2-(4-Piperidyl)ethanal and 3-(4-piperidyl)propanal

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Abstract
The title aminoaldehydes were synthesized by N-acetylation of the corresponding aminoalcohols, Kornblum oxidation to amidoaldehydes, formation of the dimethyl acetals, alkaline amide hydrolysis, and finally acidic acetal hydrolysis. Infrared, ultraviolet, and nuclear magnetic resonance spectral examination indicates that, in solution, the aminoaldehyde hydrochlorides exist in equilibrium with gem-diols or hemiacetals, depending upon the solvent, but that the free bases are reversibly converted into dimeric enamines, to which structures are tentatively assigned. No evidence could be obtained for the presence of monomeric bicyclic carbinolamine tautomers of either the free amines or their salts.