[CH3:1][O:2][C:3]1[CH:8]=[CH:7][C:6]([S:9]([CH:12]([CH3:14])[CH3:13])(=[O:11])=[O:10])=[CH:5][CH:4]=1.P(Cl)(Cl)(Cl)(Cl)Cl.[Cl:21][S:22](O)(=[O:24])=[O:23]>ClCCl>[CH3:1][O:2][C:3]1[CH:4]=[CH:5][C:6]([S:9]([CH:12]([CH3:14])[CH3:13])(=[O:11])=[O:10])=[CH:7][C:8]=1[S:22]([Cl:21])(=[O:24])=[O:23]To a solution of crude 1-methoxy-4-(propane-2-sulfonyl)benzene (8 mmol) in dry dichloromethane (20 mL), chlorosulfonic acid (1 mL) was added dropwise at 0° C. The reaction mixture was warmed to room temperature followed by the addition of PCl5 (0.5 g). The resulting reaction mixture was refluxed for 1 h. After cooling to room temperature, the reaction mixture was poured into ice water (50 mL) with vigorous stirring. The aqueous layer was then extracted with EtOAc (2×75 mL). The combined organic extracts was washed with saturated sodium chloride aqueous solution (2×50 mL), dried over anhydrous sodium sulfate, and concentrated under vacuum. The residue was purified by flash column chromatography eluting with hexanes/EtOAc (3:1) to give 1.25 g of 2-methoxy-5-(propane-2-sulfonyl)benzenesulfonyl chloride. 1H NMR (CDCl3, 400 MHz): δ 1.31 (d, 1H), 3.23 (m, 1H), 4.18 (s, 3H), 7.30 (d, 1H), 8.18 (dd, 1H). 8.46 (d, H) ppm.
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