ORGANIC
LETTERS
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Vol. XX, No. XX
Visible-Light Photoredox in Homolytic
Aromatic Substitution: Direct Arylation
of Arenes with Aryl Halides
000–000
Yannan Cheng, Xiangyong Gu, and Pixu Li*
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry,
Chemical Engineering, and Materials Science, Soochow University, 199 RenAi Road,
Suzhou, Jiangsu 215123, China
Received April 5, 2013
ABSTRACT
Direct arylation of unactivated arenes or heteroarenes with aryl halides could be carried out in the presence of potassium tert-butoxide and
dimethyl sulfoxide under visible-light irradiation. Ir(ppy) was found to be an effective photoredox catalyst for this reaction. The reactions of aryl
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iodides occurred at room temperature. Elevated temperature was required for aryl bromides. Homolytic aromatic substitution was proposed to be
the operative reaction pathway.
Biarylcompounds are ofgreat importance inthe areas of
been successfully applied in organic synthesis recently.
The ability to utilize visible light as the driving force for
chemical transformation has attracted the attention of
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pharmaceuticals, materials, and catalysis. The common
strategy to construct biaryl structures is transition-metal-
2
catalyzed cross-coupling. The recent breakthrough in
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many researchers. Aryl halides were believed to be sub-
the construction of biphenyl derivatives was mediated by
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strong bases without the involvement of transition metals.
strates not suitable for the visible-light photoredox chem-
istry because of their high redox potentials. However, two
recent reports involving unactivated organohalides in
visible-light-mediated reactions changed the view on these
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Homolytic aromatic substitution (HAS) was proposed to
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be the operating pathway.
The visible-light photoredox catalysis using ruthenium/
iridium polybipyridyl complexes as the sensitizers has
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substrates in visible-light photoredox chemistry. In both
reports, the authors proposed a common aryl halide
radical anion and an aryl radical as the key intermediates
for aryl halide substrates. The construction of arylꢀaryl
bond under visible-light photoredox conditions has been
(
1) Hassan, J.; S ꢀe vignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M.
Chem. Rev. 2002, 102, 1359.
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8
(
achieved by using aryldiazonium salts and diaryliodo-
9
nium salts as the radical precursors. In continuation of
Eds.; Wiley-VCH: Weinheim, 2004. (b) Tsuji, J. Transition Metal Reagents
and Catalysts; John Wiley & Sons: Chichester, 2000.
1
0
(
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our interest in radical addition to aromatic rings, we
proposed a visible-light photoredox HAS pathway for the
formation of biaryl compounds from aryl halides (Scheme 1).
In the proposed mechanism, aryl halide radical anion was
(
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0.1021/ol400946k r XXXX American Chemical Society