[CH2:1]([O:3][C:4](=[O:20])[CH:5]([N:7]1[C:12]2[CH:13]=[C:14]([Br:18])[C:15]([F:17])=[CH:16][C:11]=2[O:10][CH2:9][C:8]1=O)[CH3:6])[CH3:2].COC1C=CC(P2(SP(C3C=CC(OC)=CC=3)(=S)S2)=[S:30])=CC=1>C1(C)C=CC=CC=1>[CH2:1]([O:3][C:4](=[O:20])[CH:5]([N:7]1[C:12]2[CH:13]=[C:14]([Br:18])[C:15]([F:17])=[CH:16][C:11]=2[O:10][CH2:9][C:8]1=[S:30])[CH3:6])[CH3:2]To a mixture of 2-(6-bromo-7-fluoro-3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester (43.0 g, 124 mmol) in toluene (300 mL) was added Lawesson's reagent (50.6 g, 124 mmol) and the mixture was heated at reflux overnight. The reaction mixture was cooled to ambient temperature and the solvent was removed in vacuo The residue was purified by chromatography on silica gel (eluting with 5% EtOAc in petroleum ether) to give 2-(6-bromo-7-fluoro-3-thioxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester (36.0 g, 80%). 1H NMR (CDCl3, 400 MHz): δ 7.09 (d, J=6.4 Hz, 1H), 6.88 (d, J=8.4 Hz, 1H), 6.62 (brs, 1H), 4.96 (dd, J=15.2 Hz, 2H), 4.23 (m, 2H), 1.72 (d, J=7.2 Hz, 3H), 1.21 (t, J=7.2 Hz, 3H).
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