Chloroacetyl chloride → 7-hydroxy-3,4-dihydro-2H-1,4-benzoxazin-3-one

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To a solution of 4-aminobenzene-1,3-diol (2.5 g, 20 mmol) in tetrahydrofuran (30 mL), sodium bicarbonate (2.52 g, 30 mmol) was added and stirred for 10 minutes. Then 2-chloroacetyl chloride (1.6 mL, 20 mmol) was added to the above mixture. The resulting reaction mixture was stirred at ambient temperature for 18 hours. A precipitate formed and removed by filtration. The filtrate was concentrated to give the oil residue. The resulting residue was treated with 10% NaOH aqueous solution for 30 minutes. The aqueous layer was acidified with 1N hydrogen chloric acid and extracted with ethyl acetate, washed with brine and water. The organic layer was separated, dried (Na2SO4) and concentrated. The crude material was purified by silica gel chromatography using a 90:10 mixture of hexane and ethyl acetate as eluent to afford the title product as a white solid (1.4 g, 42% yield). 1H NMR (400 MHz, d6-DMSO) δ: 10.42 (1H, s), 9.23 (1H, s), 6.69 (1H, m), 6.35 (2H, m), 4.47 (2H, s). MS m/z: 164.01 [M+H]+.

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