DOI: 10.1002/anie.201007464
À
C H Activation
À
Rhodium-Catalyzed Direct Addition of Aryl C H Bonds to N-Sulfonyl
Aldimines**
Yang Li, Bi-Jie Li, Wen-Hua Wang, Wei-Ping Huang, Xi-Sha Zhang, Kang Chen, and
Zhang-Jie Shi*
Nucleophilic addition of highly reactive aryl Grignard
reagents and other related organometallic reagents to car-
bonyl compounds and their derivatives is a fundamental and
manipulation of air-and moisture-sensitive reagents and the
generation of unwanted salt waste. Recent Friedel–Crafts-
type direct alkylation of electron-rich arene compounds have
been developed. This reaction is catalyzed by a Lewis/
Brønsted acid, however, a limited substrate scope and
difficulty in regioselective control were encountered.[4] In
comparison, transition metal complexes provide a broader
outlook for the development of new transformations that may
provide tunable reactivity and selectivity. The transition-
À
important reaction for the construction of C C bonds. This
approach has been well developed (since early last century)
and broadly utilized to synthesize alcohol and amine com-
pounds.[1] Traditionally, the requirement of organohalides as
the starting materials to produce the active organometallic
reagents causes environmental problems owing to their
tedious and sluggish preparation (Scheme 1).[2] As a valuable
complementary method, directed ortho metelation (DoM) of
functionalized arene compounds has its advantages from a
synthetic point of view.[3] Apart from their tedious prepara-
tion, both Grignard and DoM approached involve the
À
metal-catalyzed addition of C H bonds to alkene and alkyne
derivatives have been extensively investigated.[5] Meanwhile,
significant contributions have been made to the field by the
À
addition of C H bonds to carbonyl compounds and their
derivatives, despite the demand for special additives or
limited substrate scope.[6] Herein we demonstrated an
À
=
“ideal” addition of “inert” aryl C H bonds to C N groups
in the absence of any additives and without any undesirable
waste under mild and neutral reaction conditions.[7]
Our research was inspired by the recent progress on the
rhodium/palladium-catalyzed addition of aryl boronic acid
towards carbonyl compounds, in which the aryl–metal
(metal = Pd or Rh) species was considered as a possible key
intermediate formed by the transmetalation.[8] In principle,
the high-valent aryl–metal species, either from direct cleavage
À
of the C H bond through electrophilic substitution or the
transmetalation of organometallic reagents should exhibit
similar reactivity. Because aromatic electrophilic metalation
of arenes with/without directing groups and their applications
À
=
Scheme 1. Rational design of direct C H addition toward C Y. Conven-
=
tional arylation of C Y through halogenations/metalation/nucleophilic
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addition-hydration sequence versus “ideal” direct C H addition to
[9]
À
À
in C C and C N bond formation have been well studied,
=
C Y, where Y=N or O. X=halogen.
À
=
the use of Pd catalysis to investigate C H addition to C N
bonds was highly preferred. Although numerous Pd catalysts
were tested, the lack of desired product was disappointing.
We finally gave up on a palladium-based system.
[*] Dr. Y. Li, B.-J. Li, Dr. W.-H. Wang, Dr. W.-P. Huang, X.-S. Zhang,
K. Chen, Prof. Dr. Z.-J. Shi
We therefore focused on Rh catalysis because of its
credible reactivity in the addition of aryl boronic acid to
Beijing National Laboratory of Molecular Sciences (BNLMS)
and Key Laboratory of Bioorganic Chemistry and Molecular
Engineering of the Ministry of Education
aldehydes[8a] and imines,[10] as well as direct C H trans-
À
formations.[11] Thus, 2-phenylpyridine (1a)[9t] and PhCH NTs
=
College of Chemistry and Green Chemistry Center
Peking University, Beijing 100871 (China)
Fax: (+86)10-6276-0890
(2a) were selected as model substrates. Different Rh species,
including RhI, RhII, and RhIII complexes, were screened
(Table 1). Fortunately, we found that [{Cp*RhCl2}2][12] in the
presence of silver salts,[13] AgSbF6, for example, gave a
reasonable yield and the structure of the final product 3a was
characterized by single-crystal X-ray crystallography[14]
(entry 3). The prepared RhIII precursor [Cp*Rh(CH3CN)3]-
[SbF6]2 is more practical and exhibited better efficiency
(entry 4). Apart from tBuOH and the many other solvents
tested, toluene gave a moderate yield for this transformation
(entry 5). Moreover, extension of the reaction time did not
enhance the reaction’s efficiency. Meanwhile, a decrease of
Prof. Dr. Z.-J. Shi
State Key Laboratory of Organometallic Chemistry
Chinese Academy of Sciences, Shanghai 200032 (China)
E-mail: zshi@pku.edu.cn
[**] Support of this study by the NSFC (No. 20672006, 20821062,
20832002, 20925207, 21002001, GZ419) and the “973” Project from
the MOST of China (2009CB825300) is gratefully acknowledged.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2011, 50, 2115 –2119
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2115