Oxidation: C-N Bond Formation by Oxidation (Aziridines)

Abstract

Enantioselective aziridination of alkenes represents a practical approach to accessing highly valuable enantioenriched aziridines, the smallest saturated azaheterocycles that serve as versatile chiral synthons for selective organic synthesis. Numerous efforts have been devoted to developing general and efficient methods for the construction of aziridines. Among these transition metal-catalyzed aziridination of alkenes with various nitrogen sources represents one of the most attractive methods. With the development of efficient catalytic systems including Cu, Rh, Mn, Ru, Ir, Ag, Fe, and Co complexes of elegant chiral ligands, the nitrogen sources have been extended beyond the initial hypervalent iodine compounds to various azide compounds with dinitrogen gas as the sole byproduct. It's noteworthy that the Co(II)-based metalloradical catalyst has been well developed and applied to aziridination of alkenes through a stepwise radical mechanism which is fundamentally different from the commonly used transition metal catalyst which through a concerted nitrene transfer mechanism or a stepwise process involving transient cationic or radical species in certain cases. This review will cover the recent developments on transition metal-catalyzed asymmetric aziridination of alkenes with various nitrogen sources. Furthermore, the newly emerged biocatalytic aziridination with hemoproteins will also be covered.