The polyunsaturated compounds of formula ##STR1## having two conjugated double bonds in the endo- and exo- positions of the pentagonal cycle indicated by the dotted lines, and wherein symbols R.sup.1 and R.sup.2, when taken separately, represent respectively a. a linear or brached C.sub.1 to C.sub.4 alkyl radical and b. an hydrogen atom or a methyl radical, or, when taken together with the carbon atoms to which they are bonded form a polymethylenic cycle such as indicated by the dotted line, containing from 5 to 12 carbon atoms, and symbol R.sup.3 stands for an hydrogen atom or a methyl radical, n being an integer equal to 0 or 1, which are useful intermediate products for the preparation of odoriferous macrocyclic ketones, are prepared according to a process comprising a vapor phase cyclization of an enone of formula ##STR2## wherein the dotted line and the symbols n, R.sup.1, R.sup.2 and R.sup.3 are defined as above, effected by means of a thermal treatment of said enone in the presence of a cyclization catalyst consisting of an aluminum, silicium, titanium or zirconium oxide.
具有公式##STR1##的多不饱和化合物,在由虚线表示的五角环的内部和外部位置具有两个共轭双键,其中符号R.sup.1和R.sup.2,当分别取时,分别表示a.线性或支链C.sub.1到C.sub.4烷基基团和b.氢原子或甲基基团,或当与它们结合的碳原子形成所示的含有5到12个碳原子的多甲基环时,符号R.sup.3代表氢原子或甲基基团,n为等于0或1的整数,这些化合物是制备具有气味的大环酮的有用中间体产物,其制备方法包括通过在铝、
硅、
钛或
锆氧化物的环化催化剂存在下,对上述公式##STR2##的烯酮进行蒸汽相环化,其中虚线和符号n,R.sup.1,R.sup.2和R.sup.3如上所定义。