[H-].[Na+].[C:3]([O:11][CH2:12][CH3:13])(=[O:10])[CH2:4][C:5]([O:7]CC)=O.[Cl:14][C:15]1[C:20](=O)[O:19][C:18](=O)[N:17](C)[C:16]=1[CH3:24]>O1CCCC1>[Cl:14][C:15]1[C:20]([OH:19])=[C:4]([C:3]([O:11][CH2:12][CH3:13])=[O:10])[C:5](=[O:7])[N:17]([CH3:18])[C:16]=1[CH3:24]To 0.43 g of sodium hydride (60%) was added 35 ml of tetrahydrofuran, 2.5 ml of a solution of 1.76 g diethyl malonate in tetrahydrofuran was further added under ice cooling, and the mixture was stirred at room temperature for 1 hour. To the mixture was added 1.74 g of 5-chloro-3,4-dimethyl-2H-1,3-oxazine-2,6(3H)-dione, and this was stirred for 3.5 hours under heat refluxing condition. The reaction mixture was concentrated under reduced pressure. To the residue, 20 ml of water and 15 ml of 1 mol/L hydrochloric acid were sequentially added, followed by extraction with 85 ml of chloroform twice. The organic layer was dried with magnesium sulfate, filtered, and concentrated. The residue was washed with n-hexane to obtain 1.52 g of ethyl 5-chloro-1.6-dimethyl-4-hydroxy-2-oxo-1,2-dihydropyridine-3-carboxylate represented by the formula:
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