A mixture of 2-methyl-5-[5-(3,4,5-trichloro-phenyl)-5-trifluoromethyl-4,5-dihydro-isoxazol-3-yl]-furan-3-carbaldehyde (2.15 g), tert-butylcarbamate (1.80 g), trifluoroacetic acid (0.78 ml) and triethylsilane (2.48 ml) in acetonitrile (23 ml) is stirred at room temperature for 20 hours. After diluting with ethyl acetate, the reaction mixture is quenched with a saturated solution of NaHCO3. The organic phase is separated and the aqueous phase is extracted once with ethyl acetate. The combined organic phases are washed with a saturated solution of NaHCO3 and with a saturated aqueous solution of NaCl, dried over MgSO4 and concentrated in vacuo. The crude product is purified on a semi-preparative HPLC to yield {2-methyl-5-[5-(3,4,5-trichloro-phenyl)-5-trifluoromethyl-4,5-dihydro-isoxazol-3-yl]-furan-3-ylmethyl}-carbamic acid tert-butyl ester (2.10 g, compound 2.4 in Table 2) as a light yellow foam. MS (HPLC/MS): 527 (MH+).
