General procedure for the synthesis of 6-bromo-3H-oxazolo[4,5-b]pyridin-2-one from 2,3-dihydropyrido[2,3-d][1,3]oxazol-2-one: In a dry 3000 mL single-necked round-bottomed flask, 1500 mL of acetonitrile and 360 mL of acetic acid were sequentially added, followed by 42.8 g of 2,3-dihydropyrido[2,3-d][1,3 ]oxazol-2-one. After the ingredients were completely dissolved, 64.2 g of N-bromosuccinimide (NBS) was added in batches and the reaction mixture was stirred at room temperature for 14 hours. The progress of the reaction was monitored by thin layer chromatography (TLC) and gas chromatography (GC), and after confirming the completion of the reaction, 20 mL of sodium persulfate (24 g) was added. At the end of the reaction, the solvent was removed by rotary evaporator and 300 mL of water was added to the residue and extracted twice with 300 mL of ether. The organic phases were combined and washed sequentially with 180 mL of 2 N sodium hydroxide solution and 300 mL of saturated saline. The organic phase was dried with anhydrous sodium sulfate overnight. The drier was removed by filtration and the filtrate was concentrated under reduced pressure to give 64.1 g of the crude product 6-bromo-3H-oxazolo[4,5-b]pyridin-2-one. The crude product was recrystallized by mixed solvent recrystallization of dichloromethane and ethyl acetate to give 59.9 g of pure product in 89% yield and 98% purity (GC assay). The melting point of the product was measured to be 231°C to 234°C (literature value: 232°C to 233°C).
![2,3-Dihydropyrido[2,3-d][1,3]oxazol-2-one](/CAS/GIF/60832-72-6.gif)
![6-BROMO-3H-OXAZOLO[4,5-B]PYRIDIN-2-ONE](/CAS/GIF/21594-52-5.gif)