H. Sajiki et al.
Conclusion
Acknowledgement
We thank N. E. Chemcat Corporation for a gift of 10% Pd/C and mea-
surement of the leached amount of palladium.
In conclusion, we have developed a ligand-free and hetero-
geneous Pd/C-catalyzed Suzuki–Miyaura coupling reaction
under mild reaction conditions. Aryl bromides underwent
the coupling reaction with various aryl boronic acids in
good-to-high yields at room temperature. Less reactive aryl
triflates were also applicable in this method and resulted in
high yields without hydrolysis. Furthermore, the reaction of
aryl vinyl boronic acids with aryl bromides afforded the
trans-stilbene derivatives as only a single stereoisomer. The
use of wet-type Pd/C in an air atmosphere and the reusabili-
ty of Pd/C will lead to industrial application. It is notewor-
thy that the palladium metal was hardly leached into the so-
lution. This methodology will provide a facile, efficient, and
environmentally friendly process for the Suzuki–Miyaura
coupling reaction because of its wide applicability to various
substrates, the use of less toxic reagents, and mild reaction
conditions.
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Experimental Section
[5] Many of supported palladium catalysts for the Suzuki–Miyaura cou-
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General methods: Unless otherwise stated, all the reactions were carried
out under argon and commercially obtained materials were used without
further purification. Aryl bromides and boronic acids were purchased
from Aldrich Chemical Co., Alfa Aesar, or Tokyo Chemical Industry Co.
Aryl triflates were prepared according to a known procedure.[22] Pd/C
was purchased from Acros Organics, Aldrich Chemical Co., Kishida
Chemical Co., Merck, Nacalai Tesque, and Wako Pure Chemical Indus-
tries or received as a gift from N. E. Chemcat Co. The bases and solvents
were purchased from Hayashi Pure Chemical Industries, Kanto Chemical
Co., Nacalai Tasque, Tokyo Chemical Industry Co., or Wako Pure Chem-
ical Industries.
General procedure for the Suzuki–Miyaura cross-coupling reaction using
the NaHCO3/MeOH system: Aryl bromide (500 mmol), aryl boronic acid
(550 mmol), NaHCO3 (147 mg, 1.75 mmol), 10% Pd/C (8.0 mg, 7.50
mmol), and MeOH (2 mL) were added to a test tube with a stirring bar,
and the system was sealed with a septum. The air inside was replaced
with argon (balloon) by three vacuum/argon cycles, and the reaction mix-
ture was stirred at room temperature. After a certain period, the reaction
mixture was diluted with H2O (10 mL) and Et2O (10 mL) and passed
through a membrane filter (Millipore, Millex-LH, 0.45 mm). The filtrate
was separated into two layers and the aqueous layer was extracted with
Et2O (210 mL). The combined organic layers were washed with brine
(10 mL), dried over MgSO4, and concentrated in vacuo. The residue was
purified by flash column chromatography on silica gel (n-hexane/EtOAc,
50:1) to give the corresponding biaryl compound.
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General procedure for the Suzuki–Miyaura cross-coupling reaction using
the Na2CO3/50% EtOH system: Pd/C (10%; 8.0 mg, 7.50 mmol), Na2CO3
(79.5 mg, 750 mmol), and H2O/EtOH (2 mL, 1:1) were used instead of
NaHCO3 (1.75 mmol) and MeOH (2 mL) in the above procedure.
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General procedure for the Suzuki–Miyaura cross-coupling reaction using
the Na3PO4/50% iPrOH system: Pd/C (10%; 2.7 mg, 2.50 mmol),
Na3PO4·12H2O (665 mg, 1.75 mmol), and H2O/iPrOH (2 mL, 1:1) were
used instead of 10% Pd/C (8.0 mg, 7.50 mmol), NaHCO3 (1.75 mmol),
and MeOH (2 mL) in the above procedure.
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5942
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Chem. Eur. J. 2007, 13, 5937 – 5943