24036-52-0

73183-34-3

943994-02-3

6-Bromo-2H-1,4-benzoxazin-3(4H)-one (2.3 g, 10 mmol) and pinacol ester of bis(boronic acid) (3.05 g, 12 mmol) were used as raw materials, which were dissolved in dioxane (20 mL), and then potassium acetate (2 g, 20 mmol) and Pd(dppf)Cl2 (730 mg, 1 mmol) were added sequentially. The reaction system was purged with nitrogen and the reaction was stirred at 90 °C overnight. After completion of the reaction, the mixture was diluted with ethyl acetate (200 mL) and filtered. The organic phase was sequentially washed with brine, dried over anhydrous sodium sulfate and concentrated under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography (eluent: petroleum ether/ethyl acetate=3:1) to afford 3-oxo-2H,4H-benzo[b][1,4]oxazine-6-boronic acid pinacol ester (1.9 g, 69% yield).