A mixture of 4-benzyloxybenzoic acid (0.780 g, 3.42 mmol), tert-butyl carbazate (0.443 g, 3.35 mmol), Et3N (0.5 mL), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (1.05 g, 5.47 mmol) and 1-hydroxybenzotriazole hydrate (0.778 g, 5.76 mmol) in N,N-dimethylformamide (27 mL) was stirred at room temperature for 2 days. The reaction was concentrated and diluted in dichloromethane. The organic phase was washed twice with water, dried with MgSO4 and concentrated. The residue was purified on column chromatography (silica gel, 5% MeOH in CH2Cl2) and tert-butyl 2-[4-(benzyloxy)benzoyl]hydrazine carboxylate (0.998 g, yield: 85%) was identified by NMR spectroscopy.
