Add diisopropyl azodicarboxylate (0.56 mL, 3.94 mmol) to a solution of (S)-tert-butyl 5-[(3,5-bistrifluoromethylbenzyl)-(2H-tetrazol-5-yl)amino]-7-methyl-8-trifluoromethyl-2,3,4,5-tetrahydrobenzo[b]azepine-1-carboxylate (2.10 g, 3.29 mmol) and triphenylphosphine (1.03 g, 3.94 mmol) in methanol (0.20 mL, 4.94 mmol) and toluene (30 mL) at 0° C. under nitrogen. Warm the mixture to room temperature and stir for 12 h. Add silica gel, remove the solvents under reduced pressure and purify the residue by column chromatography on silica gel, eluting with ethyl acetate/hexanes (1:3), to provide the title compound as a colorless oil (2.04 g, 95%). APCI MS m/z 653 (M+H)+.
