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Green Chemistry
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COMMUNICATION
Journal Name
A possible mechanism as outlined in Scheme 4 was
proposed on the basis of the present results and the previously
reported mechanisms.14,16,19 First, O2 accepted an electron
from hydroxyl ion and transformed into superoxide anion
radical in the presence of DMSO (Eq. 1), then, the combination
of superoxide anion radical with arylboronic acid gave the
radical species A (Eq. 2). Intermediate B was achieved by
hydroxide elimination of A (Eq. 3). B further reduced by
another superoxide anion radical lead to the formation of
intermediate C (Eq. 4). Subsequently, C was transformed into
intermediate D (Eq. 5), and the rearrangement of the aryl
group then afforded a phenolic species E. Finally, the phenol
derivative was obtained by acid hydrolysis (Eq. 6). Further
study of the true mechanism is in progress.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 21867011).
DOI: 10.1039/C9GC01965K
Notes and references
1
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4979–4983.
2
3
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4
5
G. Cheng, X. Zeng, X. Cui, Synthesis, 2014, 46, 295-300.
(a) A. Mahanta, P. Adhikari, U. Bora, A. J. Thakur,
Tetrahedron Lett., 2015, 56, 1780-1783; (b) A. Gogoi, U.
Bora, Synlett, 2012, 23, 1079-1081; (c) M. Gohain, M. D.
Plessis, J. H. Tonder, B. C. B. Bezuidenhoudt, Tetrahedron
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Kumar, R.K. Rapolu, B. Kandagatla, P. Rao, S. Oruganti, M.
Pal, Tetrahedron Lett., 2012, 53, 6004-6007.
(1)
(2)
3O2
CH OOCH
2O2
+
2CH3SOOH
2OH
Ar
+
+ 2(CH3)2SO
+
3
3
6
7
S. Guo, L. Lu, H. Cai, Synlett, 2013, 24, 1712-1714.
(a) G. A. Molander, L. N. Cavalcanti, J. Org. Chem., 2011, 76,
623-630; (b) J. J. Molloy, T. A. Clohessy, C. Irving, N. A.
Anderson, G. C. Lloyd-Jones, A. J. B. Watson, Chem. Sci.,
2017, 8, 1551-1559.
Ar
B(OH)2
O
O
O2
+
B(OH)2
A
OH
OH
Ar
B
8
9
P. Gogoi, P. Bezboruah, J. Gogoi, R.C. Boruah, Eur. J. Org.
Chem., 2013, 32, 7291-7294
Ar
B(OH)2
O
O
(3)
(4)
O
B
O
C. Zhu, R. Wang, J. R. Falck, Org. Lett., 2012, 14, 3494-3497.
10 N. Chatterjee, A. Goswami, Tetrahedron Lett., 2015, 56,
1524-1527.
OH
OH
+
O
Ar
B
O
C
Ar
B
+
O2
O2
11 D.-S. Chen, J.-M. Huang, Synlett, 2013, 24, 499-501.
12 12 (a) X. Zhang, K. P. Rakesh, L. Ravindar and H.-L. Qin, Green
Chem., 2018, 20, 4790-4833; (b) K. Chen, P. Zhang, Y. Wang
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O
O
OH
O
OH
B
Ar
Ar
B
(5)
(6)
O
O
O
D
OH
O
OH
O
H3O
rearrangement
Ar
B
Ar
B
E
O
+
B(OH)3
Ar OH
O
Scheme 4 Possible mechanism.
Conclusions
In summary, we have developed a novel, simple and
efficient microwave-assisted strategy for air oxidation of
boronic acids to phenols and alcohol under transition metal-
free conditions. It was found that by using KOH as the base,
DMSO as the solvent, the reaction could occurred efficiently
with broad functional group compatibility to obtain
substituted phenols in excellent yields. Moreover, our protocol
has the advantages such as short reaction time (within 5 min),
operationally simple, inexpensive and environmental
friendliness. Importantly, this is the first study for microwave-
assisted air oxidation of boronic acids to phenols and alcohol
with high yields under transition metal-free conditions. Works
to probe the detailed mechanism and apply the reaction in
organic synthesis are underway.
19 K. Hyland and C. Auclair, Biochem. Biophys. Res. Commun.,
1981, 102, 531–537.
4 | J. Name., 2012, 00, 1-3
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