CCO[CH:4](OCC)[C:5]1[CH:10]=[CH:9][C:8]([CH:11]=[O:12])=[CH:7][CH:6]=1.[S:16]1[CH2:20][C:19](=[O:21])[NH:18][C:17]1=[O:22].N1CCCCC1.Cl>C(O)C>[CH:11]([C:8]1[CH:7]=[CH:6][C:5]([CH:4]=[C:20]2[S:16][C:17](=[O:22])[NH:18][C:19]2=[O:21])=[CH:10][CH:9]=1)=[O:12]To a mixture of terephthalaldehyde mono-(diethyl acetal) (3.96 mL, 20.0 mmol) and 2,4-thiazolidinedione (2.81 g, 24.0 mmol) in ethanol (40 mL) was added piperidine (2.0 mL, 20.0 mmol). The reaction mixture was heated to reflux for 4 h. After cooling on an ice-bath, hydrochloric acid (0.2 mol/L, 100 mL) was added and the precipitated products were collected by filtration. The cake was washed with water and dried. To a solution of this product (5.50 g) in tetrahydrofuran (180 mL) was added hydrochloric acid (1 mol/L, 18 mL) and the mixture was stirred at room temperature for 2 h. Water was added, and the precipitated products were collected by filtration to give 5-(4-formylbenzylidene)-2,4-thiazolidinedione (3.91 g, 94%).
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