Reaction Steps
To a solution of 3-t-butyldiphenylsilyloxy-2-mercaptopropanol (example 41) (12.17 g, 35.12 mmol) in toluene (600 mL) were added triethylorthoformate (6.4 mL, 38.5 mmol, 1.1 eq) and pyridinium p-toluenesulfonate (catalytic) at 90° C. The solution was strirred at 90° C. for 40 min then was quenched at room temperature with sodium bicarbonate. The aqueous phase was extracted with dichloromethane and the organic layer was washed with water, dried with magnesium sulfate and evaporated under reduced pressure. The crude product was obtained in 92% yield (12.94 g) as a 2:1 mixture and was used without further purification. To a solution of 4-(t-butyldiphenylsilyloxymethyl)-2-ethoxy-1,3-oxathiolane (12.32 g, 30.6 mmol) and triethylphosphite (3.5 mL, 20.4 mmol, 0.66 eq) in dichloromethane (50 mL) were added phosphorus trichloride (890 μL, 10.2 mmol, 0.33 eq) and zinc chloride (catalytic) at 0° C. The solution was stirred at 0° C. for 1 hr and at room temperature for 3 days. The solvent was evaporated and the crude material was purified by flash chromatography with a mixture of hexane and ethyl acetate (60:40) to give the pure compound (8.02 g) in 53% yield with a ratio of 2:1 (trans:cis). ##STR70## 1H NMR (300 MHz, CDCl3) δ: 1.06 (s, 9H, t-butyl), 1.24 (t, 3H, J=7.1 Hz, CH3), 3.5-3.9 (m, 5H, CH2, CH2O, H-4), 4.14 (m, 1H, CHAHBO), 4.22 (dd, 0.33H, J=6.9 Hz, 9.2 Hz, CHAHBO), 4.45 (d, 0.66H, J=10.0 Hz, CHAHBO), 6.17 and 6.30 (2s, 1H, H-2), 7.41 and 7.64 (m, 10H, Ar-H). ##STR71## 1H NMR (300 MHz, CDCl3) δ: 1.05 (s, 9H, t-butyl), 1.36 (m, 6H, CH3), 3.63 (m, 2H, CH2O), 3.85 (m, 0.33H, CHA HBO for cis), 4.09-4.33 (m, 4H, CH2 ; 1.33H, CH2O for trans; 1H, H-4), 4.61 (d, 0.33H, J=9.0 Hz, CHAHBO for cis), 5.21 (d, 0.33H, 2JHP =9.4 Hz, H-2 for cis), 5.27 (d, 0.66H, 2JHP =9.8 Hz, H-2 for trans), 7.41 and 7.64 (m, 10H, Ar-H).
