Hydrogenation of over a dozen aromatic compounds, including both heteroarenes and arenes, over palladium on carbon (Pd/C, 1–100 mol%) with H2‐balloon pressure at room temperature is reported. Analyses using pyridine as a model substrate revealed that acetic acid was the best solvent, as using only 1 mol% Pd/C provided piperidine quantitatively. Substrate scope analysis and density functional theory calculations indicated that reaction rates are highly dependent on frontier molecular orbital characteristics and the steric bulkiness of substituents. Moreover, the established method was used for the concise synthesis of the anti‐Alzheimer drug donepezil (Aricept®).

Isodesmosine and desmosine are 1,2,3,5‐tetrasubstituted and 1,3,4,5‐tetrasubstituted pyridinium amino acids that crosslink elastin and exist naturally in a 1:1 ratio. In this work, starting from the corresponding aldehyde and amine, we achieved the selective Chichibabin pyridinium syntheses of isodesmosine and desmosine with protecting groups using 50 mol‐% Pr(OTf)3 in H2O/DMF (2:1) and H2O/CH2Cl2 (1:6), respectively. It is important to note that selective desmosine synthesis (herein called isoChichibabin pyridinium synthesis) has been discovered and reported for the first time. Meanwhile, the reaction of aldehyde and amine bearing one alanine using the same conditions as above afforded the protected isodesmosine‐(Ala)4 and desmosine‐(Ala)4 with no selectivity, suggesting that these reactions imitated the formation of the elastin crosslinkers in nature.

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