At room temperature, (1-benzyl-1H-pyrazol-4-yl)methanol (190 mg, 1.0 mmol) was dissolved in dichloromethane (8 mL) and Dess-Martin periodinane (670 mg, 1.58 mmol) was added. The reaction mixture was stirred at room temperature for 1.5 h. After stirring, the reaction was quenched with a mixture of saturated sodium thiosulfate solution and 10% sodium bicarbonate solution (1:1, v/v) and stirring was continued for 30 min. Subsequently, the reaction mixture was extracted with dichloromethane (3 x 30 mL). The organic phases were combined, washed sequentially with saturated aqueous sodium bicarbonate and brine, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by fast column chromatography (Isco CombiFlash, eluent: 0-40% ethyl acetate/heptane) to afford 1-benzyl-1H-pyrazole-4-carbaldehyde (86 mg, 46% yield). The product was confirmed by 1H NMR (400 MHz, CDCl3): δ 5.35 (s, 2H), 7.27-7.30 (m, 2H), 7.36-7.43 (m, 3H), 7.88 (s, 1H), 8.01 (s, 1H), 9.85 (s, 1H); LCMS-MS (ESI+) m/z: 186.90 ([M+H ]+).
