To a stirred solution of Ethyl 5-(4-chlorophenyl)-4-methyl-3-(4-sulfamoylphenyl)thiophene-2-carboxylate (Compound 1b, 4.0 g, 9.17 mmol) in chlorobenzene (50 ml) were added NBS (1.77 g, 10.09 mmol) and AIBN (1.65 g, 10.09 mmol) at 25° C. The reaction mixture was then stirred at 85° C. for 4 hr. The progress of the reaction was monitored by TLC. The reaction mixture was then cooled to room temperature and was quenched in aqueous sodium chloride solution (50 ml). The mixture so obtained was then extracted with Ethyl acetate (2×50 ml). The organic layer was washed with brine (1×50 ml) and dried over sodium sulfate and concentrated under reduced pressure to obtain crude product (4.0 g). The crude product was then purified by column chromatography over silica gel (100-200 mesh) using 40% ethyl acetate in hexanes as an eluent to obtain the title compound (2.8 g, 59.32%).
