Novel Ammonium Ionic Liquid Supported (ILS) Diamine-Ni(II) Complexes Catalyzed Asymmetric Michael-Henry Cascade Reaction of 1,2-Dione with Nitroolefins

摘要

Background: The asymmetric Michael-Henry cascade reaction of 1,2-dione with nitroolefinsis an important method for the preparation of chiral bicycle[3,2,1] octane derivatives, which are usefulintermediates for the synthesis of biologically active bicyclo octane skeletal compounds. However, limitedsuccess has been achieved so far for ionic liquid supported (ILS) chiral ligands in transition metalcatalyzed asymmetric cascade reactions.Methods: The catalyst was generated in situ by the combination of ammonium ILS diamine 6b ligand(3 mol%) with metal salt Ni(OAc)2 (3 mol%) in a solvent dimethylformamide. Then the substrates 1,2-cyclohexadione and nitroolefin were added and the reaction mixture was stirred at room temperature for0.3-2.7 h.Results: The ammonium ILS diamines were successfully utilized as chiral ligands in Ni(II)-catalyzedasymmetric Michael-Henry cascade reactions between 1,2-cyclohexadione and nitroolefins at roomtemperature. High yields (80-98%), high diastereoselectivities (up to 47:1) and enantioselectivities (84-94% ee) were observed for the various bicyclo [3,2,1] octane derivatives containing many functionalgroups.Conclusion: 1,2-cyclohexadione underwent asymmetric Michael-Henry cascade reaction with nitroolefinsin the presence of ammonium ILS diamine/Ni(II) catalyst to give the bicyclo [3,2,1] octane derivativesin high yields with ee ranging from 84-94%. Furthermore, the catalytic system is recyclable.