Chemoselective Cascade Synthesis of N-Fused Heterocycles via Silver(I) Triflate-Catalyzed Friedel-Crafts/N-C Bond Formation Sequence

An efficient cascade methodology toward chemoselective synthesis of N-fused heterocycles including 9H-pyrrolo[1,2-a] indole, 3H-pyrrolo[1,2-a]indole and 1H-pyrrolo[1,2-a]indole derivatives has been developed. This transformation proceeds via a silver(I) triflate-catalyzed consecutive Friedel-Crafts reaction/N-C bond formation sequence between readily available propargyl alcohols and 3-substituted 1H-indoles. Not only is excellent chemoselectivity observed according to the substitution patterns of propargyl alcohols, but also the Lewis acid-catalyzed N-C bond formation process can be carried out under base- and ligand-free conditions.