Intramolekulare Diels‐Alder ‐Additionen von 1,2‐Dihydropyridinen

Reduction of the pyridinium salts 1b‐f in methanolic sodium hydroxide solution with sodium borohydride gave the dimeric dihydropyridine derivatives 3b‐f . Heating these dimers in hydrocarbon solvents at 110–207° resulted in the formation of the tricyclic amines 4c–f , which were shown to be products of an intramolecular Diels‐Alder addition within the intermediate dihydropyridines 2c–f . The structures of 4c–f were deduced from spectroscopic, mainly NMR. data.