To a solution of methyl-3-bromo-5-(4-chlorophenyl)-4-methylthiophene-2-carboxylate (compound 1a, 2.2 g, 6.3 mmol) in a mixture of toluene: ethanol (10:30 ml) were added 4-aminosulfonylbenzene boronic acid (prepared according to the procedure given in EP 1012142, 1.28 g, 6.3 mmol) and potassium carbonate (1.76 g, 12.7 mmol) at 25° C. in a sealed tube and nitrogen gas was bubbled through the reaction mixture for 15 minutes. To this was added tetrakis(triphenylphosphine)palladium(0) (0.370 g, 0.318 mmol) under nitrogen and the reaction mixture was heated at about 95-about 100° C. for 18 hr under stirring. The progress of the reaction was monitored by TLC. The reaction mixture was cooled to 25° C. and filtered through celite. The filtrate was concentrated under reduced pressure to obtain a crude product, which was purified by column chromatography over silica gel (100-200 mesh) using 40% ethyl acetate in hexanes as an eluent to obtain the title compound (1.3 g, 48%).
