Photosensitised oxidation of model unsaturated lipid systems: (4Z,7Z)-undeca-4,7-diene and (4Z)-undec-4-en-7-yne

Abstract

Photosensitised oxidation of the skipped diene (4Z,7Z)-undeca-4,7-diene (4) gave non-conjugated and conjugated dienyl hydroperoxides (5a) and (5b) in the ratio 2 : 3. Free radical cyclisation of (5a) yielded two stereoisomeric dioxolanyl hydroperoxides (9) and (10). (4Z)-Undec-4-en-7-yne (3) led, on photosensitised oxidation, to non-conjugated and conjugated enynyl hydroperoxides (15) and (14) in the ratio 1 : 2. Undeca-4,7-diyne (2) proved comparatively resistant to photosensitised oxidation, with the relative rates of attack on (4) : (3) : (2) being 110 : 15 : ⩽ 1. There was no evidence for the abstraction of the prop-2-ynyl hydrogen by singlet oxygen in these reactions.