Direct Synthesis of N-Fused Indoles Enabled by Copper-Catalyzed Aerobic Oxygenative Rearrangement

Abstract

N-Fused indoles are typical N-heterocycles, which are extensively found in natural products and bioactive molecules. Despite their importance, the synthesis of N-fused indoles has not yet been fully developed. Herein, we report a direct, general unified copper-catalyzed aerobic oxygenative skeletal rearrangement strategy using readily available cyclic indole substrates, which provides a practical synthetic platform for the rapid construction of a wide array of N-fused indole scaffolds. This open-flask method features mild reaction conditions, high chemoselectivity, and a broad substrate scope (over 90 examples). The scaled-up synthesis and versatile transformations of the products using various nucleophiles demonstrated the scalability and utility of this protocol. Mechanistic studies revealed that, by involving a unique single-electron transfer (SET)-induced aerobic oxygenation mechanism, the reaction of tetrahydro-γ-carbolines proceeded via a formal 1,3-migration rearrangement, while that of tetrahydrocarbazoles proceeded by a Witkop–Winterfeldt/C–C cleavage cascade.