title: Experiments probing the viability of donor-acceptor norbornenes for (5 + 2)-annulation.
abstract: This Note details experiments that probe the mechanism by which donor-acceptor norbornene systems epimerize. A number of mechanistic studies indicate that epimerization in these systems occurs via a Lewis acid catalyzed retro-Diels-Alder/Diels-Alder sequence, rather than bond rotation in an intimate ion pair. These results suggest that, under the reaction conditions examined, the ring strain present in norbornene is inadequate to induce zwitterion formation analogous to that observed with donor-acceptor cyclopropanes.
authors.affiliation: Department of Chemistry, The University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Morgan M
authors.initials: MM
authors.lastname: Walker
authors.forename: C Guy
authors.initials: CG
authors.lastname: Goodman
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Johnson