Effective Synthesis of Chiral N-Fluoroaryl Aziridines through Enantioselective Aziridination of Alkenes with Fluoroaryl Azides

摘要

Catalytic aziridination of alkenes with nitrene sources through "C2+N1" addition represents a general approach for the direct synthesis of aziridines, the smallest three-membered N-heterocycles. The enantioselective version of this catalytic process allows for efficient access to chiral nonracemic aziridines, which are versatile synthetic intermediates in asymmetric synthesis. Several classes of transition-metal-based chiral catalysts, such as Mn, Fe, Cu, Rh, and Co complexes, are effective in catalyzing asymmetric olefin aziridination with different nitrene sources. Besides iminoiodanes and haloamines, organic azides, which enjoy several advantages, have been actively pursued as alternative nitrene sources for metal-catalyzed aziridination. While sulfonyl and phosphoryl azides have been effectively employed for metal-catalyzed asymmetric aziridination catalytic processes based on the use of other types of azides, such as aryl azides, are less developed. In addition to generating environmentally friendly nitrogen gas as the only by-product, the asymmetric catalytic aziridination with readily available aryl azides provides an attractive approach for the synthesis of valuable N-aryl aziridines through direct introduction of N-aryl groups concurrently with the ring formation. This method would avoid two additional steps of deprotection and N-arylation when other types of nitrene sources such as sulfonyl azides are used for preparing N-aryl aziridines. However, few catalytic systems are effective for the asymmetric olefin aziridination with aryl azides.