To a solution of the product from Step 1 (3.5 mmol) in 15 mL of THF at -0° C. was added triphenylphosphine (921 mg), followed by diethylazodicarboxylate (0.55 mL) and diphenylphosphoryl azide (0.75 mL). The solution was allowed to warm to room temperature overnight. After 48 hours, the reaction was poured into ethyl acetate and sat. aq. NaHCO3 solution, then washed with brine, dried (Na2SO4) and concentrated in vacuo to provide the crude product. Purification by chromatography on silica gel (50% CH2Cl2 /hexane) provided 360 mg of the titled compound.
