Singlet oxygen-mediated selective C-H bond hydroperoxidation of ethereal hydrocarbons

Abstract

Singlet O2 is a key reactive oxygen species responsible for photodynamic therapy and is generally recognized to be chemically reactive towards C=C double bonds. Herein, we report the hydroperoxidation/lactonization of α-ethereal C-H bonds by singlet O2 (1Δg) under exceptionally mild conditions, i.e., room temperature and ambient pressure, with modest to high yields (38~90%) and excellent site selectivity. Singlet O2 has been known for > 90 years, but was never reported to be able to react with weakly activated C-H bonds in saturated hydrocarbons. Theoretical calculations indicate that singlet O2 directly inserts into the α-ethereal C-H bond in one step with conservation of steric configuration in products. The current discovery of chemical reaction of singlet oxygen with weakly activated solvent C-H bonds, in addition to physical relaxation pathway, provides an important clue to a 35-year-old unresolved mystery regarding huge variations of solvent dependent lifetime of singlet O2.