TiO2 Photocatalytic Cyclization Reactions for the Syntheses of Aryltetralones

This work focuses on a new strategy to overcome the overoxidation in heterogeneous TiO2 photocatalysis and to realize high-efficiency photosynthesis. We demonstrate that TiO2 photocatalysis can integrate C–C and CO formation in a tandem manner to achieve efficient oxidative cyclization for the syntheses of aryltetralones. This protocol does not need any additive besides the inexpensive and/or recyclable TiO2, O2, and (solar) light. High yields with excellent diastereoselectivities are obtained for a wide scope of electron-rich substrates. Our findings demonstrate that in contrast to the conventional overoxidation, as long as the radical cations possess sufficient reactivity toward nucleophilic addition, single-electron transfer processes in TiO2 photocatalysis can be developed into a powerful tool to construct C–C bonds and even strained carbon rings.