jo0266240_si_001.pdf (71.84 kB)
Intramolecular and Intermolecular Kinetic Isotope Effects (KIE) in the Nitrosoarene Ene Reaction: Experimental Evidence for Reversible Intermediate Formation
journal contribution
posted on 2003-02-14, 00:00 authored by Waldemar Adam, Oliver Krebs, Michael Orfanopoulos, Manolis Stratakis, Georgios C. VougioukalakisThe 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-d6 (kH/kD = 3.0) and gem-TME-d6 (kH/kD = 4.0) show large intramolecular primary isotope effects.
In contrast, the intramolecular competition in cis-TME-d6 (kH/kD = 1.5) and the intermolecular
competition for the TME-d0/TME-d12 pair (kH/kD = 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 (1O2) 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.