Tetraethylammonium 2-(carbamoyl)benzoate as a bifunctional organocatalyst for one-pot synthesis of Hantzsch 1,4-dihydropyridine and polyhydroquinoline derivatives

Article abstract of DOI:10.1007/s00706-016-1666-1

Abstract: A green, convenient, and environment-friendly approach for the synthesis of biologically active Hantzsch 1,4-dihydropyridine and polyhydroquinoline derivatives in the presence of tetraethylammonium 2-(carbamoyl)benzoate, as an effective bifunctional metal-free catalyst, has been developed via a one-pot multicomponent reaction of various aldehydes, ethyl acetoacetate or cyclic 1,3-dicarbonyl compounds, and ammonium acetate in EtOH under reflux conditions. The proposed methodology is capable of providing the desired products in good to excellent yields and short reaction time with straightforward work-up and a low-cost procedure. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-016-1666-1

Monatsh Chem
DOI 10.1007/s00706-016-1666-1
ORIGINAL PAPER
Tetraethylammonium 2-(carbamoyl)benzoate as a bifunctional
organocatalyst for one-pot synthesis of Hantzsch 1,4-
dihydropyridine and polyhydroquinoline derivatives
Mahsa Yarhosseini1 Shahrzad Javanshir1 Mohammad G. Dekamin1
Mohammad Farhadnia1
•
•
•
Received: 30 November 2015 / Accepted: 10 January 2016
Ó Springer-Verlag Wien 2016
Abstract A green, convenient, and environment-friendly
approach for the synthesis of biologically active Hantzsch
1,4-dihydropyridine and polyhydroquinoline derivatives in
the presence of tetraethylammonium 2-(carbamoyl)ben-
zoate, as an effective bifunctional metal-free catalyst, has
been developed via a one-pot multicomponent reaction of
various aldehydes, ethyl acetoacetate or cyclic 1,3-dicar-
bonyl compounds, and ammonium acetate in EtOH under
reflux conditions. The proposed methodology is capable of
providing the desired products in good to excellent yields
and short reaction time with straightforward work-up and a
low-cost procedure.
Keywords Tetraethylammonium 2-(carbamoyl)
benzoate Á Multicomponent reaction Á
1,4-Dihydropyridine Á Polyhydroquinoline Á
Green chemistry
Introduction
In recent decades, organocatalysis has proven to be a
valuable and attractive tool in organic synthesis and has
received great attention from both practical and environ-
mental standpoints. Whereas transition metals sometimes
attract most of the attention in the study of catalysis, small
organic molecules without metals can also exhibit catalytic
properties, as is apparent from the fact that many enzymes
lack transition metals. However, complete replacement of
transition metal-based catalytic systems by the metal-free
organocatalyst is of important significance because of both
toxicity and difficulty in separation of metal catalysts from
the final products, particularly in the pharmaceutical
industry [1–5]. In this regard, tetraethylammonium 2-
(carbamoyl)benzoate (TEACB) may be considered as an
ideal organocatalyst since it contains both Lewis base and
Lewis acid sites in a proper geometry. Therefore, it acti-
vates nucleophilic and electrophilic substrates in the
catalytic cycle (Scheme 1).
Graphical abstract
Therefore, reactions catalyzed by TEACB are effec-
tively promoted similar to the natural catalysis by enzymes.
These requirements are fully met in the multicomponent
reaction (MCR) for synthesis of the Hantzsch 1,4-dihy-
dropyridine (1,4-DHP) and polyhydroquinoline (PHQ)
derivatives [6–8]. Considerable attention has been paid to
the synthesis of 1,4-DHP and PHQ derivatives, which is
attributed to the diversity of their biological and pharma-
cological properties such as vasodilator and bronchodilator
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-016-1666-1) contains supplementary
material, which is available to authorized users.
& Shahrzad Javanshir
shjavan@iust.ac.ir
1
Department of Chemistry, Iran University of Science and
Technology, 1684613114 Tehran, Iran
123

M. Yarhosseini et al.
the use of microwave irradiation, ultrasound, or reflux at
high temperature in the presence of Brønsted acids, Lewis
acids or bases, and ionic liquids [21–26]. However, most of
these protocols encounter problems such as long reaction
time, low yield or selectivity, expensive catalysts, or
laborious purification steps.
Scheme 1
Organocatalytic cascade reactions, which strive to
emulate nature in the construction of complicated mole-
cules, have offered many fascinating and challenging
transformation in organic synthesis. The atom economy,
convergent character, operational simplicity, structural
diversity, and complexity of the molecules are the major
advantages associated with multicomponent cascade reac-
tions. Besides this, cascade reactions are emerging as a
powerful tool in the synthesis of biologically important
compounds [27, 28]. Due to the increasing demand in
modern organic processes for avoiding expensive purifi-
cation and in connection with our interest in MCRs for the
synthesis of heterocycles demonstrating biological and
pharmacological activity [29–33], we report herein a facile
and efficient synthesis of 1,4-DHPs and PHQs via a one-
pot, multicomponent Hantzsch condensation of ethyl ace-
toacetate or cyclic 1,3-dicarbonyl compounds, different
aldehydes, and ammonium acetate using a catalytic amount
of TEACB (1) in EtOH under refluxing conditions
(Scheme 3).
[9], geroprotective [10], antitumor [11], antihypertensive
[12], neuroprotectant [13], platelet antiaggregatory activity
[14], cerebral anti-ischemic activity in the treatment of
Alzheimer’s disease [15], chemosensitizer acting in tumor
therapy [16], overcoming multidrug resistance encountered
in cancer chemotherapy [17]. Particularly, 4-aryl-1,4-DHPs
represent the most important group of calcium channel
modulating agents and have emerged as one of the most
important class of drugs for the treatment of cardiovascular
diseases [18]. Cardiovascular agents such as nifedipine,
nicardipine, felodipine, amlodipine, nimodipine, and other
related derivatives are the prototype of dihydropyridyl
group (Scheme 2) [19].
For these reasons, 1,4-DHPs and PHQs not only have
attracted the attention of chemists to synthesize but also
represent an interesting research challenge. Generally, 1,4-
DHPs and PHQs are synthesized by the Hantzsch con-
densation method, which involves cyclocondensation of
aldehyde, b-dicarbonyls, and ammonia either in acetic acid
at room temperature or refluxing in alcohol for a long time
[20]. Recently, several improved methods have been
developed for the synthesis of these compounds including
Results and discussion
In a first attempt, to find the best reaction conditions, the
one-pot four-component condensation reaction of
4-chlorobenzaldehyde (1 mmol), ethyl acetoacetate
(2 mmol for DHP or 1 mmol for PHQ), 1,3-cyclohexane-
dione (1 mmol for PHQ), and ammonium acetate
Scheme 2
123

Tetraethylammonium 2-(carbamoyl)benzoate as a bifunctional organocatalyst for one-pot synthesis…
Scheme 3
(1.2 mmol) was examined under various reaction condi-
tions. The results are summarized in Table 1.
and ammonium acetate were successfully condensed via a
one-pot reaction. As shown in Table 2, all of the reactions
proceeded efficiently and the desired products were pro-
duced in good to excellent yields in relatively short
reaction times. Aromatic aldehydes bearing electron-with-
drawing groups reacted at a faster rate in comparison to
those substituted with electron-releasing groups such as
OCH3, OH (entries 6–8). In addition, diversity and scope of
the other components of this reaction were examined. In
this order, dimedone (6b) or 1,3-cyclohexanedione (6a)
were used and they gave polyhydroquinoline derivatives
(PHQs) in good to excellent yields. The results are sum-
marized in Table 3.
Preliminary experiments indicated that the desired
products were not obtained in the absence of any catalyst in
various solvents even under reflux conditions or ambient
temperature (entries 1–3). Interestingly, the desired prod-
ucts were obtained when catalytic amounts of potassium
phthalimide-N-oxyl (PoPino), sodium carbonate, and
DABCO as a monofunctional base catalyst; benzamide,
potassium phthalimide (PPI), tetraethylammonium
hydroxide (TEAH), combination of PPI and TEAH (as
cocatalyst); combination of benzamide and TEAI (as
cocatalyst); TEACB and GABA as a bifunctional acid–
base catalyst were used in water and ethanol under reflux
conditions (entries 4–13). Among them, TEACB showed
the best activity and almost quantitative yield of product
was obtained under refluxing ethanol (entries 14–16).
Therefore, TEACB was chosen in the next optimization
experiments for the best catalyst loading (entries 17–19).
As it can be seen, 10 mol% catalyst loading gave the best
results among all, by considering the catalyst turnover
frequency (TOF) values. According to the obtained results,
10 mol% TEACB loading under refluxing condition, as
optimized conditions, was developed to other derivatives of
aldehydes. The scope and efficiency of the process was
investigated under optimized conditions and the results are
summarized in Table 2.
Recently, relevant intermediates were intercepted and
characterized for the Hantzsch DHP reaction, and three
principal pathways were proposed for the formation of
Hantzsch products [49, 50]. According to these results two
different pathways for the mechanism of one-pot four-
component reaction of different 1,3-dicarbonyls with
aldehydes and ammonium acetate, catalyzed by TEACB
can be envisaged (Schemes 4, 5).
In the first plausible mechanism, the 1,3-dicarbonyl
compound reacts with aldehyde to give the corresponding
Knoevenagel intermediate I. In the subsequent step, I re-
acts with a second molecule of 1,3-dicarbonyl through a
Michael addition and form the intermediate II. The reac-
tion of II with ammonium acetate gives the imine
intermediate III in equilibrium with the enamine form IV
which is converted by cyclization and elimination of water
to 1,4-DHP (Scheme 4).
For this purpose, a broad range of structurally diverse
aliphatic and aromatic aldehydes bearing electron-releasing
or electron-withdrawing substituents, ethyl acetoacetate,
123

M. Yarhosseini et al.
Table 1 Optimization conditions for the synthesis of DHPs and PHQs
Entry
Catalyst
Catalyst loading/mol%
Solvent
Temp
Time/min
Yielda/%
TOF/min-1
5c
7b
5c
7b
5c
7b
1
–
–
H2O
r.t.
120
120
120
110
110
100
90
100
100
100
80
Trace
Trace
Trace
70
–
2
–
–
H2O
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
r.t.
–
3
–
–
EtOH
H2O
–
4
Na2CO3
PoPINO
DABCO
GABA
Benzamide
PPI
10
10
10
10
10
10
10
10b
10c
10
10
10
10
10
7.5
5
65
65
70
70
50
57
70
55
65
82
78
80
90
70
80
70
0.063
0.061
0.07
0.083
0049
0041
0.056
0.08
0.122
0.088
0.082
0.106
0.135
0.04
0.096
0.114
0.081
0.092
0.1
5
H2O
70
68
6
H2O
70
70
7
H2O
65
75
0.107
0.05
8
H2O
110
150
120
150
110
90
100
120
75
54
9
H2O
62
0.047
0.093
0.094
0.172
0.149
0.13
10
11
12
13
14
15
16
17
18
19
TEAH
H2O
68
PPI, TEAH
Benzamide, TEAI
TEACB
PoPINO
GABA
TEACB
TEACB
TEACB
TEACB
H2O
115
75
60
H2O
68
H2O
55
80
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
95
60
78
80
50
85
0.16
70
40
95
0.225
0.077
0.21
180
120
140
90
72
Reflux
Reflux
50
87
70
80
0.2
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), dimedone (1 mmol for 7b), ethyl acetoacetate (2 mmol for 5c or 1 mmol for 7b), and
ammonium acetate (1.2 mmol)
a
The yields refer to the isolated product
b, c
5 mol% of catalyst and 5 mol% of TEAH was used as cocatalyst
In the second plausible mechanism, the 1,3-dicarbonyl
compound activated through proton transfer from TEACB
reacts with ammonium acetate to form the imine V. This
later intermediate is also activated through proton transfer
to facilitate its subsequent tautomerization to the corre-
sponding aminocrotonate VI which condenses with
activated aldehyde to form the intermediate VII. The
reaction of this intermediate with the enol form of 1,3-
dicarbonyl gives the corresponding Knoevenagel interme-
diate VIII which leans toward IX. The desired product was
obtained after ring closure and elimination of water
(Scheme 5).
The catalytic efficacy of TEACB over some reported
protocols are also overviewed. The superiority of the
present method over reported methodologies was stud-
ied by comparing the obtained results with those
reported previously (Table 4). The catalytic activity of
catalysts was compared considering mol% of the used
catalyst, temperature, reaction time, TOF, and percent-
age yields for the synthesis of 5c. Among the examined
123

Tetraethylammonium 2-(carbamoyl)benzoate as a bifunctional organocatalyst for one-pot synthesis…
Table 2 Four-component synthesis of 1,4-dihydropyridines 5a–5q via condensation of aldehydes 2a–2q, ethyl acetoacetate (3), and ammonium
acetate (4) in the presence of TEACB under refluxing condition
Entry
Aldehyde
Product
Time/min
Yielda/%
M.p./°C
1
Formaldehyde (2a)
5a
5b
5c
5d
5e
5f
75
90
90
92
95
85
96
92
92
90
92
96
94
70
72
65
88
92
95
187 (185–186 [34])
160 (158–160 [35])
145 (145–147 [35])
130 (129–131 [34])
170 (170–172 [35])
160 (158–160 [36])
222–224 (223–225 [36])
163 (160–162 [35])
132–134 (133–135 [35])
156 (156–158 [35])
163 (161–162 [35])
135 (136 [34])
2
Benzaldehyde (2b)
3
4-Chlorobenzaldehyde (2c)
2-Chlorobenzaldehyde (2d)
Thiophen-2-carbaldehyde (2e)
4-Hydroxy-3-methoxybenzaldehyde (2f)
4-Hydroxybenzaldehyde (2g)
4-Methoxybenzaldehyde (2h)
4-Methylbenzaldehyde (2i)
4-Fluorobenzaldehyde (2j)
4-Bromobenzaldehyde (2k)
4-Nitrobenzaldehyde (2l)
3-Nitrobenzaldehyde (2m)
2-Nitrobenzaldehyde (2n)
2,4-Dichlorobenzaldehyde (2o)
Furfural (2p)
70
4
90
5
75
6
80
7
5g
5h
5i
110
100
80
8
9
10
11
12
13
14
15
16
17
5j
70
5k
5l
60
100
90
5m
5n
5o
5p
5q
163 (161–163 [35])
130 (128–130 [35])
111 (108–110 [35])
159 (160–161 [35])
147 (147 [34])
100
90
85
Cinnamaldehyde (2q)
90
Reaction conditions: aromatic aldehydes (1 mmol), ethyl acetoacetate (2 mmol), and ammonium acetate (1.2 mmol)
a
The yields refer to the isolated product
catalysts, TEACB showed the highest activity i.e., the
larger TOF.
Experimental
All chemicals were purchased from Merck, Fluka, and
Sigma-Aldrich companies and were used without further
purification, except for benzaldehyde, which was used as a
fresh distilled sample. Analytical thin layer chromatogra-
phy (TLC) for monitoring reactions was performed using
Merck 0.2 mm silica gel 60 F-254 Al-plates using ethyl
acetate and n-hexane as eluents. Melting points were
determined in open capillaries using an Electrothermal
9100 instrument. Infrared (IR) spectra were acquired on a
Conclusions
In summary, we have found an efficient, directly, inex-
pensive catalyst procedure for one-pot synthesis of 1,4-
DHPs and PHQs. This protocol includes some important
aspects like the use a metal-free and easy to handle cata-
lyst, easy work-up procedure, high atom economy, and
green reaction conditions. Furthermore, the reaction has
been shown to display good functional group tolerance and
product isolation is very straightforward.
1
Shimadzu FT-IR-8400S spectrometer. H NMR (250 for
DHP, 300 for PHQ, and 500 MHz for TEACB) and 13C
NMR (125 MHz for TEACB) spectra were recorded on
123

M. Yarhosseini et al.
Table 3 Four-component synthesis of polyhydroquinolines 7a–7p and 8a–8q
Entry
Aldehyde
1,3-Diketone
Product
Time/min
Yielda/%
M.p./°C
1
2b
2c
2d
2e
2f
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
7a
7b
7c
7d
7e
7f
35
40
45
40
35
65
50
35
25
30
60
75
60
45
40
35
40
40
50
45
40
30
40
50
40
40
30
70
65
80
45
35
40
90
90
88
97
94
95
85
90
92
90
62
65
60
92
88
94
90
88
97
90
96
90
95
92
94
96
97
70
72
65
95
92
94
239 (240–241 [37])
2
238 (237–239 [38])
3
238 (236.6–237.8 [40])
230–232 (230–232 [38])
235 (236–238 [41])
4
5
6
2g
2h
2i
232–234 (234–235 [37])
193 (193–195 [37])
7
7g
7h
7i
8
240 (241–242 [37])
9
2j
241–243 (243–245 [38])
251–253 (253–254 [42])
206–208 (207–209 [38])
197–200 (198–200 [37])
191–192 (190–191 [39])
249 (245–247 [43])
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
2k
2l
7j
7k
7l
2m
2n
2o
2p
2q
2a
2b
2c
2d
2e
2f
7m
7n
7o
7p
8a
8b
8c
8d
8e
8f
212 (210–212 [44])
218 (219–221 [45])
172 (173–174 [48])
249 (250–252 [46])
248 (248–250 [46])
212 (210–212 [46])
223 (223–225 [46])
233 (235–237 [46])
2g
2h
2i
8g
8h
8i
246–249 (247–249 [46])
244–247 (245–247 [46])
268–270 (270–272 [46])
185–186 (186–187 [38])
250–252 (248–250 [38])
239–241 (239–241 [38])
240–242 (240–242 [46])
210 (210–212 [46])
2j
8j
2k
2l
8k
8l
2m
2n
2o
2p
2q
8m
8n
8o
8p
8q
238–241 (240–242 [47])
244–246 (246–247 [47])
204–205 (204–206 [47])
Reaction conditions: aromatic aldehydes (1 mmol), dimedone/1.3-cyclohexanedione (1 mmol), ethyl acetoacetate (1 mmol), and ammonium
acetate (1.2 mmol)
a
The yields refer to the isolated product
123

Tetraethylammonium 2-(carbamoyl)benzoate as a bifunctional organocatalyst for one-pot synthesis…
Scheme 4
1002 cm-1 1H NMR (500 MHz, CDCl3): d = 0.99 (t,
;
Bruker DRX Avance spectrometers with CDCl3 as solvent
at ambient temperature and tetramethylsilane (TMS) as the
internal standard. All chemical shifts are given relative to
TMS. All yields refer to the isolated products.
J = 7.20 Hz, 12H), 2.99 (t, J = 7.20 Hz, 8H), 6.15 (br s,
1H), 7.07 (t, J = 7.50 Hz, 1H), 7.18 (t, J = 7.40 Hz, 1H),
7.35 (d, J = 7.50 Hz, 1H), 7.71 (d, J = 7.75 Hz, 1H),
10.05 (br s, 1H) ppm; 13C NMR (125 MHz, CDCl3):
d = 7.6, 52.4, 126.7, 128.3, 128.4, 129.6, 130.6, 143.5,
170.8, 174.9 ppm.
Tetraethylammonium 2-(carbamoyl)benzoate
(1, C16H26N2O3)
To a 25 cm3 round-bottomed flask equipped with a
magnetic stirrer and a condenser were added 1.00 g
phthalimide (6.80 mmol) and 5.0 cm3 TEAH (6.80 mmol,
20 % w/w in water, d = 1.01 g/cm3). The mixture was
stirred at room temperature for 5 min. To this was added
5 cm3 of distilled water and the mixture was refluxed for
4 h and then allowed to cool. The solvent was evaporated
and the residue was kept at 0–4 °C for 1 h to afford pure
TEACB in quantitative yield. The white crystals were
collected and dried under reduced pressure. M.p.:
86–88 °C; IR (KBr):¯v = 3561–3208 (br s, N–H), 3067,
2988, 2953, 1666, 1580, 1550, 1487, 1400, 1173,
General procedure for the synthesis of DHP
and PHQ derivatives
A mixture of aldehyde (1 mmol), ethyl acetoacetate
(2 mmol for DHP or 1 mmol for PHQ), dimedone/1.3-cy-
clohexanedione (1 mmol for PHQ), and ammonium acetate
(1.2 mmol) and TEACB (10 mol%) in 2 cm3 absolute
ethanol was heated at 80 °C for the time indicated in
Tables 2 and 3 into a 10 cm3 round-bottomed flask
equipped with a magnetic stirrer until products were
123

M. Yarhosseini et al.
Scheme 5
Table 4 Comparison of results for the synthesis of 1,4-dihydropyridine 5c via Hantzsch reaction using other catalyst
Entry
Catalyst
Catalyst loading/mol%
Solvent
Temp.
Time/min
Yield/%
TOF/h-1
1
2
3
4
5
6
7
8
PPh3
20
10
10
10
10
12
10
10
EtOH
MeCN
EtOH
MeCN
EtOH
–
Reflux
r.t.
120
240
180
240
300
360
120
70
81 [26]
94 [51]
96 [52]
91 [53]
82 [54]
86 [55]
78 [56]
1.98
2.34
3.18
2.22
1.62
1.14
3.9
LiBr
GuHCl
r.t.
CeCl3Á7H2O
PhB(OH)2
SiO2ÁSO3H
Cellulose sulfuric acid
TEACB
r.t.
Reflux
60 °C
80 °C
Reflux
–
EtOH
95 (this work)
8.1
Acknowledgments We are grateful for the financial support from
The Research Council of Iran University of Science and Technology
(IUST), Tehran, Iran.
formed completely. The reaction progress was monitored
by TLC. After completion of the reaction, the solvent was
evaporated under vacuum to furnish a solid which was
recrystallized from ethyl acetate-hexane.
123

Tetraethylammonium 2-(carbamoyl)benzoate as a bifunctional organocatalyst for one-pot synthesis…
29. Javanshir S, Sharifi S, Maleki A, Sohrabi B, Kiasadegh M (2014)
J Phys Org Chem 27:589
References
30. Safari M, Javanshir S, Dekamin MG (2013) Sci Iran 20:742
31. Kazemi B, Javanshir S, Maleki A, Safari M, Khavasi HR (2012)
Tetrahedron Lett 53:6977
1. Ran BC, Chattopadhyay K (2009) In: Ballini R (ed) Eco-friendly
synthesis of fine chemicals, vol 5. Royal Society of Chemistry,
Cambridge
32. Hosseini-Zare MS, Mahdavi M, Saeedi M, Asadi M, Javanshir S,
Shafiee AS, Foroumadi A (2012) Tetrahedron Lett 53:3448
33. Maleki A, Javanshir S, Naimabadi M (2014) RSC Adv 4:30229
34. Wang X, Gong H, Li Z, Quan L, Ye H (2011) Synth Commun
41:3251
35. Safaei-Ghomi J, Ziarati A, Zahedi S (2012) Chem Sci 124:933
36. Pei W, Wang Q, Li X, Sun L (2010) Chin J Chem 28:483
37. Undale K, Shaikh T, Gaikwad D, Pore D (2011) C R Chim
14:511
2. Giacalone M, Gruttadauria P, Agrigentoand R (2012) Chem Soc
Rev 41:2406
3. Gaunt MJ, Johansson CC, McNally A, Vo NT (2007) Drug
Discov Today 12:8
4. Dekamin MG, Eslami M (2014) Green Chem 16:4914
5. Dekamin MG, Karimi Z, Farahmand M (2012) Catal Sci Technol
2:1375
6. Dekamin MG, Sagheb-Asl S, Naimi-Jamal MR (2009) Tetrahe-
dron Lett 50:4063
38. Maleki B, Tayebee R, Sepehr Z, Kermanian M (2012) Acta Chim
Slov 59:814
7. Dekamin MG, Varmira K, Farahmand M, Sagheb-Asl S, Karimi
Z (2010) Catal Commun 12:226
39. Mobinikhaledi A, Foroughifar N, Fard MAB, Moghanian H,
Ebrahimi S, Kalhor M (2009) Synth Commun 39:1166
40. Li J, He P, Yu C (2012) Tetrahedron 68:4138
41. Yang XH, Zhang PH, Zhou YH, Liu CG, Lin XY, Cui JF (2011) J
Org Chem 10:327
42. Nasr-Esfahani M, Hoseini SJ, Montazerozohori M, Mehrabi R,
Nasrabadi H (2014) J Mol Catal A Chem 382:99
43. Rajesh UC, Manohar S, Rawat DS (2013) Adv Synth Catal
355:3170
44. Ko S, Yao CF (2006) Tetrahedron 62:7293
45. Peng HN, Peng XM, Zheng D (2011) Asian J Chem 23:1833
46. Nagarapu L, Kumari MD, Kumari NV, Kantevari S (2007) Catal
Commun 8:1871
47. Kassaee M, Masrouri H, Movahedi F (2010) Mon Chem 141:317
48. Stankevich E, Grinshtein E, Dubur GY (1975) Chem Heterocycl
Compd 11:196
8. Dekamin MG, Ghanbari M, Moghbeli MR, Barikani M, Javanshir
S (2013) Polym Plast Technol Eng 52:1127
9. Mannhold R, Jablonka B, Voigdt W, Schoenafinger K, Schravan
K (1992) Eur J Med Chem 27:229
10. Mager PP, Coburn RA, Solo AJ, Triggle DJ, Rothe H (1992)
Drug Des Discov 8:273
11. Boer R, Gekeler V (1995) Drugs Future 20:499
12. Bossert F, Meyer H, Wehinger E (1981) Angew Chem Int Ed
20:762
13. Janis RA, Triggle DJ (1983) J Med Chem 26:775
14. Kumar RS, Idhayadhulla A, Nasser AJ, Selvin J (2011) Eur J Med
Chem 46:804
15. Bretzel RG, Bollen CC, Maese E (1993) Am J Kidney Dis 21:53
16. Bretzel RG, Bollen CC, Maeser E (1992) Drugs Future 17:465
17. Nogec I, Kohno K, Kikuchi J, Kuwano M (1989) Biochem
Pharmacol 38:519
49. Santos VG, Godoi MN, Regiani T, Gama HS, Coelho MB, Souza
OM, Eberlin MN, Garden S (2014) Chem Eur J 20:12808
50. Alvim GO, Silva Junior N, Neto AD (2014) RSC Adv 4:54282
51. Yadav D, Patel R, Srivastava V, Watal G, Yadav L (2011) Chin J
Chem 29:118
52. Baghbanian SM, Khaksar S, Vahdat SM, Farhang M, Tajbakhsh
M (2010) Chin Chem Lett 21:563
53. Sabitha G, Arundhathi K, Sudhakar K, Sastry B, Yadav J (2009)
Synth Commun 39:2843
18. Love B, Snader KM (1965) J Org Chem 30:1914
19. Safak C, Simsek R (2006) Mini Rev Med Chem 6:747
20. Hantzsch A, Arapides L (1888) Ber Bunsen Ges Phys Chem
21:941
21. Wang SX, Li ZY, Zhang JC, Li JT (2008) Ultrason Sonochem
15:677
22. Deshayes S, Liagre M, Loupy A, Luche JL, Petit A (1999)
Tetrahedron 55:10851
23. Correa WH, Scott JL (2001) Green Chem 3:296
24. Tamaddon F, Razmi Z, Jafari A (2010) Tetrahedron Lett 51:1187
25. Sirisha K, Achaiah G, Reddy VM (2010) Arch Pharm 343:342
26. Debache A, Ghalem W, Boulcina R, Belfaitah A, Rhouati S,
Carboni B (2009) Tetrahedron Lett 50:5248
27. Dalko PI, Moisan L (2004) Angew Chem Int Ed 43:5138
28. Dekamin MG, Azimoshan M, Ramezani L (2013) Green Chem
15:811
54. Debache A, Boulcina R, Belfaitah A, Rhouati S, Carboni B
(2008) Synlett 4:509
55. Gupta R, Gupta R, Paul S, Loupy A (2007) Synthesis 18:2835
56. Murthy Y, Rajack A, Taraka-Ramji M, Praveen C, Aruna-Lak-
shmi K (2012) Bioorg Med Chem Lett 22:6016
123