PURPOSE: To monoalkylate an aryl-substituted active methylene compound containing an electron attractive group at the m-position of phenyl group by using an inexpensively obtainable aldehyde.

CONSTITUTION: A compound shown by formula I [R2 is COOH, COOR3 or COR4; R3 is 1-6C alkyl; R4 is 1-10C alkyl or phenyl, 1-naphthyl, 2-naphthyl, 2-thienyl, 3-thienyl, 2-furyl or 3-furyl which may contain substituent group (halogen, 1-4C alkyl or 1-4C alkoxy); Z is COR5, benzoyl, furoyl, thenoyl or CN; R5 is 1-2C alkyl or 1-4C alkoxy] is reacted with a compound shown by the formula R1CHO [R1 is H, 1-8C alkyl, phenyl, naphthyl, phenyl-(1-4C alkyl), 2-thienyl, 3-thienyl, 2-furyl or 3-furyl] and a synthesis gas in the presence of a metallic catalyst of group VIII of the periodic table to industrially and advantageously give a compound shown by formula II useful for producing fine chemicals such as medicines and agricultural chemicals.