PURPOSE: To provide the unsaturated furan derivative usable for the perfumed compositions having woody-amber type odor properties.

CONSTITUTION: The compound of formula I (each dotted line shows a double bond.; R is H or methyl). The components comprised of a preponderant amount of 2,3a,4,5,5aβ,6,7,8,9,9a-decahydro-3aα,6,6,9aα-tetramethylnaphtho[2,1-b]furan of formula II and a minor amount of any of its isomers, (-)-(3aR)-1,2,3a,5,6,7,8,9,9 a,9bβ-decahydro-3aα,6,6,9aα-tetramethylnaphtho[2,1-blfuran of formula III and 2,3a,4,5,5a β6,7,8,9,9a-decahydro-3aα,6,6,7α,9aα-pentamethylnaphtho[2,1-b]furan of formula IV, are cited as the suitable perfuming components. The compound of formula I is obtained by cyclizing allenol of formula V by using an acidifying agent.