Asymmetric [3 + 2] Cycloaddition Employing <i>N</i>,<i>N′</i>-Cyclic Azomethine Imines Catalyzed by Chiral-at-Metal Rhodium Complex

An efficient asymmetric 1,3-dipolar cycloaddition of α,β-unsaturated 2-acyl imidazoles with <i>N</i>,<i>N′</i>-cyclic azomethine imines catalyzed by a chiral-at-metal rhodium complex is reported. The corresponding <i>N</i>,<i>N′</i>-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