Asymmetric Synthesis of Pyrrolo[1,2-a]indoles via Bifunctional Tertiary Amine Catalyzed [3+2] Annulation of 2-Nitrovinylindoles with Azlactones

Abstract

The chiral pyrrolo[1,2-a]indole represents a privileged stuctural motif in many natual products and pharmaceutical agents. Herein we developed an efficient [3+2] annulation of 2-nitrovinylindoles with azlactones via the cascade Michael addition and intramolecular acylation under the catalysis of bifunctioanl tertiary amine in combination with DABCO, delivering a wide range of pyrrolo[1,2-a]indoles in good yields with high diastereo- and enantioselectivities. Alternatively, 7-nitrovinylindoles are served as 4C-synthons to perform the enantioselective [4+2] annulation under the identical condition, smoothly giving the pyrrolo[3,2,1-ij]quinoline skeleton with good to high stereoselectivities. Furthermore, a novel enantio-enriched indole-based tetracyclic skeleton was facilely derived from the obtained pyrrolo[1,2-a]indoles.