PURPOSE: To produce the titled substance useful as an insecticide, economically, by using an optically active 4-cyclopentenone compound as a raw material, and reacting the raw material under specific condition, thereby converting the hitherto discarded compound to a reutilizable compound.

CONSTITUTION: The objective compound of formula II is produced by using the optically active compound of formula I (R is OH or OCOR'; R' is H or lower alkyl; R1 is H, alkyl or alkenyl; R2 is alkyl, alkenyl or alkynyl) as a raw material, and reacting 1mol of the raw material at 0W110°C in the presence of preferably ≥0.3mol of water and 0.5W50mol of an acidic substance such as hydro- chloric acid, polyphosphoric acid, etc. A concrete example of the compound of formula I is 3-hydroxy-2-methyl-4-cyclopentenone.