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.