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High‐Valent Cobalt‐Catalyzed C−H Activation/Annulation of 2‐Benzamidopyridine 1‐Oxide with Terminal Alkyne: A Combined Theoretical and Experimental Study
Author(s) -
Wang Yang,
Du Cong,
Wang Yanyan,
Guo Xiaokang,
Fang Lei,
Song MaoPing,
Niu JunLong,
Wei Donghui
Publication year - 2018
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201800036
Subject(s) - chemistry , annulation , alkyne , catalysis , electron transfer , deprotonation , photochemistry , proton coupled electron transfer , cobalt , solvent , electron paramagnetic resonance , chemoselectivity , organic chemistry , ion , physics , nuclear magnetic resonance
The multiple possible pathways of high‐valent cobalt catalyzed C−H activation/annulation of 2‐benzamidopyridine 1‐oxide with terminal alkyne were investigated in this combined theoretical and experimental study. The calculated results indicated that Co III catalyzed C−H activation occurs via a concerted‐metalation deprotonation (CMD) process and that the subsequent annulation involves the Co IV intermediate generated through a proton‐coupled electron transfer (PCET) process in DMSO solvent or through an intermolecular single electron transfer (SET) process in trifluoroethanol (TFE) solvent. Moreover, the theoretical calculations also revealed that Co III is the actual catalyst, and the solvent controls the chemoselectivity in the annulation stage, triggering a switch between five‐ and six‐membered ring products. Kinetic isotope effect (KIE), electron paramagnetic resonance (EPR), and TEMPO inhibition experiments were performed to confirm the computational results. The mechanistic insights should be valuable for understanding the PCET and SET processes involved in transition metal‐catalyzed C−H functionalizations.