title: Intramolecular and intermolecular kinetic isotope effects (KIE) in the nitrosoarene ene reaction: experimental evidence for reversible intermediate formation.
abstract: The intramolecular and intermolecular kinetic isotope effects (KIE) have been determined for the nitrosoarene ene reaction with deuterium-stereolabeled 2,3-dimethyl-2-butenes (TME). trans-TME-d(6) (k(H)/k(D) = 3.0) and gem-TME-d(6) (k(H)/k(D) = 4.0) show large intramolecular primary isotope effects. In contrast, the intramolecular competition in cis-TME-d(6) (k(H)/k(D) = 1.5) and the intermolecular competition for the TME-d(0)/TME-d(12) pair (k(H)/k(D) = 1.98) show considerably smaller, but mechanistically significant kinetic isotope effects. The latter fact is rationalized in terms of reversible formation of a three-membered-ring intermediate, namely the aziridine N-oxide, or a similar unsymmetrical, polarized diradical in the first step of the reaction. Such reversibility has also been implied earlier for triazolinedione (TAD) and singlet oxygen ((1)O(2)) with deuterium-stereolabeled 2-butenes, but of the three enophiles, ArNO is the most sensitive toward reversibility, which is due to its moderate reactivity and its high steric demand.
authors.affiliation: Institut für Organische Chemie, Universität Würzburg, Am Hubland D-97074 Würzburg, Germany. wadam@chemie.uni-wuerzburg.de
authors.forename: Waldemar
authors.initials: W
authors.lastname: Adam
authors.forename: Oliver
authors.initials: O
authors.lastname: Krebs
authors.forename: Michael
authors.initials: M
authors.lastname: Orfanopoulos
authors.forename: Manolis
authors.initials: M
authors.lastname: Stratakis
authors.forename: Georgios C
authors.initials: GC
authors.lastname: Vougioukalakis