Angewandte
Chemie
DOI: 10.1002/anie.201203230
Functionalizable Directing Groups
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Rhodium(III)-Catalyzed C H Activation of Arenes Using a Versatile
and Removable Triazene Directing Group**
Chengming Wang, Hu Chen, Zhaofeng Wang, Jiean Chen, and Yong Huang*
À
In the past decade, transition-metal-catalyzed arene C H
bond functionalization reactions have enjoyed tremendous
advances owing to their widespread applications to the rapid
assembly of diversified complex molecular structures, partic-
ularly in the fields of medicinal chemistry and material
groups can rarely be conveniently removed under ambient
conditions[4,7c,i] or undergo versatile cross-coupling reactions.
This restriction has greatly limited the structural diversity of
the products and subsequent application to complex molecule
synthesis, as the directing group will become part of the
product. Therefore, the need for new directing groups that
can address this drawback remains urgent. Herein, we report
the first triazene-directed, RhIII-catalyzed oxidative olefina-
tion reactions under mild conditions.[3] The directing triazene
group can either be removed at room temperature in
quantitative yield, or participate in various transformations,
such as cross coupling reactions to generate bis(aryl) olefin
products.
sciences.[1] Direct C H activation and functionalization has
À
advantages over classical cross coupling reactions based on
aryl halides.[1b,j,2] The direct method bypasses the need for
preactivated reaction partners (such as halides), and leads to
a more atom-economical process. In these reactions, a direct-
ing group combined with a proper transition metal and
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a terminal oxidant is often required to achieve C H chemo-
selectivity and catalytic turnover.[1i,3] The directing groups,
possessing functional groups containing a metal-binding
heteroatom, can either undergo further cyclizations to form
heterocycles or remain part of the products (Scheme 1). Such
The Heck-type arene olefination is arguably one of the
most important reactions in this field, owing to its excellent
compatibility with the conditions for transition-metal-cata-
[5,6]
À
lyzed C H activation.
The introduction of a chemically
versatile, a,b-unsaturated carbonyl moiety greatly increased
the synthetic applications of the Heck products. The oxidative
Heck reaction, has recently emerged as an attractive method
for olefin-arene coupling reactions, because it eliminates the
arene activation step required by classic aryl-halide-based
Heck reactions. A number of directing groups (Scheme 2) for
this particular reaction, including amides, amines, alcohols,
oximes, carboxylic acids, esters, ketones, and aldehdyes, have
been developed quite recently.[1i,5b,7]
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Scheme 1. Transtion-metal-catalyzed C H functionalization. DG=dir-
ecting group, M=metal, TM=transition metal.
[*] C. Wang, H. Chen, Z. Wang, J. Chen, Prof. Dr. Y. Huang
Key Laboratory of Chemical Genomics, School of Chemical Biology
and Biotechnology, Shenzhen Graduate School of Peking University
Shenzhen (China)
E-mail: huangyong@pkusz.edu.cn
Scheme 2. Various directing groups developed for arene olefination
[**] This work is financially supported by the National Basic Research
Program of China (2010CB833201 and 2012CB722602 to Y.H.) and
Shenzhen special funds for the development of biomedicine,
internet, new energy, and new material industries
À
through C H activation. DG=directing group, M=metal, TM=transi-
tion metal.
(JC201104210111A and JC201104210112A). Y.H. thanks the
Shenzhen government (Key Laboratory Enhancement Program:
CXB201005260059A and Distinguished Young Scientists Award:
JC201005260104A) for additional support. Y.H. thanks the Shenz-
hen municipality for the Peng-Cheng Professorship Program.
In most cases, the directing groups are attached to the
À
À
arenes by a rather stable C C or C N bond, which makes it
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difficult to remove those groups after C H activation/
functionalization. Furthermore, the complete replacement
À
À
of those directing groups by C C or C N bond cleavage
chemistry, such as cross coupling reactions or functional
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2012, 51, 1 – 5
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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