Enantioselective 1,3-Dipolar Cycloaddition of C,N‑Cyclic Azomethine Imines to Unsaturated Nitriles Catalyzed by NiII–Pigiphos

The asymmetric 1,3-dipolar cycloaddition reaction of C,N-cyclic azomethine imines with small unsaturated nitriles using a dicationic Ni­(II) complex containing the chiral triphosphine ligand bis­{(R)-1-[(Sp)-2-(diphenyl­phosphino)­ferro­cenyl]­ethyl}­cyclo­hexyl­phosphine [(R,Sp)-Pigiphos] as a catalyst has been developed. A variety of new chiral cyanopyrazolidines were obtained regio- and diastereoselectively in good to excellent yields with moderate to excellent enantioselectivities. Thus, N-benzoylimino-3,4-dihydro-6-methyl­isoquin­olinium betaine (1a) reacts at RT with acrylonitrile in the presence of 1–5 mol % catalyst to afford 3,4-trans-1-benzoyl-4-cyano-2,3-(tetra­hydro­isoquin­oline)­tetra­hydro­pyrazole (2a) in up to 84% yield and 98% ee. The regio- and stereoselectivity were confirmed in the case of compound 2a and 3,4-trans-1-benzoyl-4-cyano-2,3-(6-bromo­tetra­hydro­isoquin­oline)­tetra­hydro­pyrazole (2e) by X-ray crystallography.