The toluene solution of chiral alcohol XI prepared above (36.19 mmol, assumed 100% conversion) was diluted with an additional 100 mL of toluene, and cooled in an ice-water bath, then treated with diphenylphosphoryl azide (13.64 g, 49.57 mmol). To this solution was added 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 8.0 g, 52.46 mmol), dropwise over 20 minutes at such a rate so as to maintain the internal temperature between 1-4° C. The reaction mixture was then stirred at an internal temperature of 1-2° C. for an additional 45 minutes, then warmed to room temperature (with a water bath), and stirred at room temperature overnight. After 20 hours, the reaction mixture was treated with ice-cold water (50 mL), while maintaining the internal temperature below 24° C. The organic layer was separated and washed with 1 M aqueous citric acid solution (50 mL), saturated aqueous sodium bicarbonate (50 mL), and water (50 mL). The resulting organic phase was then concentrated under vacuum at 20 mmHg/26° C., to provide 15 g of an oil, which was used in the next step without further purification.
