Synthesis
PdCl2 (dppf) (756 mg, 0.88 mmol) and KOAc (2.587 g, 26.4 mmol) were added to degassed 1,4-dioxane (60 mL) under nitrogen protection using 5-bromothiophene-2-carboxaldehyde (1.68 g, 8.8 mmol) and pinacol ester of bis(boronic acid) (3.4 g, 13.2 mmol). The reaction mixture was stirred at 80 °C for 6 hours. Upon completion of the reaction, the reaction was quenched by the addition of water and extracted with dichloromethane. The organic phase was dried with anhydrous Na2SO4 and concentrated under reduced pressure to remove the solvent. The crude product was purified by silica gel column chromatography (eluent: petroleum ether/dichloromethane=1/3) to afford the target compound 5-formyl-2-thiopheneboronic acid pinacol ester (1.86 g, 88.9% yield) as a yellow solid. The melting point of the product was 73 °C. Mass spectra (EI) showed the molecular ion peak m/z=238 (M+).1H NMR (CDCl3, 400 MHz) δ/ppm: 9.92 (s, 1H), 7.73 (d, 1H), 7.43 (d, 1H), 1.34 (s, 12H).
References
[1] Tetrahedron, 2012, vol. 68, # 44, p. 9113 - 9118
