[CH3:1][CH:2]1[CH2:6][C:5]2[CH:7]=[C:8]([S:11]([CH3:14])(=[O:13])=[O:12])[CH:9]=[CH:10][C:4]=2[O:3]1.[Br:15]Br>C(Cl)Cl.[Fe]>[Br:15][C:10]1[C:4]2[O:3][CH:2]([CH3:1])[CH2:6][C:5]=2[CH:7]=[C:8]([S:11]([CH3:14])(=[O:13])=[O:12])[CH:9]=1To a mixture of the title compound from Step 1 (300 mg, 1.42 mmol) in DCM (10 mL) was added Fe (159 mg, 2.84 mmol) and Br2 (454 mg, 2.84 mmol) in one portion under N2. The mixture was stirred at room temperature for 6 h. The reaction mixture was washed with saturated aqueous Na2SO3 (200 mL) and extracted with DCM (30 mL×2). The combined organic layers were washed with brine (20 mL×2), dried with anhydrous Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (PE/EA=3/1) to give the title compound (300 mg, 73%) as a yellow solid. 1H NMR (CDCl3, 400 MHz) δ 7.90 (d, J=1.6 Hz, 1H), 7.64 (d, J=1.6 Hz, 1H), 5.20-5.14 (m, 1H), 3.53-3.47 (m, 1H), 3.01-2.95 (m, 1H), 3.04 (s, 3H), 1.56 (d, J=6.4 Hz, 3H). LCMS: 291.0 (M+1)+; 293.0.
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