Copper(I)-Catalyzed Dearomative (3+2) Cycloaddition of 3-Nitroindoles with Propargylic Nucleophiles: a Straightforward Entry for The Preparation of Cyclopenta[b]indolines

The copper(I)-catalyzed dearomatization of 3-nitroindoles with propargylic nucleophiles is described. In mild reaction conditions, this original dearomative (3+2) cycloaddition process gives access to a wide variety of cyclopenta[b]indolines in good to excellent yields, with high functional group tolerance. Furthermore, an enantioselective version of this reaction is reachable by employing chiral phosphorous ligands. A mechanism proposal is given, based on kinetic studies.