The use of visible light—the ultimate renewable source of energy—to enable organic reactions is a useful development. Azimines (or azo imides, example pictured in the blue box) are all-nitrogen 1,3-dipolar compounds, which can be useful, e.g., in cycloaddition reactions, as dyes, or in energetic materials. One path to azimines involves the reaction of a nitrene with an azo compound. However, this approach suffers from poor atom economy and uses stoichiometric conditions. A catalytic, light-driven approach could be a useful alternative.

Lionel Joucla, Emmanuel Lacôte, Université Claude Bernard Lyon 1, CNRS, CNES, ArianeGroup, LHCEP, Villeurbanne, France, and colleagues have developed a mild photocatalytic method to access azimines from sulfonyl azides and dialkyldiazenes (example pictured). The team reacted a variety of sulfonyl azides (RSO₂N₃) with different electron-rich azo reagents (R’N=NR’) in the presence of the iridium photocatalyst [Ir(dmppy)₂dtbbpy]PF₆ (dmppy = dimethylphenylpyridin, dtbbpy = di-tert-butyldipyridine) under blue LED light at room temperature, using CH₂Cl₂ as the solvent. The desired products were obtained in moderate to good yields.

The team proposes that the reaction might proceed via the sensitization of the azo reagent, which undergoes a tandem dipolar cycloaddition/retro cycloaddition with the azide. The method shows that photocatalysis can be harnessed to construct N–N bonds, which can be a challenging task. Interestingly, the reaction could be implemented in a continuous-flow process. This is an important feature from an industrial and safety standpoint because poly-nitrogenated structures can be hazardous and impact/friction sensitive.

• Mild Photocatalytic Synthesis of Azimines,
  Emma Gamby, François Liger, Lionel Joucla, Emmanuel Lacote,
  Eur. J. Org. Chem. 2022.
  https://doi.org/10.1002/ejoc.202201071