[Br:1][CH2:2][C@@H:3]1[CH2:7][O:6][C@@H:5](OC(C)C)[O:4]1.[P:12]([O:21]C(C)C)([O:17][CH:18]([CH3:20])[CH3:19])[O:13][CH:14]([CH3:16])[CH3:15].P(Cl)(Cl)Cl>[Cl-].[Zn+2].[Cl-]>[Br:1][CH2:2][C@@H:3]1[CH2:7][O:6][C@@H:5]([P:12]([O:17][CH:18]([CH3:20])[CH3:19])([O:13][CH:14]([CH3:16])[CH3:15])=[O:21])[O:4]1To the mixture of cis and trans 4-(bromomethyl)-2-isopropoxy-1,3-dioxolane (example 2) (6.13 g, 9:1 of isopropoxy:methoxy) was added triisopropyl phosphite (4.43 mL, 18.0 mmol, 0.66 eq.), phosphorus trichloride (0.784 mL, 8.99 mmol, 0.33 eq.) and zinc chloride (few milligrams) at 0° C. The mixture was stirred at 0° C. for 2 hr and at room temperature for 10 hr. The crude mixture of cis and trans isomers in a 2:5 ratio was purified by flash chromatography on silica gel using dichloromethane:ethyl acetate 4:1 as eluant to give the cis isomer (0.242 g), a mixture of cis and trans isomers (3.13 g) and the trans isomer (3.15 g) for a total yield of 72%. Several chromatographic purifications were performed to obtain the cis and trans isomers in pure form.
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