DOI: 10.1002/chem.201301987
Regioselective C2 Oxidative Olefination of Indoles and Pyrroles through
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Cationic Rhodium
N
Bin Li,*[a] Jianfeng Ma,[a] Weijia Xie,[a] Haibin Song,[a] Shansheng Xu,[a] and
Baiquan Wang*[a, b]
The Mizoroki–Heck reaction is one of the most important
metal-catalyzed cross-coupling reactions for the formation
Gaunt,[8h] Miura and Satoh,[8c] and Carretero and
Arrayꢁs.[8a,b] Employing N-2-pyridylmethyl as a directing
group, Ricci and co-workers reported a PdII-catalyzed regio-
controlled C2 alkenylation of indole (Scheme 1a). Gaunt
[1]
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À
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of a C C bond from a C X bond. However, direct C H
bond transformations allow the use of less expensive and
more readily available starting materials without prior func-
tionalization, and thus represent a more atom-economic and
step-simplified strategy.[2] As a result, the process of the oxi-
À
dative olefination of normally unreactive aryl C H bonds,
known as the Fujiwara–Moritani reaction,[3] is an attractive
alternative to the traditional Mizoroki–Heck reaction and
has made remarkable developments during these years.
Among the reports, palladium[4] and rhodium[5] complexes
are the most frequently used catalysts for this type of trans-
formation. For these reactions, the use of a directing group
especially a readily removable directing group, is the one of
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the most popular strategies to obtain a selective C H activa-
tion.
The indole skeleton is an important structural unit and is
widely found in bioactive natural compounds and pharma-
ceutical industry products.[6] Therefore, the efficient func-
tionalization of indole derivatives has attracted much atten-
tion from both academia and industry, especially with
Scheme 1. C2 oxidative Heck reactions of indoles.
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regard to transition-metal-catalyzed C H bond activation.
Over the past decades, many efforts have been focused on
et al. demonstrated a selective PdII-catalyzed C2- or C3- oxi-
dative alkenylation of free (NH) indoles by employing dif-
ferent solvents and additives (Scheme 1a). Later, Miura,
À
regioselective C H bond arylation at the C2- and C3-posi-
tions of indoles.[7] However, the oxidative C H olefination
À
is much less explored[8] especially for the intermolecular C2
alkenylation of indoles.[8a–c,g,h] A survey of reports on inter-
molecular C2 oxidative Heck reactions of indoles reveals
that only four palladium-catalyzed protocols have been in-
dependently developed by the research groups of Ricci,[8g]
Satoh, and co-workers described an exclusive C2 alkenyla-
II
À
tion method of indoles through Pd -catalyzed C H olefina-
tion of indole-3-carboxylic acids, in which decarboxylation
of the carboxyl group occurred during the reaction process
(Scheme 1b). Recently, Carretero and Arrayꢁs et al. devel-
oped a N-(2-pyridyl)sulfonyl group directed C2 alkenylation
of indole with a broad substrate scope of alkenes based on
[a] Prof. Dr. B. Li, J. Ma, W. Xie, Prof. Dr. H. Song, Prof. S. Xu,
Prof. Dr. B. Wang
the [PdACTHGNUTREN(NUG CH3CN)2Cl2] catalyst, in which the directing group
could be removed under mild conditions (Scheme 1a). De-
spite such exciting progress, palladium-catalyzed C2 oxida-
tive alkenylation of indoles suffers from low reaction effi-
ciency, limited substrate scope, and high catalyst loading
(often 10 mol%). Moreover, despite the wide application of
Rh complexes in the Fujiwara–Moritani reaction, Rh-cata-
lyzed C2 oxidative olefination indoles has rarely been repor-
State Key Laboratory of Elemento-Organic Chemistry
College of Chemistry, Nankai University
Tianjin 300071 (China)
Fax : (+86)22-2350-4781
[b] Prof. Dr. B. Wang
State Key Laboratory of Organometallic Chemistry
Chinese Academy of Sciences
Shanghai 200032 (China)
ted.[5l] As a continuation of our interest in metal-catalyzed
[9]
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C H functionalization, we here disclose our development
of cationic RhIII-catalyzed selective oxidative coupling of in-
doles and pyrroles with alkenes exclusively at the C2-posi-
Supporting information for this article is available on the WWW
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
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