Highly Enantioselective Synthesis of Acyclic N,N′-Acetals by Chiral Urea Derived from Quinine Catalyzed the Addition of Aryl Amines to Isatin-Derived Ketimines

N,N'-Acetals are sensitive compounds, and the challenging asymmetric synthesis of acyclic N,N'-acetals by the general addition of amines to ketimines has never been reported so far. In this study, highly enantioselective addition of aryl amines to isatin-derived ketimines catalyzed by chiral urea derived from quinine was developed. A series of new acyclic N,N'-acetals were constructed by this protocol in high to excellent yields (78-99%) and high to excellent enantioselectivities (76-96% ee).