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C H Activation
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Rhoda-Electrocatalyzed Bimetallic C H Oxygenation by Weak O-
Coordination
In memory of Professor Jean-Michel Savꢀant
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Abstract: Rhodium-electrocatalyzed arene C H oxygenation
by weakly O-coordinating amides and ketones have been
established by bimetallic electrocatalysis. Likewise, diverse
dihydrooxazinones were selectively accessed by the judicious
amounts of strong chemical oxidants, such as (diacetoxyio-
do)benzene and K2S2O8, are required, which leads to un-
desired byproducts.
Electrochemical synthesis has undergone a renaissance in
recent years towards environmentally-benign organic syn-
thesis.[8] Significant recent impetus was gained by the merger
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choice of current, enabling twofold C H functionalization.
Detailed mechanistic studies by experiment, mass spectroscopy
and cyclovoltammetric analysis provided support for an
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of electrocatalysis with oxidative C H activation, thus
unprecedented electrooxidation-induced C H activation by
avoiding the use of toxic and expensive metal oxidants.[9]
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a bimetallic rhodium catalysis manifold.
Although transition metal-catalyzed electrochemically C H
oxygenation have been recently realized,[10] this mostly
required strong N-coordination, such as bidentate quinolinyl
amides or pyridines, while the very recently devised ruthe-
nium catalysis needed rather costly aryl iodides as additional
redox mediators, jeopardizing the inherent atom-economy.[10a]
In contrast, the redox direct—mediator-free—oxidation of
homogeneous metal oxygenation catalysts at the anode
Introduction
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During the past decade, transition metal-catalyzed C H
activation has been recognized as a transformative tool in
molecular syntheses.[1] Phenols featuring an ortho-substituted
carbonyl group constitute important structural motifs of
a diversity of bioactive molecules, ranging from natural
products to drugs molecules.[2] Transition metal-catalyzed
surface typically called for a divided cell setup.[10e–g] Within
[11]
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our program on electrochemical C H activation, we have
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C H activation by weak chelation assistance provides
now devised mechanistically-distinct rhoda-electrocatalyzed
a straightforward access to the assembly of phenols.[3]
Pioneering studies with palladium catalysis were accom-
plished by Dong[4] and Rao.[5] In the same year, our group
C H oxygenations of weakly-O-coordinating amides and
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ketones (Figure 1). Salient features of our findings include
1) undivided cell without redox mediator, 2) room temper-
ature oxygenations, 3) electricity in lieu of strong oxidants,
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reported sustainable ruthenium-catalyzed C H oxygenations
with a diverse range of weakly coordinating groups.[6] In
addition, considerable efforts have been devoted to the
development of different metal catalysts, along with various
oxidants.[7] Despite indisputable advances, stoichiometric
4) high Faraday efficiency, 5) twofold electrochemical C H
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functionalization towards dihydrooxazinones,[12] and 6) de-
tailed mechanistic support for a bimetallic electrocatalysis
manifold.
[*] Dr. X. Tan,[+] L. Massignan,[+] X. Hou, Dr. J. Frey, Dr. J. C. A. Oliveira,
M. N. Hussain, Prof. Dr. L. Ackermann
Institut fꢀr Organische und Biomolekulare Chemie, Georg-August-
Universitꢁt Gçttingen
Tammannstraße 2, 37077 Gçttingen (Germany)
E-mail: Lutz.Ackermann@chemie.uni-goettingen.de
Prof. Dr. L. Ackermann
Wçhler Research Institute for Sustainable Chemistry, Georg-August-
Universitꢁt Gçttingen
Tammannstraße 2, 37077 Gçttingen (Germany)
[+] These authors contributed equally to this work.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
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Figure 1. Rhoda-electrocatalyzed C H oxygenation.
ꢂ 2021 The Authors. Angewandte Chemie International Edition
published by Wiley-VCH GmbH. This is an open access article under
the terms of the Creative Commons Attribution Non-Commercial
License, which permits use, distribution and reproduction in any
medium, provided the original work is properly cited and is not used
for commercial purposes.
Results and Discussion
At the outset of our studies, various reaction conditions
were explored for the envisioned redox-mediator-free, rhoda-
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electrocatalyzed C H oxygenation of 1a in an operationally
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ꢀ 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 2 – 9
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