Rh(III)-Catalyzed C-H Activation/[3 + 2] Cycloaddition for the Synthesis of Functionalized Pyrrolo[1,2-a]imidazole Derivatives.

We report a Rh(III)-catalyzed C-H activation/[3 + 2] cycloaddition of heterocyclic ketene aminals (HKAs) 1 with 2,3-diaryl-2H-azirines 2, affording functionalized pyrrolo[1,2-a]imidazoles 3 in moderate to excellent yields. The native nitrogen atom of HKAs serves as an intrinsic directing group, enabling selective α-C-H activation without prior substrate functionalization. The azirines act as unusual C2 synthons, enabling a distinct and highly regioselective [3 + 2] annulation mode complementary to those of alkynes and alkenes. The reaction proceeds under [Cp*RhCl2]2/AgBF4/HOAc catalysis in refluxing acetonitrile under air and exhibits broad substrate scope and excellent functional-group tolerance. Mechanistic studies support exclusive α-C-H activation and a plausible Rh(III)-catalyzed pathway. This method provides a practical, atom- and step-economical route to structurally diverse pyrrolo[1,2-a]imidazoles.