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Catalysis Science & Technology
Page 3 of 4
DOI: 10.1039/C5CY02069G
Journal Name
COMMUNICATION
1
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Chem. Res., 2014, 47, 3459; (d) M. Zhang, Y. Zhang, X. Jie, H.
phenylmethanol to generate the corresponding ester 3p in 83%
yield (Scheme 1, eqn 3). The results indicated that the
aldehyde should be the key intermediate of the current
aerobic oxidative esterification. It was noted that the Ph2PO2H
perhaps only worked in the oxidation of methyl group, since
the reaction of 3a-a with phenylmethanol proceeded
quantitatively without addition of Ph2PO2H (Scheme 1, eqn 4);
however only a trace amount of 3p was detected in the
absence of both copper catalyst and acid (Scheme 1, eqn 5).
The two results implied that copper catalyst also played an
important role in the oxidative coupling between the aldehyde
and alcohol. The kinetic isotope effect (KIE) experiments also
were performed, and a kinetic isotope effect (kH/kD = 2.4) was
obtained, indicating that the C-H bond in the methyl group
Zhao, G. Li and W. Su, Org. Chem. Front., 2014,
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2
3
would play
a
significant effect during the present
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F.
F.
transformation (Scheme 1, eqn 6).
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N. Houk, N. K. Garg, Nature, 2015, 524, 79-83.
The reaction did not work with toluene and 3-
methylquinoline, and the methyl group should be located at 2-
4
5
(a) A. Schoenberg, I. Bartoletti and R. F. Heck, J. Org. Chem.,
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position, indicating that the nitrogen atom in
crucial. Besides, acid was required. Thus, on the basis of the
control experiments described above and literatures,[10]
1 would be
a
plausible reaction path was proposed in Scheme 2. Under the
oxygen atmosphere, in the presence of copper catalyst and
acid, N-heteroaryl methanes are firstly oxidized to produce the
intermediate aldehydes, which then oxidatively couple with
(a) T. Seki, T. Nakajo and M. Onaka, Chem. Lett., 2006, 35
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49, 6513. (h) X.-Q. Huang, X.-Y. Li, M.-C. Zou, S. Song, C.-H.
alcohols to produce the corresponding N-heteroaryl esters 3.
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,
14858; (i) C. Liu, S. Tang, L.-W. Zheng, D. Liu, H. Zhang and A.
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Guin, K. K. Ghara, A. Banerjee and B. K. Patel, Org. Lett.,
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6
7
(a) C. Liu, J. Wang, L. Meng, Y. Deng,Y. Li and A. Lei, Angew.
Chem, Int. Ed., 2011, 50, 5144; (b) A. B. Powell and S. S. Stahl,
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Y. Chen, X.-J. Zeng, R.-Z. Fu and R.-X. Yuan, Org. Biomol.
Chem., 2014, 12, 6549.
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R. Meier, Green Chem., 2014, 16, 3266.
Scheme 2 Proposed mechanism for the copper-catalysed aerobic oxidative
esterification.
Conclusions
8
9
(a) S. Hirashima, T. Nobuta, N. Tada, T. Miura and A. Itoh,
Org. Lett., 2010, 12, 3645; (b) X.-Z. Xu, W. Ding, Y.-G. Lin and
Q.-L. Song, Org. Lett., 2015, 17, 516.
When 4-methylquinoline was allowed to react with ethanol
under the present reaction conditions (Ph2P(O)OH as acid), a
mixture of esters and acetals was given in ca. 30% yield with
a ratio of 1:5.
In summary, we have developed an efficient copper
catalysed direct aerobic oxidative esterification of sp3C-H
bonds of N-heteroarylmethans with alcohols. Various
substrates including both aliphatic and aromatic alcohols are
applicable to this transformation, producing the corresponding
N-heteroaryl esters in good to high yields.
10 (a) Q. Li, Y. Huang, T. Chen, Y. Zhou, Q. Xu, S.-F. Yin and L-B.
Han, Org. Lett., 2014, 16, 3672; (b) H. Xie, Y.-F. Liao, S.-Q.
Partial financial supports from NFSC (21403062, 21373080,
21273067), HNNSF 2015JJ3039 and the Fundamental Research
Funds for the Central Universities (Hunan University) are
gratefully acknowledged.
Chen, Y. Chen and G.-J. Deng, Org. Biomol. Chem., 2015, 13
,
6944; (c) Y. Huang, T. Chen, Q. Li, Y. Zhou and S.-F. Yin, Org.
Biomol. Chem., 2015, 13, 7289; (d) J.-M. Liu, X. Zhang, H. Yi,
C. Liu, R. Liu, H. Zhang, K.-L. Zhuo and A. Lei, Angew. Chem,
Int. Ed., 2015, 54, 1261.
Notes and references
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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