LETTER
Cross-Coupling Reactions with Unactivated Halides
2073
[(RO)2Cu–M+].16 We believe that the nature of the Raney
Ni-Al alloy plays an important role during the formation
of such an intermediate. We suggest that in the presence
of K2CO3, as a cocatalyst, Raney Ni-Al alloy participates
in the formation of the reactive intermediate, thereby
increasing the rate of its subsequent reaction. While
the exact mechanism for the coupling reaction remains
unknown, we believe that a good procedure has been
developed for the synthesis of diaryl ethers.
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C. G. Tetrahedron Lett. 2003, 44, 4927.
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and references cited therein.
(12) (a) Mukumoto, M.; Mashimo, T.; Tsuzuki, H.; Tsukinoki,
T.; Uezu, N.; Mataka, S.; Tashiro, M.; Kakinami, T. T. J.
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Chem. Commun. 2003, 514.
In summary, we have developed a new and highly effi-
cient procedure for the Raney Ni-Al alloy/copper-cocata-
lyzed coupling of a wide range of unactivated aryl
chlorides, bromides and iodides with phenols. This proce-
dure is characterized by the ease of the reaction, simplicity
to manipulate and mildness of the reaction conditions.
Low cost is also one of the method’s advantages. The
Raney Ni-Al alloy is readily available commercially and
is, of course, cheaper than Raney Ni catalyst prepared
from it. In addition, the ligandless method is important in
rendering it more useful in organic synthesis and industri-
alization. This procedure could turn out to be a convenient
and practical method to synthesize the diaryl ethers.
Acknowledgment
We thank the National Natural Science Foundation of China for
financial support of this work (29933050).
References
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(13) Typical Experimental Procedure. An oven-dried resealable
Schlenk tube was fitted with a rubber septum and was cooled
to room temperature under N2 purge. The septum was
removed, and the tube was charged with CuI (10 mol%), 10–
50 mg Raney Ni-Al alloy, K2CO3 (2.0 mmol), aryl halides
(1.0mmol), and phenols (1.2–1.4 mmol). The tube was
capped with the septum and purged with N2, and then
dioxane(2ml) was added through the septum. The reaction
mixture was stirred at 110 °C for 12–24 h (reaction times
were not optimized). The reaction mixture was allowed to
cool to room temperature and then diluted with ether and
poured into a separating funnel. The mixture was washed
with 1 M NaOH and brine, and then the organic fraction was
dried over anhydrous magnesium sulfate, filtered, and
concentrated. The crude material was purified by flash
chromatography on silical gel.
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(17) All the products were identified by NMR and GC-MS
(Agilent 6890N GC/5973N MS, HP-5MS). Selected data for
the product of entry 13: 1H NMR (300 MHz, CDCl3): 7.86
(d, J = 8.7 Hz, 2 H), 7.41–6.92 (18 H), 6.81 (d, J = 8.4 Hz, 2
H); 13C NMR (300 MHz, CDCl3): 157.45, 152.54, 134.19,
129.705, 129.58, 129.26, 128.01, 126.55, 125.75, 124.59,
123.19, 122.64, 119.27, 118.88.
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Tetrahedron 1984, 40, 1433. (c) Chan, D. M. T.; Winters,
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Synlett 2003, No. 13, 2071–2073 © Thieme Stuttgart · New York