4-Methylpent-4-en-2-yn-1-ols and 6-hydroxy-2, 3-dihydro-6H-pyran-3-ones are condensed in different ways to a series of tricyclic dioxadienones which contain the basic framework of the cadlinolides. A mechanism of the intramolecular enyne-ene cycloisomerization and the origin of the resulting type I and type II dienes is proposed.