A FORMAL TOTAL SYNTHESIS OF (-TETRONOLIDE, THE AGLYCON OF THE TETROCARCINS - ENANTIOSELECTIVE AND DIASTEREOSELECTIVE SYNTHESES OF THE OCTAHYDRONAPHTHALENE (BOTTOM-HALF) AND SPIROTETRONATE (TOP-HALF) FRAGMENTS())

A formal total synthesis of (+)-tetronolide, the aglycon of the tetroc arcins, has been achieved by virtue of the development of highly diast ereo-and enantioselective syntheses of the bottom- and top-half fragme nts 4 and 5 reported herein. These fragments previously served as key intermediates in Yoshii's pioneering total synthesis of (+)-tetronolid e, The synthesis of the bottom-half octahydronaphthalene unit 4 featur es the intramolecular Diels-Alder reaction of tetraenal 20 and proceed s in 17 steps and 5-6% yield from D-glyceraldehyde pentylidene acetal 8. The synthesis of the spirotetronate fragment 5 features the highly enantioselective exo selective Diels-Alder reaction of triene 37 and c hiral dienophile 25b and proceeds in 14 steps and 10% overall yield fr om cis-2-butene-1,4-diol (38). An enantioselective synthesis of Boeckm an's top-half cyclohexene fragment 6 sia the exo selective Diels-Alder reaction of diene 24 and dienophile 25a was also developed, but this route was deemed too inefficient for use in a projected total synthesi s of the natural product. The syntheses of 5 and 6 provide important i nformation on the utility of chiral dienophiles 25a and 25b in organic synthesis.