[CH3:1][O:2][C:3]([CH:5]=[CH:6][C:7]1[CH:12]=[C:11]([O:13][CH3:14])[CH:10]=[CH:9][C:8]=1[NH:15][C:16](=[O:23])[CH2:17][C:18]([O:20][CH2:21]C)=[O:19])=[O:4].C[O-].[Na+].[Cl-].[NH4+]>CO>[CH3:14][O:13][C:11]1[CH:12]=[C:7]2[C:8](=[CH:9][CH:10]=1)[NH:15][C:16](=[O:23])[CH:17]([C:18]([O:20][CH3:21])=[O:19])[CH:6]2[CH2:5][C:3]([O:2][CH3:1])=[O:4]To a stirred, chilled (0° C.) suspension of crude 3-[[2-[(methoxycarbonyl)ethenyl]-4-methoxyphenyl]amino]-3oxopropanoic acid, ethyl ester from step 3 in 700 ml of methanol was added, dropwise, a solution of 66.5 g of sodium methoxide (25% in methanol) in 250 ml of methanol. The resulting mixture was heated to reflux over 0.75 hour, cooled to 0° C., and poured into a cold saturated ammonium chloride solution. The aqueous layer was extracted with dichloromethane and the combined organic layers were washed with 10% hydrochloric acid solution and saturated sodium chloride solution, dried over anhydrous magnesium sulfate, filtered and concentrated to afford 1,2,3,4-tetrahydro-6-methoxy-3-(methoxycarbonyl)-2-oxo-4-quinoline acetic acid, methyl ester.
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