NEW MATERIAL:A cyclopentanone derivative of formula I (R1, R2 are lower alkyl).

EXAMPLE: 3-Methyl-2-p-toluylcyclopentenone.

USE: Medicine having antifungal activity, and an intermediate for the preparation of natural sesquiterpenes.

PROCESS: The compound of formula I is prepared by (1) hydrolyzing a furan derivative of formula II with an acid such as acetic acid at 0W150°C, and (2) subjecting the resulting diketone compound of formula III to the ring-closing reaction with a base such as sodium hydroxide. The furan derivative of formula II used as the raw material can be obtained easily, e.g. by reacting the lithium compound of the corresponding furan with the corresponding benzyl halide derivative.