Chiral Bis(imidazolidine)pyridine-Cu(OTf)_2: Catalytic Asymmetric Endo-Selective [3 + 2] Cycloaddition of Imino Esters with Nitroalkenes

摘要

Pyrrolidines, which are five-membered N-heterocycles, are widely observed in biologically significant compounds and thus have become a core skeleton of many drug candidates. Catalytic asymmetric 1,3-dipolar cyclization using chiral metal catalysts (containing metals such as Co, Zn, Ag, Cu, Ca, and Ni) and organocatalysts for the stereoselective construction of the pyrrolidine ring has been successfully developed. In particular, the reaction of the azomethine ylide generated from an imino ester and a nitroalkene is a fascinating reaction system in which an additional nitro functionality can be introduced onto the pyrrolidine ring.