[Br:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][C:3]=1[S:8][CH:9]([CH3:11])[CH3:10].[OH:12]OS([O-])=O.[K+].[OH2:18]>CO>[Br:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][C:3]=1[S:8]([CH:9]([CH3:11])[CH3:10])(=[O:12])=[O:18]To 21A (0.7 g, 3.0 mmol) in methanol (5 mL) was added oxone®8 (5.6 g, 9.0 mmol) in water (5 mL). The reaction was stirred at rt for 4 h. The reaction was quenched with 5% NaHSO3 and then neutralized with 1 M NaOH. The organic solvent was evaporated and the aqueous layer was extracted with dichloromethane (3×). The combined extracts were washed with brine and dried over sodium sulfate. The solvent was removed to give 0.53 g of product 21B (67% yield). 1H NMR (400 MHz, Methanol-d4) δ ppm 1.26 (d, J=6.85 Hz, 6H) 3.80-4.00 (m, 1H) 7.45-7.68 (m, 2H) 7.87 (dd, J=7.46, 1.59 Hz, 1H) 8.10 (dd, J=7.34, 2.20 Hz, 1H).
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