Covalent adducts from 1,3-disubstituted pyridinium salts and piperidine

Covalent adducts 3a-f have been isolated from the reaction between piperidine and pyridinium salts 1a-f. 3a-f are stable both in the solid state and in apolar solvents, whereas their fast dissociation back to piperidine and pyridinium ions occurs in aqueous solution. The latter, in the alkaline environment produced by the amine, yields the correspondent pseudobases, which are key intermediates of the subsequent reactions. For instance, the pseudobases from 1a,b can undergo either a ring-opening reaction or a redox process with the corresponding pyridinium cations.