2-Chlorobenzenesulfonyl chloride → 2-Chlorobenzene-1-sulfonic acid

3-Benzyloxyphenol (2.97 g, 15 mmol), as prepared in the preceding step, in methylene chloride (50 mL) was treated with diisopropylethylamine (2 mL) and 2-chlorobenzenesulfonyl chloride (3.27 g, 15.5 mmol) at 0° C. for 2 h and at room temperature for 2 h. The reaction mixture was diluted with 200 mL of methylene chloride, washed sequentially with saturated NaHCO3 (2×50 mL) and brine (2×50 mL), and dried over Na2SO4. The solvent was removed in vacuo and the residue was purified by flash column chromatography (1:1 hexane:methylene chloride) to give the title compound as a colorless liquid (5.35 g, 95%). 1H-NMR (300 MHz, CDCl3) δ 4.97 (s, 2H), 6.71 (dd, 1H, J=1.1, 4.1 Hz), 6.78 (t, 1H, J=2.3 Hz), 6.85 (dd, 1H, J=1.1,4.1 Hz), 7.17 (t, 1H, J=8.3 Hz), 7.37 (m, 5H), 7.58 (m, 2H), and 7.91 (dd, 1H, J=1.1, 4.1 Hz).