Transannular Diels-Alder reaction of the 14-membered (E,E,E)-trienone 9 and a discussion of its high diastereoselectivity based on MM2 transition-state model are presented. Macrocyclic reactions should follow a predictable course in organic synthesesl). if preparations and rapid conformational analyses of macrocycles could be easily managed. Recently transannular Diels-Alder reactions of the (E.E.El-trienes 1 and 2 were reported from P. Deslongchamps'2al and our laboratory2bl respectively. In these studies, the reaction of 1 produced a 1 : 2 mixture of tricycles havmg the cis-anti-trans and the trans-ant&is geometry In B-ring. while the reaction of 2 gave only the cIs-antItrans geomem. We report here transannular Diels-Alder reaction of the 14-membered (E.E.E)-trlenone 4. constructed by the intramolecular alkylation3) of the cyanohydrin 3. along with a discusslon of the stereochemfcal prtdlction based on MM2 transition-state models. Macrocycles have the n-orbltals of the olefin oriented In the plane of the ring to minimize transannular nonbonded repulslons4) (FIg.l. 41. Therefore. If two reactive centers In 4 are rIgidly locked at a short distance with two carbon chains. the transannular Dlels-Alder reaction should give the tricycllc compound 5 in better chemical yield and with higher stereoselectlvlty in comparison wlth an acyclic Dlels-Alder reaction like 3. because of the stereoelectronlc and entropy eflects in a macrocyclic system.