New Polycyclic Diamine Scaffolds from Dimerization of 3-Alkyl-1,4-dihydropyridines in Acidic Medium

3-Alkyl-1,4-dihydropyridines dimerize in acidic medium, at low temperature, to give polycyclic imminium salts derivatives that were reduced to afford new polycyclic diamine scaffolds. The reaction can be extended to enantiopure series starting from R-(+)- or S-(−)-1-phenylethylamine. Long exposure of the polycyclic imminium salt intermediates to air moisture at 20 °C resulted in formation of new amide derivatives. This is probably due to the addition of water followed by an intramolecular oxido-reduction process.