To a solution of triphenylphosphine (101 g, 385 mmol, 2 eq) in THF (1.5 L) was added diisopropylazodicarboxylate (76 mL, 386 mmol, 2 eq) at 0° C. The mixture was stirred at 0° C. for 1 hr and was followed by the addition of a solution of methyl 3-t-butyldiphenylsilyloxy-2-hydroxypropionate (example 39) (68.89 g, 192 mmol) and thioacetic acid (27.6 mL, 386 mmol, 2 eq.) in THF, to the same temperature. The mixture was stirred at 0° C. for 1 hr and at room temperature for 18 hr. The solution was concentrated to dryness and the solid was washed with hexane (5×300 mL). The organic solution was filtered and evaporated under reduced pressure. The crude material was purified by flash chromatography with a mixture of hexane and ethyl acetate (95:5) to give the pure compound (49.3 g) in 62% yield.
