Catalytic Hydroetherification of Unactivated Alkenes Enabled by Proton‐Coupled Electron Transfer

• Published in: Angewandte Chemie International Edition 2020-07, Vol.59 (29), p.11845-11849
• Main Authors: Tsui, Elaine, Metrano, Anthony J., Tsuchiya, Yuto, Knowles, Robert R.
• Format: Article
• Language: English
• Subjects: alcohols; Alkenes; Alkenes - chemistry; Catalysis; Catalysts; Electron transfer; Electron Transport; ethers; Ethers - chemistry; hydroetherification; Intermediates; Iridium; Irradiation; Light irradiation; Models, Molecular; Molecular Structure; photocatalysis; Protons; Radiation; radicals; Substrates
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202003959

We report a catalytic, light‐driven method for the intramolecular hydroetherification of unactivated alkenols to furnish cyclic ether products. These reactions occur under visible‐light irradiation in the presence of an IrIII‐based photoredox catalyst, a Brønsted base catalyst, and a hydrogen‐atom transfer (HAT) co‐catalyst. Reactive alkoxy radicals are proposed as key intermediates, generated by direct homolytic activation of alcohol O−H bonds through a proton‐coupled electron‐transfer mechanism. This method exhibits a broad substrate scope and high functional‐group tolerance, and it accommodates a diverse range of alkene substitution patterns. Results demonstrating the extension of this catalytic system to carboetherification reactions are also presented. Alkoxy radicals generated directly by the activation of alcohol O−H bonds under light‐driven catalytic conditions can be leveraged for the intramolecular hydroetherification of unactivated olefins. This strategy enables productive C−O bond formation from highly reactive alkoxy radical intermediates and accommodates a broad substrate scope with high functional‐group tolerance. PCET=proton‐coupled electron transfer, HAT=hydrogen‐atom transfer.