Stereochemistry of olefin and fatty acid oxidation. Part 2. Photosensitised oxidation of hexene and hepta-2,5-diene isomers

Abstract

The stereochemistry of the photosensitised oxidation of hex-1-ene, cis- and trans-hex-2-ene, cis- and trans-hex-3-ene, and of the three geometrical isomers of hepta-2,5-diene, has been investigated by the reduction or hydrogenation of the hydroperoxides produced and analysis of the resulting allylic or saturated alcohols. The isomeric distribution of hydroperoxides from hexene isomers is that expected from the concerted ene reaction of singlet oxygen with the parent olefin oriented so as to favour the cis, cyclic process. In contrast to autoxidation, photosensitised oxidation of hepta-2,5-diene isomers produces a mixture of conjugated (67–70%) and nonconjugated (30–33%) hydroperoxides. The conjugated products formed are explicable in terms of the conformations of the parent dienes which have the least steric interactions.