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base
Ar-BH2(OH)2
Ar-B(OH)2
Ar CuII
X
CuIIX2
transmetalation
B(OH)3
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transmetalation
B(OH)3
Ar(OH)2
oxidation
O2
oxidation
reductive elimination
Ar CuIII
Ar
CuIX
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X
Ar Ar
Scheme 4 Plausible mechanism for the base-accelerated, copper-cata-
lyzed homocoupling of arylboronic acids
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unlike palladium catalytic cycles in coupling reactions, cop-
per cycles are enormously complex and no information is
currently available on the active intermediate species; con-
sequently, it is very difficult to identify the true reaction
pathway.
In summary, we have developed a ligand-free copper-
catalyzed homocoupling of (het)arylboronic acids to afford
a wide range of bi(het)aryl compounds at room tempera-
ture in the presence of air. Importantly, we found that
Na2CO3 or other bases can be used in catalytic amounts to
accelerate the reaction. The coupling proceeds in high
yields in only 15 minutes. This simple method is widely ap-
plicable to a variety of (het)arylboronic acids and exhibits
good tolerance toward electron- donating or electron-with-
drawing substituents. 22
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Acknowledgment
This work is supported by NSFC (No. 31570341) and Key Technology
Support Program of Sichuan Province, China (No. 2015SZ0105). We
thank Professor Patrick J. Walsh (Department of Chemistry, Universi-
ty of Pennsylvania) for polishing the language of this manuscript and
for his valuable suggestions.
Supporting Information
Supporting information for this article is available online at
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References and Notes
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© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–F