PURPOSE: To obtain the titled compound useful as a raw material for preparing a physiologically active substance such as pheromone, etc. or perfume such as cis-jasmone, etc. relatively simply in high yield, by reacting (Z)-4-hexenolide as a raw material with a specific organocopper complex.

CONSTITUTION: (Z)-4-hexwnolide shown by the formula II is reacted with an orgnocopper complex shown by the formula III [R is alkyl, or aryl; M is Li or MgX (X is Cl, Br, or I )] such as lithium dimethylcopper in a solvent such as diethyl ether, etc. at -40W10°C for 30minW1hr to give the aimded compound such as (Z)-4heptenoic acid, etc. A molar ratio of the compound shown by the formula II to the organocopper complex shown by the formula III added is 1:0W1:2. The organocopper complex, for example, is obtained by dissoling 1mol cuprous iodide in a solvent such as diethyl ether, etc. to give 4l solution, and the reacting the solution with 2moc organolithium compound such as a compound shown by the formula RLi in an inert gas atmosphere of A, etc.