Trienes 1 and 3 were obtained in five steps from ethyl 4-acetoxy-3-oxobutanoate and 6-iodo-3-methyl-1,3-hexadiene. Intramolecular Diels−Alder cyclization of 1 and 3 gave tricyclic lactones 2and 4 as the major products, respectively. The key intermediate 4 was converted in two steps totrans-dihydroconfertifolin (5).