Copper(I)-Catalyzed Dearomative (3 + 2) Cycloaddition of 3-Nitroindoles with Propargylic Nucleophiles: An Access to 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. The proof of concept that an enantioselective version of this reaction is accessible by employing chiral phosphorous ligands was obtained. A mechanism proposal is given based on kinetic studies.