PURPOSE: To introduce an N-heteroaromatic ring into an ester at the 3-position by reacting a 2,6-dimethyl-4-phenyl-1,4-dihydropyridine-3,5-dicarboxylic acid diester with an alkali metal carboxylate in the presence of a phase-transfer catalyst.

CONSTITUTION: A compound expressed by formula I (R1 and R2 are H, halogen, CF3 or NO2; X is halogen; R is lower alkyl; n is 2 or 3) is reacted with a compound expressed by formula II (Y is alkali metal; R3 is heteroaromatic ring group containing N as a heteroatom or condensed heteroaromatic ring group condensed with carboaromatic ring) in the presence of a phase-transfer catalyst in a solvent, such as toluene, at 50-120°C for 20min to 1 day to afford a compound expressed by formula III. A quaternary ammonium salt (e.g. benzyltrimethylammionium chloride), large ring polyether (e.g. 15-crown-5 or 18-crown-6), etc., are used as the phase-transfer catalyst. Thereby, the objective substance is obtained in high yield.