Triphenylphosphine (16.2 g, 61.9 mmol) and diisopropylazodicorboxylate (12.5 g, 61.8 mmol) were added to a solution of 2-oxo-2-{[4-(pentafluoro-λ6-sulfanyl)phenyl]amino}ethyl acetate (Intermediate 42, 8.50 g, 26.2 mmol) in THF (100 mL) at 0° C. and the mixture was stirred for 30 min. Trimethylsilyl azide (7.11 g, 61.7 mmol) was added dropwise at room temperature and the mixture was heated to reflux for 4 hr. The reaction mixture was diluted with EtOAc and washed with ice-water and brine solution, dried over anhydrous Na2SO4, and concentrated under reduced pressure to give the crude product (5.32 g). This was used for the next step without further purification.
