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Generation of Phosphoranyl Radicals via Photoredox Catalysis Enables Voltage–Independent Activation of Strong C–O Bonds

preprint
submitted on 24.05.2018, 19:58 and posted on 25.05.2018, 13:41 by Erin Stache, Alyssa B. Ertel, Tomislav Rovis, Abigail G. Doyle
Alcohols and carboxylic acids are ubiquitous functional groups found in organic molecules that could serve as radical precursors, but C–O bonds remain difficult to activate. We report a synthetic strategy for direct access to both alkyl and acyl radicals from these ubiquitous functional groups via photoredox catalysis. This method exploits the unique reactivity of phosphoranyl radicals, generated from a polar/SET crossover between a phosphine radical cation and an oxygen centered nucleophile. We first show the desired reactivity in the reduction of benzylic alcohols to the corresponding benzyl radicals with terminal H-atom trapping to afford the deoxygenated product. Using the same method, we demonstrate access to synthetically versatile acyl radicals which enables the reduction of aromatic and aliphatic carboxylic acids to the corresponding aldehydes with exceptional chemoselectivity. This protocol also transforms carboxylic acids to heterocycles and cyclic ketones via intramolecular acyl radical cyclizations to forge new C–O, C–N and C–C bonds in a single step.

Funding

NIGMS R01 GM100985

History

Email Address of Submitting Author

agdoyle@princeton.edu

Email Address(es) for Other Author(s)

estache@princeton.edu aertel@princeton.edu tr2504@columbia.edu

Institution

Princeton University

Country

USA

ORCID For Submitting Author

0000-0002-6641-0833

Declaration of Conflict of Interest

The authors declare no competing financial interests.

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