Singlet oxygen (1O2) exhibits a substantial reactivity toward electron-rich organic molecules, leading to the formation of allylic hydroperoxides, dioxetanes, or endoperoxides. 1 Singlet oxygen has been shown to be generated in biological systems. 2 As possible biological sources of 1O2, we may mention enzymatic processes catalyzed by peroxidases or oxygenases, 3 reactions of hydrogen peroxide with hypochlorite4 or peroxynitrite, 5 ...