatography (EtOAc/hexane from 0/100 to 25/75 in 55 minute, additional 1.4 g obtained). Total Yield: 23 g, 60%. 1H NMR (CDCl3 400 MHz δ 7.00 (m, 1H), 6.63 (m, 1H), 4.67 (d, J=12.4 Hz, 1H), 4.27 (m, 2H), 3.84 (d, J=4.4 Hz, 1H).
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