Particular behavior of 'C6C2 units' in the Chichibabin pyridine synthesis and biosynthetic implications

Several aspects of the unusual behavior of C6C2 aldehydes and amines during the formation of pyridiniums in analogy with the historical Chichibabin pyridine synthesis are clarified in this Letter. Interesting biosynthetic consequences are also discussed within two classes of polycyclic alkaloids of marine origin.