1-(Tetrahydropyran-2-yl)-1H-pyrazole-5-boronic acid pinacol ester

76-09-5

449758-17-2

903550-26-5

1. 1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazole (14.1.A, 83 mmol) and 100 mL of anhydrous THF were added to a 500 mL triple-necked flask and dissolved with stirring. 2. The reaction system was cooled to -78 °C (dry ice/acetone bath) and n-butyllithium (1.6 M hexane solution, 52 mL, 83 mmol) was slowly added dropwise, keeping the temperature below -70 °C. The reaction system was cooled to -78 °C (dry ice/acetone bath). 3. After the dropwise addition, the reaction was continued with stirring at -78 °C for 5 min, followed by the addition of pinacolborane (9.8 g, 83 mmol). 4. 4. After keeping the reaction at a low temperature for 5 minutes, slowly add triisopropyl borate (19 g, 103 mmol) dropwise. 5. 5. Control the rate of temperature increase and bring the reaction system to room temperature over 90 minutes. 6. 6. The reaction was continued with stirring for 16 hours at room temperature (TLC to monitor the progress of the reaction). 7. Upon completion of the reaction, the reaction was quenched to pH 7-8 with saturated aqueous NH4Cl. 8. Extracted with ethyl acetate (3 x 50 mL), the organic phases were combined and dried over anhydrous Na2SO4. 9. After concentration under pressure, purification by silica gel column chromatography (eluent: petroleum ether/ethyl acetate gradient elution) afforded the white solid product 1-(tetrahydro-2H-pyran-2-yl)-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (14.1.B, 7.2 g, 38% yield).