There is disclosed a process for preparing unsaturated ketones especially terpenoid ketones, by subjecting a substituted propargyl alcohol of formula (II) ##STR1## wherein R is a group containing 1 or 2 substituted or unsubstituted alkyl- or alkylene units containing 4 carbon atoms each to a thermal treatment sufficient to rearrange its structure in order to obtain structurally isomeric unsaturated ketones of formula I ##STR2## wherein one of the substituents X.sub.3 and X.sub.4 is hydrogen and the other and Z.sub.2 together form a bond. The process can be effected in the presence of an isomerization catalyst, which leads to high percentage of .alpha...beta.,.gamma...delta.-unsaturated ketones. The ketones of formula I are useful as perfumes and as intermediates for the production of terpenoid compounds.