To a 0° C. solution of the amide of step 3 (13.2 g, 33.9 mmol) in 150 mL of anhydrous pyridine was added trifluoroacetic anhydride (5.50 mL, 38.9 mmol) dropwise slowly over a 3 min period. The reaction mixture was stirred for 15 min and then poured into a slurry of ice and 1N HCl solution. The mixture was extracted with 500 mL of ethyl acetate, and washed with three 400 mL portions of 1N HCl, 400 mL of water, dried over sodium sulfate, filtered and concentrated to give a crude solid. Recrystallization from ethyl acetate/hexanes gave 11.3 g of [2-(1-Cyano-3-methyl-butylcarbamoyl)-cyclohexyl]-carbamic acid benzyl ester as a white solid. Yield: 90%, MS: 394 (M+Na+), mp=103.6-106.5° C.
