Carbon monoxide was introduced by bubbling to a mixture of 2-(4-tert-butylthiazol-2-yl)benzofuran-5-yl trifluoromethanesulfonate (6.0 g), palladium acetate (99.7 mg), 1,3-bis(diphenylphosphono)propane (183 mg, 0.44 mmol) and triethylamine (4.13 ml) in a mixed solvent of methanol (15 ml) and N,N-dimethylformamide (30 ml) at room temperature for 1 hour. The mixture was warmed to 70° C. and stirred under carbon monoxide balloon for 3 hours. The resulting mixture was filtered through celite and the residue was washed with ethyl acetate. The filtrate and washing solution was combined and evaporated under reduced pressure. The residue was purified by column chromatography on silica gel using ethyl acetate-n-hexane as eluent to give methyl 2-(4-tert-butylthiazol-2-yl)benzofuran-5-carboxylate (3.92 g) as a colorless powder.
