Stereocontrol of intramolecular Diels-Alder reactions: Synthetic studies and transition structure modeling with C5-substituted 1,3,8-nonatrienes and nonadienynes

An investigation into the endo/exo selectivity and iz-diastereofacial selec tivity of ester-tethered intramolecular Diels-Alder reactions is reported. High levels of exo selectivity are realized with terminally substituted die nophiles, and high Lk rr-diastereofacial selectivities are induced by the p resence of a bulky dioxolanyl substituent at the allylic position of the te ther. Precursors 19S, 20S, and 21S, readily prepared from glucose, provide densely functionalized bicyclic lactones of predictable stereochemistry in high yields in enantiomerically pure form upon thermolysis at 110 degreesC. B3LYP/6-31G(d) theory provides good descriptions of transition structures for these reactions and allows an understanding of the formation of the maj or cycloadducts.