1,4-Dihydropyridine equivalents: a novel approach to 2,6-dicyanopiperidine derivatives

For the first time, it has been shown that 2,6-dicyanopiperidines are formed in the Fry reaction via 1,4-dihydropyridine intermediates. A new synthetic approach for building 2,6-dicyanopiperidine derivatives by an extension of the sodium dithionite reduction of pyridinium salts is described. The stereochemistry of 2,6-dicyanopiperidine derivatives formed is discussed.