General procedure for the synthesis of 1-methyl-4-hydroxy-1H-pyrazole from 1-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole: To 1-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (1.0 g, 120.2 mmol) was added slowly, under the condition of 0 °C (ice bath cooling), to a 1-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole ( 25.0 g, 120.2 mmol) in tetrahydrofuran solution (600.9 mL, 0.2 M) was slowly added to aqueous sodium hydroxide solution (80.1 mL, 3 M, 240.3 mmol) followed by hydrogen peroxide (27.3 mL, 240.3 mmol). The reaction mixture was stirred at 0-25°C for 3 hours. After completion of the reaction, the reaction mixture was neutralized in a small heart with 12N hydrochloric acid (18.6 mL) and diluted with a solvent mixture of dichloromethane and methanol (90:10, 200 mL). The aqueous layer was extracted with a solvent mixture of dichloromethane and methanol (90:10, 3 x 200 mL). The organic layers were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by column chromatography to afford the target product 1-methyl-4-hydroxy-1H-pyrazole.
