Synergistic Decatungstate and Brønsted Acid Catalysis Enables Direct C-H Indolation of Alkanes and Aldehydes

Abstract

Indole skeletons are ubiquitous in natural products, pharmaceuticals, and agricultural agents, making direct C-H indolation strategies highly significant. Direct radical alkylation of indoles, however, is often hampered by the inherent polarity mismatch between nucleophilic alkyl radicals and the electron-rich indole ring. Herein, we report that synergistic decatungstate and Brønsted acid catalysis enables the direct radical C-H indolation of alkanes and aldehydes with 2indolylmethanols. The acid-mediated ionization of 2-indolylmethanols generates delocalized carbocations, which efficiently capture alkyl or acyl radicals derived from the decatungstate-catalyzed hydrogen atom transfer (HAT) process. This cascade delivers C3-functionalized indoles with high regioselectivity under mild conditions. Mechanism studies suggest the Brønsted acid plays a dual role by facilitating the formation of key carbocation intermediates and accelerating the HAT step. The latestage C-H indolation of complex natural products and pharmaceutical agents further demonstrates the synthetic versatility of this protocol.