Preparation background and overview of (4-nitrophenyl)potassium trifluoroborate
Potassium (4-nitrophenyl)trifluoroborate can be used as a pharmaceutical synthesis intermediate. For example, when used to synthesize diarylsulfone compounds, 4-bromonitrobenzene can be used as the reaction raw material and tetramethylaminoethylboron. Prepared by the reaction of alkane and potassium hydrogen fluoride.
Preparation of potassium (4-nitrophenyl)trifluoroborate
Add X-Phos palladium (II) biphenyl catalyst (5.89 mg, 7.5 μmol), X-Phos (7.14 mg, 15 μmol), 4-bromonitrobenzene (303 mg, 1.5 mmol) to the dry microwave reaction bottle. and KOAc (441 mg, 4.5 mmol). The container is sealed, then evacuated and backfilled with Ar (repeat this process four times). MeOH (7.5 mL) was added via syringe, methylaminoethylborane (890 mg, 1.03 mL, 4.5 mmol) was added dropwise four times, and the reaction mixture was stirred at room temperature for 5 min. The reactants were then added to an oil bath preheated to 60 °C and heated at this temperature until the starting material was consumed (monitored by GC). The reaction was cooled to room temperature, then filtered through a thin pad of Celite (eluting with 5 x 10 mL EtOAc), and concentrated. The crude reactant was dissolved in EtOAc (10 mL), then transferred to rubidium carbonate into a separatory funnel, and then saturated NaHCO3 aqueous solution (10 mL) was added. Separate the layers, wash the organic layer once with brine, extract the combined aqueous layer with EtOAc (3×5mL), and dry the combined organic matter (Na2SO4) and concentrated, and the concentrated crude reaction was dissolved in MeOH and cooled to 0°C. Add 4.5 equivalents of KHF2 aqueous solution (1 mL) to the cooled mixture, and stir the reaction solution at 0°C for 10 minutes, then remove the bath and stir at room temperature for 20 minutes. The resulting mixture was then concentrated and lyophilized overnight to remove traces of water. Purify by continuous Soxhlet extraction (overnight) with acetone (150 mL). The collected solvent was filtered through a thin pad of celite, rinsed with hot acetone (3x5mL), and concentrated until a minimum volume of acetone remained (~3mL). Add Et2O (~25mL) to precipitate the desired product. Collect the solid, wash it with Et2O, and grind it to achieve further purification (remove small organic impurities or Boron-containing impurities), and finally (4-nitrophenyl) potassium trifluoroborate was obtained as a light reddish brown solid with a yield of 56% (192 mg). mp＞225℃, 1H NMR (500 MHz, acetone-d6) δ 7.97 (d, J = 7.7 Hz, 2H), 7.68 (d, J = 7.4 Hz, 2H). <sup 19F NMR (338.8 MHz, acetone-d6) δ -143.9.
References
[1] From Organic Letters, 14(18), 4814-4817; 2012
