The general procedure for the synthesis of 3-methylsulfonylbenzenesulfonyl chloride from phenylmethylsulfone was as follows: the intermediate 3-methylsulfonylbenzene-1-sulfonyl chloride was synthesized with reference to the method reported by Park et al. in J. Med. Chem. 2007, 51(21):6902-6915. The operation was as follows: methylsulfonylbenzene (110 g, 0.7 mol) was mixed with chlorosulfonic acid (450 mL, 6.7 mol), and the reaction was heated at 90 °C for 18 hours. Upon completion of the reaction, the reaction mixture was cooled to about 21 °C and subsequently slowly poured onto crushed ice. The resulting slurry was extracted twice with EtOAc (2 L each). The organic phases were combined, washed with brine (50 mL) and subsequently dried over sodium sulfate, filtered and concentrated under reduced pressure to give the intermediate sulfonyl chloride (125 g, 75% yield) as an off-white solid. The product was characterized by 1H NMR (400 MHz, CDCl3) with the following chemical shifts: δ 8.61 (1H, t, J = 1.7 Hz), 8.35-8.31 (2H, m), 7.90 (1H, t, J = 7.9 Hz), 3.15 (3H, s).
