Ring-Degenerate Rearrangement Resulting from the Azo Coupling Reaction of a 3‑Aryl-1,3a,6a-triazapentalene

The 3-(4-(methoxy­carbonyl)­phenyl)­triaza­pentalene is a highly fluorescent small molecule which is readily accessible via a two-step synthesis. In the search for postfunctionalization methods, a radical CH-arylation with diazonium salts was attempted. However, azo coupling resulted in a ring-degenerate rearrangement toward a 2-aryl-4-azotriazapentalene, which was confirmed via crystallographic analysis. A mechanism involving the generation of a nitrilimine is proposed. In addition, reduction of the azo group led to cleavage of the triazapentalene core. The present results further demonstrate the sensitivity of the triazapentalene fluorophore.