Divergent C-H Annulation for Multifused N-Heterocycles: Regio- and Stereospecific Cyclizations of N-Alkynylindoles

Abstract

N-Alkynylindoles were divergently cyclized for the synthesis of multifused N-heterocycles. An ortho-aryl palladium species was added to the α position of an ynamine to generate (Z)-6-alkylidene/benzylidene-6H-isoindolo[2,1-a]indoles, while Pt-catalyzed β-addition through π-activation gave 5-alkyl/arylindolo[2,1-a]isoquinolines. Double cyclizations using PdCl₂ and oxidant afforded bright yellow benzo[7,8]indolizino[2,3,4,5-ija]quinolines, the synthesis of which was also demonstrated in a different synthetic route.

Keywords: C−H activation; annulation; fused-ring systems; ynamines; π-activation.