Dichloromethane → 2,5-Dichloro-4-methylthiophene-3-sulfonyl chloride

To a cooled (10° C.) solution of 3-methylthiophene (5 g, 50 mmol) in dichloromethane (15 mL) was added a solution of sulfuryl chloride (8.6 mL) in dichloromethane (5 mL). The reaction mixture was maintained at 10° C. for 30 minutes, then at ambient temperature for 16 hours. The reaction was concentrated and redissolved in dichloromethane (30 mL) and cooled to −10° C. To the cooled solution was added chlorosulfonic acid (2 mL, 100 mmol). The reaction was maintained at −10° C. for 30 minutes, then at ambient temperature for 16 hours, at which time it was poured into ice water (50 mL) and extracted with dichloromethane (50 mL). The organic layer was dried (Mg2SO4) and concentrated to furnish a brown oil (3.3 g, 25%).