Synthesis of 5-Iodopyrrolo[1,2-a]quinolines and Indolo[1,2-a]quinolines via Iodine-Mediated Electrophilic and Regioselective 6-endo-dig Ring Closure

The endo-cyclic ring closure of 1-(2-(substituted ethynyl)phenyl)-1H-pyrroles 3a–t and 1-(2-(substituted ethynyl)phenyl)-H-indole 4a–o mediated by Lewis acid (I2) under mild conditions afforded substituted 5-iodopyrrolo[1,2-a]quinolines 5a–t and 5-iodoindolo[1,2-a]quinolines 6a–o in good to excellent yields. The reaction shows selective C–C bond formation on the more electrophilic alkynyl carbon, resulting in the regioselective 6-endo-dig-cyclized product. Iodo derivatives of pyrrolo- and indoloquinolines allow functional group diversification on the quinoline nucleus, which proves to be highly advantageous for structural and biological activity assessments.