N-(1,1-Dimethylethoxycarbonyl)phenylalanine (6.36 g, 24 mmol) in ethyl acetate (50 mL) at 0° C. was added to dicyclohexylcarbodiimide (4.95 g, 24 mmol) and pentafluorophenol (4.42 g, 24 mmol) in ethyl acetate (50 mL) at 0° C. The mixture was stirred for 2.75 h at 0° C. The suspension was filtered and the solvent was evaporated under reduced pressure from the filtrate. The residue was dissolved in ethyl acetate. The suspension was filtered and the solvent was evaporated under reduced pressure from the filtrate to give N-(1,1-dimethylethoxycarbonyl)phenylalanine pentafluorophenyl ester (10.32 g, quantitative).
