Triphenylphosphine Oxide

• Pyridinium p-Toluenesulfonate (= PPTS) [P0942]
• Triphenylphosphine Oxide [T0625]
• Trifluoromethanesulfonic Anhydride (=Tf₂O) [T1100]
• Pentafluorophenol [P0919]
• Triethylamine (= Et₃N) [T0424]
• Dichloromethane

Under nitrogen atmosphere, triphenylphosphine oxide (1.057 g, 3.798 mmol) was dissolved in dichloromethane (20 mL) and cooled to 0 °C. Then trifluoromethanesulfonic anhydride anhydride (0.295 mL, 1.80 mmol) was added and stirred for 1 h. After confirming the formation of intermediate 1 by ³¹P-NMR, PPTS (0.452 g, 1.80 mmol) was added and the mixture was stirred for 30 min. After that, a solution of triethylamine (0.28 mL, 2.00 mmol) and pentafluorophenol (0.370 g, 2.00 mmol) in dichloromethane (5 mL) was added dropwise with a syringe to this solution. Then the mixture was warmed to room temperature and stirred for 1 h. After completion of the reaction, the mixture was diluted with dichloromethane (20 mL) and then 2 mol/L HCl (30 mL) was added to quench. The two layers were separated and the organic layer was washed with brine (20 mL), dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel chromatography (hexane:ethyl acetate = 9:1) to afford pentafluorophenyl p-toluenesulfonate as a yellow solid (540 mg, 88% yield).

The reaction mixture was monitored by ¹H-NMR and ³¹P-NMR (CDCl₃).
Dichloromethane was used for the reaction after dehydration with molecular sieves and bubbling with nitrogen.

Pentafluorophenyl p-Toluenesulfonate

¹H NMR (400 MHz, CDCl₃); δ 7.86 (d, J = 8.4 Hz, 2H), 7.42 (d, J = 8.2 Hz, 2H), 2.51(s, 3H).

• Direct Synthesis of Sulfonamides and Activated Sulfonate esters From Sulfonic Acids
  • S. Caddick, J. D. Wilden, D. B. Judd, J. Am. Chem. Soc. 2004, 126, 1024.

• The Structure of Polymer-Supported Triphenylphosphine Ditriflate: A Potentially Useful Reagent in Organic Synthesis
  • M. J. Petersson, I. D. Jenkins, W. A. Loughlin, J. Org. Chem. 2008, 73, 4691.