[NH:1]1[CH2:6][CH2:5][CH2:4][CH2:3][CH2:2]1.[C:7](=O)([O-])[O-].[K+].[K+].O.[C:14](O)(=O)[CH2:15][C:16]([CH2:21][C:22](O)=O)([C:18]([OH:20])=O)O>CN(C=O)C>[N:1]1([C:15]2[CH:14]=[CH:7][CH:22]=[CH:21][C:16]=2[CH:18]=[O:20])[CH2:6][CH2:5][CH2:4][CH2:3][CH2:2]1To a solution of the aldehyde 3a (20 g, 161.1 mmol) in dry DMF (160 mL), piperidine (19.1 mL, 193.4 mmol, 1.2 eq) and potassium carbonate (26.73 g, 193.4 mmol, 1.2 eq) were successively added. The suspension was heated at 130° C. for 3 h. The reaction mixture was then poured into cold water and acidified with citric acid up to pH 5. The aqueous layer was extracted 3X with EtOAc and the combined organic extract was successively washed with water, saturated NaHCO3 and brine. After drying the organic extract over MgSO4, filtration and concentration, the desired 2-piperidinobenzaldehyde 3b was isolated as a red oil (28.23 g, 92% yield).
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