The present invention describes the process for the preparation of novel sesquiterpene oxide 3S,3aR,7aR,-6 isopropyl-1,1,3,3a-tetramethyl 1,3,3a,4,7,7a-hexahydro-isobenzofuran, of formula (I) by the reaction of elemol with per acid at a temperature range of 20 to 30.degree. C. The invention also deals with the use of compound of formula (1) as a perfuming and flavoring agent ##STR00001##