N-Aminopyridinium Reagents as Traceless Activating Groups in the Synthesis of N-Aryl Aziridines

N-functionalized aziridines, which are both useful intermediates and are present in important synthetic targets, can be envisioned as arising from the direct addition of nitrenes (i.e., NR fragments) to olefinic substrates. The exceptional reactivity of most nitrenes, in particular with respect to unimolecular decomposition reactions, prevents general application of nitrene-transfer chemistry to the synthesis of N-functionalized aziridines. Here we describe a strategy for the synthesis of N-aryl aziridines based on 1) olefin aziridination with N-aminopyridinium reagents to afford N-pyridinium aziridines followed by 2) Ni-catalyzed C–N cross-coupling of the N-pyridinium aziridines with aryl boronic acids. The N-pyridinium aziridine intermediates also participate in ring-opening chemistry with a variety of nucleophiles to afford 1,2-aminofunctionalization products. Preliminary mechanistic investigations indicate aziridine cross-coupling proceeds via a noncanonical mechanism involving initial aziridine opening promoted by the bromide counterion of the Ni catalyst, C–N cross-coupling, and finally aziridine reclosure. Together, these results provide new opportunities to achieve selective incorporation of generic aryl nitrene equivalents in organic molecules.