N-Hydroxyphthalimide/TiO₂ Catalyzed Addition of Ethers, Alkylarenes and Aldehydes to Azodicarboxylates under Visible...

The addition of carbon-centered radicals to double bonds is one of the most atom-efficient approaches to the formation of new C-C or C-heteroatom bonds. Existing approaches for the generation of carbon-centered radicals often require elevated temperatures, UV radiation or expensive transition metal catalysts. In this work, a photocatalytic system based on a heterogeneous TiO₂ catalyst and a redox organocatalyst N-hydroxyphthalimide is proposed for the generation of carbon-centered radicals from C(sp³)-H substrates or aldehydes at room temperature under visible light irradiation. The developed approach was successfully applied to the addition of ethers, alkylarenes and aldehydes to azodicarboxylates. Titanium oxide acts as a photocatalyst, producing phthalimide-N-oxyl radicals from N-hydroxyphthalimide, thereby enabling the organocatalytic process in solution. Phthalimide-N-oxyl radicals act as catalytically active species that cleave C-H bonds to form carbon-centered radicals.