Stereoselective Synthesis of Pyrroloquinolines by a Brønsted Acid Catalyzed [4+2]‐Heterocyclization of Indole‐7‐Carbaldehydes, Anilines and Electron‐Rich Alkenes

Abstract

Thep yrrolo[3,2,1-ij]quinoline heterocyclic core is found in the structure of av ariety of compounds with interesting applications andt hen, new efficient andf lexible strategies to construct this skeleton are required. Here,anewd iastereoselective tetrafluoroboric acid (HBF 4 )-catalyzed threecomponent coupling reactiono f1 H-indole-7-carbaldehyde derivatives,a nilines and electron-rich alkenes to givep yrrolo[3,2,1-ij]quinolines is described. Thereactioninvolves an unusual [4+ +2]-heterocyclization between an in situ formed imine and an alkene.T he new catalytic method,w here water is the only by-product, is efficient, robust and flexible,and allows for multigram-scale synthesis.