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Updated: Oct 25, 2026

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
Rh(III)-Catalyzed C-H Activation/[3 + 2] Cycloaddition for the Synthesis of Functionalized Pyrrolo[1,2-a]imidazole
Yi-Ting Wang1, Zhi-Bo Xie1, Qin Luo1
1Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, School of Chemical Science and Technology, Yunnan University, Kunming650091, P. R. China.
Abstract:
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.
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