The present invention discloses a process for the preparation of a compound according to formula ##STR1## wherein R.sup.1 is a C.sub.3 -C.sub.7 alkyl group and R.sup.2 is a C.sub.1 to C.sub.4, linear or branched, alkyl radical, more preferably a methyl group, characterized in that the process includes the isomerisation of an epoxide of formula ##STR2## wherein R.sup.1 and R.sup.2 have the meaning given in formula (I), in the presence of an acidic isomerisation agent, a thermal treatment or a combination thereof. The process according to the invention allows the preparation of the cyclopentenyl compounds of formula (I) on an industrial scale. The compounds are important starting products for the production of appreciated perfuming ingredients in particular methyl dihydrojasmonates.