[CH2:1]([N:3]1[C:8]2[CH:9]=[CH:10][C:11]([O:15][CH3:16])=[C:12]([O:13][CH3:14])[C:7]=2C(=O)O[C:4]1=O)[CH3:2].[CH2:19]([O:21][C:22](=[O:26])/[CH:23]=[CH:24]\[O-:25])[CH3:20].[Na]>CN(C)C=O>[CH2:1]([N:3]1[C:8]2[C:7](=[C:12]([O:13][CH3:14])[C:11]([O:15][CH3:16])=[CH:10][CH:9]=2)[C:24](=[O:25])[C:23]([C:22]([O:21][CH2:19][CH3:20])=[O:26])=[CH:4]1)[CH3:2]Under N2, 1-ethyl-5,6-dimethoxy-1H-benzo[d][1,3]oxazine-2,4-dione (12 g, 43.5 mmol) in N,N-Dimethylformamide (DMF) (250 mL) was added to a solution of (Z)-3-ethoxy-3-oxoprop-1-en-1-olate, Sodium salt (18.01 g, 130 mmol) in N,N-Dimethylformamide (DMF) (150 mL) with stirring. The resulting solution was stirred at 110° C. for 3 h. After cooling down, the mixture was concentrated in vacuo and the orange residue was taken up in water. The aqueous solution was washed with ethyl ether (3×), acidified to pH˜2 with 6 N HCl, and extracted with DCM (4×). The organic extracts were dried over Na2SO4, filtered and concentrated. The residue was purified by normal phase silica gel chromatography (CombiFlash), eluting with MeOH/DCM (0-15%) to afford ethyl 1-ethyl-5,6-dimethoxy-4-oxo-1,4-dihydroquinoline-3-carboxylate (4.5 g, 14.74 mmol, 33.9% yield) as a brown oil that turned into a brown solid after overnight. LCMS: (M+H)+: 306.4.
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