PURPOSE: To prepare the titled compounds including novel substances useful as intermediates for the preparation of vitamin B6, etc., easily, by using a specific 1,2,4-triazine derivative as a raw material, and reacting with an olefin.

CONSTITUTION: A 1,2,4-triazine derivative of formulaI(R1 is a group convertible to carboxylic acid group, e.g. H, alkyl, amino, alkoxy, alkylthio, aryl, carboxyl, alkoxycarbonyl, cyano, etc.; R2 and R3 are H, alkyl, amino, alkoxy, alkylthio, or aryl) is made to react with an olefin of formula II[A and B are cyano, carboxyl, alkoxycarbonyl, halogenocarbonyl, formyl, or carbamoyl, or A and B together form -COOCO-, -COSCO- or heterocyclic group of formula IV or formula V (R4 and R5 are alkyl)]to obtain a pyridine derivative of formula III (when R1 is as defined above excepting alkyl, and R2 and R3 are not H at the same time, the compound is novel substance).