Page 5 of 7
ACS Catalysis
Programme of the Chinese Academy of Sciences
Photosensitizer Ir(ppy)3 is initially irradiated by visible
1
2
3
4
5
6
7
8
(XDB17030201), and the Chinese Academy of Sciences is
gratefully acknowledged.
light to reach its excited state Ir(ppy)3*, then the electron-
transfer from Ir(ppy)3* to cobaloxime complex leads to
the formation of IrIV and CoII. The generated IrIV further
abstracts one electron from 1a to produce 1a•+ and to
regenerate photosensitizer Ir(ppy)3. The resulting 1a•+ lose
one proton to form 1a• which is in resonance with 1b, for
intramolecular radical addition to give rise to 1c, which
was subsequently oxidized to form 1d. Deprotonation of
1d followed by tautomerization would afford the desired
product indole 2a finally.9d,10b Simultaneously, proton and
electron eliminated from substrate 1a are efficiently
transformed into H2 catalyzed by cobaloxime. The
reduced CoI species reacts with proton to form CoIII-H
hydride, the hydride can react with another hydride to
eliminate H2 and produced CoII, or it can be protonated,
release H2, and generate CoIII. Alternatively, the CoIII-H
can be reduced further to yield CoII-H, which can react via
an analogous homolytic or heterolytic pathway.14
REFERENCES
(1) (a) Janicki, S. Z.; Schuster, G. B., J. Am. Chem. Soc. 1995, 117,
8524-8527. (b) Somei, M.; Yamada, F., Nat. Prod. Rep. 2004, 21,
278-311. (c) Somei, M.; Yamada, F., Nat. Prod. Rep. 2005, 22, 73-
103. (d) Smart, B. P.; Oslund, R. C.; Walsh, L. A.; Gelb, M. H., J.
Med. Chem. 2006, 49, 2858-2860. (e) Ishikura, M.; Yamada, K.;
Abe, T., Nat. Prod. Rep. 2010, 27, 1630-1680. (f) Kochanowska-
Karamyan, A. J.; Hamann, M. T., Chem. Rev. 2010, 110, 4489-
4497.
(2) (a) Robinson, B., Chem. Rev. 1963, 63, 373-401. (b) Robin-
son, B., Chem. Rev. 1969, 69, 227-250. (c) Hegedus, L. S., Angew.
Chem. Int. Ed. 1988, 27, 1113-1126. (d) Gribble, G. W., Contemp.
Org. Synth. 1994, 1, 145-172. (e) Cacchi, S.; Fabrizi, G., Chem. Rev.
2005, 105, 2873-2920. (f) Humphrey, G. R.; Kuethe, J. T., Chem.
Rev. 2006, 106, 2875-2911. (g) Krüger, K.; Tillack, A.; Beller, M.,
Adv. Synth. Catal. 2008, 350, 2153-2167. (h) Cacchi, S.; Fabrizi, G.,
Chem. Rev. 2011, 111, PR215-PR283. (i) Shiri, M., Chem. Rev. 2012,
112, 3508-3549. (j) Guo, T.; Huang, F.; Yu, L.; Yu, Z., Tetrahedron
Lett. 2015, 56, 296-302.
(3) (a) Fischer, E.; Jourdan, F., Ber. Dtsch. Chem. Ges. 1883, 16,
2241-2245. (b) Wagaw, S.; Yang, B. H.; Buchwald, S. L., J. Am.
Chem. Soc. 1998, 120, 6621-6622. (c) Köhling, P.; Schmidt, A. M.;
Eilbracht, P., Org. Lett. 2003, 5, 3213-3216. (d) Leogane, O.; Lebel,
H., Angew. Chem. Int. Ed. 2008, 47, 350-352. (e) Barluenga, J.;
Jiménez-Aquino, A.; Aznar, F.; Valdés, C., J. Am. Chem. Soc.
2009, 131, 4031-4041.
(4) (a) Stuart, D. R.; Bertrand-Laperle, M.; Burgess, K. M. N.;
Fagnou, K., J. Am. Chem. Soc. 2008, 130, 16474-16475. (b) Shi, Z.;
Zhang, C.; Li, S.; Pan, D.; Ding, S.; Cui, Y.; Jiao, N., Angew. Chem.
Int. Ed. 2009, 48, 4572-4576. (c) Stuart, D. R.; Alsabeh, P.; Kuhn,
M.; Fagnou, K., J. Am. Chem. Soc. 2010, 132, 18326-18339. (d)
Ackermann, L.; Lygin, A. V., Org. Lett. 2012, 14, 764-767. (e)
Zhang, G.; Yu, H.; Qin, G.; Huang, H., Chem. Commun. 2014, 50,
4331-4334. (f) Shen, D.; Han, J.; Chen, J.; Deng, H.; Shao, M.;
Zhang, H.; Cao, W., Org. Lett. 2015, 17, 3283-3285.
(5) (a) Gogoi, A.; Guin, S.; Rout, S. K.; Patel, B. K., Org. Lett.
2013, 15, 1802-1805. (b) Xia, X.-F.; Zhang, L.-L.; Song, X.-R.; Niu,
Y.-N.; Liu, X.-Y.; Liang, Y.-M., Chem. Commun. 2013, 49, 1410-
1412. (c) Gogoi, A.; Modi, A.; Guin, S.; Rout, S. K.; Das, D.; Patel,
B. K., Chem. Commun. 2014, 50, 10445-10447. (d) Chen, Y.-y.;
Chen, J.-h.; Zhang, N.-n.; Ye, L.-m.; Zhang, X.-J.; Yan, M., Tetra-
hedron Lett. 2015, 56, 478-481.
(6) (a) Stokes, B. J.; Liu, S.; Driver, T. G., J. Am. Chem. Soc.
2011, 133, 4702-4705. (b) Nguyen, Q.; Nguyen, T.; Driver, T. G., J.
Am. Chem. Soc. 2013, 135, 620-623. (c) Kong, C.; Jana, N.; Driver,
T. G., Org. Lett. 2013, 15, 824-827. (d) Jones, C.; Nguyen, Q.; Driv-
er, T. G., Angew. Chem. Int. Ed. 2014, 53, 785-788. (e) Alt, I. T.;
Plietker, B., Angew. Chem. Int. Ed. 2016, 55, 1519-1522.
(7) (a) Tan, Y.; Hartwig, J. F., J. Am. Chem. Soc. 2010, 132, 3676-
3677. (b) Nanjo, T.; Tsukano, C.; Takemoto, Y., Org. Lett. 2012,
14, 4270-4273. (c) Liu, B.; Song, C.; Sun, C.; Zhou, S.; Zhu, J., J.
Am. Chem. Soc. 2013, 135, 16625-16631. (d) Wang, C.; Huang, Y.,
Org. Lett. 2013, 15, 5294-5297. (e) Yan, H.; Wang, H.; Li, X.; Xin,
X.; Wang, C.; Wan, B., Angew. Chem. Int. Ed. 2015, 54, 10613-
10617. (f) Deng, G.-B.; Zhang, J.-L.; Liu, Y.-Y.; Liu, B.; Yang, X.-H.;
Li, J.-H., Chem. Commun. 2015, 51, 1886-1888. (g) Lerchen, A.;
Vásquez-Céspedes, S.; Glorius, F., Angew. Chem. Int. Ed. 2016, 55,
3208-3211.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In summary, we have developed an oxidant-free
strategy for indoles synthesis via intramolecular C-C bond
construction under visible light irradition for the first
time. By using catalytic amount of photosensitizer
Ir(ppy)3 and cobaloxime catalyst Co(dmgH)2(4-
CO2Mepy)Cl, various N-aryl enamines can be highly and
selectively transformed into their corresponding indoles,
and H2 is the only by-product. Investigations of the
mechanism reveal that the photosensitizer Ir(ppy)3 is
oxidized by Co(dmgH)2(4-CO2Mepy)Cl to generate IrIV,
which is used to oxidize the enamines, and the
cobaloxime complex acts as a catalyst to capture the
protons and electrons eliminated from the substrate for
H2 production. Compared with previous methods, this
strategy undergoes smoothly with no use of oxidants,
thus avoids the generaton of undesirable by-products,
and we believe that this mild strategy would be suitable
for other heterocyclic compounds synthesis, which is
actively undergoing in our laboratory.
ASSOCIATED CONTENT
Supporting Information.
Experimental procedures, methods, and product characteri-
zation.
This material is available free of charge via the Internet at
AUTHOR INFORMATION
Corresponding Author
*E-mail: lzwu@mail.ipc.ac.cn
Author Contributions
†These authors contribute equally to this work
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
(8) Würtz, S.; Rakshit, S.; Neumann, J. J.; Dröge, T.; Glorius,
F., Angew. Chem. Int. Ed. 2008, 47, 7230-7233.
(9) (a) Bernini, R.; Fabrizi, G.; Sferrazza, A.; Cacchi, S., Angew.
Chem. Int. Ed. 2009, 48, 8078-8081. (b) Yu, W.; Du, Y.; Zhao, K.,
Financial support for this research from the Ministry of Sci-
ence and Technology of China (2013CB834804, 2014CB239402
and 2013CB834505), the National Natural Science Foundation
of China (21390404, 91427303 and 21402217), the Key Research
ACS Paragon Plus Environment