Synthesis of Azo Dyes from Mesoionic Carbenes and Nitrous Oxide

다국어 초록 (Multilingual Abstract)

Covalent adducts of imidazole‐based mesoionic carbenes and nitrous oxide (N2O, “laughing gas”) can be converted into azo dyes by reaction with arenes in the presence of AlCl3 or HCl. The azo coupling can be achieved with electron‐rich aromatic compounds such as mesitylene, trimethoxybenzene, azulene, or dibenzo‐18‐crown‐6. The latter coupling reaction allows for the easy preparation of a colorimetric sensor for potassium or sodium ions. As a putative intermediate of the reaction with acid, we were able to isolate and structurally characterize a rare diazohydroxide. Using imidazolium compounds with two N2O groups, it was possible to prepare amine‐substituted azo dyes or dyes with two azoarene groups attached to the heterocycle. A triazole‐based mesoionic carbene was also found to form a stable covalent adduct with N2O. The adduct could be used to prepare novel azo triazolium dyes in good yields.
Live and let dye: N2O adducts of mesoionic carbenes are shown to be suitable starting materials for the preparation of dyes. AlCl3‐ or HCl‐induced azo coupling with electron‐rich aromatic compounds gives dyes with strong absorption bands in the λ=372–517 nm range. The possibility to use plain aromatic compounds as coupling partners is a distinct advantage of this methodology.