[CH2:1]([O:3][CH:4]([O:15][CH2:16][CH3:17])[CH2:5][CH:6]([C:10]([O:12][CH2:13][CH3:14])=[O:11])[C:7]([O-:9])=O)[CH3:2].[K+].[Cl-].[Mg+2].[Cl-].C(N(CC)CC)C.[CH3:29][O:30][CH2:31]C(Cl)=O.S([O-])(O)(=O)=O.[K+]>C(OCC)(=O)C>[CH2:16]([O:15][CH:4]([O:3][CH2:1][CH3:2])[CH2:5][CH:6]([C:7](=[O:9])[CH2:29][O:30][CH3:31])[C:10]([O:12][CH2:13][CH3:14])=[O:11])[CH3:17]
To 11 L of dehydrated ethyl acetate solution containing 2.45 Kg (8.54 mol) of potassium 4,4-diethoxy-2-ethoxycarbonylbutanoate obtained in Reference example 15-(a) were added 1.63 Kg (17.1 mol) of anhydrous magnesium chloride and 3.12 L (22.2 mol) of triethylamine under argon atmosphere, and the mixture was stirred at 75° C. for 1 hour. Then, 974 g (8.97 mol) of methoxyacetyl chloride was added dropwise to the mixture at 15° C. or lower under cooling in ice-bath, and the mixture was further stirred at room temperature for 6 hours. After completion of the reaction, the reaction mixture was poured into 10 L of ice-water, neutralized with 20% aqueous potassium hydrogen sulfate solution and extracted with ethyl acetate. The organic layer after separation was washed with a saturated aqueous solution of sodium chloride, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to obtain 1.68 kg (purity: 66.4%) of the title compound as a yellowish oil. (Yield: 47.3%)
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