On the illusive nature of o-formylazobenzenes: exploiting the nucleophilicity of the azo group for cyclization to indazole derivatives.

Facile rearrangement of azobenzenes is shown to occur in cases where the azo group is placed in the ortho position to carbonyl electrophiles to furnish the indazole skeleton. While this study demonstrates the illusive nature of o-formylazobenzenes, it offers potential for the synthesis of indazoles and related heterocycles.