A solution of 440 mg (0.93 mmol) of mesylate 10 in 22 mL acetone was treated with a solution of 604 mg (9.29 mmol) of sodium azide in 6.4 mL water. The mixture was warmed at reflux for 18 hours. The mixture was cooled and a solution of 600 mg of sodium azide in 6 mL water was added followed by warming at reflux for an additional 18 hours. The mixture was cooled and a solution of 1.2 g of sodium azide in 12 mL water was added followed by warming at reflux for 24 hours. The mixture was cooled and diluted with 60 mL water and extracted with ethyl acetate (3×75). The combined organic layers were extracted with 100 mL saturated NaCl solution followed by drying (Na2SO4). Concentration in vacuo afforded 358 mg (92%) of azide 11 as a white solid, mp=130.5° C.-132.5° C., sufficiently pure for use in the next step.
