Preparative Example 2-1 Synthesis of methyl 4,5-dibromofuran-2-carboxylate Procedure: a catalytic amount of oxalyl chloride (210 μL, 2.4 mmol) was added slowly and dropwise to a mixed solution of dichloromethane (5.0 mL) and N,N-dimethylformamide containing 4,5-dibromofuran-2-carboxylic acid (500 mg, 1.9 mmol) at 0 °C. The reaction mixture was stirred at room temperature for 1 hour. Subsequently, the solvent was removed by distillation under reduced pressure, triethylamine (340 μL, 2.4 mmol) and methanol (4.0 mL) were added, and stirring was continued for 1 h at room temperature. Upon completion of the reaction, the solvent was again removed by distillation under reduced pressure, saturated aqueous sodium bicarbonate was added, and extraction was carried out with ethyl acetate. The organic layer was washed sequentially with water and saturated brine and dried with anhydrous sodium sulfate. Finally, the solvent was removed by reduced pressure distillation to afford the target product methyl 4,5-dibromofuran-2-carboxylate (460 mg, 88% yield). The product was characterized by 1H-NMR (400 MHz, CDCl3) with chemical shifts δ (ppm) of 3.90 (s, 3H), 7.18 (s, 1H).
