[C:1]([C:4]1[CH:5]=[CH:6][C:7]2[O:12][CH2:11][C:10](=[O:13])[NH:9][C:8]=2[CH:14]=1)(=[O:3])[CH3:2].C([O-])([O-])=O.[K+].[K+].[CH2:21]([O:23][C:24](=[O:28])[CH:25](Br)[CH3:26])[CH3:22]>CC(C)=O>[CH2:21]([O:23][C:24](=[O:28])[CH:25]([N:9]1[C:8]2[CH:14]=[C:4]([C:1](=[O:3])[CH3:2])[CH:5]=[CH:6][C:7]=2[O:12][CH2:11][C:10]1=[O:13])[CH3:26])[CH3:22]To a mixture of 6-acetyl-4H-benzo[1,4]oxazin-3-one (Alfa, 5 g, 26.18 mmol) and K2CO3 (5.4 g, 39.2 mmol) in acetone (50 mL) was added 2-bromo-propionic acid ethyl ester (14.14 g, 78.54 mmol) and the mixture was heated to reflux for 3 h. The reaction mixture was cooled to ambient temperature and evaporated in vacuo. The residue was purified by column chromatography on silica gel (eluting with 5% EtOAc in petroleum ether) to give 2-(6-acetyl-3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester as a white solid (6.14 g, 86%). 1H NMR (CDCl3, 400 MHz): δ 7.62 (dd, J=2 Hz, J=8.4 Hz, 1H), 7.52 (d, J=2 Hz, 1H), 7.07 (d, J=8.4 Hz, 1H), 5.29 (t, J=6.8 Hz, 1H), 4.68 (d, J=15.6 Hz, 2H), 4.22 (q, J=7.2 Hz, 2H), 2.56 (s, 3H), 1.65 (d, J=6.8 Hz, 3H), 1.22 (t, J=7.2 Hz, 3H).
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