Silver-Catalyzed [3+2] Cycloaddition for the Diastereoselective Synthesis of anti-3-Substituted Hydroindolin-2-Imines

We describe a silver catalyzed [3+2] diastereoselective annulation of p-quinamines and ketenimine zwitterionic salts, leading to anti-3-substituted hydroindolin-2-imines under mild conditions. Ketenimine zwitterionic salts participate in the [3+2] cycloadditions as a monoolefin (2 pi-system). The relative stereoselectivity of the reaction was regulated by the tert-butyl ester. This protocol is complementary to the synthesis of functionalized hydroindoles moiety and expands the application of ketenimine zwitterionic salts.