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 by the reaction of elemol with per acid at a temperature range of 20 to 30 ° c . the invention also deals with the use of compound of formula as a perfuming and flavouring agent .