Merging Photoredox with Brønsted Acid Catalysis: The Cross-Dehydrogenative C-O Coupling for sp C-H Bond Peroxidation.

A photoredox and Brønsted acid synergistically catalyzed cross-dehydrogenative C-O coupling reaction is developed in which isochroman peroxyacetals are formed through sp C-H bond peroxidation. The reported method is characterized by its extremely mild reaction conditions, excellent yields, and broad substrate scope. An oxocarbenium ion p-chlorobenzenesulfonate was speculated to be the reactive intermediate. The role of hemiacetals and oxygenated dimers on the effective stabilization of the oxocarbenium ion was investigated; the presence of acid appeared to establish equilibrium between hemiacetals and oxygenated dimers with the oxocarbenium ion pairs. The broad applicability of the method highlights the potential of the protocol for molecule synthesis.