Studies of the Reissert-Kaufmann-type Reaction of 4-Nitropyridine N-Oxide and Its Homologues

The Reissert-Kaufmann-type reaction of substituted N-methoxy-4-nitropyridinium methylsulfates gave the corresponding 2-cyano-4-nitropyridines in satisfactory yields. When 3-methyl-4-nitropyridine N-oxide was used as the starting material, a cyano group was introduced not into the 6-position, but into the 2-position. This preference may be explained by proposing a hyperconjugation effect of the 3-methyl group. The resulting nitriles were quantitatively hydrolyzed to the corresponding 4-nitropicolinic acids. These reactions provided a new route for the preparation of nitropyridinecarboxylic acids from pyridine homologues. Further, some nucleophilic substitution reactions of the products were carried out.