4-(4-Chloro-phenylsulfanyl)-5,8-difluoro-chroman-3-ol (23.2, 71 mmole) was dissolved in 200 ml DCM and MCPBA (77%, 31.7 g, 142 mmole) was added. The reaction was stirred at room temperature for 3 hours. 10 g Na2S2O3 in 50 ml water was added to quench the reaction. The organic layer washed with 1N NaOH solution (2×100 ml), brine (100 ml), dried over Na2SO4 and concentrated. The residue was dissolved in 200 ml DCM, mesyl chloride (16.1 g, 142 mmole) and triethylamine (14.3 g, 142 mmole) were added. The reaction was stirred at room temperature for one hour. The reaction solution washed with brine (100 ml), dried over Na2SO4 and concentrated. The residue was recrystallized from EtOAc/Hexane solution to give rise to 8.4 g pure product. The residue from mother liquor was purified by column chromatography (EtOAc/hexane from 0/100 to 25/75 in 55 minute, 7.1 g). Total yield: 15.5 g, 64%. 1H NMR (CDCl3 400 MHz δ 7.84 (dd, J=8.8 and 2.2 Hz, 2H), 7.51 (d, J=8.1 Hz, 2H), 7.30 (t, J=4.4 Hz, 1H), 7.00 (m, 1H), 6.54 (m, 1H), 4.99 (d, J=4.4 Hz, 2H).
