Mechanistic Insights into the FeCl₃-Catalyzed Oxidative Cross-Coupling of Phenols with 2-Aminonaphthalenes

Abstract

The selective FeCl 3 -catalyzed oxidative crosscoupling reaction between phenols and primary, secondary, and tertiary 2-aminonaphthalene derivatives was investigated. The generality of this scalable method provides a sustainable alternative for preparing N,O-biaryl compounds that are widely used as ligands and catalysts. Based on a comprehensive kinetic investigation, a catalytic cycle involving a ternary complex that binds to both the coupling partners and the oxidant during the key oxidative coupling step is postulated. Furthermore, the studies showed that the reaction is regulated by off-cycle acid−base and ligand exchange processes.

Iron‐Catalyzed Oxidative C−O and C−N Coupling Reactions Using Air as Sole Oxidant**

“…Cleavage of the boron trifluoride from the resulting cyclohexadienyl radical, oxidation by another SET to a cyclohexadienyl cation, and proton loss afford the diaryl ether. The presence of boron trifluoride as additive appears to be crucial for the success of this oxidative C−O coupling since in the presence of Brønsted acid the C−C cross coupling generally is preferred [13k,18] …”

Iron-Catalyzed Oxidative Cross-Coupling of Phenols and Tyrosine Derivatives with 3-Alkyloxindoles

“…The metal-catalyzed oxidative cross-coupling reaction is a powerful method for preparing new carbon–carbon bonds from two unfunctionalized carbon–hydrogen bonds. − Inspired by the mode of action of metalloenzymes that assemble phenolic oligomeric and polymeric structures from simple phenolic units, iron complexes , that promote oxidative cross-coupling between phenols and π-nucleophiles have been developed . These π-nucleophiles include arenes, phenols, − , anilines, , and polyaromatic hydrocarbons, , as well as enolizable β-ketoesters, α-substituted-β-ketoesters, 1,3-diketones, and 2′-hydroxyacetophenones . The products of these reactions are widely applicable in various fields, serve as ligands in asymmetric catalysis, and are key intermediates in natural product syntheses. , 3-Substituted oxindoles are highly nucleophilic compounds that have been used as coupling partners in C–H activation reactions .…”

Catalytic Oxidative Coupling of Phenols and Related Compounds

“…While there have been many successful methods for homocoupling of aminonaphthalenes and a few reports for cross-coupling , of aminonaphthalenes with phenols, methods for the corresponding anilines are underdeveloped. As was the case for phenols vs naphthols, anilines are more difficult to selectively oxidize than aminonaphthalenes.…”