Experiments from the group of Mike Jung in the Department of Chemistry and Biochemistry at UCLA have shown that intramolecular Diels-Alder cycloadditions in which the tether between the diene and dienophile contains an ester group produce products arising from boatlike transition states. Jung proposed that this unusual stereochemical outcome is the result of the energetic penalty associated with twisting the ester out of planarity in the cycloaddition transition statesÑan effect which should be larger in chairlike transition states than in the boatlike cases. This proposal was validated through density functional calculations of transition state geometries and energies. Calculations on related cycloadditions with amide tethers suggest that the boatlike preference will be even greater in these systems; experiments to test this prediction are underway.
Tantillo, D. J.; Houk, K. N.; Jung, M. E. J. Org. Chem. 2001, 66, 1938-1940: "Origins of Stereoselectivity in Intramolecular Diels-Alder Cycloadditions of Dienes and Dienophiles Linked by Ester and Amide Tethers"
