Nucleophilic vinylic substitution in bicyclic methyleneaziridines: SNVπ or SNVσ?

A stereodefined monodeuterated methylene aziridine is shown to be prepared via coordinated reductive ring-opening of an alkynyl epoxide and diastereoselective tethered allene aziridination. Ring-opening of this aziridine with copper-based organometallics follows a pathway that results in stereoretentive substitution, replacing the exo-C–N bond with a corresponding C–C bond; this stereochemical outcome supports either an overall SNVπ mechanism or a C–N insertion / reductive coupling process