337463-88-4

Compound 3.1 (2.7 g, 8.85 mmol) was used as raw material and mixed with iron powder (2.48 g, 44.3 mmol) in acetic acid (40 mL). The reaction mixture was stirred at 100 °C for 2 hours. After the reaction was completed, it was cooled to room temperature and the reaction solution was filtered through diatomaceous earth. Water (100 mL) was added to the filtrate and extracted with dichloromethane (20 mL x 3). The organic phases were combined, dried over anhydrous sodium sulfate and concentrated. The residue was purified by silica gel column chromatography (petroleum ether/ethyl acetate= 3/1) to afford the target product, 6-bromo-2H-pyrido[3,2-b][1,4]oxazin-3(4H)-one (Compound 3.2, 1.9 g, Yield: 95%) as a pale yellow liquid.

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