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reactions of free radicals with other coupling partners are under
investigation in our laboratory.
Acknowledgements
Scheme 4 Transformations of 3-nitroquinoline N-oxide.
We gratefully acknowledge the Chinese Academy of Sciences
and the National Natural Science Foundation of China
(21133011 and 21373246) and the “Strategic Priority Research
Program” of the Chinese Academy of Sciences (XDA09030104)
for generous nancial support.
Notes and references
1
For an excellent review on aromatic nitro compounds, see:
G. Yan and M. Yang, Org. Biomol. Chem., 2013, 11, 2554.
(a) N. Ono, The Nitro Group in Organic Synthesis, Wiley-VCH,
2
2001; (b) K. Schoeld, Aromatic Nitrations, Cambridge
University Press, Cambridge, 1980; (c) H. Feuer and
A. T. Nielson, Nitro Compounds: Recent Advances in
Synthesis and Chemistry, VCH, Weinheim, 1990; (d)
G. A. Olah, R. Malhotra and S. C. Narang, Nitration:
Methods and Mechanisms, VCH, Weinheim, 1989.
Scheme 5 Radical trapping experiments.
3
For selected reports on nitrate salts as the nitro source, see:
(
a) S. Manna, S. Maity, S. Rana, S. Agasti and D. Maiti, Org.
(
1
Scheme 5, eqn (a) and (b)). The reaction was also inhibited by
Lett., 2012, 14, 1736; (b) N. Nowrouzi, A. M. Mehranpour,
E. Bashiri and Z. Shayan, Tetrahedron Lett., 2012, 53, 4841;
(
H. G. Kruger, Z. Asgari, V. Khakyzadeh and M. Kazem-
Rostami, J. Org. Chem., 2012, 77, 3640; (d) J. Jacoway,
G. G. K. S. N. Kumar and K. K. Laali, Tetrahedron Lett.,
,1-diphenylethylene, and 1,1-diphenyl-2-nitroethylene was
6b
isolated in 55% yield (Scheme 5, eqn (c)). These results may
suggest that the reaction undergo a free radical process and NO
radical was involved in present transformation. Aer the reac-
tion, tertiary butanol was detected by GC-MS, which showed
that t-BuONO may generate BuO radical and NO radical, and
the latter could be easily oxidized to NO radical via a SET
2
process.
Based on the above control experiments, a plausible mech-
anism was proposed as shown in Scheme 6. Initially, TBN
generates NO radical, which could be oxidized to NO
c) M. A. Zolgol, A. Khazaei, A. R. Moosavi-Zare, A. Zare,
2
t
2
012, 53, 6782.
For selected reports on nitrite salts as the nitro source, see:
a) Y.-M. Li, X.-H. Wei, X.-A. Li and S.-D. Yang, Chem.
4
16
(
Commun., 2013, 49, 11701; (b) B. P. Fors and
S. L. Buchwald, J. Am. Chem. Soc., 2009, 131, 12898; (c)
P. J. A. Joseph, S. Priyadarshini, M. L. Kantam and
H. Maheswaran, Tetrahedron Lett., 2012, 53, 1511; (d)
G. Yan, L. Zhang and J. Yu, Lett. Org. Chem., 2012, 9, 133;
2
radical via
5c,16
a SET process.
Then the NO radical and quinoline N-oxides
2
generated radical A through an electrophilic radical addition
process. Eventually, the desired product was generated via a
(
e) H. J. Yang, Y. Li, M. Jiang, J. M. Wang and H. Fu,
single-electron oxidation process with the assistance of NO
2
or
Chem.–Eur. J., 2011, 17, 5652.
t
BuO radical.
5
6
(a) X. Wu, J. Schranck, H. Neumann and M. Beller, Chem.
Commun., 2011, 47, 12462; (b) X. Wu, H. Neumann and
M. Beller, Chem. Commun., 2011, 47, 7959; (c) T. Shen,
Y. Yuan and N. Jiao, Chem. Commun., 2014, 50, 554; (d)
S. Wang, C. Shu, T. Wang, J. Yu and G. Yan, Chin. Chem.
Lett., 2012, 23, 643.
(a) S. Maity, S. Manna, S. Rana, N. Togati, A. Mallick and
D. Maiti, J. Am. Chem. Soc., 2013, 135, 3355; (b) S. Maity,
N. Togati, U. Sharma and D. Maiti, Org. Lett., 2013, 15,
In summary, we have successfully developed a direct and
eco-friendly methodology for the regioselective synthesis of 3-
nitroquinoline N-oxides in the absence of any metal catalyst and
external oxidant. This transformation is realized due to the
higher electron density of C3 position and the electrophilic
2
property of NO radical. Furthermore, it is worth noting that
such transformation could also be smoothly scaled up. The
3384; (c) S. Manna, S. Jana, T. Saboo, A. Maji and D. Maiti,
Chem. Commun., 2013, 49, 5286; (d) N. Togati, S. Maity,
U. Sharma and D. Maiti, J. Org. Chem., 2013, 78, 5949; (e)
I. Jovel, S. Prateeptongkum, R. Jackstell, N. Vogl,
C. Weckbecker and M. Beller, Adv. Synth. Catal., 2008, 350,
2493.
7
(a) Y.-F. Liang, X. Li, X. Wang, Y. Yan, P. Feng and N. Jiao,
ACS Catal., 2015, 5, 1956; (b) F. Xie, Z. Qi and X. Li, Angew.
Scheme 6 Plausible reaction mechanism.
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