In this paper, we report our investigations employing either substrate or catalyst control to divert the fate of intermediate aziridinium ylides along differing mechanistic pathways to favor formation of highly substituted azetidines or dehydropiperidines. The identity of the carbene precursor can impact whether ring expansion occurs in a concerted fashion to effectively transfer stereochemical information from the substrate to the product, or whether the reaction occurs in a stepwise fashion via formation of zwitterioninc intermediates. Switching from a conventional Rh2(esp)2 to an amide-supported Rh2(espn)2Cl catalyst for the key carbene transfer reverses the preference for a 4-vs. 6-membered N-heterocyclic product. Both the azetidines and piperidines are decorated with multiple functional handles to enable divergent elaborations of the products. A combination of computations and mechanistic studies provided support for our experimental observations.