We used rigid bicyclic aziridines (Scheme 1C), generated via silver-catalyzed nitrene transfer of homoallenic and homoallylic carbamates, as precursors to aziridinium ylides. The nitrogen of the carbamate tether in the bicyclic aziridine possesses a hybridization of ~ sp , where the nitrogen lone pair is unable to engage in effective orbital overlap with the π-system of the carbonyl group. As a result, the carbamate behaves as a σ-electron-withdrawing group and raises the barrier to N-pyramidal inversion. The geometric constraint imposed by the bicyclic nature of the tether also raises the nitrogen inversion barrier; 17 a similar effect is observed in rigid cyclic amines such as sparteine and Trӧger's base. Both of these unique structural characteristics can be exploited to generate diastereomerically pure aziridinium ylides that ultimately furnish highly substituted methyleneazetidines 20a-b and dehydropiperidines in excellent yield and dr (Scheme 1C). This strategy effectively circumvents competing pathways that have been observed in previous attempts to leverage the reactivity of aziridinium ylides. However, despite this progress, the future development of productive chemistry of aziridinium ylides requires a more detailed understanding of how the identity of the carbene precursor, potential dynamic behavior in the ylide intermediate and non-covalent interactions influence the ultimate outcome of the reaction. In this work, we describe our mechanistic findings to explain divergent reaction pathways from aziridinium ylides generated by leveraging ketone-containing carbenes, derived from Rh catalysis, to furnish fully substituted dehydromorpholines (Scheme 1D). Both experimental and computational studies are presented that will inform future efforts of our and other groups' work on these fascinating and versatile reactive species.