Chlorosulfonic acid → 4-((S)-2-Fluoro-1-methyl-ethyl)-benzenesulfonyl chloride

3.5 g of ((S)-2-fluoro-1-methyl-ethyl)-benzene (25.32 mmol) were dissolved in 80 ml of dichloromethane. At 0-5° C., 11.81 g of chlorosulfonic acid (101.31 mmol), dissolved in 20 ml of dichloromethane, were added dropwise. The reaction mixture was stirred for 30 min at room temperature and 2 h at 30° C. The solvent was evaporated. 150 ml of diethyl ether were added to the residue, washed once with 150 ml of water, and the organic layer was dried over magnesium sulfate, filtered, and the solvent evaporated under reduced pressure. The crude product was purified via silica gel chromatography with n-heptane-dichloromethane (6:4) as eluent to give 1.5 g of the title compound.