Tris(2,2,2-trifluoroethyl) Borate

Experimental procedure:
A solution of tris(2,2,2-trifluoroethyl) borate (3.0 mmol, 3.0 eq.) in CPME (1 mL)　is added dropwise to a mixture of an unprotected amino acid (1.0 mmol, 1.0 eq.) and propylamine (3.0 mmol, 3.0 eq.) in CPME (1 mL) over 1 h at 80 °C or 125 °C. The resulting mixture is stirred for 5 - 15 h. Upon completion, the mixture is diluted with EtOAc or CH₂Cl₂ (3 mL) and water (0.5 mL). Amberlite IRA-743 and Amberlyst A-26(OH) are added and stirred for 30 min. The mixture is dried over MgSO₄ and then filtered. The solids are washed with EtOAc (3 × 20 mL) and the product concentrated in vacuo. The volatile propylamine is removed in vacuo by the addition of CHCl₃ to get the clean product.