To 5-bromo-2-furancarboxaldehyde (2.43 g, 13.9 mmol) and 4-methoxycarbonylphenylboronic acid (2.50 g, 13.9 mmol) were added tris(dibenzylideneacetone)palladium(0) (192 mg, 0.2 mmol), potassium fluoride (2.42 g), and hexane solution of tri-tertiary-butylphosphine (10 wt.%. 101 mg, 0.5 mmol). The reaction mixture was heated at 65-70°C for 4 hours. After completion of the reaction, the mixture was cooled to room temperature and diluted with dichloromethane (150 mL). After stirring for 10 minutes, the mixture was filtered through diatomaceous earth and the filtrate was concentrated under reduced pressure. The residue was purified by fast silica gel chromatography using ethyl acetate-hexane (1:1) as eluent to afford the target product methyl 4-(5-formyl-2-furyl)benzoate (2.6 g, 81% yield). The 1H NMR (300 MHz, CDCl3) data of the product were as follows: δ 9.70 (s, 1H), 8.10 (d, 2H), 7.90 (d, 2H), 7.35 (d, 1H), 6.95 (d, 1H), 3.98 (s, 3H).
