.
Angewandte
Communications
DOI: 10.1002/anie.201302784
Catalytic Amination
À
Direct C H Amination of Arenes with Alkyl Azides under Rhodium
Catalysis**
Kwangmin Shin, Yunjung Baek, and Sukbok Chang*
Dedicated to Professor Chul-Ho Jun on the occasion of his 60th birthday
Since the seminal study by Curtius on the use of alkyl azides in
À
organic chemistry, particularly in C N bond-forming reac-
tions, these readily available compounds have been widely
used as one of the most convenient amino sources.[1] The four
most notable examples of such reactions are the Schmidt
rearrangement,[2] the aza-Wittig reaction,[3] cycloaddition
with alkynes,[4] and the Staudinger ligation[5] (Scheme 1).
Whereas an amide bond is readily generated in the Schmidt
reaction, imine formation is facile under the aza-Wittig
conditions. The copper-mediated reaction of alkyl azides
with 1-alkynes has been well developed as a connecting tool in
various fields of research. Furthermore, alkyl azides are a key
component of the Staudinger ligation for the formation of
amides even in vivo.[6]
Despite the significant advances made in the use of alkyl
À
azides as the nitrogen source for C N bond formation, the use
of these widely available compounds in metal-mediated direct
C H amination has rarely been investigated.[7–9] Although N-
À
alkylimido (nitrenoid) metal complexes are known to be
generated,[10] the alkyl groups used are very limited even with
specially designed ligand systems. Moreover, only a few
À
examples of C N bond formation upon treatment of the
corresponding N-alkylimido metal species with hydrocarbons
have been reported.[10e,f,h] When compared to the Buchwald–
À
Scheme 1. a) Previously developed C N bond-forming reactions with
alkyl azides. b) The reaction developed in this study: a rhodium-
Hartwig amination procedure, in which (hetero)aryl halides
are treated with amines,[11] the direct C H amination of
À
À
catalyzed direct C H amination with alkyl azides. DG=directing
group, LA=Lewis acid.
(hetero)arenes displays notable advantages as
a more
À
straightforward route to C N bond formation. As a result,
À
extensive studies on direct C H amination have been carried
out, mainly with palladium[12] and copper catalysts.[13] How-
ever, amino sources are limited largely to amides, although
reaction conditions have been improved to enable the use of
During our continuing efforts to develop the direct
introduction of amino groups into (hetero)arenes with high
synthetic utility,[16] we recently reported rhodium-catalyzed
À
À
a broader range of substrates. Direct C H amination with N-
C H amination procedures with sulfonyl and aryl azides as
hydroxy-[14] and N-chloroamines has also been investiga-
ted,[13e,15] but its scope is still limited to the use of secondary
amine precursors to afford tertiary amine products.
unique amino sources.[17,18] The reactions proceed without an
external oxidant to release molecular nitrogen as the only by-
product. Although they feature broad substrate generality
with high functional-group tolerance, the installation of an
alkylamino group was also envisioned to be highly desirable,
as synthetically more important and diverse N-alkylaniline
products could be accessed directly by such an approach.
Furthermore, owing to the development of click cycloaddition
chemistry,[4] a wide range of alkyl azides are available,
including biologically relevant compounds, such as sugars
and peptides. In this context, we report herein the first
[*] K. Shin, Y. Baek, Prof. Dr. S. Chang
Center for Catalytic Hydrocarbon Functionalizations (IBS) and
Department of Chemistry
Korea Advanced Institute of Science and Technology (KAIST)
Daejeon 305-701 (Korea)
E-mail: sbchang@kaist.ac.kr
À
rhodium-catalyzed direct C H amination of arenes with alkyl
azides.
[**] This research was supported financially by the Institute of Basic
Science (IBS).
We first sought an optimal catalytic system for the direct
Supporting information for this article is available on the WWW
À
amination of arene C H bonds with a series of benzyl and
2
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 1 – 7
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