Divergent and Enantioselective Synthesis of Three Types of Chiral Polycyclic N-Heterocycles via Copper-Catalyzed Dearomative Cyclization

Abstract

Significant advancements have been made in the catalytic asymmetric dearomatization of indoles for constructing valuable chiral polycyclic N-heterocycles. However, the asymmetric dearomative cyclopropanation of indoles continues to pose a formidable challenge. Furthermore, the diverse transformations of indoline-fused cyclopropanes via strain release remain largely unexplored, potentially unveiling new chemistry. Here, we disclose a Cu-catalyzed asymmetric dearomative cyclopropanation of indole-diynes and subsequent [3 + 2] cycloaddition with oxygen, facilitating the divergent and atom-economical synthesis of enantioenriched cyclopropane- and 1,2-dioxolane-fused indolines with moderate to excellent yields and generally outstanding diastereo- and enantioselectivities with broad substrate scope. Importantly, this protocol not only represents the first asymmetric dearomative cyclopropanation of indoles utilizing alkynes as carbene precursors but also constitutes the first catalytic asymmetric construction of chiral 1,2-dioxolanes with high stereoselectivity. Interestingly, Brønsted acid-promoted ring-opening and rearrangement of cyclopropane-fused indolines display distinctive chemoselectivity to afford enantioenriched cyclohepta[b]indoles in good to excellent efficiency and enantiocontrol. In addition, both potential reaction pathways and the origins of chiral control within this Cu-catalyzed asymmetric tandem sequence are robustly supported by control experiments and theoretical calculations.

A Cu-catalyzed asymmetric cyclopropanation of diynes, followed by controllable transformations, has been reported to synthesize three types of chiral N-heterocycles in high yields and stereocontrols.