Stereochemistry of the singlet oxygenation of simple alkenes: A stereospecific transformation

The stereochemistry of the allylic oxidation (ene reaction) mediated by singlet oxygen (O-1(2)), using the optically active alkene (S,S)-cis-1,4-diphenyl-2-butene-1,4-d(2), in MeOH and aprotic solvents was investigated. Our findings indicate that the title reaction is a highly stereospecific suprafacial process, independent of solvent polarity. The observation of an isotope effect, which matches the stereogenic ratio exactly, rules out biradical or open dipolar intermediates.