Synthesis
Step 2 Synthesis of N,N'-bis(benzyloxycarbonyl)-1H-pyrazole-1-carboxamidine: N-(benzyloxycarbonyl)-1H-pyrazole-1-carboxamidine (58.62 g, 239 mmol) was dissolved in 600 mL of anhydrous THF, and the reaction mixture was cooled to 0 °C and stirred under nitrogen atmosphere. 60% NaH (28.8 g) was added to the reaction mixture in batches and the reaction temperature was maintained at 0 °C. Subsequently, 60 mL of anhydrous THF solution of benzyl chloroformate (40.9 mL) was added dropwise over 30 minutes. The reaction mixture was continued to be stirred at 0 °C for 2 hours and then brought to room temperature and stirred for 18 hours. The reaction mixture was again cooled to 0 °C and saturated aqueous Na2SO4 solution was slowly added to quench the reaction. The reaction mixture was diluted with EtOAc and filtered through diatomaceous earth. The organic layer was dried with MgSO4, filtered and concentrated under reduced pressure to give a viscous oil. After washing with hexane and drying under reduced pressure, N,N'-bis(benzyloxycarbonyl)-1H-pyrazole-1-carboxamidine was obtained as 67.81 g in 75% yield.
