The formation of substituted 1,2-diamines via nucleophilic ring opening of a trisubstituted ethynyl aziridine was performed with complete regio- and stereoselective control. Various amines with different levels of nucleophilicity were employed and gave similar results. The ring opening reaction is not limited to ethynyl aziridines, as other alkyl trisubstituted aziridines gave the same results. This method allows for the formation of unique vicinal diamines while providing a fully substituted carbon center in a stereoselective manner under mild conditions.