Organocatalytic nitrogen transfer to unactivated olefins via transient oxaziridines

Organocatalytic nitrogen transfer to C=C bonds provides straightforward access to aziridines under mild conditions with low financial and environmental impacts; however, previous methods were typically limited to conjugated C=C bonds (that is, activated olefins), whereas aziridination of isolated C=C bonds (that is, unactivated olefins) remains underexplored. Here we demonstrate a strategy for nitrogen transfer to unactivated olefins by utilizing electron-deficient ketones as catalysts. An oxaziridine intermediate, generated in situ from the ketone catalyst and a nitrogen source, transfers nitrogen to unactivated C=C bonds preferentially over activated C=C bonds. This ‘unusual’ chemoselectivity, as well as the enantioselectivity realized through the use of a chiral ketone catalyst, cannot be achieved by previously developed methods that are based on either organocatalysts or metal catalysts. Moreover, mechanistic studies through modified mass spectrometry allow capture and further investigation of the transient oxaziridine intermediate, establishing its essential role in this nitrogen transfer process. There are very few methods for the organocatalytic aziridination of unactivated olefins. Here the authors report a simple ketone catalyst for the transfer of nitrogen to isolated carbon–carbon double bonds, with good substrate scope and in high yields.