[CH3:1][C:2]1([CH3:21])[N:6]([C:7]([O:9][CH2:10][C:11]2[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=2)=[O:8])[C@@H:5]([C:17]([O:19]C)=O)[CH2:4][O:3]1.[Cl-].[NH4+].[CH2:24](OCC)[CH3:25]>CC(C)[O-].CC(C)[O-].CC(C)[O-].CC(C)[O-].[Ti+4]>[OH:19][C:17]1([C@H:5]2[CH2:4][O:3][C:2]([CH3:1])([CH3:21])[N:6]2[C:7]([O:9][CH2:10][C:11]2[CH:12]=[CH:13][CH:14]=[CH:15][CH:16]=2)=[O:8])[CH2:25][CH2:24]1To a solution of 3-benzyl 4-methyl(4R)-2,2-dimethyl-1,3-oxazolidine-3,4-dicarboxylate (6.66 g) and titanium tetraisopropoxide (3.33 mL) in diethyl ether (200 mL) was added dropwise 3M ethyl magnesium bromide diethyl ether solution (18.9 mL) over 20 min under ice-cooling. The reaction mixture was stirred at room temperature overnight, and to the reaction mixture was added saturated aqueous ammonium chloride solution. The precipitated solid was removed by filtration. The filtrate was extracted with ethyl acetate, and the organic layer was separated, washed with saturated brine, dried over magnesium sulfate, and concentrated. The residue was purified by silica gel column chromatography (ethyl acetate/hexane) to give the title compound (2.52 g).
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