Nucleophilic vinylic substitution in bicyclic methyleneaziridines: SV or SV?

A stereodefined monodeuterated methyleneaziridine 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 S N V π mechanism or a C-N insertion/reductive coupling process. A stereoselective synthesis of the monodeuterated methyleneaziridine shown allowed the stereochemical course of formal S N V-mode ring-opening with copper-based organometallics to be assigned.