The addition of singlet oxygen (O-1(2)) to the proximal alkene of auxi
liary-tethered 1,4-dienes and the addition of triplet oxygen (O-3(2))
to the proximal position of the corresponding pentadienyl radicals bot
h produce conjugated diene hydroperoxides in moderate to high diastere
omeric excess. Negligible stereoselection is observed for additions of
O-1(2) to the distal alkene of Z,Z-heptadienes due to the lack of con
trol of alkene conformation. Despite evidence for the intermediacy of
highly constrained pentadienyl radicals, poor diastereoselection is al
so observed for distal addition of O-3(2). The extent of olefin isomer
ization observed during radical oxygenations can be correlated with st
eric constraints on the intermediate pentadienyl and peroxyl radicals
and may be relevant to literature reports of olefin isomerization duri
ng enzymatic oxygenations of unnatural fatty acids. Copyright (C) 1996
Elsevier Science Ltd