Muscone of the formula I ##STR1## is prepared by a process in which an open-chain 2,15-diketone of the general formula IICH.sub.3 --CO--X--CO--CH.sub.3 (II)whereX is one of the radicals--(--CH.sub.2 --).sub.12 -- (a)--CH.dbd.CH--(--CH.sub.2 --).sub.8 --CH.dbd.CH-- (b)--CH.sub.2 --CH.dbd.CH--(--CH.sub.2 --).sub.6 --CH.dbd.CH--CH.sub.2 --(c)--CH.sub.2 --CH.sub.2 --CH.dbd.CH--(--CH.sub.2 --).sub.4 --CH.dbd.CH--CH.sub.2 --CH.sub.2 -- (d)or--CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.dbd.CH--(--CH.sub.2 --).sub.2 --CH.dbd.CH--CH.sub.2 --CH.sub.2 --CH.sub.2 -- (e)is brought into contact, at from 300.degree. to 400.degree. C. in the presence of from 5 to 15% by weight, based on the amount of catalyst, of water, in the gas phase, with a fixed-bed catalyst containing TiO.sub.2, CeO.sub.2 or ThO.sub.2 as the catalytically active compound and the unsaturated cyclic ketone formed by intramolecular aldol condensation is subjected to catalytic hydrogenation. Furthermore, the open-chain unsaturated ketones of the formulae IIb, IIc and IId and advantageous processes for their preparation and their use as intermediates for a simple industrial synthesis of muscone are claimed.