At 0°C, 500 mg (2.9 mmol) of (1-phenyl-1H-pyrazol-3-yl)methanol and 0.8 ml (5.7 mmol) of triethylamine were dissolved in 10 ml of dichloromethane and mixed with stirring. 690 mg (4.3 mmol) of pyridine sulfur trioxide was dissolved in 5 ml of dimethyl sulfoxide and this solution was slowly added to the above reaction mixture. After 3 hours of reaction, ethyl acetate was added to the reaction system and subsequently washed with water. The organic phase was separated, dried with anhydrous magnesium sulfate, filtered and purified by column chromatography to give 220 mg of 1-phenyl-1H-pyrazole-3-carbaldehyde in 45% yield. The product was characterized as follows: 1H-NMR (CDCl3) δ 9.98 (1H, s), 8.44 (1H, s), 8.17 (1H, s), 7.74-7.71 (2H, m), 7.53-7.49 (2H, m), 7.42-7.38 (1H, m); mass spectrum (EI): m/z 173 (M++1).
