3
Am. Chem. Soc. 2013, 135, 971–974; (c) Yang, G. Q.; Zhang, W. B.
As illustrated in Scheme 2, the desired product cyclic imine 2a
Angew. Chem. Int. Ed. 2013, 52, 7540–7544; (d) Zhou, B.; Li, K. Z.;
Jiang, C. H.; Lu, Y. X.; Hayashi, T. Adv. Synth. Catal. 2017, 359,
1969–1975.
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was obtained with 80% isolated yield.
O
O
O
O
S
3
4
S
Ir(ppy)2(dtbpy)PF6 (2 mol%)
NH
N
KF 2H O (1.5 eq.), air,
·
2
MeCN, blue LED, rt, 12h
Ph
Ph
1a
1.1g
2a
880mg, 80% yield
Scheme 2. Gram scale experiment.
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Based on the control experiments (Table 1, entries 10-12) and
the related literatures, a plausible mechanism is proposed in
Scheme 3. First, the sulfonamide 1 is deprotonated to form a
sulfonamide anion 5 under a base. Irradiation with visible light
generates an excited state Ir(III)*. The excited Ir(III)* is then
reductively quenched via a single electron transfer from anion 5
to produce Ir(II) and sulfonamide N-radical cation 6. After a
formal 1,2-H shift via intermolecular HAT [13], a benzylic free
radical 7 is formed. In the presence of oxygen, electron is
transferred from Ir(II) to molecular oxygen, which in turn
produces superoxide anion radical O2•− and regenerate Ir(III)
species. At last, the cyclic radical 7 lost an electron and a proton
to produce the final oxidation product 2.
5
6
O
S
O
S
O
O
SET
e
N
N
7
8
9
Ph
Ph
H
H
5
6
reductive
formal 1,2-H shift
via intermolecule HAT
quenching
-H+
base
O
S
O
O
S
Ir( )*
Ⅲ
Ir(
)
Ⅱ
Photoredox
cycle
O
H
N
HN
Ph
[O2]
Ph
7
H
[O2]
1
hv
Ir(
)
Ⅲ
O2
HOO
O
S
O
N
Ph
2
10 Liu, Q.; Li, Y. N.; Zhang, H. H.; Chen, B.; Tung, C. H.; Wu, L. Z. J.
Org. Chem. 2011, 76, 1444–1447.
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Chem. Soc. 2015, 137, 13492–13495; (b) Choi, G. J.; Knowles, R. R.
J. Am. Chem. Soc. 2015, 137, 9226–9229; (c) Gentry, E. C.; Knowles,
R. R. Acc. Chem. Res. 2016, 49, 1546–1556.
12 (a) Chen, J. R.; Hu, X. Q.; Lu, L. Q.; Xiao, W. J. Acc. Chem. Res.
2016, 49, 1911–1923; (b) Zhao, Q. Q.; Chen, J.; Yan, D. M.; Chen, J.
R.; Xiao, W. J. Org. Lett. 2017, 19, 3620–3623; (c) Chen, J.; Guo, H.
M.; Zhao, Q. Q.; Chen, J. R.; Xiao, W. J. Chem. Commun. 2018, 54,
6780–6783.
Scheme 3. Proposed mechanism of the photocatalyzed aerobic oxidation
To summarize, using Ir(ppy)2(dtbpy)PF6 as catalyst, we have
achieved a photochemical approach to access cyclosulfonimide.
Two kinds of cyclic sulfonamides can be successfully converted
to the corresponding N-sulfonyl imine product with good to
excellent yields at room temperature, and the whole process is
environmentally benign. Efforts toward further mechanistic
understanding and extension of this oxidative dehydrogenation
process are currently underway.
13 Karmakar, S.; Datta, A. Angew. Chem. Int. Ed. 2014, 53, 9587-9591.
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (21772195) and the Fundamental Research
Funds for the Central Universities (DUT18RC3051)
References and notes
1
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