Cascade Radical Cyclization of N-Propargylindoles: Substituents Dictate Stereoselective Formation of N-Fused Indolines versus Indoles

An efficient protocol for the synthesis of pyrrolo[1,2-a]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.