Under argon atmosphere, a solution of ethyl 5-(5-bromothiophen-2-yl)-5-oxovalerate (10.09 g), 4-methylphenyl borate (5.39 g) and potassium carbonate (9.14 g) in toluene-ethanol-water (320-32-32 ml) was stirred at room temperature for 1 hour. To the reaction mixture was added tetrakistriphenylphosphinepalladium (1.14 g), and the mixture was refluxed for 8 hours and cooled to room temperature. The organic layer was washed with saturated sodium chloride solution, dried with magnesium sulfate and concentrated under reduced pressure. The residue was separated and purified with column chromatography (ethyl acetate/hexane=1:4→1:3→1:2→1:1) to give ethyl 5-[5-(4-methylphenyl)thiophen-2-yl]-5-oxovalerate (10.23 g) as colorless crystals.
