In conclusion, we have demonstrated a new method for the synthesis of highly substituted dehydromorpholines through the intermediacy of aziridinium ylides. The development of this chemistry has enabled the extension of aziridinium ylide chemistry to the concomitant formation of both a C-N and a C-O bond in a manner that preserves the stereochemical information embedded in the substrate aziridine. The chemistry is tolerant of a wide range of functionalities that we will employ for attachment to DNA in DEL synthesis to prepare diverse libraries of heterocycles with useful bioactivity. In addition, we have uncovered several key insights that describe the importance of steric effects, rotational barriers around the C-N bond of the aziridinium ylide, and NCIs on the ultimate reaction outcome. These critical insights will assist in the further development of this chemistry to generate novel and complex N-heterocycles that will further expand complex amine chemical space.