Lewis Acid Mediated Cascade Friedel–Craft/Alkyne Indol-2-yl Cation Cyclization/Vinyl Cation Trapping for the Synthesis of <i>N</i>‑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 <i>N</i>-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

Cascade Radical Cyclization of <i>N</i>‑Propargylindoles: Substituents Dictate Stereoselective Formation of <i>N</i>‑Fused Indolines versus Indoles

An efficient protocol for the synthesis of pyrrolo­[1,2-<i>a</i>]­indole derivatives having sulfide functionality using cascade radical cyclization on propargylindole is described. The nature of the substituents at the propargylic carbon bearing nitrogen of the indole has a profound effect on the rate, yield, and nature of the product obtained by the cascade radical cyclization. An expeditious one-pot route for cascade radical cyclization–desulfurization is also presented. Products obtained were elaborated to the core of the putative structure of the yuremamine and indoline derivative with five contiguous stereocenters

Counter-Ion-Dependent Alkyne Iminium Ion Cyclization for Divergent Synthesis of <i>N</i>‑Fused Indolylidine, Indole, and Indoline Derivatives Promoted by the Lewis/Bronsted Acid

Divergent synthesis of <i>N</i>-fused indolylidine, indole, and indoline derivatives using alkyne iminium ion cyclization is described. Trapping of vinyl cation intermediate generated after alkyne iminium ion cyclization was found to be dependent on the Lewis/Bronsted acid and solvent used. <i>N</i>-Fused indolylidine triflate could be used in the divergent synthesis of <i>N</i>-fused indole derivatives

Lewis Acid Promoted Oxonium Ion Driven Carboamination of Alkynes for the Synthesis of 4‑Alkoxy Quinolines

Lewis acid mediated multisegment coupling cascade is designed for the synthesis of densely substituted 4-alkoxy quinolines via an oxonium ion triggered alkyne carboamination sequence involving C–C and C–N bond formations. Cyclic ether fused-quinolines could also be accessed using this fast, operationally simple, high yielding, chemoselective and functional group tolerant method. Versatility and utility of this methodology is demonstrated by postfunctionalization of products obtained and its use in synthesis of potent drug molecules