N,N,N',N'-Tetramethyl-O-(N-succinimidyl)uronium Tetrafluoroborate

Experimental procedure: the compound 1 (2.0 g, 7.2 mmol) is dissolved in anhydrous acetonitrile (30 mL). The solution is cooled to ?5 °C, and triethylamine (1.0 mL, 7.2 mmol) and then TSTU (2.17 g, 7.2 mmol) are added. The mixture is stirred for 1 h at ?5 °C, and then a solution of 2 (1.28 g, 14.4 mmol) and NaHCO₃ (1.21 g, 14.4 mmol) in water (20 mL) is added. The reaction mixture is mixed 3 h at room temperature. The solvent is evaporated in vacuo to dryness. Then water (20 mL) is added, and pH of the mixture is brought to 3. The product is extracted from water by chloroform (2 × 150 mL). The organic layer is washed by 1 mol/L HCl (2 × 50 mL) and water (50 mL), then dried with Na₂SO₄, ?ltered, and the solvent is evaporated in vacuo. The resulting oily residue is dissolved in diethylether (50 mL), and the precipitate is collected by ?ltration and dried to give 3 in 81% yield.