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

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To the mixture of 6-chloro-4-fluoroindolin-2-one (Natrochem, 85% purity) (1.1 g, 5.0 mmol) and 3-chloro-2-fluorobenzaldehyde (2.4 g, 15 mmol) (Oakwood) in methanol (50 mL) was added piperidine (1.7 g, 20 mmol) (Aldrich) dropwise. The mixture was then heated at 50° C. for 3 h. After cooled to 4° C., the mixture was filtered and resulting precipitate was collected, washed with cold methanol, dried to give the first batch of desired product (1.22 g). The filtrate was concentrated, and the residue was partitioned between ethyl acetate and water. The organic layer was separated, washed with water, brine, dried over MgSO4, and concentrated. The residue was purified by chromatography (20-35% EtOAc in hexanes) to give the second batch of desired product (0.32 g). The two batches were combined to give E/Z-6-chloro-3-(3-chloro-2-fluoro-benzylidene)-4-fluoro-1,3-dihydro-indol-2-one as a yellow solid (Yield 1.54 g, 94%).

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