[Cl:1][C:2]1[CH:7]=[C:6]([Cl:8])[CH:5]=[CH:4][N:3]=1.C([N-]C(C)C)(C)C.[Li+].[CH:17](N1CCCCC1)=[O:18].C(O)(=O)C>C1COCC1>[Cl:1][C:2]1[C:7]([CH:17]=[O:18])=[C:6]([Cl:8])[CH:5]=[CH:4][N:3]=1To a solution of 2,4-dichloropyridine (10 g) in THF (100 mL) was added dropwise lithium diisopropylamide solution (2M, 37 mL) at −78° C. The reaction mixture was stirred at −78° C. for 1 hr. To the reaction mixture was added dropwise 1-formylpiperidine (7.7 g) at −78° C. The reaction mixture was stirred at −78° C. for 2 hr. The reaction mixture was added to 10% aqueous acetic acid solution, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated aqueous sodium hydrogencarbonate solution and saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate/petroleum ether) to give the title compound (7.0 g).
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