[CH3:1][O:2][C:3](=[O:12])[CH2:4][C:5]1[CH:10]=[CH:9][C:8]([Cl:11])=[CH:7][CH:6]=1.[H-].[Na+].[CH3:15][O:16][C:17](=O)[O:18]C.Cl>C1COCC1>[CH3:1][O:2][C:3](=[O:12])[CH:4]([C:5]1[CH:10]=[CH:9][C:8]([Cl:11])=[CH:7][CH:6]=1)[C:17]([O:16][CH3:15])=[O:18]At 35° C. a solution of 4-chlorophenylacetic acid methyl ester (52 g) in THF (170 ml) was carefully added over a period of 70 min to a suspension of NaH (15.6 g) in dry THF (550 ml). Stirring was continued for 40 min without heating and the temperature dropped to 290C. The evolution of gas had stopped before dimethylcarbonate (94.8 ml) was added dropwise while the temperature of the mixture was maintained at 25–28° C. After the evolution of gas had ceased, the mixture was diluted with THF (200 ml) and stirring was continued for 72 h at rt. The mixture was carefully acidified with aq. HCl before bulk of the THF was removed in vacuo. The residue was dissolved in diethyl ether (1200 ml), washed three times with 1 N aq. HCl and once with brine, dried over MgSO4 and evaporated. The residue formed was collected, washed with diethyl ether and dried to give 2-(4-chloro-phenyl)-malonic acid dimethyl ester (42 g) as white crystals.
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