4-(Chlorosulfonyl)benzoic acid → Benzoic Acid

To a stirred solution of compound 757-A (4.99 g, 25.0 mmol) in pyridine (50 mL) and methylene chloride (25 mL), cooled on an ice bath, was added 4-(chlorosulfonyl)benzoic acid (5.52 g, 25.0 mmol), portion-wise, for 4 min, and the reaction was allowed to stir at ambient temperature for 4 days. The reaction mixture was concentrated under reduced pressure, the residue stirred with 1N HCl (100 mL), the resulting solid filtered, washed with 1N HCl and air dried. The crude product was triturated with MeOH (15 mL), filtered, rinsed with MeOH (2×5 mL) and air-dried to afford crude benzoic acid (not shown). The benzoic acid was suspended in MeOH (100 mL), treated with concentrated H2SO4 (0.1 mL) and the reaction mixture refluxed for 5 days. The reaction mixture was cooled, the solvent evaporated under reduced pressure, and the residue was triturated with MeOH (15 mL), filtered, washed with methanol (2×5 mL) and once with another portion of methanol (10 mL). The solid was dried to afford 6.31 g of compound 398-A as a tan-yellow powder. 1H-NMR (DMSO-d6) δ: 2.02 (s, 3H), 3.89 (s, 3H), 7.40-7.29 (m, 2H), 7.67-7.61 (m, 1H), 7.83-7.77 (m, 1H), 7.89 (d, 2H), 8.14 (d, 2H), 10.66 (s, 1H); MS: m/z 360.2 (M-H+).