A solvent mixture (DME/H2O/Toluene/EtOH = 10:1:6:7, 7 mL) of 5-bromo-2-methoxypyrimidine (800 mg, 4.26 mmol) and potassium acetate (1.25 g, 12.77 mmol) was added to the reaction vial. Pd(dppf)Cl2-DCM (700 mg, 0.85 mmol) and bis(pinacolato)diboron (2.44 g, 9.6 mmol) were subsequently added. The reaction mixture was degassed and replaced three times with nitrogen before the reaction was stirred at 85 °C overnight. The reaction progress was monitored by TLC and after confirming the completion of the reaction, the reaction mixture was cooled to room temperature. The mixture was diluted with water (10 mL) and extracted with ethyl acetate (30 mL × 3). The organic phases were combined, dried with anhydrous Na2SO4, filtered and concentrated. Purification by silica gel column chromatography (eluent ratio PE:EA = 5:1) afforded the target product 2-methoxypyrimidine-5-boronic acid pinacol ester (24-4) as a yellow solid (1.0 g, 98% yield).
