Ethyl 5-amino-3-(2-((tert-butyldiphenylsilyl)oxy)ethyl)-1-(3-chlorophenyl)-1H-pyrazole-4-carboxylate: To a solution of Intermediate 9A (1.34 g, 3.1 mmol) in DMF (5 mL) was added NCS (0.455, 3.41 mmol) and stirred at rt. After 4 h, the reaction mixture was quenched with H2O (100 mL) and extracted with EtOAc (2×). The organic layers were dried (MgSO4) and evaporated to a reddish oil. Separately ethylcyanoacetate (0.351 g, 3.10 mmol) was dissolved in EtOH (5 mL) and to this solution was added NaOEt (21%) (1.16 mL, 3.10 mmol) and the reaction was stirred at rt for 0.5 h followed by the introduction of the iminochloride crude mixture. The above mixture was then stirred at rt. After 2 h, the reaction was quenched with H2O and extracted with EtOAc (2×). The organic layers were dried (MgSO4) and evaporated to yield orange-red oil. The crude product was then purified using silica gel chromatography. Two peaks were isolated—one is the desired product and the other is the chlorinated pyrazoline compound and the two products were taken to the next step as a crude mixture. MS(ESI) m/z: 548.1 (M+H)+.
