Our group previously reported a C2 + N1 catalytic aziridination with an iron-NHC catalyst. This catalyst was successful with aliphatic alkenes and aryl azides although excess alkene was required. However, for catalytic C2 + N1 aziridination to be effective in organic synthesis a variety of functionalities on the nitrogen must be available. Furthermore, the reaction must be effective with both protic and non-protic functional groups on the aziridine. More subtly, the alkene to nitrene ratio must be reasonable. We are addressing all of these aspects with a variety of next-generation catalysts. A second generation iron complex with borate based NHC system provides superior catalytic activity for aziridination with aryl azides and is also effective with alkyl azides, leading to the first example of this methodology for fully alkyl aziridination. Five- and six-membered bicyclic tertiary aziridines were synthesized via intramolecular reactions which are key in natural products with aziridines. Chromium catalysts are effective for protic functional group tolerance and allow lower alkene loading than the iron catalysts. Finally, we discuss a reaction mechanism based on DFT and experimental results and how this allows development of improved catalysis.

Towards effective catalytic C2 + N1 aziridination with organic azides for organic synthesis

253rd National Meeting (2017)

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