Competition of Endoperoxide and Hydroperoxide Formation in the Reaction of Singlet Oxygen with Cyclic, Conjugated Dienes

The hydroperoxides 2–6 have now been detected as new products of the photooxidation of 1 with 1O2; the formation of two endoperoxides had already been demonstrated. On the basis of the product pattern, a common intermediate is proposed for the [4 + 2]-cycloaddition to give the endoperoxides and the ene reaction to give the hydroperoxides.