Visible-light-mediated C2-amination of thiophenes by using DDQ as an organophotocatalyst

Article abstract of DOI:10.1039/c7cc01339f

In this work, a direct C-H activation of thiophenes was presented via an oxidation pathway under visible-light irradiation, in which the thiophene radical cation serves as the key intermediate. Various thiophenes and azoles could be transformed into the corresponding amination products well, and H₂O was the only byproduct which is environmentally benign. Our results showed that tert-butyl nitrite (TBN) served as the electron transfer mediator and O₂ as the terminal oxidant to regenerate the photocatalyst DDQ and revive the photocatalytic cycle.

Full text of DOI:10.1039/c7cc01339f

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Visible-light-mediated C2-amination of thiophenes by
using DDQ as organophotocatalyst
Cite this: DOI: 10.1039/x0xx00000x
a
Chunlan Song,
Lei*a,b
‡
a Hong Yi,
‡
Bowen Dou,a Yiying Li,a Atul K. Singh,a and Aiwen
Received 00th January 2014,
Accepted 00th January 2014
DOI: 10.1039/x0xx00000x
www.rsc.org/
In this work, a direct C-H activation of thiophenes was demonstrated great versatility in photocatalysis and often used in
presented via oxidation pathway under visible-light organic synthesis. Different from transitionꢀmetal promoted
irradiation, in which the thiophene radical cation serves as photocatalysis, the organic photoredox catalysis, in which several
the key intermediate. Various thiophenes and azoles could be organic molecules could be used as the photocatalysts, has presented
transformed into the corresponding amination products well, a new way for photocatalysis and received wide attention.8 Recent
and H2O was the only byproduct which is environmentally advances defined that photocatalysis could provide a mild and
benign. Our results showed tert-butyl nitrite (TBN) served general route for CꢀN bond formation,9 especially the development
the electron transfer mediator and O2 as the terminal oxidant of oxidative CꢀH/NꢀH cross coupling reactions.10 The 2,3ꢀdichloroꢀ
to regenerate photocatalyst DDQ and revive the 5,6ꢀdicyanoꢀpꢀbenzoquinone (DDQ) is commercially available and
photocatalytic cycle.
cheap, and be known as a powerful organic oxidizing reagent for a
number of organic transformations11 relying on its oneꢀelectron
The functionalized thiophenes, vital heterocyclic compounds, have reduction potential of DDQ (Ered = 0.51 V vs SCE). What’s more,
long been privileged structures in the natural products, DDQ can also be excited by visible light to triplet state with a high
pharmaceuticals and conjugated polymers.1 Moreover, 2ꢀ oxidation potential (Ered = 3.18 V vs SCE), which shows the great
aminothiophene and its derivatives are always employed as the
building blocks in bioactive compounds.2 Therefore, the sustainable
preparation of these valuable 2ꢀaminothiophenes is important for
organic synthesis. As we know, the transitionꢀmetal catalyzed cross
coupling of aryl halides has served as a powerful tool for
constructing CꢀN bonds.3 The transitionꢀmetal catalyzed (Pd, Cu etc)
amination of halothiophenes have been developed to construct 2ꢀ
aminothiophenes (Scheme 1A).4 Nevertheless, directly using simple
arene (ArꢀH) to replace aryl halide (ArꢀX) is undoubtedly the most
stepꢀ and atomꢀeconomical method, representing an ideal route for
CꢀN bond formation.5 Along with this direct strategy, the synthesis
of 2ꢀaminothiophene partners have been achieved via direct C−H
amination of thiophenes (Scheme 1B).6 However, these strategies
required high temperatures and stoichiometric quantities of oxidant,
Scheme 1. Strategies for C2ꢀAmination of Thiophene. (A) Transitionꢀmetal
which caused the high consumption of materiel and energy.
(Pd or Cu) catalyzed amination of halothiophene. (B) Copperꢀcatalyzed
amination of thiophene. (C) This work: visibleꢀlightꢀmediated C2ꢀamination
Therefore, developing an environmentally friendly and metalꢀfree
catalytic system was highly desired, especially when removal of
metal traces is of real concern to the pharmaceutical industry.
Over these years, the photocatalysis mediated by visible light has
been widely developed, serving as a mild and powerful tool for bond
formations.7 The ruthenium and iridium polypyridyl complexes have
of thiophene.
capacity of DDQ to participate in organic transformation as a
photocatalyst.12 In recent years, Fukuzumi and coꢀworkers have
pioneered the development of oxidative CꢀO bond formation to
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DOI: 10.1039/C7CC01339F
phenol derivatives from benzene derivatives by using DDQ as a
photocatalyst.12c The development of CꢀH amination of thiophenes
mediated by triplet DDQ catalyst is important and highly desirable
(Scheme 1C).
Entry
Variation from Standard Conditionsa
GCꢀYield (%)[b]
The CꢀH activation of thiophene was usually with the assistance
of transitionꢀmetal.13 In this work, we presented a new route for CꢀH
activation of thiophene via oxidation pathway. Our idea on CꢀH
amination of thiophene was described in Scheme 2. The thiophene
derivatives 1 can be initially oxidized by the excitedꢀstate of
1
2
3
4
standard conditions
benzoquinone instead of DDQ
pꢀchloranil instead of DDQ
82
trace
11
10 mol% DDQ, 10 mol%TBN were used
68
3
photocatalyst DDQ* to generate the radical cation intermediate I.
5
6
7
8
9
20 mol% DDQ, 20 mol%TBN were used
O2 instead of air
80
77
Subsequently, the addition of Nꢀcontaining nucleophile would
furnish a carbon radical intermediate II, which is further oxidized by
DDQ•− to form the C2ꢀfunctionalization product 3 and DDQH2. And
the regioselective was controlled by radical cation intermediate I,
which the radical located on C2 position DDQH2 is known to be
oxidized by reaction with TBN via NO2 to generate DDQ.14 Hu and
coꢀworkers demonstrated a series work that the TBN can be
regenrated by O2.15 This method we herein reported would provide a
new strategy for direct oxidative CꢀH/CꢀN coupling of thiophene
with DDQ as a photocatalyst.
no light
N.D.[c]
N.D.
13
no photosensitizer DDQ
no catalyst TBN
[a] Standard conditions: reactions were performed with 1a (1.0 mmol), 2a
(0.5 mmol), DDQ (15 mol %, 0.075 mmol), and TBN (15 mol %,
0.075mmol) in 3 mL 1,2ꢀdichloroethane irradiated by blue LEDs for 4 h. [b]
GC yields are determined by using biphenyl as an internal standard. [c] N.D.
implies no product was detected by GCꢀMS and GC.
To probe the versatility of this catalytic system, the scope and
limitation of thiophenes were evaluated. As shown in Table 2,
thiophenes containing an electronꢀdonating group such as methyl,
dioxolan or trimethylsiyl reacted smoothly under the optimized
conditions and gave the corresponding products (3b, 3c, 3e and 3f)
with good efficiency.
Table 2. Substrate Scope of Thiophenes a
Scheme 2. Our Strategy for VisibleꢀLightꢀMediated C2ꢀAmination of
Thiophenes using DDQ as Organophotocatalyst.
With above hypothesis, we initially chose thiophene and
pyrazole derivatives as the substrates to synthesize valuable
compounds, by using DDQ as a photocatalyst, tertꢀbutyl nitrite
(TBN) as electron mediator and oxygen as terminal oxidant under
visibleꢀlight irradiation. In a typical reaction mixture for the
photocatalytic reaction, 1 mmol of the thiophene (1a), 0.5 mmol of
the 4ꢀchloroꢀ1Hꢀpyrazole (2a), 15 mol % of DDQ and 15 mol % of
TBN, in 3 mL 1,2ꢀdichloroethane (DCE) with an airꢀballoon were
used to give the desired product 3a in 82% yield, which was under
the irradiation of blue LEDs light for 4 h (Table 1, Entry 1). When
choosing other quinones as the photocatalyst, such as benzoquinone
and tetrachloroꢀpꢀbenzoquinone, the yields of 3a were much lower
than model reaction (Table 1, Entry 2ꢀ3). Neither increasing nor
decreasing the amount of catalyst could improve the yield (Table 1,
Entry 4ꢀ5). Moreover, when oxygen instead of air as a reaction gas
atmosphere was used, the transformation gave a slight decrease in
the yield (Table 1, Entry 6). Control experiments indicated no
desired reaction would be observed without the photocatalyst DDQ
or light (Table 1, Entry 7ꢀ8). Only a spot of the product could be
detected in the absence of catalyst TBN, because the photocatalyst
couldn’t be recycled (Table 1, Entry 9).
a Standard conditions: reactions were performed with 1 (1.0 mmol), 2a (0.5
mmol), DDQ (15 mol %, 0.075mmol), and TBN (15 mol %, 0.075mmol) in 3
mL 1,2ꢀdichloroethane was irradiated by blue LED for 4 h. Unless otherwise
Table 1. Optimization of Reaction Conditionsa
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C7CC01339F
noted, isolated yields are shown. Regioselectivity was determined by NMR.
bThe yields were determined by GC with the biphenyl of an internal standard.
mL 1,2ꢀdichloroethane was irradiated by blue LED for 4 h. Unless otherwise
noted, isolated yields are shown. Regioselectivity was determined by NMR.
However, the oxidation side reaction of ethyl group resulted in a The presence of αꢀsubstitution on the aromatic ring was wellꢀ
slight decrease in yield of 3d. Furthermore, with no effect on tolerated (4h). As expected, diꢀmethyl substituted benzotriazole is
halogen group, the C2 or C3 position amination of halide substituted furnishing the expected adducts with medium yield (4i). We were
thiophenes (3gꢀ3i) could be reacted well and provided a handle for also pleased to observe that triazole were willing to react, albeit in
further synthetic manipulations. The bromo substituent at the C2 slightly diminished yield (4jꢀ4k). The slight lower yield of some
position of the thiophenes gave the lower yields compared with the substractes ratio due to the poor reactivity with low conversion.
chloro substituent on thiophene ring (3h). Monoꢀ and diꢀ halide What’s more, pyrazols substituted with bromine or nitryl had good
substituted thiophenes were both suitable in this reaction system (3jꢀ reactivities and obtained the desired products in moderated yields
3l). Moreover, it should be mentioned that two different functional (4lꢀ4m).
groups on thiophenes were also performed well, with moderate to
good levels of yields (3mꢀ3n).
To further explore the utility of this method for constructing C2ꢀ
amination of thiophenes, we tried to expand the reaction to gram
scale. A good reaction selectivity and yield could still be obtained
(Scheme 3). Obviously, this photocatalysis system had a great
advantage over the palladium or copper mediated processes
according to the demand for metalꢀfree, atomꢀeconomical and
sustainable chemistry.
Subsequently, various nitrogen sources were also explored for this
amination reaction (Table 3). Multifarious benzotriazole could be
tolerated in this transformation with moderate yields, including
different electronꢀwithdrawing or electronꢀdonating substituted
benzotriazoles (4aꢀ4i). When substituted benzotriazoles were used as
substrates, the product obtained was a mixture of two isomers.
Benzotriazole and 5ꢀmethylꢀbenzotriazole could give the desired
product in 58% and 45% yields (4a and 4b). Halide substituents on
the aromatic ring were well tolerated in this transformation and
afforded the moderate yields (4cꢀ4e). Notably, benzotriazoles
bearing the strong electronꢀdeficient substituents such as
trifluoromethyl or ester were also suitable in the reaction system (4fꢀ
4g)
Scheme 3. Gram Scale Reaction
To understand the reaction process of this system, the
intermolecular isotope effect experiments were also carried out
(Scheme S1). When the following two reactions containing 1m
and 1m-D proceeded under the standard conditions for 10
minutes respectively, the products 3ml and 3ml' could be
Table 3. Scope of Nitrogen Source Coupling Partner a
obtained at the ratio of kH/kD = 1.4. This result indicated that the
CꢀH bond cleavage of thiophene might not be involved in the
rateꢀdetermined step of the reaction. The radicalꢀinhibiting
experiments indicated that the reaction might be involved a
radical process (Scheme S2). Furthermore, on the basis of the
control experiments (Scheme S3), we could reach the
following conclusion that ground state DDQ couldn’t oxidize a
substrate, even under high temperatures. And an equivalent DDQ
could also achieve this transformation in 60% yield under visible
light irradiation. Based on above mechanistic studies, we could
conclude that the DDQ served as not only the photocatalyst but
also the oxidant in this CꢀH amination reaction.
In conclusion, we have developed the direct C2ꢀamination of
thiophene under visibleꢀlight irradiation for the first time. By using a
catalytic amount of cheap photocatalyst DDQ, electron mediator
TBN and terminal oxidant oxygen, various thiophenes could be
selectively transformed into their corresponding amination products
in high yields and H2O is the only byproduct. This strategy could
tolerate multiple halogens, facilitating a handle for the further
synthetic manipulations. Compared with previous methods, this
transformation undergoes smoothly with no use of metal, thus avoids
the post treatment process, which is economical and has high
efficiency.
a Standard conditions: reactions were performed with 1 (1.0 mmol), 2 (0.5
mmol), DDQ (15 mol %, 0.075mmol), and TBN (15 mol %, 0.075mmol) in 3
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4734ꢀ4743; (d) C. K. Prier, D. A. Rankic and D. W. C. MacMillan,
Chem. Rev., 2013, 113, 5322ꢀ5363; (e) M. N. Hopkinson, B. Sahoo, J.ꢀ
L. Li and F. Glorius, Chem. Eur. J., 2014, 20, 3874ꢀ3886; (f) J. Xuan
and W.ꢀJ. Xiao, Angew. Chem. Int. Ed., 2012, 51, 6828ꢀ6838; (g) J. M.
This work was supported by the National Natural Science
Foundation of China (21390400, 21520102003, 21272180,
21302148), the Hubei Province Natural Science Foundation of China
(2013CFA081), the Research Fund for the Doctoral Program of
Higher Education of China (20120141130002), and the Ministry of
Science and Technology of China (2012YQ120060). The Program
of Introducing Talents of Discipline to Universities of China (111
Program) is also appreciated.
R. Narayanam and C. R. J. Stephenson, Chem. Soc. Rev., 2011, 40
,
102ꢀ113.
8. (a) S. Fukuzumi, S. Kuroda and T. Tanaka, J. Am. Chem. Soc., 1985,
107, 3020ꢀ3027; (b) O. Kei and F. Shunichi, B. Chem. Soc. Jpn., 2009,
82, 303ꢀ315; (c) S. B. Bharate, Synlett, 2006, 2006, 0496ꢀ0497; (d) U.
Megerle, M. Wenninger, R.ꢀJ. Kutta, R. Lechner, B. Konig, B. Dick
and E. Riedle, Phys. Chem. Chem. Phys., 2011, 13, 8869ꢀ8880; (e) D.
Ravelli, M. Fagnoni and A. Albini, Chem. Soc. Rev., 2013, 42, 97ꢀ113;
Notes and references
(f) S. Fukuzumi and K. Ohkubo, Chem. Sci., 2013, 4, 561ꢀ574.
a College of Chemistry and Molecular Sciences, the Institute for Advanced
Studies, Wuhan University, Wuhan, Hubei 430072, People’s Republic of
China. Fax: (+86)-27-68754672; Tel: (+86)-27-68754672; E-mail:
aiwenlei@whu.edu.cn.
9. (a) L. J. Allen, P. J. Cabrera, M. Lee and M. S. Sanford, J. Am. Chem.
Soc., 2014, 136, 5607ꢀ5610; (b) J. R. Chen, X. Q. Hu, L. Q. Lu and W.
J. Xiao, Chem. Soc. Rev., 2016, 45, 2044ꢀ2056; (c) H. Kim, T. Kim, D.
G. Lee, S. W. Roh and C. Lee, Chem. Commun., 2014, 50, 9273ꢀ9276;
(d) L. Song, L. Zhang, S. Luo and J. P. Cheng, Chem. Eur. J., 2014, 20
,
bState Key Laboratory for Oxo Synthesis and Selective Oxidation,
Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, P. R. China.
14231ꢀ14234; (e) X.ꢀQ. Hu, J.ꢀR. Chen, Q. Wei, F.ꢀL. Liu, Q.ꢀH. Deng,
A. M. Beauchemin and W.ꢀJ. Xiao, Angew. Chem. Int. Ed., 2014, 53
,
12163ꢀ12167.
10. (a) A. U. Meyer, A. L. Berger and B. Konig, Chem. Commun., 2016,
52, 10918ꢀ10921; (b) K. Tong, X. Liu, Y. Zhang and S. Yu, Chem. Eur.
J., 2016, 22, 15669ꢀ15673; (c) N. A. Romero, K. A. Margrey, N. E.
Tay and D. A. Nicewicz, Science, 2015, 349, 1326ꢀ1330; (d) Y. W.
Zheng, B. Chen, P. Ye, K. Feng, W. Wang, Q. Y. Meng, L. Z. Wu and
C. H. Tung, J. Am. Chem. Soc., 2016, 138, 10080ꢀ10083; (e) H. Yi, L.
Niu, C. Song, Y. Li, B. Dou, A. K. Singh and A. Lei, Angew Chem Int
Ed, 2017, 56, 1120ꢀ1124; (f) L. Niu, H. Yi, S. Wang, T. Liu, J. Liu and
†
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here. See
DOI: 10.1039/b000000x/
‡ Chunlan Song and Hong Yi contributed equally
1. I. L. Pinto, R. L. Jarvest and H. T. Serafinowska, Tetrahedron Lett.
,
2000, 41, 1597ꢀ1600.
A. Lei, Nat. Commu., 2017, 8, 14226.
2. (a) H.ꢀY. Xiao, D.ꢀR. Wu, M. F. Malley, J. Z. Gougoutas, S. F. Habte,
M. D. Cunningham, J. E. Somerville, J. H. Dodd, J. C. Barrish, S. G.
Nadler and T. G. M. Dhar, J. Med. Chem., 2010, 53, 1270ꢀ1280; (b) G.
De Martino, G. La Regina, A. Di Pasquali, R. Ragno, A. Bergamini, C.
Ciaprini, A. Sinistro, G. Maga, E. Crespan, M. Artico and R. Silvestri,
J. Med. Chem., 2005, 48, 4378ꢀ4388; (c) Q. Huang, P. F. Richardson,
N. W. Sach, J. Zhu, K. K. C. Liu, G. L. Smith and D. M. Bowles, Org.
Process. Res. Dev., 2011, 15, 556ꢀ564; (d) L. Aurelio, C. Valant, B. L.
Flynn, P. M. Sexton, A. Christopoulos and P. J. Scammells, J. Med.
Chem., 2009, 52, 4543ꢀ4547; (e) S. Lethu, M. Ginisty, D. Bosc and J.
Dubois, J. Med. Chem., 2009, 52, 6205ꢀ6208; (f) T. P. Heffron, L.
Salphati, B. Alicke, J. Cheong, J. Dotson, K. Edgar, R. Goldsmith, S. E.
Gould, L. B. Lee, J. D. Lesnick, C. Lewis, C. Ndubaku, J. Nonomiya,
A. G. Olivero, J. Pang, E. G. Plise, S. Sideris, S. Trapp, J. Wallin, L.
Wang and X. Zhang, J. Med. Chem., 2012, 55, 8007ꢀ8020.
11. (a) A. E. Wendlandt and S. S. Stahl, Angew. Chem. Int. Ed., 2015,
127, 14848ꢀ14868; (b) Z. Shen, L. Sheng, X. Zhang, W. Mo, B. Hu, N.
Sun and X. Hu, Tetrahedron Lett., 2013, 54, 1579ꢀ1583; (c) D. Walker
and J. D. Hiebert, Chem. Rev., 1967, 67, 153ꢀ195.
12. (a) K. Ohkubo, K. Hirose and S. Fukuzumi, Chem. Asian. J, 2016, 11
2255ꢀ2259; (b) F. Rusch, J.ꢀC. Schober and M. Brasholz,
ChemCatChem, 2016, , 2881ꢀ2884; (c) K. Ohkubo, A. Fujimoto and S.
,
8
Fukuzumi, J. Am. Chem. Soc., 2013, 135, 5368ꢀ5371.
13. (a) K. Ueda, S. Yanagisawa, J. Yamaguchi and K. Itami, Angew.
Chem. Int. Ed., 2010, 49, 8946ꢀ8949; (b) S. Kirchberg, S. Tani, K.
Ueda, J. Yamaguchi, A. Studer and K. Itami, Angew. Chem. Int. Ed.
,
2011, 50, 2387ꢀ2391.
14. (a) Z. Shen, J. Dai, J. Xiong, X. He, W. Mo, B. Hu, N. Sun and X. Hu,
Adv. Synth. Catal., 2011, 353, 3031ꢀ3038; (b) J. Piera and J.ꢀE.
Bäckvall, Angew. Chem. Int. Ed., 2008, 47, 3506ꢀ3523.
15. (a) Y. Xie, W. Mo, D. Xu, Z. Shen, N. Sun, B. Hu and X. Hu, J. Org.
Chem., 2007, 72, 4288ꢀ4291; (b) R. Liu, X. Liang, C. Dong and X. Hu,
J. Am. Chem. Soc., 2004, 126, 4112ꢀ4113; (c) X. Liang, D. Fu, R. Liu,
3. (a) J. F. Hartwig, Acc. Chem. Res., 2008, 41, 1534ꢀ1544; (b) D. Ma and
Q. Cai, Acc. Chem. Res., 2008, 41, 1450ꢀ1460; (c) J. P. Wolfe, S.
Wagaw, J.ꢀF. Marcoux and S. L. Buchwald, Acc. Chem. Res., 1998, 31
,
805ꢀ818; (d) F. Monnier and M. Taillefer, Angew. Chem. Int. Ed., 2009,
48, 6954ꢀ6971; (e) C. Sambiagio, S. P. Marsden, A. J. Blacker and P. C.
McGowan, Chem. Soc. Rev., 2014, 43, 3525ꢀ3550; (f) J. Bariwal and E.
Van der Eycken, Chem. Soc. Rev., 2013, 42, 9283ꢀ9303; (g) M. D.
Q. Zhang, T. Y. Zhang and X. Hu, Angew. Chem. Int. Ed., 2005, 44
,
5520ꢀ5523.
Charles, P. Schultz and S. L. Buchwald, Org. Lett., 2005, 7, 3965ꢀ3968.
4. (a) I. P. Beletskaya, D. V. Davydov and M. MorenoꢀMañas,
Tetrahedron Lett., 1998, 39, 5617ꢀ5620; (b) M. W. Hooper, M.
Utsunomiya and J. F. Hartwig, J. Org. Chem., 2003, 68, 2861ꢀ2873.
5. (a) A. A. Kantak, S. Potavathri, R. A. Barham, K. M. Romano and B.
DeBoef, J. Am. Chem. Soc., 2011, 133, 19960ꢀ19965; (b) M.ꢀL.
Louillat and F. W. Patureau, Chem. Soc. Rev., 2014, 43, 901ꢀ910; (c) J.
Jiao, K. Murakami and K. Itami, ACS Catalysis, 2016, 6, 610ꢀ633; (d)
R. Shrestha, P. Mukherjee, Y. Tan, Z. C. Litman and J. F. Hartwig, J.
Am. Chem. Soc., 2013, 135, 8480ꢀ8483; (e) K. Sun, Y. Li, T. Xiong, J.
Zhang and Q. Zhang, J. Am. Chem. Soc., 2011, 133, 1694ꢀ1697; (f) S.
H. Cho, J. Y. Kim, J. Kwak and S. Chang, Chem. Soc. Rev., 2011, 40
5068ꢀ5083; (g) K. Sun, X. Wang, L. Liu, J. Sun, X. Liu, Z. Li, Z.
Zhang and G. Zhang, ACS Catalysis, 2015, , 7194ꢀ7198; (h) H. Kim
and S. Chang, ACS Catalysis, 2016, , 2341ꢀ2351.
6. (a) X. Wang, K. Sun, Y. Lv, F. Ma, G. Li, D. Li, Z. Zhu, Y. Jiang and
F. Zhao, Chem. Asian. J, 2014, , 3413ꢀ3416; (b) K. Sun, Z. Zhu, J.
Sun, L. Liu and X. Wang, J. Org. Chem., 2016, 81, 1476ꢀ1483.
7. (a) T. P. Yoon, M. A. Ischay and J. Du, Nat Chem, 2010, , 527ꢀ532;
(b) D. Ravelli, S. Protti and M. Fagnoni, Chem. Rev., 2016, 116, 9850ꢀ
,
5
6
9
2
9913; (c) D. P. Hari and B. König, Angew. Chem. Int. Ed., 2013, 52
,
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