Electrocatalytic Ketyl-Olefin Cyclization at a Favorable Applied Bias Enabled by a Concerted Proton–Electron Transfer Mediator
Abstract
Recent studies showcase reductive concerted proton–electron transfer (CPET) as a powerful strategy for transferring a net hydrogen atom to organic substrates; however, direct application of CPET in the context of C–C bond formation beyond homocoupling is underexplored. We report herein the expansion of electrocatalytic CPET (eCPET) using a Brønsted base-appended cobaltocene mediator ([CpCoCp^(NMe₂)][OTf]) with keto-olefin substrates that undergo cyclization subsequent to ketyl radical generation via eCPET. Using acetophenone-derived substrates with tethered acrylates as radical acceptors, in the presence of tosylic acid, we demonstrate that ketyl-olefin cyclization is achieved by characterization of cis-lactone and alkene products. Mechanistic analysis of this 2 H⁺/2 e⁻ process reveals a mixed order in substrate and acid and a Hammett plot with a modest negative slope, highlighting the contribution of sequential CPET and ET/PT steps involved in the overall rate of the reaction and providing support for initial O–H bond formation. The ability to access ketyl radicals at comparatively mild reduction potentials via controlled potential electrolysis enables functional group tolerance across a range of substrates.
Additional Information
© 2022 American Chemical Society. Received: March 14, 2022; Published: April 18, 2022. The authors are grateful to the Department of Energy Basic Energy Sciences for support via Grant DE-SC0019136 and the donors of the American Chemical Society Petroleum Research Fund for support. J.D. thanks the Arnold and Mabel Beckman Foundation for a postdoctoral fellowship, and P.G.-B. thanks the Ramón Areces Foundation for a postdoctoral fellowship. J.C.P. acknowledges the Resnick Sustainability Institute for support of laboratory facilities. The authors declare no competing financial interest.Attached Files
Supplemental Material - ic2c00839_si_001.pdf
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Additional details
- Eprint ID
- 114382
- DOI
- 10.1021/acs.inorgchem.2c00839
- Resolver ID
- CaltechAUTHORS:20220419-936112000
- Department of Energy (DOE)
- DE-SC0019136
- American Chemical Society Petroleum Research Fund
- Arnold and Mabel Beckman Foundation
- Ramón Areces Foundation
- Resnick Sustainability Institute
- Created
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2022-04-20Created from EPrint's datestamp field
- Updated
-
2022-05-24Created from EPrint's last_modified field
- Caltech groups
- Resnick Sustainability Institute