C(OC(=O)C(=N[NH:8][C:9]1[CH:14]=[C:13]([Cl:15])[CH:12]=[CH:11][C:10]=1[F:16])C)C.[C:18]1(C)C=CC(S(O)(=O)=O)=C[CH:19]=1.O.[C:30](=[O:33])(O)[O-:31].[Na+].[C:35]1(C)C=CC=C[CH:36]=1>>[CH2:35]([O:31][C:30]([C:18]1[NH:8][C:9]2[C:14]([CH:19]=1)=[C:13]([Cl:15])[CH:12]=[CH:11][C:10]=2[F:16])=[O:33])[CH3:36]2-[(5-Chloro-2-fluoro-phenyl)-hydrazono]-propionic acid ethyl ester (13.2 g, 51 mmol) was dissolved in toluene, p-toluenesulfonic acid (10 g, 51 mmol) was added and the mixture was heated to reflux for 24 h with separation of water. The mixture was cooled, neutralized with saturated sodium bicarbonate (400 mL) and extracted thrice with ethyl acetate. Organic phases were pooled, washed with brine, dried with MgSO4 and the solvent was removed in vacuo. The residue was triturated with hexane to yield the title product as yellowish solid (2.9 g, 23%); EI-MS: m/e=241.1 (M+).
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