General procedure for the synthesis of p-bromobenzyl sulfonyl chloride from 4-bromo-α-toluene thioacetic acid: N-chlorosuccinimide (NCS, 3.3 g, 24.6 mmol) was added batchwise to a solution of acetonitrile (30 mL) containing 2 M HCl (1.547 mL) at 0 °C. The reaction mixture was stirred at 0 °C for 5 min. Subsequently, a solution of 4-bromophenylmethanesulfonyl chloride (1.5 g, 6.15 mmol) in acetonitrile (3 mL) was added dropwise to the mixture at the same temperature, with the dropwise addition time being controlled at 1 min. After continuing to stir the reaction mixture for 10 minutes, anhydrous sodium sulfate (about 5 g) was added and the solid was removed by filtration. The filtrate was concentrated and the resulting residue was purified by silica gel column chromatography (petroleum ether/ethyl acetate = 10/1) to afford p-bromobenzylsulfonyl chloride (1.2 g, 73% yield) as a white solid.1H NMR (300 MHz, CDCl3): δ = 7.62 (d, J = 8.4 Hz, 2H), 7.37 (d, J = 8.4 Hz, 2H), 4.83 (s 2H).
