Stereochemistry of the singlet oxygenation of simple alkenes: a stereospecific transformation.

The stereochemistry of the allylic oxidation (ene reaction) mediated by singlet oxygen ((1)O2), using the optically active alkene (S,S)-cis-1,4-diphenyl-2-butene-1,4-d2 , 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.