Hyperconjugative Aromaticity and Antiaromaticity Control the Reactivities and ?-Facial Stereoselectivities of 5-Substituted Cyclopentadiene Diels-Alder Cycloadditions.

ABSTRACT: The reactivities and ?-facial stereoselectivities of Diels-Alder reactions of 5-substituted cyclopentadienes were studied using density functional theory. Burnell and co-workers previously showed that the ?-facial selectivities result from the energies required to distort the reactants into the transition state geometries. We have discovered the origins of these distortions. C5-X ?-donors predistort the cyclopentadiene into an envelope conformation that maximizes the stabilizing hyperconjugative interaction between the C5-X ?-bond and the diene ?-system. This envelope conformation geometrically resembles the anti transition state. To minimize the destabilizing effect of negative hyperconjugation, C5-X ?-acceptors predistort in the opposite direction toward an envelope geometry that resembles the syn transition state. We now show how hyperconjugative effects of the C5-X substituent influence the stereoselectivities and have developed a unified model rationalizing the stereoselectivities and reactivities of 5-substituted cyclopentadiene Diels-Alder reactions.

SUBMITTER: Levandowski BJ 

PROVIDER: S-EPMC6467786 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature