Cornforth reagent → toluene-4-sulfonic acid 5-acetyl-4-cyclopentyl-1H-pyrazol-3-yl ester

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Reaction Steps

To toluene-4-sulfonic acid 4-cyclopentyl-5-(1-hydroxyethyl)-1H-pyrazol-3-yl ester (3.65 g, 10.43 mmol) in dichloromethane (250 ml) was added pyridinium dichromate (3.92 g, 1 molar eq) and the resulting slurry was stirred at room temperature for 1 h. The mixture was poured directly onto a column of silica gel, and the crude product was eluted off with ethyl acetate. Evaporation and further purification on silica gel using 0 to 20% ethyl acetate in isohexane as eluent yielded toluene-4-sulfonic acid 5-acetyl-4cyclopentyl-1H-pyrazol-3-yl ester as a colourless oil (1.36 g). 1H NMR (400 MHz, CDCl3) δ 1.62-1.91 (8H, m), 2.46 (3H, 8), 2.53 (3H, s), 3.26 (1H, m), 7.37 (2H, d, J=6.8 Hz), 7.90 (2H, d, J=6.8 Hz); MS (ES+) m/e 349 [MH]+.

Provenance & Evidence