Unconventional Ring Opening Triggers Intramolecular C–H Amination of Anthranils via Electrocyclization under Cobalt Catalysis

Abstract

Transition metal-catalyzed anthranil ring opening offers a robust and versatile approach for constructing a wide range of nitrogen-containing heterocycles. Here, we report an unprecedented ring opening of anthranil that triggers its intramolecular C–H amination through an electrocyclization pathway. This novel mechanistic approach enabled the first Cp*Co(III)-catalyzed intramolecular C–H amination of anthranils utilizing C7 aryl/alkenyl-substituted congeners to access carbazoles and indoles under redox-neutral conditions. The mechanistic and computational investigation revealed that anthranil derivatives undergo “unconventional” ring opening facilitated by electron donation from the aryl ring at the C7 position to form a unique cobalt-nitrenoid species, which follows an electrocyclization pathway to achieve the intramolecular C–H amination. The “true” electronic nature of the Co-nitrenoid species has been revealed through meticulous electronic structure analysis. The developed synthetic protocol is 100% atom-economic, ensuring no byproduct formation while maintaining exceptional efficiency. Notably, the reaction demonstrated remarkable regioselectivity, preferentially yielding the carbazole derivative over the acridone derivative. Moreover, we showcased the synthetic versatility of the synthesized carbazole derivative through successful formyl C–H amidation and arylation reactions.