Diethyl Oxalate → 5-Bromo-7-fluoro-1,4-dihydroquinoxaline-2,3-dione

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The title compound was prepared using an adaptation of the method of Cheeseman (Cheeseman, G. W. H., J. Chem. Soc. 1171 (1962)). A mixture of diethyl oxalate (3.31 mL, 24.4 mmol) and 1,2-diamino-3-bromo-5-fluorobenzene (500 mg, 2.44 mmol) was heated to reflux under N2 for 5 h. The reaction mixture was dark brown. The reaction was allowed to cool to room temperature and the solid collected by vacuum filtration and rinsed with EtOH (30 mL). The brown solid was air dried for 1 hr to give 250 mg (39.6% crude yield). A portion of this solid was removed and dissolved in 1N NaOH (10 mL) and a few insoluble particles were removed by gravity filtration. The solution was treated with decolorizing carbon and the mixture was filtered through a pad of celite and the resulting solution acidified with 1N HCl. White crystals formed that were isolated by vacuum filtration and washed with water (20 mL). The crystals were dried in a drying pistol (0.05 torr, 78° C.) to yield 54.1 mg, mp 308°-310° C. (dec). 1H NMR (d6 -DMSO) δ6.2 (dd, 1H, JH6-8 =2.7, JH-F =9.3, ArH), 7.35 (dd, 1H, JH6-8 =2.4, JHF =8.4 Hz), 11.1 (br s, 1H, NH), 12.1 (brs, 1H, NH). EIHRMS calc. for C8H4BrFN2O2 : 257.9440, found 257.9455.

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