Bronsted Acid Catalyzed [3+2]-Cycloaddition of 2-Vinylindoles with In Situ Generated 2-Methide-2H-indoles: Highly Enantioselective Synthesis of Pyrrolo[1,2-a]indoles

Pyrrolo[1,2-a]indoles are privileged structural elements of many natural products and pharmaceuticals. An efficient one-step process for their highly diastereo- and enantioselective synthesis, comprising a direct [3+2]-cycloaddition, has been developed. A chiral BINOL-derived phosphoric acid catalyzes the reaction of in situ-generated 2-methide-2H-indoles with 2-vinylindoles, furnishing the target products incorporating three contiguous stereogenic centers as single diastereoisomers and with excellent yields and enantioselectivities.