Direct Photocatalyzed Hydrogen Atom Transfer (HAT) for Aliphatic C–H Bonds Elaboration

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Abstract

Direct photocatalyzed hydrogen atom transfer ( d-HAT) can be considered a method of choice for the elaboration of aliphatic C–H bonds. In this manifold, a photocatalyst (PC _HAT) exploits the energy of a photon to trigger the homolytic cleavage of such bonds in organic compounds. Selective C–H bond elaboration may be achieved by a judicious choice of the hydrogen abstractor (key parameters are the electronic character and the molecular structure), as well as reaction additives. Different are the classes of PCs _HAT available, including aromatic ketones, xanthene dyes (Eosin Y), polyoxometalates, uranyl salts, a metal-oxo porphyrin and a tris(amino)cyclopropenium radical dication. The processes (mainly C–C bond formation) are in most cases carried out under mild conditions with the help of visible light. The aim of this review is to offer a comprehensive survey of the synthetic applications of photocatalyzed d-HAT.

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Kazimer L. Skubi, Travis Blum, Tehshik Yoon (2016)

The interaction between an electronically excited photocatalyst and an organic molecule can result in the genertion of a diverse array of reactive intermediates that can be manipulated in a variety of ways to result in synthetically useful bond constructions. This Review summarizes dual-catalyst strategies that have been applied to synthetic photochemistry. Mechanistically distinct modes of photocatalysis are discussed, including photoinduced electron transfer, hydrogen atom transfer, and energy transfer. We focus upon the cooperative interactions of photocatalysts with redox mediators, Lewis and Brønsted acids, organocatalysts, enzymes, and transition metal complexes.

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Synthetic chemists aspire both to develop novel chemical reactions and to improve reaction conditions to maximize resource efficiency, energy efficiency, product selectivity, operational simplicity, and environmental health and safety. Carbon-carbon bond formation is a central part of many chemical syntheses, and innovations in these types of reactions will profoundly improve overall synthetic efficiency. This Account describes our work over the past several years to form carbon-carbon bonds directly from two different C-H bonds under oxidative conditions, cross-dehydrogenative coupling (CDC). We have focused most of our efforts on carbon-carbon bonds formed via the functionalization of sp(3) C-H bonds with other C-H bonds. In the presence of simple and cheap catalysts such as copper and iron salts and oxidants such as hydrogen peroxide, dioxygen, tert-butylhydroperoxide, and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), we can directly functionalize various sp(3) C-H bonds by other C-H bonds without requiring preactivation. We demonstrate (1) reaction of alpha-C-H bonds of nitrogen in amines, (2) reaction of alpha-C-H bonds of oxygen in ethers, (3) reaction of allylic and benzylic C-H bonds, and (4) reaction of alkane C-H bonds. These CDC reactions can tolerate a variety of functional groups, and some can occur under aqueous conditions. Depending on the specific transformation, we propose the in situ generation of different intermediates. These methods provide an alternative to the separate steps of prefunctionalization and defunctionalization that have traditionally been part of synthetic design. As a result, these methods will increase synthetic efficiencies at the most fundamental level. On an intellectual level, the development of C-C bond formations based on the reaction of only C-H bonds (possibly in water) challenges us to rethink some of the most fundamental concepts and theories regarding chemical reactivities. A successful reaction requires the conventionally and theoretically less reactive C-H bonds to react selectively in the presence of a variety of functional groups. With further investigation, we expect that C-C bond formations based on cross-dehydrogenative coupling will have a positive economic and ecological impact on the next generation of chemical syntheses.

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Author and article information

Journal

Journal ID (nlm-ta): Chem Rev

Journal ID (iso-abbrev): Chem Rev

Journal ID (publisher-id): cr

Journal ID (coden): chreay

Title: Chemical Reviews

Publisher: American Chemical Society

ISSN (Print): 0009-2665

ISSN (Electronic): 1520-6890

Publication date (Electronic): 06 August 2021

Publication date (Print): 26 January 2022

Volume: 122

Issue: 2 , Photochemical Catalytic Processes

Pages: 1875-1924

Affiliations

[† ]Flow Chemistry Group, Van’t Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam , Science Park 904, 1098 XH Amsterdam, The Netherlands

[‡ ]PhotoGreen Lab, Department of Chemistry, University of Pavia , Viale Taramelli 12, 27100 Pavia, Italy

Author notes

[* ]Email: fagnoni@ 123456unipv.it .

Author information

Luca Capaldo https://orcid.org/0000-0001-7114-267X

Davide Ravelli https://orcid.org/0000-0003-2201-4828

Maurizio Fagnoni https://orcid.org/0000-0003-0247-7585

Article

DOI: 10.1021/acs.chemrev.1c00263

PMC ID: 8796199

PubMed ID: 34355884

SO-VID: f308edc1-75f3-4458-8c52-e874f607d192

License:

Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained ( https://creativecommons.org/licenses/by/4.0/).

History

Date received : 30 March 2021

Funding

Funded by: H2020 Marie SkÃ…?odowska-Curie Actions, doi 10.13039/100010665;

Award ID: 101023615

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document-id-new-14 cr1c00263

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ScienceOpen disciplines: Chemistry

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ScienceOpen disciplines: Chemistry

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