[CH2:1]([O:3][C:4](=[O:15])[C:5]([C:7]1[CH:12]=[CH:11][C:10]([Cl:13])=[CH:9][C:8]=1[Cl:14])=O)[CH3:2].[Na+].[Cl-].[CH2:18]([O:20][CH2:21][CH3:22])[CH3:19].C([OH:25])C>>[CH2:1]([O:3][C:4](=[O:15])[C:5]([C:7]1[CH:12]=[CH:11][C:10]([Cl:13])=[CH:9][C:8]=1[Cl:14])=[CH:19][C:18]([O:20][CH2:21][CH3:22])=[O:25])[CH3:2]An ethanolic solution of sodium ethylate, obtained from sodium (3.35 g; 0.1457 moles) and dry ethanol (276 ml), kept under stirring in inert atmosphere, was added at 20° C. with a solution of (2,4-dichloro-phenyl)-oxo-acetic acid ethyl ester obtained as described in example 2 (36 g; 0.147 moles), and triethyl phosphonoacetate (34.2 g; 0.152 moles) in dry ethanol (70 ml). The reaction mixture was then brought and kept at reflux for 16-20 hours. After cooling to 25° C., the mixture was poured under stirring into a solution of saturated NaCl (500 ml), ethyl ether was added (150 ml) and the phases were separated. The aqueous phase was extracted again with ethyl ether (150 ml). The joined organic phases were washed with water (100 ml), anhydrified over dry Na2SO4, evaporated to dryness. The thus obtained residue was purified by chromatography (SiO2; hexane/ethyl ether 9/1) to give 24.6 g of (E) 2-(2,4-dichlorophenyl)-butendioic acid diethyl ester (yield 53%) as a colourless oil.
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