PURPOSE: To obtain an oxocarboxylic acid derivative useful for synthesizing liquid crystals, polymer compounds, etc., by reacting a cyclohexenecarboxylic acid derivative with a Lewis acid.

CONSTITUTION: A derivative of formula I [R is H, (substituted)alkyl or aryl; X is H or ]is made to react with a Lewis acid (preferably concentrated sulfuric acid) preferably in a solvent such as hexane or dichloromethane, preferably at 0-30°C for 0.2-1hr to afford the objective compound of formula II. Furthermore, the concentrated sulfuric acid is used in an amount of preferably 3-5mol based on the compound of formula I.