Highly efficient Br?nsted acid and Lewis acid catalysis systems for the Friedl?nder Quinoline synthesis

Article abstract of DOI:10.1080/00397911.2018.1428346

The efficient and green Br?nsted acid or Lewis acid catalysis systems for the Friedl?nder synthesis of 2,3,4-trisubstituted quinolines from the condensation of 2-aminoarylketones and β-ketoesters/ketones had been developed. The results confirmed that 4-to

Full text of DOI:10.1080/00397911.2018.1428346

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Highly efficient Brønsted acid and Lewis acid
catalysis systems for the Friedländer Quinoline
synthesis
Xiao-Yu Zhou, Xia Chen & Liang-Guang Wang
To cite this article: Xiao-Yu Zhou, Xia Chen & Liang-Guang Wang (2018): Highly efficient
Brønsted acid and Lewis acid catalysis systems for the Friedländer Quinoline synthesis, Synthetic
Communications, DOI: 10.1080/00397911.2018.1428346
To link to this article: https://doi.org/10.1080/00397911.2018.1428346
View supplementary material
Published online: 06 Mar 2018.
Submit your article to this journal
Article views: 3
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=lsyc20

SYNTHETIC COMMUNICATIONS®
https://doi.org/10.1080/00397911.2018.1428346
Highly efficient Brønsted acid and Lewis acid catalysis systems
for the Friedländer Quinoline synthesis
Xiao-Yu Zhoua, Xia Chena, and Liang-Guang Wangb
b
aSchool of Chemistry and Materials Engineering, Liupanshui Normal University, Liupanshui, China; College of
Chemistry and Chemical Engineering, Anshun University, Anshun, China
ABSTRACT
ARTICLE HISTORY
Received 6 December 2017
The efficient and green Brønsted acid or Lewis acid catalysis systems
for the Friedländer synthesis of 2,3,4-trisubstituted quinolines from
the condensation of 2-aminoarylketones and β-ketoesters/ketones
had been developed. The results confirmed that 4-toluenesulfonic
acid, magnesium chloride, and cupric nitrate were the desired catalyst
independently. This protocol had the advantages of mild conditions,
operational simplicity, and excellent yields.
KEYWORDS
Brønsted acid; catalysis;
Friedländer; Lewis acid;
Quinoline
GRAPHICAL ABSTRACT
Quinolines are one of the most privileged azaheterocyclic scaffolds, which are commonly
found in many pharmaceuticals[1] and natural products.[2] Besides, they are wildly applied
to the preparation of metal complexes as ligand.[3] Thus, the exploration of synthetic
methods of quinolines is a topic area for organic synthesis chemists.[4] In the past decades,
several classical approaches had been developed for the construction of quinoline
derivatives, including the Skraup–Doebnervon Miller,[5] Pfitzinger,[6] Combes reactions,[7]
and Friedländer quinoline synthesis.[8] Among these methods, the Friedländer reaction is
one of the simplest protocols, which involves condensation of 2-aminoaryl ketones and
β-ketoesters/ketones possessing a reactive α-methylene group.
Recently, many novel Brønsted acid or Lewis acid catalysis systems have been
developed. For example, Heydari’s group[9] developed the one-pot domino approach to
realize Friedländer quinoline synthesis in aqueous medium, using SO3H-functionalized
ionic liquid as a water-tolerant acidic catalyst. In 2012, Rao’s group[10] reported
(bromodimethyl)sulfonium bromide-catalyzed Friedländer quinoline synthesis in
CONTACT Xiao-Yu Zhou
Zhouxiaoyu20062006@126.com
School of Chemistry and Materials Engineering,
Liupanshui Normal University, Liupanshui 553004, China.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data (Full experimental detail, 1H and 13C NMR spectra) can be accessed on the publisher’s website.
© 2018 Taylor & Francis

2
X.-Y. ZHOU ET AL.
solvent-free conditions. In 2013, Pérez-Mayoral et al.[11] developed a series of acidic activated
carbon material-catalyzed Friedländer reactions and the results indicated that the most acidic
microporous carbon materials were efficient catalysts and a cheap alternative for the syn-
thesis of quinolines through Friedländer condensation. In 2014, the ball milling technique
was used for Friedländer reactions in the presence of 4-toluenesulfonic acid under sol-
vent-free conditions.[12] In 2015, Esmaeilpour and Javidi[13] developed green and reusable
Fe3O4@SiO2-imid-PMAn and Fe3O4@SiO2-imid-PMAb nanoparticle-catalyzed Friedländer
reactions of 2-aminobenzophenones and ethylacetoacetate or ketones.
In addition, several modified Friedländer reactions had been developed, involving the
reactions of aromatic 2-aminosubstituted carbonyl compounds with various other
substrates, such as alkynes,[14] alkenes,[15] alcohols,[16] 2-aminoaryl methanols,[17]
2-iodoanilines,[18] and 2-nitroaryl aldehydes.[19] In 2016, Ying et al.[20] developed
heterogeneous Ag-Pd/C alloy nanoparticle-catalyzed modified Friedländer reactions, with
ketones and primary alcohols as substrates, to give polysubstituted quinolines in moderate
to good yields. In the same year, Jiang’s group[21] reported the palladium-catalyzed aerobic
oxidative approach to afford functionalized 2-substituted quinolines in moderate to good
yields from readily available allylbenzenes with aniline. Subsequently, Kirchner et al.[22]
reported hydride Mn(I) PNP complex-catalyzed Friedländer-type quinoline synthesis with
2-aminobenzyl alcohols and secondary alcohols as substrates. Most recently, Popowycz
et al.[23] developed a Friedländer-type quinoline synthesis method starting from substituted
anthranilonitriles. And 4-aminoquinolines were prepared in the presence of superacidic
trifluoromethanesulfonic acid. The methods are effective, but there still are many
drawbacks. They require the use of expensive reagents or metal catalysts, harmful organic
solvents, or large excess amount of metal salts, which will limit their usefulness in
large-scale production.
4-Toluenesulfonic acid, magnesium salts, and copper salts are a kind of most useful
reagents in organic synthesis and can be used as cheap Brønsted acid or Lewis acid
catalysts. To the best of our knowledge, the magnesium chloride and cupric nitrate-
catalyzed Friedländer quinoline synthesis have not been reported previously. Herein, we
reported three efficient catalysis systems for the Friedländer quinoline synthesis, using
4-toluenesulfonic acid (TsOH · H2O), magnesium chloride (MgCl2 · 6H2O), and cupric
nitrate (Cu(NO3)2 · 3H2O) as the catalyst independently (Scheme 1).
In the course of our continuous research on copper-catalyzed enamination of ketones
for the synthesis of enaminones,[24] 1-(2,4-dimethylquinolin-3-yl)ethanone (3a) was
prepared unexpectedly when 1-(2-aminophenyl)ethanone (1a) and pentane-2,4-dione
(2a) were chosen as starting materials. Then, the initial experiment began with copper(I)
chloride (CuCl) as catalyst in ethanol at 80 °C. The product 3a was isolated with 57% yield
Scheme 1. Brønsted acid- and Lewis acid-catalyzed Friedländer quinoline synthesis.

SYNTHETIC COMMUNICATIONS®
3
Table 1. Optimization conditions for the Friedländer quinoline synthesis.a
Entry
Cat.(x)
Solvent (T)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
MeOH (80)
Acetonitrile (80)
1,4-dioxane (80)
THF (80)
Toluene (80)
EtOH (60)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
EtOH (80)
Yield (%)b
1
CuCl (10)
57
63
16
Trace
Trace
>99
83
2
CuBr (10)
3
CuI (10)
4
Cu(OAc)2 · H2O (10)
Cu(acac)2 (10)
Cu(NO3)2 · 3H2O (10)
TsOH · H2O (10)
TsOH · H2O (20)
TsOH · H2O (20)
TsOH · H2O (20)
TsOH · H2O (20)
TsOH · H2O (20)
TsOH · H2O (20)
TsOH · H2O (20)
TsOH · H2O (20)
TsOH · H2O (20)
LiCl (40)
5
6
7
8
>99
>99
65
9
10
11
12
13
14
15c
16d
17
18
19
20
21
22
23
24
25
56
Trace
41
81
70
78
71
LiCl (100)
NaCl (100)
81
19
FeCl3 · 6H2O (10)
CoCl3 · 6H2O (10)
Zn(OAc)2 (10)
MgCl2 · 6H2O (10)
MgO (10)
86
97
nr
>99
Trace
12
EtOH (80)
EtOH (80)
MgSO4 (10)
aUnless otherwise stated, all reactions are performed with 1a (68 mg, 0.5 mmol), 2a (100 mg, 1.0 mmol), catalyst, and solvent
(3.0 mL) in air, 12 h.
bIsolated yields are provided.
c2a (60 mg, 0.6 mmol) was added.
d2a (75 mg, 0.75 mmol) was added.
THF, tetrahydrofuran.
(Table 1, entry 1). This result encouraged us to expand catalysis system of Friedländer
reactions. Then the catalysts, solvents, and temperature were evaluated to improve the
yields of the reaction, respectively.
First, the other copper salts, CuBr (10 mol%), CuI (10 mol%), Cu(OAc)2 · H2O
(10 mol%), Cu(acac)2 (10 mol%), and Cu(NO3)2 · 3H2O (10 mol%) were tested as the cata-
lyst (entries 2–6) in EtOH at 80 °C and >99% yield was obtained when Cu(NO3)2 · 3H2O
(10 mol%) was chosen as catalyst (entry 6). The results indicated that the catalyst with
stronger Lewis acidic properties favored to activate the ketones in the condensation. Then,
4-toluenesulfonic acid (TsOH · H2O, 10 mol%) (entry 7) was tested as a Brønsted acidic
catalyst and 83% yield was obtained. The yield was increased to >99% when 20 mol%
TsOH · H2O was added (entry 8).
To evaluate the effect of solvent, methanol (MeOH, >99%, entry 9), acetonitrile (65%,
entry 10), 1,4-dioxane (56%, entry 11), tetrahydrofuran (trace, entry 12), and toluene
(41%, entry 13) were tested as solvent, respectively. The results showed that both
EtOH and MeOH were the best choice. Due to the convenient operation of experiment,
EtOH was chosen as solvent in the following reaction optimization process. Subsequently,
the temperature and amount of substrate 2a were tested (entries 14–16). The results

4
X.-Y. ZHOU ET AL.
confirmed that the best temperature was 80 °C and the best amount of 2a was 2.0
equivalents.
To investigate whether the other metal salts with Lewis acid could be used as catalyst in
the Friedländer quinoline synthesis, lithium chloride (LiCl, 71% yield with 40 mol% load-
ing and 81% yield with 100 mol% loading, entries 17–18), NaCl (100 mol%, 19%, entry 19),
FeCl3 · 6H2O (10 mol%, 86%, entry 20), CoCl3 · 6H2O (10 mol%, 97%, entry 21), Zn(OAc)2
(10 mol%, no product was detected, entry 22), MgCl2 · 6H2O (10 mol%, >99%, entry 23),
MgO (10 mol%, trace, entry 24), and MgSO4 (10 mol%, 12%, entry 25) were evaluated
independently and the MgCl2 · 6H2O showed the best result with >99% yield. In con-
clusion, cupric nitrate (Cu(NO3)2 · 3H2O, 10 mol%), 4-toluenesulfonic acid (TsOH · H2O,
20 mol%), and magnesium chloride (MgCl2 · 6H2O, 10 mol%) were all the best catalyst
for the Friedländer quinoline synthesis.
Thus, the standard conditions were established as follows: 4-toluenesulfonic acid
(TsOH · H2O, 20 mol%), magnesium chloride (MgCl2 · 6H2O, 10 mol%), or cupric nitrate
(Cu(NO3)2 · 3H2O, 10 mol%) were used as catalysts in EtOH at 80 °C. Based on the opti-
mized conditions, the substrate scope of the Friedländer quinoline synthesis was tested
independently. The results are shown in Table 2.
Under the optimal conditions, a variety of 2-aminoarylketones and β-ketoesters/ketones
were subjected to 4-toluenesulfonic acid (TsOH · H2O, 20 mol%), magnesium chloride
(MgCl2 · 6H2O, 10 mol%), and cupric nitrate (Cu(NO3)2 · 3H2O, 10 mol%)-catalyzed
Friedländer reaction, respectively, as shown in Table 2. For the condensation of substrates
1a–1e and 1g–1i (Table 2, entries 1–5, 7–9) with different substituents reacted with
pentane-2,4-dione (2a) under the optimal reaction conditions A, B, and C, good to
excellent yields (64– >99% yields) of 3a–3e and 3g–3i were achieved, respectively. The
reaction was inhibited when substrate 1f was applied to the synthesis of quinoline under
optimal reaction conditions (entry 6). The reactivity of 1f may be weakened by the steric
hindrance of chlorogroup of 2-chlorophenyl and the stronger electron-withdrawing
property of substituent –NO2. It is worth to note that the catalysis system also can be
applied to the substrate (2-aminophenyl)methanol 1j, but only with 37–64% yield under
the above three catalysis systems, respectively (entry 10).
Then, heptane-3,5-dione (2b, entry 11), 1-phenylbutane-1,3-dione (2c, entry 12), ethyl
3-oxobutanoate (2d, entry 13), and iso-propyl 3-oxobutanoate (2e, entry 14) were chosen
as the substrate and reacted with 1a, respectively. About 94%- >99% yields of target
products were isolated. And when 2c reacted with 1a, only 19–74% yields of 3n were
isolated. The reason was speculated that the substrate 2c with phenyl substituent increased
the steric hindrance.
To test the scale-up procedure of Brønsted acid- and Lewis acid-catalyzed Friedländer
quinoline synthesis, 1-(2-aminophenyl)ethanone 1a (5.0 g) was input into the reaction
under the optimized reaction conditions. And 1-(2,4-dimethylquinolin-3-yl)ethanone 3a
was attained with 94.6, 97.3, and 91.9% yields in the optimized catalysis systems A, B,
and C, respectively. (Table 3). And the yields have decreased distinctly in the conditions
A and C due to the raw material 1a does not react completely (entries 1 and 3). The result
indicated that magnesium chloride (MgCl2 · 6H2O) catalyst may be more appropriate for
the scale-up procedure.
In summary, 4-toluenesulfonic acid (TsOH · H2O), magnesium chloride
(MgCl2 · 6H2O), and cupric nitrate (Cu(NO3)2 · 3H2O)-catalyzed Friedländer reaction of

SYNTHETIC COMMUNICATIONS®
5
Table 2. The test of substrate scope for Friedländer quinoline synthesisa.
Entry
1
Substrate 1
Product
Conditions
Yield (%)b
A
B
C
>99
>99
>99
2
3
A
B
C
>99
>99
96
A
B
C
>99
93
92
4
5
A
B
C
92
>99
90
A
B
C
97
>99
91
6
7
A
B
C
Trace
Trace
nr
A
B
C
75
86
64
8
9
A
B
C
87
>99
93
A
B
C
>99
>99
>99
10
11
A
B
C
37
64
44
A
B
C
98
>99
94
(Continued)

6
X.-Y. ZHOU ET AL.
Table 2. Continued.
Entry
12
Substrate 1
Product
Conditions
Yield (%)b
A
B
C
33
74
19
13
14
A
B
C
>99
>99
96
A
B
C
>99
>99
>99
aReaction conditions A:1 (0.5 mmol), 2 (1.0 mmol), TsOH · H2O (19.0 mg, 0.1 mmol), and EtOH (3.0 mL) in air, 80 °C, 12 h; reaction
conditions B: 1 (0.5 mmol), 2 (1.0 mmol), MgCl2 · 6H2O (10.2 mg, 0.05 mmol), and EtOH (3.0 mL) in air, 80 °C, 12 h; reaction
conditions C: 1 (0.5 mmol), 2 (1.0 mmol), Cu(NO3)2 · 3H2O (12.1 mg, 0.05 mmol), and EtOH (3.0 mL) in air, 80 °C, 12 h.
bIsolated yield.
2-aminoaryl ketones and β-ketoesters/ketones had been successfully developed under
green, efficient, and mild reaction conditions independently. The process afforded polysub-
stituted quinolines with moderate to excellent yields. And these catalysis systems will pro-
vide a powerful means to develop new applications of Brønsted acid or Lewis acid catalysts
in the activation of carbonyl compounds and expand the synthesis approach for the prep-
aration of heterocyclic compounds.
Experimental section
General methods: All commercially available reagents were used without further
purification. Column chromatography was performed on silica gel (200–400 mesh). The
1
chemical shifts (δ) of the H NMR (400 MHz) signals are reported in ppm relative to
tetramethylsilane (TMS) and using the residual solvent resonance as the internal standard.
Data are reported in the following order: chemical shift, multiplicity [s (singlet),
d (doublet), dd (doublet of doublets), t (triplet), q (quartet), and m (multiplet)], coupling-
constants (Hz), and integration. The chemical shifts (δ) of 13CNMR (100 MHz) signals are
reported in ppm relative TMS and using the solvent resonance as the internal standard.
Table 3. The scale-up procedure for the synthesis of 3aa.
Entry
Reaction conditions
m (1a)
m (3a)
Yield (%)b
1
2
3
A
B
C
5.0 g
5.0 g
5.0 g
7.0 g
7.2 g
6.8 g
94.6
97.3
91.9
aReaction conditions A: 1a (5.0 g), 2a (7.4 g), TsOH · H2O (1.41 g), and EtOH (50 mL) in air, 80 °C, 12 h; reaction conditions B: 1a
(5.0 g), 2a (7.4 g), MgCl2 · 6H2O (0.75 g), and EtOH (3.0 mL) in air, 80 °C, 12 h; reaction conditions C: 1a (5.0 g), 2a (7.4 g), Cu
(NO3)2 · 3H2O (0.89 g), and EtOH (3.0 mL) in air, 80 °C, 12 h.
bIsolated yield.

SYNTHETIC COMMUNICATIONS®
7
Procedure A
A mixture of 2-aminoaryl ketones 1 (0.50 mmol), β-ketoesters/ketones 2 (1.0 mmol), and
4-toluenesulfonic acid (TsOH · H2O, 19.0 mg, 0.10 mmol) in EtOH (3 mL) was added into
a Schlenk flask (25 mL) and the mixture was stirred at 80 °C until the reaction was finished.
Then the solvent was evaporated under reduced pressure and the residue was purified by
column chromatography.
Procedure B
A mixture of 2-aminoaryl ketones 1 (0.50 mmol), β-ketoesters/ketones 2 (1.0 mmol), and
magnesium chloride (MgCl2 · 6H2O, 20.3 mg, 0.10 mmol) in EtOH (3 mL) was added into
a Schlenk flask (25 mL) and the mixture was stirred at 80 °C until the reaction was finished.
Then the solvent was evaporated under reduced pressure and the residue was purified by
column chromatography.
Procedure C
A mixture of 2-aminoaryl ketones 1 (0.50 mmol), β-ketoesters/ketones 2 (1.0 mmol), and
cupric nitrate (Cu(NO3)2 · 6H2O, 24.2 mg, 0.10 mmol) in EtOH (3 mL) was added into a
Schlenk flask (25 mL) and the mixture was stirred at 80 °C until the reaction was finished.
Then the solvent was evaporated under reduced pressure and the residue was purified by
column chromatography.
1-(2,4-dimethylquinolin-3-yl)ethanone (3a):[8e] Yield A:> 99%, 100.2 mg, B: >99%,
98.9 mg, C: >99%, 99.2 mg, light yellow oil. 1H NMR (400 MHz, CDCl3) δ 7.92
(d, J ¼ 8.4 Hz, 1H), 7.84 (dd, J ¼ 8.4, 0.7 Hz, 1H), 7.62-7.58 (m, 1H), 7.45-7.41 (m, 1H),
2.54 (s, 3H), 2.49 (s, 3H), 2.46 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 206.6, 152.5,
146.8, 138.6, 135.6, 129.7, 129.1, 126.3, 125.9, 123.6, 32.6, 23.5, 15.2.
Funding
The work was supported by the Youth Science and Technology Talent Development Project in
Education Department of Guizhou Province (Grant No.qianjiaohe KY zi [2017] number 261), the
Union Foundation of Science and Technology Department of Guizhou Province (Grant No.
qiankehe LH zi [2015] number 7614) and Innovation Team of Liupanshui Normal University (Grant
No. LPSSYKJTD201601).
References
[1] For the quinoline in pharmaceuticals see: (a) Carrigan, C. N.; Bartlett, R. D.; Esslinger, C. S.;
Cybulski, K. A.; Tongcharoensirikul, P.; Bridges, R. J.; Thompson, C. M. J. Med. Chem.
2002, 45, 2260. (b) Hoekstra, W. J.; Patel, H. S.; Liang, X.; Blanc, J.-B. E.; Heyer, D. O.; Willson,
T. M.; Iannone, M. A.; Kadwell, S. H.; Miller, L. A.; Pearce, K. H.; J. Med. Chem. 2005, 48, 2243.
(c). Höglund, I. P. J.; Silver, S.; Engström, M. T.; Salo, H.; Tauber, A.; Kyyrönen, H.-K.; Saar-
enketo, P.; Hoffrén, A.-M.; Kokko, K.; Pohjanoksa, K.; et al. J. Med. Chem. 2006, 49, 6351. (d)
Lord, A.-M.; Mahon, M. F.; Lloyd, M. D.; Threadgill, M. D. J. Med. Chem. 2009, 52, 868. (e)
Laras, Y.; Hugues, V.; Chandrasekaran, Y.; Blanchard-Desce, M.; Acher, F. C.; Pietrancosta,
N. J. Org. Chem. 2012, 77, 8294. (f) Degorce, S. L.; Barlaam, B.; Cadogan, E.; Dishington, A.;
Ducray, R.; Glossop, S. C.; Hassall, L. A.; Lach, F.; Lau, A.; McGuire, T. M.; J. Med. Chem.
2016, 59, 6281. (g) Galabos, J.; Bielik, A.; Krasavin, M.; Orgován, Z.; Domány, G.; Nógrádi,
K.; Wágner, G.; Balogh, G. T.; Béni, Z.; Kóti, J.; J. Med. Chem. 2017, 60, 2470.

8
X.-Y. ZHOU ET AL.
[2] El-Sayed, K. E.; Al-Said, M. S.; El-Feraly, F. S.; Ross, S. A. J. Nat. Prod. 2000, 63, 995.
[3] For the quinoline application in metal complexes see: (a) Peng, H. M.; Song, G.; Li, Y.; Li, X.
Inorg. Chem. 2008, 47, 8031. (b) Laguna, E. M.; Olsen, P. M.; Sterling, M. D.; Eichler, J. F.;
Rheingold, A. L.; Larsen, C. H. Inorg. Chem. 2014, 53, 12231.
[4] (a) Marco-Contelles, J.; Pérez-Mayoral, E.; Samadi, A.; do Carmo Carreiras, M.; Soriano, E.
Chem. Rev. 2009, 109, 2652. (b) Naidoo, S.; Jeena, V. Synthesis 2017, 49, 2621.
[5] (a) Sakai, N.; Aoki, D.; Hamajima, T.; Konakahara, T. Tetrahedron Lett. 2006, 47, 1261. (b)
Lamberth, C.; Kessabi, F. M.; Beaudegnies, R.; Quaranta, L.; Trah, S.; Berthon, G.; Cederbaum,
F.; Vettiger, T.; Prasann, C. S. Synlett. 2014, 25, 858.
[6] (a) Rineh, A.; Khalilzadeh, M. A.; Hashemi, M. M.; Rajabi, M.; Karimi, F. J. Heterocycl. Chem.
2012, 49, 789. (b) Gök, D.; Kasımoğullar, R.; Cengiz, M.; Mert, S. J. Heterocycl. Chem. 2014, 51,
224. (c) Sangshetti, J. N.; Zambare, A. S.; Shinde, D. B. Mini-Rev. Org. Chem. 2014, 11, 225.
[7] (a) West, A. P. Jr.; Van Engen, D.; Paskal, R. A. Jr. J. Org. Chem. 1992, 57, 784. (b) Piechowska,
J.; Gryko, D. T. J. Org. Chem. 2011, 76, 10220. (c) Xu, X.; Liu, W.; Wang, Z.; Feng, Y.; Yan, Y.;
Zhang, X. Tetrahedron Lett. 2016, 57, 226.
[8] (a) McNaughton, B. R.; Miller, B. L. Org. Lett. 2003, 5, 4257. (b) Wu, J.; Zhang, L.; Diao, T.-N.
Synlett. 2005, 2653. (c) Selvam, N. P.; Saravanan, C.; Muralidharan, D.; Perumal, P. T. J. Het-
erocyclic Chem. 2006, 43, 1379. (d) Degtyarenko, A. S.; Tolmachev, A. A.; Volovenko, Y. M.;
Tverdokhlebov, A. V. Synthesis 2007, 2007, 3891. (e) Zhang, L.; Wu, J. Adv. Synth. Catal.
2007, 349, 1047. (f) Jiang, B.; Dong, J.-J.; Jin, Y.; Du, X.-L.; Xu, M. Eur. J. Org. Chem. 2008,
2008, 2693. (g) Diedrich, C. L.; Haase, D.; Saak, W.; Christoffers, J. Eur. J. Org. Chem. 2008,
2008, 1811. (h) Satheeshkumar, R.; Shankar, R.; Kaminsky, W.; Prasad, K. J. ChemistrySelect
2016, 1, 6823–6829. (i) Zhang, S.-L.; Deng, Z.-Q. Org. Biomol. Chem. 2016, 14, 8966. (j) Ghar-
pure, S. J.; Nanda, S. K.; Adate, P. A.; Shelke, Y. G. J. Org. Chem. 2017, 82, 2067. (k) Yadav, J. S.;
Reddy, B. V. S.; Sreedhar, P.; Rao, R. S.; Nagaiah, K. Synthesis 2004, 2004, 2381–2385.
[9] Akbari, J.; Heydari, A.; Kalhor, H. R.; Kohan, S. A. J. Comb. Chem. 2010, 12, 137.
[10] Venkatesham, R.; Manjula, A.; Rao, B. V. J. Heterocyclic Chem. 2012, 49, 833.
[11] López-Sanz, J.; Pérez-Mayoral, E.; Soriano, E.; Omenat-Morán, D.; Durán, C. J.; Martín-
Aranda, R. M.; Matos, I.; Fonseca, I. ChemCatChem. 2013, 5, 3736.
[12] Javanshira, S.; Sharifia, S.; Malekia, A.; Sohrabia, B.; Kiasadegh, M. J. Phys. Org. Chem. 2014, 27,
589.
[13] Esmaeilpoura, M.; Javidi, J. J. Chin. Chem. Soc. 2015, 62, 328.
[14] (a) Jiang, B.; Si, Y.-G. J. Org. Chem. 2002, 67, 9449. (b) Chanda, T.; Verma, R. K.; Singh, M. S.
Chem. Asian J. 2012, 7, 778. (c) Czerwiński, P.; Michalak, M. J. Org. Chem. 2017, 82, 7980.
[15] Senadi, G. C.; Hu, W.-P.; Garkhedkar, A. M.; Boominathan, S. S. K.; Wang, J.-J. Chem.
Commun. 2015, 51, 13795.
[16] Martínez, R.; Ramón, D. J.; Yus, M. Eur. J. Org. Chem. 2007, 2007, 1599.
[17] Mierde, H. V.; Voort, P. V. D.; Vos, D. D.; Verpoort, F. Eur. J. Org. Chem. 2008, 2008, 1625.
[18] Korivi, R. P.; Cheng, C.-H. J. Org. Chem. 2006, 71, 7079.
[19] Li, A.-H.; Beard, D. J.; Coate, H.; Honda, A.; Kadalbajoo, M.; Kleinberg, A.; Laufer,
R.; Mulvihill, K. M.; Nigro, A.; Rastogi, P.; et al. Synthesis 2010, 2010, 1678.
[20] Chen, B. W. J.; Chng, L. L.; Yang, J.; Wei, Y.; Yang, J.; Ying, J. Y. ChemCatChem 2013, 5, 277.
[21] Li, C.; Li, J.; An, Y.; Peng, J.; Wu, W.; Jiang, H. J. Org. Chem. 2016, 81, 12189.
[22] Mastalir, M.; Glatz, M.; Pittenauer, E.; Allmaier, G.; Kirchner, K. J. Am. Chem. Soc. 2016, 138,
15543.
[23] Lavrard, H.; Larini, P.; Popowycz, F. Org. Lett. 2017, 19, 4203.
[24] Qu, Y.; Wang, L.; Zhou, X.; Feng, X.; Bao, M. Chin. J. Org. Chem. 2013, 33, 860.