Synthesis of Indole Derivatives via Aryl Triazole Ring-Opening and Subsequent Cyclization

A metal-free two-step synthetic approach for obtaining indole derivatives from aryl triazole fragment-containing compounds has been developed. In the first step, the Dimroth equilibrium, followed by nitrogen extrusion, Wolff rearrangement, and amine nucleophile addition, leads to the formation of <i>N</i>-aryl ethene-1,1-diamines. In the second step, the latter intermediates are cyclized into the target 1<i>H</i>-indoles in the presence of iodine. The developed method ensures the synthesis of indoles that possess <i>N</i>-substituents at the indole <i>C</i>2 position. Depending on the applied <i>N</i>-nucleophile, the indolization step provides a selectivity either towards 1<i>H</i>-indoles or 1-aryl-1<i>H</i>-indoles.