Azoxy Compounds-From Synthesis to Reagents for Azoxy Group Transfer Reactions

The azoxy functional group is an important structural motif and represents the formally oxidized counterpart of the azo group. Azoxy compounds find numerous applications ranging from pharmaceuticals to functional materials, yet their synthesis remains underdeveloped with a main focus on the formation symmetric azoxy compounds. To overcome challenges in the synthesis of such unsymmetric azoxy compounds, we designed a process employing readily accessible nitroso compounds and iminoiodinanes. This method builds on the use of visible light irradiation to generate a triplet nitrene from iminoiodinanes, which is trapped by nitroso arenes to give access to sulfonyl-protected azoxy compounds with a good substrate scope and functional group tolerance. We further describe two applications of these sulfonyl-protected azoxy compounds as radical precursors in synthesis, where the whole azoxy group can be transferred and employed in C(sp3)-H functionalization of ethers or 1,2-difunctionalization of vinyl ethers. All of the reactions occurred at room temperature under visible light irradiation without the addition of any photoredox catalysts and additives. Control experiments, mechanism investigations, and DFT studies well explained the observed reactivity.

Automated summary

The azoxy functional group is an important structural motif, and its synthesis, especially unsymmetric azoxy compounds, remains underdeveloped. In this study, we designed a method using readily accessible nitroso compounds and iminoiodinanes to synthesize sulfonyl-protected azoxy compounds. Visible light irradiation was used to generate a triplet nitrene from iminoiodinanes, which then reacted with nitroso arenes. The resulting sulfonyl-protected azoxy compounds showed good substrate scope and functional group tolerance. We also demonstrated the use of these compounds as radical precursors in two synthesis applications without the need for photoredox catalysts and additives.