To a solution of 2-{[4-cyano-3-(trifluoromethyl)phenyl]amino}-2-oxoethyl acetate (Intermediate 21, 65 g) in THF (300 mL) was added triphenylphosphine (161 g, 0.615 mol) and diisopropylazodicarboxylate (124 g, 0.615 mol) at 0° C. The reaction mixture was stirred for 30 minutes. Trimethylsilylazide (71.1 g, 0.615 mol) was added dropwise at room temperature and then heated to reflux for 4 hours. The reaction mixture was diluted with ethyl acetate and washed with ice-water. The organic layer was separated and washed with brine solution, dried over anhydrous Na2SO4 and concentrated under reduced pressure. The crude product was purified by column chromatography using an eluent of 20% ethyl acetate in petroleum ether to yield 1-[4-cyano-3-(trifluoromethyl)phenyl]-1H-tetrazol-5-yl}methyl acetate (45 g).
