Synthesis of Indolo- and Benzothieno[2,3-]quinolines by a Cascade Cyclization of -Alkynylisocyanobenzene Derivatives.

A new synthetic approach for the synthesis of indolo[2,3-]quinolines and benzothieno[2,3-]quinolines has been developed by employing the freshly prepared -alkynylisocyanobenzenes derived from -alkynylformamide derivatives as substrates. The synthetic transformations involved chloride-ion-triggered 6- cyclization of -alkynylisocyanobenzenes to generate 2-chloroquinolines in situ, which further cyclized intramolecularly with nitrogen or sulfur atom via a cascade process to provide the corresponding indolo[2,3-]quinolines and benzothieno[2,3-]quinolines, respectively, in moderate to excellent yields.