4-Chlorobenzaldehyde → Z-6-chloro-3-(4-chloro-benzylidene)-1,3-dihydro-indol-2-one

To the mixture of 6-chlorooxindole (16.2 g, 92 mmol) (Crescent) and 4-chlorobenzaldehyde (12.9 g, 92 mmol) (Aldrich) in methanol (100 mL) was added pyrrolidine (6.55 g, 92 mol) (Aldrich) dropwisely. The mixture was then heated at 70° C. for 3 h. After cooling to 4° C., the resulting precipitate was collected and dried to give 21 g of E/Z-6-chloro-3-(4-chloro-benzylidene)-1,3-dihydro-indol-2-one as a bright yellow solid. MS: 291 (M+H)+.