Journal of the American Chemical Society
Page 6 of 7
Scheme 9. The reaction starts with the selective oxidation of the
acknowledged for help with X-ray diffraction data. Robert J. Mayer
(LMU Munich) is kindly acknowledged for help with cyclic volt-
ammetry data. We would like to thank the Chemical Industry Fund
(FCI), the Deutsche Forschungsgemeinschaft (DFG grant DI
2227/2-1 + JA 2794/1-1), Sonderforschungsbereich SFB749), and
the Ludwig-Maximilians-Universität München (LMU) for finan-
cial support.
1
2
3
4
5
6
7
8
most electron-rich aromatic ring of 1a (supported by quantum-
chemical calculations, as shown in Figure 1, giving intermediate
[A]) and is followed by a pseudo-1,2-metallate rearrangement. This
can be done via -bond cleavage or through -addition, given that
the reaction proceeds exclusively in an intramolecular way (as
demonstrated with crossover experiments, Scheme 8). Although no
calculations could be performed on this step, we assume - for geo-
metrical reasons - that the rearrangement takes place through -or-
bitals and gives the radical cationic boracyclopropane species [C].
Such intermediate was already proposed in previous literature re-
ports.18,19 It is important to note however that a -bond cleavage
would result in the same intermediate [B]. Two different pathways
can follow in the elimination / rearomatization process. Either an
additional electron abstraction can occur (second oxidation, [D]) or
a direct elimination of a boron-radical species. As supported by gal-
vanostatic experiments (Figure 2) and tests under chemical oxida-
tion, we assume that the rearomatization likely occurs through a
one-electron process, furnishing the biaryl compound 2a.
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In summary, we have demonstrated that a broad range of het-
erosubstituted TAB salts are accessible using simple and rapid lig-
and-exchange reactions on potassium trifluoroborates. We have
furthermore shown, that these salts are smoothly oxidized exploit-
ing the power of electrochemistry to furnish substituted heterocy-
clic biaryl systems without the necessity of any additives or transi-
tion-metals. This conceptual two-pot approach has shown to be ro-
bust towards moisture and air and therefore allowed us to routinely
synthesize small drug-like molecules on gram scale. A great variety
of functional groups were tolerated, including several heterocyclic
systems. Lastly, theoretical calculations analyzing the electronic
structure of these systems combined with measured oxidation po-
tentials, crossover- and potentiostatic experiments allowed us to ra-
tionalize the outcome of the oxidative electrocoupling presented.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications
website
at
DOI:.
Experimental procedures, compound characterization, theoretical
calculation, cyclic voltammetry, X-ray diffraction data (PDF)
AUTHOR INFORMATION
Corresponding Author
*Dorian Didier, ORCID: 0000-0002-6358-1485,
Present Addresses
†Allan Plantefol, Sorbonne University, Campus Pierre and Marie
Curie, 4 Place Jussieu, 75005 Paris (France).
Author Contributions
(10) (a) Yoshida, J.-i.; Shimizu, A.; Hayashi, R. Electrogenerated Cati-
onic Reactive Intermediates: The Pool Method and Further Advances.
Chem. Rev. 2018, 118, 4702−4730. (b) Morofuji, T.; Shimizu, A.; Yoshida,
J.-i. Electrochemical C−H Amination: Synthesis of Aromatic Primary
Amines via N‑Arylpyridinium Ions. J. Am. Chem. Soc. 2013, 135,
5000−5003. (c) Yoshida, J.-i.; Nishiwaki, K. Redox selective reactions of
organo-silicon and -tin compounds. J. Chem. Soc., Dalton Trans. 1998,
2589−2596.
‡These authors contributed equally.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
Dr. Robert Francke (University Rostock) is gratefully acknowl-
edged for his help with initial electrochemical measurements and
for technical support. Dr. Peter Mayer (LMU München) is kindly
(11) (a) Elsler, B.; Schollmeyer, D.; Dyballa, K. M.; Franke, R.; Waldvo-
gel, S. R. Metal- and Reagent-Free Highly Selective Anodic Cross-Cou-
pling Reaction of Phenols. Angew. Chem. Int. Ed. 2014, 53, 5210−5213. (b)
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