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LETTER
On the basis of these results and reports in the literature,13
we propose the mechanism shown in Scheme 3. Initially,
copper(II) ferrite nanoparticles react with the substrate on
their surface to generate intermediate A. This is then
transformed into intermediate B in the presence of base,
which completes the catalytic cycle by reductive elimina-
tion of the coupled product.
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H
R2
N
N
R1
R1
R2
O
O
X
CuFe2O4
nanoparticles
1
2
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R2
H
R2
N
N
R1
R1
O
O
X
A
B
base
Scheme 3 Possible mechanism for copper(II) ferrite catalyzed syn-
thesis of benzoxazoles
In conclusion, we have developed a simple and efficient
magnetic copper ferrite nanoparticle-catalyzed method
for the synthesis of substituted benzoxazoles by Ullmann-
type coupling under ligand-free conditions. The protocol
uses cheap, readily available, air-stable, recyclable cop-
per(II) ferrite as the catalyst and substituted N-(2-halophe-
nyl)benzamides as starting materials, and it gives the
corresponding benzoxazoles in good to excellent yields
under mild conditions. This method provides a new strat-
egy for the synthesis of heterocycles. The strategy, which
involves inexpensive, and efficient recyclable magnetic
copper ferrite catalyst, will attract much attention in both
academia and industry. Studies on further applications of
copper(II) ferrite magnetic nanoparticles in the synthesis
of heterocycles are in progress in our laboratory.
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Acknowledgments
For financial support, the authors wish to thank the National Natural
Science Foundation of China (Nos. 21302110, 21302109, and
21375075), the Taishan Scholar Foundation of Shandong Province,
the Project of Shandong Province Higher Educational Science and
Technology Program (J13LD14), the Natural Science Foundation
of Shandong Province (ZR2013BQ017), and the Scientific Re-
search Foundation of Qufu Normal University (BSQD 2012021).
Domínguez, E. Tetrahedron 2007, 63, 10425. (d) Saha, P.;
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Commun. 2008, 5529.
Supporting Information for this article is available online at
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