Accessing polysubstituted oxazolidines, pyrrolidines and imidazolidines by regioselective [3+2] annulations of ketenimines with donor-acceptor oxiranes and aziridines

Efficient [3 + 2] annulations of N-aryl-C, C-diphenyl ketenimines with metallo-carbonyl and metallo-azomethine ylides, generated via the respective Yb(OTf)(3) and Y(OTf)(3) promoted carbon-carbon bond heterolysis of donor-acceptor oxiranes and aziridines, have been accomplished. These reactions proceeded under mild conditions and supplied a general methodology for the regioselective construction of structurally complex oxazolidines and pyrrolidines. Moreover, heating neat mixtures of N-aryl-C, C-diphenyl ketenimines and diethyl aziridine-2,3-dicarboxylates led to imidazolidine derivatives. A computational study concluded in stepwise mechanisms for these [3 + 2] annulations, also shedding light on their regioselectivity, concerning which of the two cumulated double bonds of the ketenimine becomes involved in the reaction with the ylide.