To a mixture of 1-Boc-6-methoxyindole-2-boronic acid prepared in step B above (0.36 g, 1.25 mmol), 2-(4-iodophenyl)isothiazolidine-1,1-dioxide (0.32 g, 1.0 mmol) and PdCl2(dppf) (0.037 g, 0.05 mmol) in DMF (4.0 mL), is added aqueous K2CO3 solution (1.5 mL, 2.0 M, 3.0 mmol). The mixture is stirred at room temperature overnight and then poured into ice-water (100 mL). The precipitate is collected and washed with water and purified by flash column chromatography (silica gel, DCM/EtOAc, 9/1) to furnish 1-Boc-2-[4-(1,1-dioxidoisothiazolidin-2-yl)phenyl]-6-methoxy-1H-indole (0.43 g, 98%).
