The Mannich-type addition of O,O-di-n-butyl phosphite to 2-fluorobenzaldehyde and p-trifluoromethylaniline was carried out without solvent in the presence of BF₃•Et₂O under ultrasonic irradiation at 78～80 ℃ for 0.5 h to afford the title compound -aminophosphonate 4 in good yield. The structure was verified by ele-mental analysis, ¹H NMR, IR and MS spectra. The X-ray diffraction analysis indicated that the crystal of compound 4 belongs to monoclinic system with space group P2(1)/c, a＝1.348(4) nm, b＝1.734(4) nm, c＝1.099(3) nm, α＝90°, β＝109.71(4)°, γ＝90°, V＝2.417(11) nm³, Z＝4, D_c＝1.268 g/m³, ＝0.166 mm^－1, F(000)＝968. The final R＝0.0727, wR₂＝0.1751 for 7780 unique reflections.

Key words: ultrasonic, synthesis, crystal structure, α-aminophosphonate