Cl[CH:2]([C:8]1[CH:13]=[CH:12][C:11]([CH3:14])=[C:10]([CH3:15])[CH:9]=1)[C:3](OCC)=[O:4].[NH2:16][C:17](N)=[S:18].Cl.[OH2:21]>C(OCCO)C>[CH3:15][C:10]1[CH:9]=[C:8]([CH:2]2[S:18][C:17](=[O:21])[NH:16][C:3]2=[O:4])[CH:13]=[CH:12][C:11]=1[CH3:14]2.26 g of ethyl α-chloro-α-(3,4-dimethylphenyl)acetate and 910 mg of thiourea, in 15 ml of ethylene glycol monoethyl ether, are stirred under reflux for 2 hours. Then, 1 ml of concentrated HCl is added and the mixture is further heated under reflux for 3.5 hours. After cooling, water is added and extraction is carried out with ethyl acetate. The extract is washed with water and dried (MgSO4). After the solvent is distilled off, column chromatography is carried out on the oily residue with 100 g of silica gel. The eluate with chloroform-ethyl acetate (5:1) yields crystals of 5-(3,4-dimethylphenyl)thiazolidine-2,4-dione 1.32 g (60%). Recrystallization from cyclohexane-ethyl acetate gives colorless prisms, m.p. 121°-122° C.
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