Chiral-Boron-Complex-Catalyzed Asymmetric [3 + 2] Cycloaddition of β-Trifluoromethyl α,β-Unsaturated Ketones with N,N′-Cyclic Azomethine Imines

The ( R )-3,3′-(3,5-(CF 3 ) 2 -C 6 H 3 ) 2 -BINOL–boron–complex-catalyzed asymmetric 1,3-dipolar cycloaddition of β-trifluoromethyl α,β-unsaturated ketone with N,N ′-cyclic azomethine imines was developed to afford N,N ′-bicyclic pyrazolidine derivatives bearing a stereogenic carbon center containing CF 3 motifs in high yields with excellent diastereo- and enantioselectivities (up to >20:1 dr, and >99% ee). This catalytic system features mild reaction conditions, high efficiency, and a broad substrate scope.