Synthesis
Step 2: In a dry flask, 1-cyclopropyl-4-iodo-1H-pyrazole (405 mg, 1.73 mmol) was dissolved in anhydrous THF (8.0 mL) and the solution was cooled to 0 °C. Under nitrogen protection, isopropylmagnesium chloride solution (2.0 M in THF, 1.04 mL, 2.08 mmol) was slowly added dropwise, keeping the reaction temperature at 0 °C. After the dropwise addition, the reaction mixture was stirred at 0 °C for 45 min. Subsequently, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.53 mL, 2.60 mmol) was added and the reaction mixture was allowed to warm up slowly to room temperature over 1 hour. Upon completion of the reaction, the reaction was quenched with 50% saturated aqueous NH4Cl and extracted with EtOAc. The organic phases were combined, washed with saturated aqueous NaCl, dried over anhydrous MgSO4, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: 20-50% EtOAc/heptane) to afford 405 mg (83% yield) of 1-cyclopropyl-1H-pyrazole-4-boronic acid pinacol ester as a colorless viscous oil.
