1, 3-Disulfonic acid imidazolium hydrogen sulphate as an efficient and reusable ionic liquid for the multicomponent synthesis of polyhydroquinoline derivatives under solvent-free conditions

Article abstract of DOI:10.1007/s11164-015-2134-y

A facile and highly effective one-pot synthesis of polyhydroquinoline derivatives is reported via Hantzsch condensation of aldehydes, 1,3-dicarbonyl compounds, ethyl acetoacetate, and ammonium acetate in the presence of 1,3-disulfonic acid imidazolium hyd

Full text of DOI:10.1007/s11164-015-2134-y

Res Chem Intermed
DOI 10.1007/s11164-015-2134-y
1, 3-Disulfonic acid imidazolium hydrogen sulphate
as an efficient and reusable ionic liquid
for the multicomponent synthesis of polyhydroquinoline
derivatives under solvent-free conditions
Kamal Mohammadi1 Farhad Shirini1
•
•
Asieh Yahyazadeh1
Received: 14 April 2015 / Accepted: 6 June 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A facile and highly effective one-pot synthesis of polyhydroquinoline
derivatives is reported via Hantzsch condensation of aldehydes, 1,3-dicarbonyl
compounds, ethyl acetoacetate, and ammonium acetate in the presence of 1,3-
disulfonic acid imidazolium hydrogen sulfate as an efficient and recyclable ionic
liquid under solvent-free conditions. This methodology offers several advantages
such as short reaction times, high yields, environmentally benign, mild reaction
conditions, simple work-up procedure, and reusability of the ionic liquid.
Keywords 1, 3-Disulfonic acid imidazolium hydrogen sulfate Á Recyclable ionic
liquid Á Polyhydroquinoline derivatives Á Hantzsch condensation Á Solvent-free
conditions
Introduction
Multicomponent reactions (MCRs) have gained great attention as efficient and
attractive synthetic procedures in modern organic synthesis and medicinal
chemistry. They are one-pot processes that generate complex products from a
combination of three or more substrates simultaneously [1, 2]. Also, MCRs have
remarkable benefits in terms of simplicity and synthetic efficiency over formal
Electronic supplementary material The online version of this article (doi:10.1007/s11164-015-2134-
y) contains supplementary material, which is available to authorized users.
&
&
1
Farhad Shirini
shirini@guilan.ac.ir; fshirini@gmail.com
Asieh Yahyazadeh
yahyazadehphd@yahoo.com
Department of Chemistry, College of Science, University of Guilan, Post Box: 1914,
41335 Rasht, I.R. Iran
123

K. Mohammadi et al.
chemical reactions [3] and show high atom economy and high selectivity [4, 5].
Therefore, the use of MCRs as well as domino reaction sequences has significantly
increased for a large number of products [6].
Recently, an immense interest has been focused on the multicomponent synthesis
of 1, 4-dihydropyridines (1, 4-DHPs) because of their wide range of biological and
pharmacological properties such as antihypertensive, antitherosclerotic, hepatopro-
tective, antimutagenic, vasodilator, bronchodilator, antitumor, geroprotective,
antimalarial, antibacterial, and antidiabetic activities [7–12]. The 1, 4-DHPs as
analogues of NADH coenzymes, such as nifedipine, nicardipine, and amlodipine,
are well known as calcium channel blockers for the treatment of cardiovascular
disorder including angina, hypertension, and cardiac arrhythmias [13]. Widespread
studies have revealed that these compounds show diverse medical applications,
which include neuroprotectant, platelet anti-aggregatory activity, and cerebral
antischaemic activity in the treatment of Alzheimer’s disease and chemosensitizer
behavior in tumour therapy [14–17]. These examples clearly indicate the
considerable potency of novel DHP derivatives as a source of valuable drug
candidates.
In view of the significance of polyhydroquinoline derivatives, several procedures
have been reported for their synthesis [18–20]. In 1882, and for the first time, the
synthesis of 1, 4-DHPs via the one-pot condensation of aldehydes with ethyl
acetoacetate and ammonia in acetic acid or by refluxing in alcohols was reported by
Hantzsch [21]. In recent years, several new efficient methods have been developed
including the use of TMSCl [22], L-proline [23], polymers [24], Yb(OTf)3 [25],
HClO4–SiO2 [26], heteropoly acid [27], CAN [28], p-TSA [29], InCl3 [30], I2 [31],
nanocrystalline TiO2 [32], Bakers’ yeast [33], grinding [34], conventional heating
[35, 36], microwave irradiation, and ultrasound [37]. However, some of the reported
methods suffer from some drawbacks such as long reaction times, harsh reaction
conditions, utilization of volatile and hazardous solvents, high temperature, using
expensive and nonreusable catalysts that are harmful to the environment, and low
product yields. Therefore, the improvement of a mild and efficient catalytic system
for the synthesis of these compounds is still a challenging task for the organic
chemists.
The principles of Green Chemistry have been introduced to eliminate or reduce
the use or generation of hazardous materials in chemical processes. One of the key
areas of green chemistry is the replacement of hazardous solvents with environ-
mentally benign ones or the elimination of solvents altogether [38–40]. In recent
years, application of sulfonic acid functionalized ionic liquids (ILs) as ‘‘designer
solvents’’ have attracted considerable attention of chemists due to their unique
properties such as high thermal stability, negligible vapor pressure, low flamma-
bility, environmental compatibility, reusability, greater selectivity, and ease of
isolation [41]. They are known as catalysts or as a dual catalyst-solvent for a wide
range of chemical reactions such as Hantzsch, Mannich, Biginelli and Friedlander
quinoline synthesis [42–45]. The above-mentioned advantages encouraged us to
explore the new applications of this IL in organic synthesis.
123

1, 3-Disulfonic acid imidazolium hydrogen sulphate as an…
Experimental
Chemicals were purchased from the Fluka and Merck companies. Melting points were
recorded on an electrothermal digital melting point apparatus model IA9100 in open
capillary tubes. The IR spectra were run on a Perkin-Elmer model Spectrum One FT-IR
1
Spectrometer. The H NMR spectra were recorded on a Bruker AVANCEIII-400
spectrometer using TMS as an internal reference. The 13C NMR spectra were also
recorded on the same instrument at 100 MHz. The purity determination of the substrate
and reaction monitoring were accomplished by TLC on silica-gel polygram SIL G/UV
254 plates. Yields refer to isolated products. Products were characterized by their
physical constants, comparison with authentic samples, and IR and NMR spectroscopy.
A mixture of the aldehyde (1 mmol), dimedone or 1, 3-cyclohexanedione
(1 mmol), ethyl acetoacetate (1 mmol), ammonium acetate (1 mmol), and DSIMHS
(0.25 mmol) was heated in an oil bath (70 °C) under stirring. The progress of the
reaction was monitored by TLC (n-hexane/ethyl acetate, 8:2). After completion, the
reaction mixture was washed with water, because DSIMHS is soluble in water, and
the product was precipitated with high purity. Then the crude solid product was
filtered off and recrystallized from ethanol.
Selected spectral data
Ethyl 2,7,7-trimethyl-4-(4-bromophenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-
1
carboxylat (Table 2, entry 1): m.p. 254–256 °C; H NMR (400 MHz, CDCl3): d
0.95 (s, 3H), 1.09 (s, 3H), 1.22 (t, J = 7.2 Hz, 3H), 2.15–2.37 (m, 4H), 2.40 (s, 3H),
4.08 (q, J = 7.2 Hz, 2H), 5.04 (s, 1H), 6.12 (br s,1H), 7.21 (d, J = 8.4 Hz, 2H),
7.34 (d, J = 8.4 Hz, 2H) ppm; IR (KBr) m = 3275, 3190, 3075, 2965, 1703, 1607,
1517, 1492, 1345, 1215, 1167, 1072, 832, 697 cm-1
.
Ethyl 2,7,7-trimethyl-4-(4-nitrophenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-
1
carboxylat (Table 2, entry 3): m.p. 241–243 °C; H NMR (400 MHz, CDCl3): d
0.92 (s, 3H), 1.09 (s, 3H), 1.24 (t, J = 7.2 Hz, 3H), 2.13–2.37 (m, 4H), 2.40 (s, 3H),
4.07 (q, J = 7.2 Hz, 2H), 5.18 (s, 1H), 6.72 (br s, 1H), 7.51 (d, J = 8.8 Hz, 2H),
8.10 (d, J = 8.8 Hz, 2H) ppm; IR (KBr) m = 3275, 3207, 3078, 2958, 1703, 1648,
1605, 1487, 1381, 1220, 1191 cm-1
.
Ethyl 2,7,7-trimethyl-4-(2-chloro-6-fluorophenyl)-5-oxo-1,4,5,6,7,8-hexahydro-
quinoline-3-carboxylat (Table 2, entry 12): m.p. 164–166 °C; 1H NMR
(400 MHz, DMSO-d6): d 0.88 (s, 3H), 1.03 (m, 6H), 1.91 (d, J = 16 Hz, 1H),
2.17 (m, 5H), 2.39 (d, J = 17.2 Hz, 1H), 3.91 (q, J = 7.2 Hz, 2H), 5.44 (s, 1H),
7.04 (m, 1H), 7.14 (m, 2H), 9.15 (s, 1H) ppm; IR (KBr) m = 3299, 3080, 2956,
1691, 1649, 1610, 1473, 1217, 1112, 1072, 786 cm-1
.
Results and discussion
Very recently we have reported the preparation and application of DSIMHS as a
green, efficient, and reusable IL in organic transformations [46–48]. Herein and in
continuation of these studies, we wish to report the one-pot Hantzsch condensation
123

K. Mohammadi et al.
of 1, 3-dicarbonyl compounds with various aromatic aldehydes, ethyl acetoacetate,
and NH4OAc in the presence of this IL (Scheme 1).
To find the optimal conditions, the reaction of 4-chlorobenzaldehyde, ethylace-
toacetate, dimedone, and ammonium acetate in 1:1:1:1 ratios was chosen as a
model. Optimization of the reaction conditions was performed using various
amounts of DSIMHS at different temperatures under solvent-free conditions. The
results are summarized in Table 1.
As it shown in Table 1, the best result was obtained by carrying out the reaction
using 0.25 mmol of DSIMHS at 70 °C (Table 1, entry 5). Increasing the amount of
IL and the temperature in this method did not lead to significant improvement in the
yields and times (Table 1, entry 4 and 7). In addition, when the mentioned
procedure is progressed at room temperature, the yield of the corresponding product
was low after 300 min (Table 1, entry 1). Also, Table 1 clearly indicates that
without any IL at 70 °C, the product was isolated in poor yield after a long reaction
time (Table 1, entry 2).
To show the efficiency and the applicability of this protocol, various substituted
aromatic aldehydes were efficiently reacted with dimedone, ethyl acetoacetate, and
ammonium acetate in the same conditions. The results are presented in Table 2. It
can be seen that both the aromatic aldehydes containing electron-withdrawing
groups (such as nitro and halide groups) and electron-donating groups (such as
hydroxyl and alkoxy groups) reacted successfully to give the corresponding
H+ from
R1
HSO4
N
N
HO3S
SO3H
0.25 mmol
70 oC, Solvent-free
O
O
O
CHO
O
O
OEt
Me
+
NH OAC
+
+
R2
4
Me
OEt
R2
N
O
R2
R1
H
R2
Scheme 1 The synthesis of polyhydroquinoline derivatives in the presence of DSIMHS under solvent-
free conditions
Table 1 The effect of different amounts of DSIMHS and temperature on the synthesis of ethyl 2, 7,
7-trimethyl-4-(4-chlorophenyl)-5-oxo-1, 4, 5, 6, 7, 8- hexahydroquinoline-3-carboxylatea
Entry
DSIMHS (mmol)
Temperature (°C)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
a
0.25
–
25
70
70
75
70
60
70
300
300
6
30
12
78
93
93
90
94
0.15
0.25
0.25
0.25
0.35
3
3
7
3
Reaction condition: 4-chlorobenzaldehyde (1 mmol), dimedone (1 mmol), ethylacetoacetate (1 mmol),
and ammonium acetate (1 mmol) at different temperatures under solvent free conditions
b
Isolated yield
123

1, 3-Disulfonic acid imidazolium hydrogen sulphate as an…
Table 2 Hantzsch synthesis of polyhydroquinolines using DSIMHS under solvent-free conditionsa
Entry
R1
R2
Time (min)
Yield (%)b
m.p. (°C)
Measured
Reported [Refs.]
1
4-Br
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
H
6
92
93
91
89
91
89
90
88
94
92
92
88
89
90
91
91
89
89
249–251
233–235
239–241
172–174
225–227
180–182
231–233
253–255
203–205
175–177
209–211
164–166
257–259
225–227
203–206
248–250
209–211
246–248
252–253 [26]
233–235 [49]
241–243 [32]
174–176 [32]
228–230 [49]
184–186 [29]
233–235 [50]
255–257 [32]
203–205 [49]
179–181 [32]
206–208 [29]
–
2
4-Cl
3
3
4-NO2
3-NO2
4-OH
4-F
5
4
8
5
10
7
6
7
3-Br
8
8
4-OCH3
H
15
5
9
10
11
12
13
14
15
16
17
18
a
4-CH(Me)2
2-Cl
15
7
2-Cl-6-F
4-Br
12
5
253–254 [50]
221–222 [51]
205–206 [51]
250–251 [32]
212–215 [32]
243–244 [51]
4-OH
4-NO2
4-Cl
H
10
8
H
H
10
10
10
4-OCH3
4-F
H
H
All products were characterized by comparison of their mp, IR, 1HNMR spectra with those of authentic
samples
b
Isolated yield
polyhydroquinoline in good to excellent yields and short reaction times. Results
have shown that the aromatic aldehydes with electron-withdrawing groups showed
an increased reaction rate. Next, we investigated the effect of substitution in the
dimedon system using 1, 3-cyclohexanedione. Interestingly, dimedone reacts faster
than 1, 3-cyclohexanedione in the presence of DSIMHS as a promoter to afford the
corresponding products in excellent yields (Table 2).
Considering the importance of the catalyst recovery, we studied the recyclability
and the reusability of DSIMHS from the reaction mixture in the model process.
After completion of the reaction, the precipitated mixture was filtered and the solid
product was washed with water completely to separate IL from the other materials,
because DSIMHS is soluble in water. All water that is collected in this way was
washed with CH2Cl2 (2 9 10 mL) to remove organic impurities. Then, water was
evaporated under reduced pressure and IL was recovered and reused. The obtained
results clearly indicated that the recovered IL could be reused directly in the next
run without any significant loss of its activity even after the fourth run (Fig. 1).
A possible mechanism for the formation of polyhydroquinoline derivatives in the
presence of DSIMHS as a promoter is shown in Scheme 2. On the basis of this
mechanism, DSIMHS catalyzes the reaction and polyhydroquinoline 5 may be
123

K. Mohammadi et al.
Fig. 1 Results of the reusability of DSIMHS in the synthesis of ethyl 2,7,7-trimethyl-4-(4-chlorophenyl)-
5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate under solvent-free conditions (Table 3, entry 2)
HSO4
O
O
HO3S
N
S
N
H
O
Ar
O
O
O
H
OEt
+
R2
HSO4
H
H2N
Me
O
R2
O
HO3S
H2O
N
S
(1)
(2)
N
O
-H2O
O
(II)
H
(I)
Ar
DSIMHS (III)
O
O
NH4OAC
NH3
OEt
R2
H
O
O
O
R2
Ar
O
Me
O
OEt
AcOH
O
R2
N
Me
R2
H
R2
R2
(5)
NH4OAC
OEt
O
H
O
Me
NH3
AcOH
(V)
(VI)
DSIMHS
Ar
(IV)
H2O
H
-H2O
O
O
H
N
S
N
Ar
OEt
SO3H
O
O
O
HSO4
SO3H
O
H
O
+
H
N
S
N
R2
O
Me
O
NH2
R2
O
HSO4
(3)
(4)
HO3S
DSIMHS =
N
SO3H
N
R1
Ar =
HSO4
Scheme 2 Suggested mechanism for the Hantzsch condensation
formed either through steps I–III or through steps IV–VI. The role of DSIMHS comes
in steps I and IV, where it catalyzes the Knoevenagel type coupling of aldehydes with
active methylene compounds and in steps III and VI, where it catalyzes the Michael
type addition of intermediates 1, 2 and 3, 4 to give the product 5.
123

1, 3-Disulfonic acid imidazolium hydrogen sulphate as an…
Table 3 Comparison of the synthesis of polyhydroquinoline in the presence of different catalysts
Entry Catalyst
Conditions
Time (min) Yield (%) [Refs.]
1
2
3
4
5
6
DSIMHS (0.25 mmol)
70 °C, solvent-free
EtOH, ambient temp. 120
3
93
90
96
92
95
90
This work
[29]
p-TSA (10 mol %)
Hf(NPf2)4 (1 mol %)
PPA-SiO2 (30 mg)
60 °C, C10F18
80 °C, solvent-free
120
45
[52]
[53]
[TBA]2[W6O19] (7 mol %) 110 °C, solvent-free
CAN (10 mol %)
20
[54]
EtOH, ambient temp. 150
[55]
In order to show the activity of DSIMHS (Table 3, entry 1) in comparisons with
other reported catalysts (Table 3, entry 2–6) for the same reactions, we have
summarized some of the results in Table 3. The results indicate that the present
method is more effective than the other reports in terms of yield and reaction time.
Conclusion
In conclusion, we have successfully developed a simple and efficient procedure for
the synthesis of polyhydroquinoline derivatives from the reaction of different
aromatic aldehydes, 1, 3-dicarbonyl compounds (dimedone or 1, 3-cyclohexane-
dione), ethyl acetoacetate, and ammonium acetate in the presence of little amounts
of DSIMHS as an eco-friendly and inexpensive catalyst under solvent-free
conditions. The present method offers several advantages including short reaction
times, high yield of the products, easy work-up, mild reaction conditions, lower
catalytic loading, and ease of separation of the used IL. Also, DSIMHS could be
easily recovered and reused at least four times without significant loss of activity.
Acknowledgments The authors acknowledge financial support for this work from the Iran National
Science Foundation (INSF) (Grant Number 93014856) and partial support of this work by the Research
Council of the University of Guilan. F. Shirini and K. Mohammadi also wish to thank the Sobhandarou
Company for the partial facilities.
References
1. G. Guillena, D.J. Ramon, M. Yus, Tetrahedron Asymmetry 18, 693 (2007)
2. A. Domling, I. Ugi, Angew. Chem. Int. Ed. 39, 3168 (2000)
3. J. Zhu, H. Bienayme (eds.), Multicomponent Reactions (Wiley, Weinheim, 2005)
4. I. Ugi, Pure Appl. Chem. 73, 187 (2001)
5. C.C.A. Cariou, G.J. Clarkson, M. Shipman, J. Org. Chem. 73, 9762 (2008)
6. L. Yu, B. Chen, X. Huang, Tetrahedron Lett. 48, 925 (2007)
7. P.N. Kalaria, S.P. Satasia, D.K. Raval, Eur. J. Med. Chem. 78, 207 (2014)
8. S.C. Karad, V.B. Purohit, D.K. Raval, P.N. Kalaria, J.R. Avalani, P. Thakor, V.R. Thakkar, RSC
Adv. 5, 16000 (2015)
9. P.P. Mager, R.A. Coburn, A.J. Solo, D.J. Triggle, H. Rothe, Drug Des. Discov. 8, 273 (1992)
10. A. Sausins, G. Duburs, Heterocycles 27, 269 (1988)
11. R. Manmhold, B. Jablonka, W. Voigdt, K. Schoenafinger, E. Schraven, J. Med. Chem. 27, 229 (1992)
12. A.C. Gaudio, A. Korokovas, Y. Takahata, J. Pharm. Sci. 83, 1110 (1994)
123

K. Mohammadi et al.
13. D.J. Triggle, in Comprehensive Medicinal Chemistry, vol. II, ed. by J.C. Emmet (Pergamon, Oxford,
1990)
14. V. Klusa, Drugs Future 20, 135 (1995)
15. R.G. Bretzel, C.C. Bollen, E. Maeser, K.F. Federlin, Am. J. Kidney Dis. 21, 53 (1993)
16. R.G. Bretzel, C.C. Bollen, E. Maeser, Drugs Future 17, 465 (1992)
17. R. Boer, V. Gekeler, Drugs Future 20, 499 (1995)
18. Z. Zarnegar, J. Safari, Z. Mansouri, Kafroudi. Catal. Commun. 59, 216 (2015)
19. V.K. Ahluwalia, B. Goyal, U. Das, J. Chem. Res. (s) 7, 266 (1997)
20. S. Margarita, O. Estael, V. Yamila, P. Beatriz, M. Lourdes, M. Nazario, Q. Margarita, S. Carlos, L.S.
Jose, N. Hector, B. Norbert, M.P. Oswald, Tetrahedron 55, 875 (1999)
21. A. Hantzsch, Ann. Chem. 1, 215 (1882)
22. G. Sabitha, G.S.K.K. Reddy, C.S. Reddy, J.S. Yadav, Tetrahedron Lett. 44, 4129 (2003)
23. N.N. Karade, V.H. Budhewar, S.V. Shinde, W.N. Jadhav, Lett. Org. Chem. 4, 16 (2007)
24. A. Dondoni, A. Massi, E. Minghini, V. Bertolasi, Tetrahedron 60, 2311 (2004)
25. L.M. Wang, J. Sheng, L. Zhang, J.W. Han, Z. Fan, H. Tian, C.T. Qian, Tetrahedron 61, 1539 (2005)
26. M. Maheswara, V. Siddaiah, G.L. Damu, C.V. Rao, ARKIVOC ii, 201 (2006)
27. M.M. Heravi, K. Bakhtiri, N.M. Javadi, F.F. Bamoharram, M. Saeedi, H.A. Oskooi, J. Mol. Catal.
A Chem. 264, 50 (2007)
28. S. Ko, C.F. Yao, Tetrahedron 62, 7293 (2006)
29. S.R. Cherkupally, R. Mekala, Chem. Pharm. Bull. 56, 1002 (2008)
30. G. Babu, P.T. Perumal, Aldrichimica Acta 33, 16 (2000)
31. S. Ko, M.N.V. Sastry, C. Lin, C.F. Yao, Tetrahedron Lett. 46, 5771 (2005)
32. F. Shirini, S.V. Atghia, M.A. Khoshdel, Iran. J. Catal. 1, 93 (2011)
33. A. Kumar, R.A. Maurya, Tetrahedron Lett. 48, 3887 (2007)
34. S. Kumar, P. Sharma, K.K. Kapoor, M.S. Hundal, Tetrahedron 64, 536 (2008)
35. J.B. Sainani, A.C. Shah, V.P. Aray, Indian J. Chem. 33B, 526 (1994)
36. N.K. Ladani, D.C. Mungra, M.P. Patel, R.G. Patel, Chin. Chem. Lett. 22, 1407 (2011)
37. A. Kumar, R.A. Maurya, Synlett 6, 883 (2008)
38. P.T. Anastas, J.C. Warner, Green Chemistry: Theory and Practice (Oxford University Press, Oxford,
1998)
39. M. Poliakoff, M.J. Fitzpatric, T.R. Farren, P.T. Anastas, Green Chemistry: Science and Politics of
change. Science 297, 807 (2002)
´
40. I.T. Horvath, P.T. Anastas, Innovations and green chemistry. Chem. Rev. 107, 2169 (2007)
41. Z. Chen, Q. Zhu, W. Su, Tetrahedron Lett. 52, 2601 (2011)
42. H.G.O. Alvim, G.A. Bataglion, L.M. Ramos, A.L. de Oliveira, H.C.B. de Oliveira, M.N. Eberlin, J.L.
de Macedo, W.A. da Silva, B.A.D. Neto, Tetrahedron 70, 3306 (2014)
43. H.G.O. Alvim, T.B. de Lima, H.C.B. de Oliveira, F.C. Gozzo, J.L. de Macedo, P.V. Abdelnur, W.A.
Silva, B.A.D. Neto, ACS Catal. 3, 1420 (2013)
44. R. Fu, Y. Yang, W. Lai, Y. Ma, Z. Chen, J. Zhou, W. Chai, Q. Wang, R. Yuan, Synth. Commun. 45,
467 (2015)
45. J. Akbari, A. Heydari, H.R. Kalhor, S.A. Kohan, J. Comb. Chem. 12, 137 (2010)
46. F. Shirini, N.G. Khaligh, S. Akbari-Dadamahaleh, J. Mol. Catal. A Chem. 365, 15 (2012)
47. F. Shirini, N.G. Khaligh, J. Mol. Liq. 177, 386 (2013)
48. F. Shirini, A. Yahyazadeh, K. Mohammadi, Chin. Chem. Lett. 25, 341 (2014)
49. M. Tajbakhsh, H. Alinezhad, M. Norouzi, S. Baghery, M. Akbari, J. Mol. Liq. 177, 44 (2013)
50. M. Nasr-Esfahani, T. Abdizadeh, Orient. J. Chem. 28, 1249 (2012)
51. X.L. Zhang, S.R. Sheng, X.L. Liu, X.L. Liu, ARKIVOC xiii, 79 (2007)
52. M. Hong, C. Cai, W.B. Yi, J. Fluorine Chem. 131, 111 (2010)
53. A. Khojastehnezhad, F. Moeinpour, A. Davoodnia, Chin. Chem. Lett. 22, 807 (2011)
54. A. Davoodnia, M. Khashi, N. Tavakoli-Hoseini, Chin. J. Catal. 34, 1173 (2013)
55. C.S. Reddy, M. Raghu, Chin. Chem. Lett. 19, 775 (2008)
123