[C:1](Cl)(=O)C.[Na+].[Cl-].[Cl:7][C:8]1[CH:9]=[C:10]([C:15]2[CH2:19][CH:18]([CH2:20][C:21]([OH:23])=[O:22])[O:17][N:16]=2)[CH:11]=[CH:12][C:13]=1[Cl:14].Cl>CO>[CH3:1][O:22][C:21](=[O:23])[CH2:20][CH:18]1[O:17][N:16]=[C:15]([C:10]2[CH:11]=[CH:12][C:13]([Cl:14])=[C:8]([Cl:7])[CH:9]=2)[CH2:19]1Acetyl chloride (5 eq) was added to MeOH (50 vol) externally cooled with a mixture saturated aqueous NaCl solution and ice. After 10 minutes the solution was warmed to room temperature. After a further 90 minutes, [3-(3,4-dichloro-phenyl)-4,5-dihydro-isoxazol-5-yl]-acetic acid (1.0 eq) in MeOH (25 vol) was added to the hydrogen chloride methanolic solution and stirred for 16 hours. The solvent was concentrated under reduced pressure and the residue was purified by flash column chromatography (eluent: [3:7] EtOAc:heptane) to afford [3-(3,4-dichloro-phenyl)-4,5-dihydro-isoxazol-5-yl]-acetic acid methyl ester.
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