Synthesis of 2-Arylindoles by Rhodium-Catalyzed/Copper-Mediated Annulative Coupling of N-Aryl-2-aminopyridines and Propargyl Alcohols via Selective C-H/C-C Activation

Article abstract of DOI:10.1021/acs.orglett.9b02767

A versatile rhodium-catalyzed/copper-mediated C-H/C-C activation and cascade annulation reaction was described to form 2-arylindole derivatives. Highly selective C-C bond cleavage of ?-substituted tert-propargyl alcohols occurred, together with pyridine-directed ortho C(sp²)-H bond activation, affording a series of 2-arylindoles with yields up to 90%. Subsequent derivations were smoothly conducted to access polyfunctionalized 2-arylindoles, illustrating the potential applications of this method.

Full text of DOI:10.1021/acs.orglett.9b02767

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Synthesis of 2‑Arylindoles by Rhodium-Catalyzed/Copper-Mediated
Annulative Coupling of N‑Aryl-2-aminopyridines and Propargyl
Alcohols via Selective C−H/C−C Activation
Xufei Yan, Runyou Ye, Huihui Sun, Jing Zhong, Haifeng Xiang, and Xiangge Zhou*
College of Chemistry, Sichuan University, 29 Wangjiang Road, Chengdu 610064, P. R. China
S
* Supporting Information
ABSTRACT: A versatile rhodium-catalyzed/copper-mediated C−H/C−C activation and cascade annulation reaction was
described to form 2-arylindole derivatives. Highly selective C−C bond cleavage of γ-substituted tert-propargyl alcohols
occurred, together with pyridine-directed ortho C(sp2)−H bond activation, affording a series of 2-arylindoles with yields up to
90%. Subsequent derivations were smoothly conducted to access polyfunctionalized 2-arylindoles, illustrating the potential
applications of this method.
ndole skeletons are crucial structural motifs existing in
1
Iabundant natural products and drug molecules. Conven-
tional syntheses of multisubstituted indoles, for example, the
Fischer, Bischler, Larock, and Bartoli indole synthetic methods,
have emerged as practical and efficient routes up to now.2
Nonetheless, transition-metal (Co, Ru, Rh, Ir, Pd, etc.)-
catalyzed direct C−H activation reactions with auxiliary
directing groups have attracted increasing attention in indole
Figure 1. Selected examples of 2-arylindole-containing biologically
active molecules.
skeleton construction with synthetic diversity and general
substance availability in recent years (Scheme 1).3 In
particular, 2-arylindoles are well established as important
elegant approaches to 2-arylindoles were reported recently by
components of various biological active compounds, such as
tubulin polymerization inhibitors and strong antiplasmodial
the Cui3t and Huang3u groups, respectively. In spite of this
progress in 2-arylindole synthesis, the feasibility to derivations
and abundance in biological active molecules still render it
highly appealing for facile synthesis.
activity molecular (isocryptolepine) and antiviral hepatitis C
virus (HCV) inhibitors (Figure 1).4 It is well noted that two
On the other hand, propargyl alcohols have served as flexible
Scheme 1. Transition-Metal-Catalyzed Indole Derivative
Synthesis
building blocks involved in allene and alkyne formation as well
as cyclization reactions.5 Especially, they could act as terminal
alkyne precursors via C−C bond activation, which participated
in cross coupling reactions with alkynes,6 alkenes,7 aryl
halides,8 H-phosphonates,9 or benzylic carbonates.10 For
example, Wen and co-workers reported Rh/Cu-catalyzed
reactions merging C−C cleavage of γ-substitued tert-propargyl
alcohols and C−H activation with directing group assistance to
afford C2-selective alkynylated indoles (R = Me) and
pyrido[2,1-a]indoles (R = H), respectively, in 2016 (Scheme
Received: August 5, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b02767
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
2a).11 In continuation of our work on C−C activation12 and
a
Table 1. Optimization of the Reaction Conditions
synthesis of heterocyclic compounds,13 herein we disclosed
Scheme 2. Propargyl Alcohols Involved C−H/C−C
Activation Reactions
b
entry
catalyst
solvent
yield (%)
1
2
3
4
5
6
7
8
[Cp*RhCl2]2
Ni(OAc)2·4H2O
Co(OAc)2·4H2O
[RuCl2(p-cymene)]2
Pd(OAc)2
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
DCE
toluene
MeCN
DMF
DMSO
55
0
0
0
0
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
18
27
50
41
39
45
66
trace
0
62
49
42
42
37
81(77)
75
0
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
rhodium-catalyzed/copper-mediated aniline derivative ortho
C−H alkynylation and cascade intramolecular annulation
reactions toward 2-arylindole derivatives in one pot (Scheme
2b). This work features the following items: highly selective
C−C cleavage of propargyl alcohols, ortho C−H alkynylation
of aniline derivatives, and one-pot cascade reaction to form 2-
arylindoles.
MeOH
c
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
d
c e
,
c f
,
c g
,
c h
,
Our investigation commenced with the reaction between N-
4-methylphenyl-2-animopyridine (1a) and 2-methyl-4-phenyl-
but-3-yn-2-ol (2a) in 1,4-dioxane in the presence of 5 mol %
[Cp*RhCl2]2 and 2.0 equiv of Cu(OAc)2 at 120 °C for 12 h
under air. As shown in Table 1, the desired C−H/C−C
activation and annulation product 3a was obtained in 55%
yield. Sequential metal salt screening revealed that Ni(II),
Co(II), Ru(II), and Pd(II) were not beneficial to the reaction
without formation of 3a (Table 1, entries 2−5). Solvent effects
were then explored, and 1,4-dioxane was shown to be better
than others including DCE, toluene, MeCN, DMF, DMSO,
and MeOH (Table 1, entries 6−11). We then equipped this
reaction under a N2 or O2 atmosphere, and a dramatic
increased yield (66%) was observed with N2 while only a trace
of 3a was detected, which would be possibly caused by the
instability of 1a under an O2 atmosphere (Table 1, entries 12
and 13). Meanwhile, when the temperature was decreased to
100 °C, this reaction was almost suppressed (Table 1, entry
14). We also increased the temperature to 130 °C, but no
better yield was achieved (Table 1, entry 15). Meanwhile, acid
(HOAc and PivOH) or base (K2CO3 and Cs2CO3) additives
were also studied, affording inferior product yields (Table 1,
entries 16−19). To our delight, the reaction was significantly
improved to give 3a in 77% isolated yield with a loading of 3.0
equiv of 2a and 2.5 equiv of Cu(OAc)2 (Table 1, entry 20).
Prolonging the reaction time to 24 h did not facilitate the
formation of 3a (Table 1, entry 21). At last, control
experiments indicated the necessity of [Cp*RhCl2]2 and
Cu(OAc)2, as no 3a was formed in the absence of either of
them (Table 1, entries 22 and 23). Phenylacetylene instead of
2a was employed in this reaction with only a trace amount of
3a being obtained (Table 1, entry 24). Therefore, 5 mol %
[Cp*RhCl2]2, 2.5 equiv of Cu(OAc)2, and 3.0 equiv of 2a in
1,4-dioxane (1.0 mL) at 120 °C for 12 h under N2 were
selected as the optimal reaction conditions.
c i
,
c j
,
c k
,
c kl
,
,
c
c m
,
[Cp*RhCl2]2
[Cp*RhCl2]2
0
trace
c n
,
a
General conditions: 1a (0.2 mmol), 2a (0.4 mmol), catalyst (5 mol
%), and Cu(OAc)2 (2.0 equiv) in solvent (1.0 mL) were stirred at
120 °C for 12 h in the air. NMR yields using CH2Br2 as the internal
standard and isolated yields were shown in parentheses. Under N2
b
c
d
e
atmosphere. Under O2 atmosphere. Reaction temperature 100 °C.
f
g
h
Reaction temperature 130 °C. HOAc (2.0 equiv). PivOH (2.0
i
j
k
equiv). K2CO3 (2.0 equiv). Cs2CO3 (2.0 equiv). 2a (3.0 equiv) and
l
m
n
Cu(OAc)2 (2.5 equiv). 24 h. Without Cu(OAc)2. Phenylacetylene
(3.0 equiv) instead of 2a.
methyl group gave a yield of 26% (3p), while 77% (3a) and
67% (3l) yields were obtained in the case of para and meta
methyl group substituted substrates. In addition, para
isopropyl (3c), −OMe (3d), phenyl (3e), and −Ac (3h)
substituted N-aryl-2-aminopyridines as well as N-phenyl-2-
aminopyridine (3b) could be employed well with moderate to
good yields. It was worth noting that substrates containing a
chloro (3f and 3m) or bromo group (3g) could also be
applicable in this reaction, which indicated the potential
derivative applications. Dimethyl and dichloro substrates also
underwent these transformations smoothly (3n and 3o).
Meanwhile, the substrates with strong electron-withdrawing
groups (−CF3, −CN, and −F) delivered relatively lower yields
of 55% (3i), 39% (3j), and 31% (3k), respectively.
Next, the scope of tert-propargyl alcohols was explored as
shown in Scheme 4. Substrates with an ortho methyl
substituent gave the desired product (3q, 65%) in a relatively
lower yield compared with the meta methyl substituted one
(3r, 76%) and the para methyl substituted one (3s, 77%) due
to the possible steric hindrance. Substrates bearing other para
substituents (3t−3z) afforded the corresponding products in
moderate to good yields, among which the strong electron-
withdrawing moiety (−CN) suppressed this reaction to some
With the optimized reaction conditions in hand, a series of
substituted N-aryl-2-aminopyridines were investigated, and the
reactions were performed smoothly with yields ranging from
26 to 90%, as depicted in Scheme 3. Steric effects seemed to be
vital for the reaction. For example, substrate bearing an ortho
B
DOI: 10.1021/acs.orglett.9b02767
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a b
,
To further demonstrate the utility of this C−H/C−C
activation and cascade annulation reaction, ongoing derivations
toward the synthesis of versatile 1,2,3-trisubstitued indoles
were implemented. As shown in Scheme 5, 2-phenyl-5-methyl
Scheme 3. Scope of N-Aryl-2-aminopyridines
a
Scheme 5. Product Transformations and a Scale-Up
b
Experiment
a
1 (0.2 mmol), 2a (3.0 equiv), [Cp*RhCl2]2 (5 mol %), and
Cu(OAc)2 (2.5 equiv) were stirred in 1,4-dioxane (1.0 mL) at 120 °C
b
for 12 h in N2. Isolated yields.
extent (3z). 1-Naphthalenyl (3aa), 2-naphthalenyl (3ab), 9-
phenanthrenyl (3ac), and 1-pyrenyl (3ad) were successfully
involved in this reaction approach to more conjugated 2-
substitued indole derivatives. The dimethyl substituent was
also tolerated, giving the product 3ae in 77% yield. Thiophene-
containing propargyl alcohol smoothly participated in this
reaction as well with a reasonable 51% yield of 3af.
a
Reaction conditions: (1) POCl3, DMF, 50 °C, 5 h, air; (2) NBS,
CHCl3, rt, 5 h, air; (3) CuI, PhCH2CN, DMF, 130 °C, 40 h, air; (4)
(4-MeOC6H4S)2, KIO3, glycerol, 100 °C, 6 h, air; (5) MeOTf, DCM,
0 °C to rt, 12 h, air followed by Pd(OH)2/C, NH4HCO3, MeOH, 60
°C, 24 h, air; (6) Tf2O, Ph3PO, DCM, rt, 15 min, air; (7) POCl3,
a b
,
Scheme 4. Scope of tert-Propargyl Alcohols
b
xylene, 120 °C, 15 min, air. Reaction conditions: 1a (1.0 mmol,
0.184 g), 2a (3.0 mmol, 0.480 g), [Cp*RhCl2]2 (0.05 mmol, 0.031 g),
and Cu(OAc)2 (2.5 mmol, 0.5 g) were stirred in 1,4-dioxane (5.0 mL)
at 120 °C for 12 h in N2.
N-pyridine indoles bearing 3-CHO, 3-Br, 3-CN, and 3-SAr
functional groups that could be successfully achieved with
moderate to good yields incorporated 3a with DMF, NBS,
benzyl cyanide, and aryl disulfide, respectively (Scheme 5a).14
Meanwhile, tert-propargyl alcohol containing an ortho NHAc
group was applicable in this reaction and gave product 3bb in a
45% yield. 3bb underwent cleavage of the 2-pyridyl directing
group, affording N-[2-(1H-indol-2-yl)phenyl]acetamide (8).15
Compound 8 has been reported to undergo intramolecular
cyclizations, smoothly leading to 6-methyl-11H-indolo[3,2-
c]quinoline (9) and 6-methylindolo[1,2-c]quinazoline (10),
respectively (Scheme 5b).16 Also, the pyridyl directing group
of more general products such as 3a could be removed
according to the literature (Scheme 5c).17 By the way, a scale-
up experiment of 1a (1.0 mmol) was conducted to give the
desired product 3a in 68% yield (Scheme 5d). These strategies
came up with novel and feasible synthesis routes to
functionalized indole skeletons, which existed abundantly in
biological active compounds, as mentioned in Figure 1.
a
1a (0.2 mmol), 2 (3.0 equiv), [Cp*RhCl2]2 (5 mol %), and
Cu(OAc)2 (2.5 equiv) were stirred in 1,4-dioxane (1.0 mL) at 120 °C
for 12 h in N2. Isolated yields.
b
C
DOI: 10.1021/acs.orglett.9b02767
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
To gain some insight into the possible reaction pathways, a
series of experiments were carried out, as shown in Scheme 6.
Scheme 7. Plausible Mechanistic Pathway
Scheme 6. Studies of the Reaction Pathway
In summary, we have developed a one-pot rhodium-
catalyzed/copper-mediated C−H/C−C activation and annu-
lation reaction to assemble 2-arylindoles. This synthetic
methodology features broad substrate scope, highly selective
C−C bond cleavage of tert-propargyl alcohols, and pyridine-
directed ortho C(sp2)−H bond activation. Expedient deriva-
tions to 1,2,3-trisubstitued indoles, 6-methyl-11H-indolo[3,2-
c]quinoline, and 6-methylindolo[1,2-c]quinazoline verified the
practicability of this reaction. Further attempts to access more
heterocycles on the basis of auxiliary C−H activation and
propargyl alcohols are currently underway in our laboratory.
ASSOCIATED CONTENT
* Supporting Information
■
S
First, the H/D exchange experiment of 1b with D2O (10
equiv) led to 56% ortho deuterated [D]-1b, indicating the ortho
C−H cleavage might be reversible during the reaction
(Scheme 6, eq 1). Parallel and intermolecular competitive
reactions were also performed, and the kinetic isotope effect
values (kH/kD) were determined to be 1.0 and 1.1, respectively
(Scheme 6, eqs 2 and 3). These results implied the ortho C−H
activation process might not be involved in the rate-
determining step. In addition, 2a was reacted only in the
presence of Cu(OAc)2 in 1,4-dioxane, and the corresponding
Glaser coupling product 12 was obtained in 55% yield, which
showcased the pathway of Cu(OAc)2-mediated C−C bond
cleavage of 2a (Scheme 6, eq 4). Then, N-phenyl-2-
aminopyridine-Rh(III) complex 13 was synthesized according
to the literature (Scheme 6, eq 5).18 The catalytic and
stoichiometric reactions by using complex 13 were performed,
affording the desired product in 65 and 62% yields, which
implied complex 13 would be involved in the catalytic
reactions (Scheme 6, eqs 6 and 7).
On the basis of the above experimental results and related
literature,11a,19 a proposed reaction pathway is illustrated below
(Scheme 7). At first, the rhodium complex IM1 was formed via
proton abstraction and ortho C(sp2)−H metalation. C−C
bond cleavage of 2a occurred in situ with the assistance of
Cu(OAc)2, delivering alkynylcopper species. Alkynylrhodium
IM2 was then obtained via transmetalation. At last, IM2 went
through reductive elimination followed by sequential Lewis
acid (rhodium or copper salts) promoted cyclization via
nucleophilic attack of the amino group to the activated alkynyl
moiety to afford the desired product 3b. Meanwhile, the
oxidation of Rh(I) to the reactive Rh(III) species by Cu(II)
completed the catalytic cycle.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b02767.
Experimental details and characterization data (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: zhouxiangge@scu.edu.cn.
ORCID
Haifeng Xiang: 0000-0002-4778-2455
Xiangge Zhou: 0000-0001-5327-6674
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the National Natural Science Foundation of
China (Grant No. 21472128) and Sichuan Science and
Technology Program (No. 2018JY560) for financial support.
We also acknowledge Comprehensive Training Platform of
Specialized Laboratory, College of Chemistry, Sichuan
University, for HRMS analysis.
REFERENCES
■
(1) (a) Somei, M.; Yamada, F. Nat. Prod. Rep. 2005, 22, 73.
(b) Kochanowska-Karamyan, A. J.; Hamann, M. T. Chem. Rev. 2010,
110, 4489. (c) Stempel, E.; Gaich, T. Acc. Chem. Res. 2016, 49, 2390.
(d) Li, L.; Chen, Z.; Zhang, X.; Jia, Y. Chem. Rev. 2018, 118, 3752.
(2) (a) Fischer, E.; Jourdan, F. Ber. Dtsch. Chem. Ges. 1883, 16, 2241.
(b) Robinson, B. Chem. Rev. 1963, 63, 373. (c) Bischler, A. Ber. Dtsch.
Chem. Ges. 1892, 25, 2860. (d) Bischler, A.; Fireman, P. Ber. Dtsch.
D
DOI: 10.1021/acs.orglett.9b02767
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Chem. Ges. 1893, 26, 1336. (e) Larock, R. C.; Yum, E. K. J. Am. Chem.
Soc. 1991, 113, 6689. (f) Larock, R. C.; Yum, E. K.; Refvik, M. D. J.
Org. Chem. 1998, 63, 7652. (g) Bartoli, G.; Dalpozzo, R.; Nardi, M.
Chem. Soc. Rev. 2014, 43, 4728.
(16) Xu, M.; Hou, Q.; Wang, S.; Wang, H.; Yao, Z.-J. Synthesis 2011,
2011, 626.
(17) Liang, L.; Fu, S.; Lin, D.; Zhang, X.-Q.; Deng, Y.; Jiang, H.;
Zeng, W. J. Org. Chem. 2014, 79, 9472.
(18) Allu, S.; Ravi, M.; Kumara Swamy, K. C. Eur. J. Org. Chem.
2016, 2016, 5697.
(19) (a) Clentsmith, G. K. B.; Field, L. D.; Messerle, B. A.; Shasha,
A.; Turner, P. Tetrahedron Lett. 2009, 50, 1469. (b) Gao, J.; Shao, Y.;
Zhu, J.; Zhu, J.; Mao, H.; Wang, X.; Lv, X. J. Org. Chem. 2014, 79,
9000.
(3) (a) Ackermann, L.; Lygin, A. V. Org. Lett. 2011, 13, 3332.
(b) Punji, B.; Song, W.; Shevchenko, G. A.; Ackermann, L. Chem. -
Eur. J. 2013, 19, 10605. (c) Lu, M.-Z.; Lu, P.; Xu, Y.-H.; Loh, T.-P.
Org. Lett. 2014, 16, 2614. (d) Tiwari, V. K.; Kamal, N.; Kapur, M.
Org. Lett. 2015, 17, 1766. (e) Wang, L.; Qu, X.; Li, Z.; Peng, W.-M.
Tetrahedron Lett. 2015, 56, 3754. (f) Chen, J.; Song, G.; Pan, C.; Li,
X. Org. Lett. 2010, 12, 5426. (g) Lygin, A. V.; Ackermann, L. Org. Lett.
2012, 14, 764. (h) Liu, B.; Song, C.; Sun, C.; Zhou, S.; Zhu, J. J. Am.
Chem. Soc. 2013, 135, 16625. (i) Wang, C.; Sun, H.; Fang, Y.; Huang,
Y. Angew. Chem., Int. Ed. 2013, 52, 5795. (j) Zhao, D.; Shi, Z.;
Glorius, F. Angew. Chem., Int. Ed. 2013, 52, 12426. (k) Lerchen, A.;
́
́
Vasquez-Cespedes, S.; Glorius, F. Angew. Chem., Int. Ed. 2016, 55,
3208. (l) Hermann, G. N.; Jung, C. L.; Bolm, C. Green Chem. 2017,
19, 2520. (m) Sharma, U.; Kancherla, R.; Naveen, T.; Agasti, S.;
Maiti, D. Angew. Chem., Int. Ed. 2014, 53, 11895. (n) Cai, S.; Lin, S.;
Yi, X.; Xi, C. J. Org. Chem. 2017, 82, 512. (o) Manna, M. K.; Bairy, G.;
Jana, R. J. Org. Chem. 2018, 83, 8390. (p) Qi, Z.; Yu, S.; Li, X. Org.
Lett. 2016, 18, 700. (q) Jiang, H.; Gao, S.; Xu, J.; Wu, X.; Lin, A.; Yao,
H. Adv. Synth. Catal. 2016, 358, 188. (r) Guo, X.; Han, J.; Liu, Y.;
Qin, M.; Zhang, X.; Chen, B. J. Org. Chem. 2017, 82, 11505. (s) Lv,
H.; Shi, J.; Wu, B.; Guo, Y.; Huang, J.; Yi, W. Org. Biomol. Chem.
2017, 15, 8054. (t) Jie, L.; Wang, L.; Xiong, D.; Yang, Z.; Zhao, D.;
Cui, X. J. Org. Chem. 2018, 83, 10974. (u) Cui, X.; Ban, Z.; Tian, W.;
Hu, F.; Zhou, X.; Ma, H.; Zhan, Z.; Huang, G. Org. Biomol. Chem.
2019, 17, 240. (v) Luo, Y.; Guo, L.; Yu, X.; Ding, H.; Wang, H.; Wu,
Y. Eur. J. Org. Chem. 2019, 2019, 3203.
(4) (a) Lal, S.; Snape, T. J. Curr. Med. Chem. 2012, 19, 4828.
(b) Yet, L. 2-(Hetero)arylindoles in Privileged Structures in Drug
Discovery: Medicinal Chemistry and Synthesis, 1st ed.; John Wiley &
Sons, Inc.: 2018; pp 321−355.
(5) Qian, H.; Huang, D.; Bi, Y.; Yan, G. Adv. Synth. Catal. 2019, 361,
3240.
(6) Funayama, A.; Satoh, T.; Miura, M. J. Am. Chem. Soc. 2005, 127,
15354.
(7) Nishimura, T.; Araki, H.; Maeda, Y.; Uemura, S. Org. Lett. 2003,
5, 2997.
(8) (a) Hu, H.; Yang, F.; Wu, Y. J. Org. Chem. 2013, 78, 10506.
(b) Sun, F.; Li, M.; Gu, Z. Org. Chem. Front. 2016, 3, 309. (c) Chang,
F.; Liu, Y. Synth. Commun. 2017, 47, 961.
(9) Li, X.; Sun, S.; Yang, F.; Kang, J.; Wu, Y.; Wu, Y. Org. Biomol.
Chem. 2015, 13, 2432.
(10) Mi, Z.; Tang, J.; Guan, Z.; Shi, W.; Chen, H. Eur. J. Org. Chem.
2018, 2018, 4479.
(11) (a) Li, T.; Wang, Z.; Qin, W.-B.; Wen, T.-B. ChemCatChem
2016, 8, 2146. (b) Li, T.; Wang, Z.; Zhang, M.; Zhang, H.-J.; Wen, T.-
B. Chem. Commun. 2015, 51, 6777.
(12) (a) Jiang, Z.; Huang, Q.; Chen, S.; Long, L.; Zhou, X. Adv.
Synth. Catal. 2012, 354, 589. (b) Yan, X.; Sun, H.; Xiang, H.; Yu, D.-
G.; Luo, D.; Zhou, X. Chem. Commun. 2018, 54, 8606.
(13) (a) Qu, Y.; Ke, F.; Zhou, L.; Li, Z.; Xiang, H.; Wu, D.; Zhou, X.
Chem. Commun. 2011, 47, 3912. (b) Wu, Z.; Huang, Q.; Zhou, X.;
Yu, L.; Li, Z.; Wu, D. Eur. J. Org. Chem. 2011, 2011, 5242. (c) Deng,
H.; Li, Z.; Ke, F.; Zhou, X. Chem. - Eur. J. 2012, 18, 4840. (d) Che, R.;
Wu, Z.; Li, Z.; Xiang, H.; Zhou, X. Chem. - Eur. J. 2014, 20, 7258.
(e) Chen, J.; Xiang, H.; Yang, L.; Zhou, X. RSC Adv. 2017, 7, 7753.
(14) (a) Kaufmann, D.; Pojarova, M.; Vogel, S.; Liebl, R.; Gastpar,
R.; Gross, D.; Nishino, T.; Pfaller, T.; von Angerer, E. Bioorg. Med.
Chem. 2007, 15, 5122. (b) So, C. M.; Chow, W. K.; Choy, P. Y.; Lau,
C. P.; Kwong, F. Y. Chem. - Eur. J. 2010, 16, 7996. (c) Yuen, O. Y.;
Choy, P. Y.; Chow, W. K.; Wong, W. T.; Kwong, F. Y. J. Org. Chem.
2013, 78, 3374. (d) Rafique, J.; Saba, S.; Franco, M. S.; Bettanin, L.;
Schneider, A. R.; Silva, L. T.; Braga, A. L. Chem. - Eur. J. 2018, 24,
4173.
(15) Liu, W.; Richter, S. C.; Mei, R.; Feldt, M.; Ackermann, L. Chem.
- Eur. J. 2016, 22, 17958.
E
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