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Photochemical reductive C-C coupling with a guanidine electron donor

The metal‐free photoinduced reductive C–C coupling reactions of a number of substituted benzyl halides (15 examples) with the organic electron‐donor 2,3,5,6‐tetrakis(tetramethylguanidino)pyridine are evaluated. Depending on the substituents at the benzyl group, a C–C coupling product yield in the ra...

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Bibliographic Details
Main Authors: Wiesner, Sven (Author) , Walter, Petra (Author) , Wagner, Arne (Author) , Kaifer, Elisabeth (Author) , Himmel, Hans-Jörg (Author)
Format: Article (Journal)
Language:English
Published: 27 September 2016
In: European journal of organic chemistry
Year: 2016, Issue: 29, Pages: 5045-5054
ISSN:1099-0690
DOI:10.1002/ejoc.201600978
Online Access:Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1002/ejoc.201600978
Verlag, lizenzpflichtig, Volltext: https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/ejoc.201600978
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Author Notes:Sven Wiesner, Petra Walter, Arne Wagner, Elisabeth Kaifer, and Hans-Jörg Himmel
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Summary:The metal‐free photoinduced reductive C–C coupling reactions of a number of substituted benzyl halides (15 examples) with the organic electron‐donor 2,3,5,6‐tetrakis(tetramethylguanidino)pyridine are evaluated. Depending on the substituents at the benzyl group, a C–C coupling product yield in the range 50–95 % is achieved. The photochemical benzyl‐radical formation by homolytic N–C bond cleavage of the initially formed benzyl‐pyridinium salts is the rate‐determining step of these reactions. Electron‐withdrawing as well as ‐donating substituents at the phenyl group increase the reaction rate. Quantum chemical computations did not reveal any correlation between either the enthalpy or Gibbs free energy of the N–C bond cleavage step and the experimentally determined first‐order rate constants. Instead, the structural difference between the excited state generated by irradiation and the electronic ground state of the pyridinium ions could be used to rationalize the differences in the reaction rates.
Item Description:Gesehen am 12.08.2020
Physical Description:Online Resource
ISSN:1099-0690
DOI:10.1002/ejoc.201600978

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