Synthetic applications of N–N linked heterocycles. Part 4. The reaction between 1-pyridinio-4-pyridone cations and cyanide ion: mechanism of cyanopyridine formation, and a regioselective synthesis of 4-cyanopyridines

Abstract

The 1-pyridinio-4-pyridone cations (1) give with aqueous sodium cyanide mixtures of 2- and 4-cyanopyrigines, 2-cyanopyridine formation being favoured by high cyanide ion concentration, and 4-cyanopyridine formation by low cyanide ion concentration, when small amounts of the intermediate 1,4-dihydro-4-cyano-adducts (7) or (9) are also observed. The 2,6-dimethyl-1-pyridinio-4-pyridone cations (2) in contrast give high yields of the 1,4-dihydro-4-cyano-adducts (8) or (10), the former being decomposed quantitatively by heat to 4-cyanopyridines and 2,6-dimethyl-4-pyridone. Only very small amounts of 2-cyanopyridines are formed. Mechanisms for the two reactions are proposed which account for the experimental observations.