Lewis Acid Mediated Cascade Friedel-Craft/Alkyne Indol-2-yl Cation Cyclization/Vinyl Cation Trapping for the Synthesis of N-Fused Indole Derivatives.

A Lewis acid promoted cascade Friedel-Craft/alkyne indol-2-yl cation cyclization/vinyl cation trapping for an efficient and divergent synthesis of N-fused indoles is developed. The present study illustrates the first example of an alkyne as a nucleophile on the less explored indol-2-yl cation. The method efficiently affords pharmaceutically important pyrrolizino-quinolines and complex fused indole derivatives in high yields.