NEW MATERIAL:The title compound of formula I (X1,2 are H, 1-2C lower alkyl, Cl, CN, carboalkoxyl).

EXAMPLE: 5-Chloro-3-(trichloromethyl)cyclopentene.

USE: A perfume component having citrous or green grass odor. It is also useful as a chlorinated hydrocarbon-type or oxyacid ester-type liquid plasticizer because of its high Cl-content (40W60%), and excellent flame-retardancy and solubility.

PROCESS: The objective cis- or trans-compound I is prepared by reacting cyclopentadiene with a chlorine compound II (e.g. CCl4, CCl3COOCH3, CCl3CN, etc.) in an inert atmosphere, in the presence of a transition metal complex such as phosphine- ruthenium complex, etc.,(e.g. [RuCl2(PPh3)3], RuH(SiMe2Cl)(PPh3)3, etc.). Both trans- and cis-compound I are fragrant.