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

Abstract

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.

Aziridination via Nitrogen-Atom Transfer to Olefins from Photoexcited Azoxy-Triazenes

“…28 In the preparation of this manuscript, the Koenigs group illustrated that tosyl-protected azoxyarenes are capable of undergoing direct visible-light excitation leading to N-S bond homolysis to achieve group transfer of the azoxy to alkenes. 29 Conversely, we postulated that the use of a phthalimide-protected azoxy-triazene, featuring a stronger N-N over an N-S bond, may lead to a nitrogen-atomtransfer of a phthalimide-protected amine under visible-light irradiation for the functionalization of alkenes. To test our hypothesis, we subjected 4-fluorostyrene (1a) and readily synthesized 1-phenyl-2-phthalimidodiazene-1oxide (AT1) 28,30,31 in dichloromethane to 390 nm light irradiation, which resulted in the desired nitrogen-atom-transfer event leading to the aziridine product (2a) in 70% 1 H NMR yield.…”

Visible-light-mediated catalyst-free synthesis of trifluoromethyl(spiro)-epoxides bearing contiguous quaternary centers

“…Over the last decades, visible-light-mediated organic synthesis has been recognized as a powerful and sustainable route to construct small molecules. 38–51 Indeed, the first metal-catalysed epoxide synthesis mediated by visible light (halogen lamp) was reported by Katsuki's group. 52 Even though the mechanism of this epoxidation was not fully clarified, it still tremendously advanced the domain of epoxidation chemistry.…”

Aziridination via Nitrogen-Atom Transfer to Olefins from Photoexcited Azoxy-Triazenes

“…In 1981, Hoesch and Köppel reported a single example of using azoxyarenes as nitrene precursors under harsh UV light . Recently, the Koenigs group illustrated that tosyl-protected azoxyarenes can undergo direct visible-light excitation leading to N–S bond homolysis to achieve group transfer of the azoxy to alkenes . Conversely, we postulated that the use of a phthalimide-protected azoxy-triazene, featuring a stronger N–N over an N–S bond, may lead to a nitrogen-atom transfer of a phthalimide-protected amine under visible-light irradiation for the functionalization of alkenes.…”