Metalloradical activation of carbonyl azides for enantioselective radical aziridination

The carbonyl azide TrocN3 (2,2,2-trichloroethoxycarbonyl azide) is a potent nitrogen radical precursor for radical olefin aziridination via Co(II)-based metalloradical catalysis (MRC). The cobalt(II) complex of D2-symmetric chiral amidoporphyrin 3,5-DitBu-QingPhyrin proves to be an efficient catalyst that can activate TrocN3 at room temperature to aziridinate various styrene derivatives, providing chiral N-carbonyl aziridines in high yields with excellent enantioselectivities. The new Co(II)-based catalytic system can even enable asymmetric aziridination of electron-deficient alkenes, such as methyl and ethyl acrylates. In addition to facile removal of Troc group for generation of unprotected aziridines, the resulting N-Troc-aziridines can be effectively opened by different types of nucleophiles to afford a series of chiral amine derivatives with excellent stereospecificity. Several lines of computational and experimental evidence support the underlying stepwise radical mechanism for Co(II)-catalyzed olefin aziridination. This represents the first example of asymmetric intermolecular olefin aziridination that employs carbonyl azides as the nitrogen source.