[CH2:1]([O:3][C:4](=[O:22])[CH:5]([N:7]1[C:12]2[CH:13]=[C:14]([N+:18]([O-])=O)[C:15]([F:17])=[CH:16][C:11]=2[O:10][CH2:9][C:8]1=[S:21])[CH3:6])[CH3:2].[Cl-].[NH4+]>CO.C1COCC1.[Zn]>[CH2:1]([O:3][C:4](=[O:22])[CH:5]([N:7]1[C:12]2[CH:13]=[C:14]([NH2:18])[C:15]([F:17])=[CH:16][C:11]=2[O:10][CH2:9][C:8]1=[S:21])[CH3:6])[CH3:2]To a solution of 2-(7-fluoro-6-nitro-3-thioxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester (3.05 g, 9.29 mmol) in MeOH (45 ml) and THF (45 mL) was added zinc powder (6.07 g, 92.9 mmol) and ammonium chloride (4.97 g, 92.9 mmol). The reaction mixture was heated to reflux for 3 h then cooled to ambient temperature. The reaction mixture was filtered through a pad of Celite® and the filtrate was concentrated in vacuo. The residue was purified by column on silica gel (eluting with 0-30% EtOAc in petroleum ether to give 2-(6-amino-7-fluoro-3-thioxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester (0.458 g, 16%). 1H NMR (DMSO-d6, 400 MHz): δ 6.89 (d, J=11.2 Hz, 1H), 6.61 (d, J=8.4 Hz, 1H), 6.21 (brs, 1H), 5.04 (brs, 2H), 4.78 (s, 2H), 3.99-4.03 (m, 2H), 1.62 (d, J=7.2 Hz, 3H), 1.07 (t, J=7.2 Hz, 3H).
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