Cobalt-Catalyzed Enantioselective Vinyl Carbene Annulation: A Versatile Platform for Semisaturated Heterocycles.

Abstract

Semisaturated heterocycles are privileged scaffolds in natural products and pharmaceuticals, yet a general and versatile catalytic strategy to access these chiral architectures remains a formidable challenge. Herein, we report a unified synthetic platform utilizing the earth-abundant cobalt coupled with a chiral N,N'-dioxide ligand to unlock the tandem reactivity of vinyl carbenes for the enantioselective construction of diverse semisaturated heterocycles. We have achieved three distinct cascade transformations for modular and efficient access to 2,3-disubstituted dihydrobenzofurans, 1,2,3-trisubstituted indolines, and 2,3,4-trisubstituted benzomorpholines in excellent yields, exceptional enantioselectivities, and high diastereoselectivities, respectively. Mechanistic investigations, including kinetic studies and density functional theory (DFT) calculations, have elucidated that the cascade pathway involves vinylougous C(sp2)-H or N-H insertion of carbenoids, followed by an intramolecular conjugate addition cascade.The practical utility of this protocol is further highlighted by gram-scale syntheses and versatile product derivatizations, offering a powerful and practical tool for the synthesis of chiral heterocycles.