In the cyclization of gamma-delta or delta-epsilon unsaturated alcohols in order to obtain certain tetrahydrofuran and tetrahydropyran derivatives which are useful in the perfuming of detergents, the improvement consisting in that the alcohol to be cyclized is reacted with a cationic ion-exchange resin. The useful temperature range is from 20.degree. C. to 150.degree. C.: in practice the alcohol and the resinare boiled together or refluxed until the reaction is completed. A number of examples is reported and physicochemical data are given.