Intermediates in the ene reactions of singlet oxygen and N-phenyl-1,2,4-triazoline-3,5-dione with olefins

Article abstract of DOI:10.1021/ja00165a053

The reaction between singlet oxygen and cis- and trans-2-butene-1,1,1-d₃ has been studied. The product isotope effects (k(H)/k(D)) were found to be 1.38 and 1.25, respectively. Similarly, N-phenyl-1,2,4-triazoline-3,5-dione (PTAD) reacts readily with these substrates and shows isotope effects that are larger (5.36, 1.29) but in the same direction. 2-Methyl-1-propene-3,3,3-d₃ is unreactive with singlet oxygen but reacts easily with PTAD with a product isotope effect of 1.25. The intermolecular (kinetic) and intramolecular (product) isotope effects on the reactions of singlet oxygen with cis-1,4-diphenyl-2-butene were found to be 1.07 and 1.50, respectively. cis-Butene is 18 times more reactive with singlet oxygen than the trans isomer. Ene reactions for both singlet oxygen and PTAD probably proceed through the reversible formation of an intermediate with structural requirements similar to a perepoxide or aziridinium imide, respectively.