General procedure for the synthesis of 2-piperidinyl-1-benzaldehyde from hexahydropyridine and 2-fluorobenzaldehyde: To a solution of 2-fluorobenzaldehyde (20 g, 161.1 mmol) in anhydrous DMF (160 ml) was added piperidine (19.1 ml, 193.4 mmol, 1.2 eq.) and potassium carbonate (26.73 g, 193.4 mmol, 1.2 eq.), in that order. . The suspension was heated with stirring at 130 °C for 3 hours. After completion of the reaction, the reaction mixture was poured into cold water. The pH was adjusted with citric acid to 5. The aqueous layer was extracted three times with ethyl acetate (EtOAc), the organic phases were combined and washed sequentially with water, saturated sodium bicarbonate (NaHCO3) solution and brine. The organic phase was dried with anhydrous magnesium sulfate (MgSO4), filtered and concentrated to give the target product 2-piperidinyl-1-benzaldehyde as a red oil (28.23 g, 92% yield).
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