141956-92-5Relevant articles and documents
Stepwise mechanisms in the ene reaction of α,β-unsaturated esters with N-phenyl-l,2,4-triazoline-3,5-dione and Singlet oxygen. Intermolecular primary and secondary hydrogen isotope effects
Elemes, Yiannis,Foote, Christopher S.
, p. 6044 - 6050 (2007/10/02)
Intermolecular primary and secondary isotope effects on the ene reaction of N-phenyl-l,2,4-triazoline-3,5-dione (PTAD) and singlet oxygen (1O2) with deuterium-substituted (E)-2-methylbuten-2-oic (tiglic) acid methyl esters have been determined. In the case of 1O2, the primary isotope effect is 1.30-1.49 and the α and β secondary isotope effects are near unity, consistent with a stepwise reaction path via a perepoxide intermediate, where the allylic hydrogen-abstraction step is rate determining. On the other hand, the existence of both primary (1.44) and inverse α and β secondary isotope effects (0.91 and 0.77, respectively) in the PTAD reaction is consistent with either a concerted or a stepwise mechanism. Experiments in which both intermolecular primary and secondary isotope effects were measured at the same time suggest that, like singlet oxygen, PTAD reacts in a stepwise manner with the formation of the aziridinium imide interme diate (AI) in the rate-determining-step.
