3-Chloroperoxybenzoic acid (77%; 8.05 g, 36 mmol) was added portionwise to a solution of methyl 3-{[7-(4-fluorophenyl)quinolin-3-yl]thio}propanoate (5.57 g, 16 mmol) in dichloromethane (150 mL). The resulting mixture was stirred at room temperature under nitrogen for 1 hour. Calcium hydroxide (5.1 g, 69 mmol) was added portionwise and the resulting slurry stirred for 30 minutes. The mixture was filtered and the filter cake washed thoroughly with dichloromethane. The filtrate was evaporated and the residue purified by flash chromatography, eluting with 10-15% ethyl acetate/isohexane, to give methyl 3-{[7-(4-fluorophenyl)quinolin-3-yl]sulfonyl}propanoate as a white solid (5.09 g, 84%). 1H NMR (500 MHz, CDCl3) δ 9.30 (1H, d, J 2.2 Hz), 8.77 (1H, d, J 2.0 Hz), 8.39 (1H, s), 8.06 (1H, d, J 8.5 Hz), 7.95 (1H, dd, J 1.7, 8.5 Hz), 7.77-7.73 (2H, m), 7.25-7.21 (2H, m), 3.61 (3H, s), 3.59 (2H, t, J 7.5 Hz), 2.86 (2H, t, J 7.5 Hz); m/z (ES+) 374 [MH+].
