[C:1]1(=[O:17])[N:5]([CH2:6][CH2:7][O:8][CH2:9][CH2:10][OH:11])[C:4](=[O:12])[C:3]2=[CH:13][CH:14]=[CH:15][CH:16]=[C:2]12.[H-].[Na+].Cl[CH2:21][C:22](=[O:29])[CH2:23][C:24]([O:26][CH2:27][CH3:28])=[O:25].Cl>O1CCCC1>[CH2:27]([O:26][C:24](=[O:25])[CH2:23][C:22](=[O:29])[CH2:21][O:11][CH2:10][CH2:9][O:8][CH2:7][CH2:6][N:5]1[C:4](=[O:12])[C:3]2=[CH:13][CH:14]=[CH:15][CH:16]=[C:2]2[C:1]1=[O:17])[CH3:28]77 g of 2-[2-(phthalimido)ethoxy]ethanol are added, in portions, to a suspension of 31 g of sodium hydride in 400 ml of tetrahydrofuran, while maintaining the temperature in the vicinity of 25° C. The mixture is stirred for one hour and 53.6 g of ethyl chloroacetoacetate are then added, while maintaining the temperature of the mixture at -20° C. The mixture is allowed to stand overnight at ambient temperature and then hydrolyzed with 1 l of 1N hydrochloric acid. Decantation, followed by extraction with ether are carried out and the organic phases are combined. The combined organic phase is washed with water and then dried over magnesium sulfate. It is concentrated and the residue thereby obtained (110 g) is purified by silica column chromatography using a dichloromethane:acetone (95:5) mixture as the eluting solvent. After removing the eluting solvent, 35.7 g of 10-phthalimido-3-oxo-5,8-dioxadecanoic acid ethyl ester are obtained.
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