Reaction Steps
To 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. ##STR21## 1H NMR (300 MHz, CDCl3) δ: 1.36 (d, 12H, J=6.1 Hz, CH(CH3)2), 3.36 (dd, 1H, J=8.0 Hz, 10.2 Hz, CHAHB Br), 3.48 (dd, 1H, J=4.4 Hz, 10.5 Hz, CHAHBBr), 3.91 (dd, 1H, J=4.6 Hz, 8.0 Hz, H-5a), 4.39 (dd, 1H, J=6.3 Hz, 8.3 Hz, H-5b), 4.63 (m, 1H, H-4), 4.80 (m, 2H, CH(CH3)2), 5.32 (d, 1H, 2JHP =30.4 Hz, H-2) ##STR22## 1H NMR (300 MHz, CDCl3) δ: 1.37 (d, 12H, J=6.1 Hz, CH(CH3)2), 3.50 (dd, 1H, J=8.9 Hz, 9.9 Hz, CHAHBBr), 3.58 (dd, 1H, J=5.3 Hz, 9.9 Hz, CHAHBBr), 4.14 (d, 2H, J=6.0 Hz, H-5), 4.41 (m, 1H, H-4), 4.80 (m, 2H, CH(CH3)2) and 5.18 (d, 1H, 2JHP =29.6 Hz, H-2).
