Oxidative [4+2] annulation of styrenes with alkynes under external-oxidant-free conditions

The sequenced Diels–Alder/oxidation reaction represents a powerful route for the construction of aromatic compounds in organic synthesis. The oxidative Diels–Alder reaction with H 2 evolution would be a more ideal approach that can avoid the additional oxidation procedure and stoichiometric oxidant. Herein, an oxidative [4 + 2] annulation reaction of styrene derivatives with electron-rich dienophiles accompanying the H 2 generation has been developed by using the synergistic merger of photoredox and cobaloxime catalyst. With respect to atom and step-economy ideals, this dual catalytic system enables the formation of high-value molecules from feedstock chemicals in a single step under room temperature. A sequence of a Diels–Alder reaction and oxidation is a powerful route to valuable aromatic compounds. Here, the authors report a more atom-economical oxidant-free strategy involving a Diels–Alder with H 2 evolution under noble-metal-free photoredox conditions.