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Donabauer, Karsten ; König, Burkhard

Strategies for the Photocatalytic Generation of Carbanion
Equivalents for Reductant-Free C−C Bond Formations

Donabauer, Karsten and König, Burkhard (2021) Strategies for the Photocatalytic Generation of Carbanion
Equivalents for Reductant-Free C−C Bond Formations.
Accounts of chemical research 54, pp. 242-252.

Date of publication of this fulltext: 22 Dec 2020 05:53
Article


Abstract

CONSPECTUS: The use of photocatalysis in organic chemistry has encountered a surge of novel transformations since the start of the 21st century. The majority of these transformations are driven by the generation and subsequent reaction of radicals, owing to the intrinsic property of common photocatalysts to transfer single electrons from their excited state. While this is a powerful and elegant ...

CONSPECTUS: The use of photocatalysis in organic chemistry has encountered a surge of novel transformations since the start of the 21st century. The majority of these transformations are driven by the generation and subsequent reaction of radicals, owing to the intrinsic property of common photocatalysts to transfer single electrons from their excited state. While this is a powerful and elegant method to develop novel transformations, several research groups recently sought to further extend the toolbox of photocatalysis into the realm of polar ionic reactivity by the formation of cationic as well as anionic key reaction intermediates to furnish a desired product. Our group became especially interested in the photocatalytic formation of anionic carbon nucleophiles, as the overall transformation resembles classical organometallic reactions like Grignard, Barbier, and Reformatsky reactions, which are ubiquitous in organic synthesis with broad applications especially in the formation of valuable C-C bonds. Although these classical reactions are frequently applied, their use still bears certain disadvantages; one is the necessity of an (over)stoichiometric amount of a reducing metal. The reducing, low-valent, metal is solely applied to activate the starting material to form the organometallic carbanion synthon, while the final reaction product does generally not contain a metal species. Hence, a stoichiometric amount of metal salt is bound to be generated at the end of each reaction, diminishing the atom economy. The use of visible light as mild and traceless activation agent to drive chemical reactions can be a means to arrive at a more atom economic transformation, as a reducing metal source is avoided. Beyond this, the vast pool of photocatalytic activation methods offers the potential to employ easily available starting materials, as simple as unfunctionalized alkanes, to open novel and more facile retrosynthetic pathways. However, as mentioned above, photocatalysis is dominated by open-shell radical reactivity. With neutral radicals showing an intrinsically different reactivity than ionic species, novel strategies to form intermediates expressing a polar behavior need to be developed in order to achieve this goal. In the last couple of years, several methods toward this aim have been reported by our group and others. This Account aims to give an overview of the different existing strategies to photocatalytically form carbon centered anions or equivalents of those in order to form C-C bonds. As the main concept is to omit a stoichiometric reductant source (like a low-valent metal in classical organometallic reactions), only redox-neutral and reductant-free transformations were taken into closer consideration. We present selected examples of important strategies and try to illustrate the intentions and concepts behind the methods developed by our group and others.



Involved Institutions


Details

Item typeArticle
Journal or Publication TitleAccounts of chemical research
Publisher:AMER CHEMICAL SOC
Place of Publication:WASHINGTON
Volume:54
Page Range:pp. 242-252
Date2021
InstitutionsChemistry and Pharmacy > Institut für Organische Chemie > Lehrstuhl Prof. Dr. Burkhard König
Identification Number
ValueType
10.1021/acs.accounts.0c00620DOI
KeywordsHYDROGEN-ATOM TRANSFER; PHOTOREDOX; ALDEHYDES; ALCOHOLS; REAGENTS; ALKENES; DECARBOXYLATION; BENZYLATION; DERIVATIVES; POTENTIALS
Dewey Decimal Classification500 Science > 540 Chemistry & allied sciences
StatusPublished
RefereedYes, this version has been refereed
Created at the University of RegensburgYes
URN of the UB Regensburgurn:nbn:de:bvb:355-epub-443345
Item ID44334

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