Asymmetric [3+2] Cycloaddition Employing N,N'-Cyclic Azomethine lmines Catalyzed by Chiral-at-Metal Rhodium Complex

An efficient asymmetric 1,3-dipolar cycloaddition of alpha,beta-unsaturated 2-aryl imidazoles with N,N'-cyclic azomethine imines catalyzed by a chiral-at-metal rhodium complex is reported. The corresponding N,N'-bicyclic pyrazolidine derivatives with three contiguous tertiary stereocenters were obtained in good yields (up to 99%) with excellent stereoselectivities (>20:1 dr and >99% ee). Remarkably, as little as 0.5 mol % of a chiral Rh(III) complex can promote a gram-scale reaction with excellent yield and enantioselectivity.