A drastic acceleration of a Diels-Alder reaction under adsorption conditions

A Study of the Diastereoselectivity of Diels-Alder Reactions on the Ce-SiO2as Support

“…23 Vesselovskii and coworker have proposed that the adsorption of reactants on the surface of silica particles may facilitate the formation and stabilization of pre-reaction complexes by bringing the reacting moieties within each reactant into closer proximity. 24 A related theory has been advanced by Menger who suggested that the rigid anchoring of functional groups can fix reactants in proximity to each other less than the critical bonding distance, thus leading to significant rate enhancements. 25 An alternative theory introduced by Parlar and Baumann 26 who suggested that only a small fraction of reactants are actually strongly adsorbed on the silica surface and that the enhanced rates and selectivities are caused by symmetry controlled secondary orbital interactions between strongly adsorbed species and species that are free to move about on the surface.…”