MnO2-MWCNT nanocomposites as efficient catalyst in the synthesis of Biginelli-type compounds under microwave radiation

Article abstract of DOI:10.1016/j.molcata.2013.02.021

A novel Biginelli-like cyclocondensation reaction is efficiently catalyzed by MnO₂-CNT nanocomposites as a new catalyst under microwave irradiation and solvent-free conditions in excellent yields. The major advantages of the present method are high yields, short reaction times and solvent-free reaction conditions, reducing reaction steps and purification of products by non-chromatographic methods. The activity, recovery and reusability of the catalyst are found to be good.

Full text of DOI:10.1016/j.molcata.2013.02.021

Journal of Molecular Catalysis A: Chemical 373 (2013) 72–77
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
MnO –MWCNT nanocomposites as efficient catalyst in the synthesis of
2
Biginelli-type compounds under microwave radiation
∗
Javad Safari , Soheila Gandomi-Ravandi
Laboratory of Organic Compound Research, Department of Organic Chemistry, College of Chemistry, University of Kashan, P.O. Box 87317-51167, Kashan, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel Biginelli-like cyclocondensation reaction is efficiently catalyzed by MnO –CNT nanocompos-
2
Received 13 January 2013
Received in revised form 20 February 2013
Accepted 23 February 2013
Available online xxx
ites as a new catalyst under microwave irradiation and solvent-free conditions in excellent yields. The
major advantages of the present method are high yields, short reaction times and solvent-free reaction
conditions, reducing reaction steps and purification of products by non-chromatographic methods. The
activity, recovery and reusability of the catalyst are found to be good.
©
2013 Elsevier B.V. All rights reserved.
Keywords:
Biginelli-type reaction
MnO2–CNT nanocomposites
Pyrimidinone
Heterogeneous catalyst
1
. Introduction
Recently, the application of metal oxides as catalysts has
attracted worldwide attention because of their high catalytic activ-
ity and improved selectivity [13–16]. Among the transition metal
The dihydropyrimidinone (DHPMs) derivatives have various
types of biological activity and hold interest as modulators for the
transport of calcium ions across the cell membrane [1]. These het-
erocyclic compounds are active antihypertensive agents, [2,3] ␣1a
adrenoceptor-selective antagonists, [4] and kinesin Eg5 inhibitors.
oxides, manganese oxide (MnO ) is particularly attractive and has
2
been widely used in Lithium-ion batteries and, recently, in super-
capacitors [17,18]. Metal oxide–carbon composites have gained
much interest in recent years owing to their potential applica-
tions. Recently, many efforts have been focused on the synthesis
[
5] Therefore, the preparation of this heterocyclic nucleus has
gained great importance in organic synthesis. While the biologi-
cal interest of DHPM exploded, [6] the Biginelli reaction has been
the subject of high synthetic activity. Though conventional Big-
inelli involves aldehydes, urea, and active methylene compounds
of nanoscale MnO /CNT composites to make the best of both
the excellent electrical conductivity of CNTs and the high capac-
2
itance of manganese oxide [19–23]. In the case of MnO /CNT
2
nanocomposite, MnO2 possesses several advantages on top of car-
bon material, such as high electrochemical capacitance, low cost,
natural abundance, and environmentally friendliness [24–26]. Due
to the importance of Biginelli compounds, the discovery and intro-
duction of better and milder conditions using new catalysts has
been under attention. In this report, we describe a convenient
and efficient advancement microwave-accelerated of Biginelli-type
(
1,3-dicarbonyl), Authors demonstrated that even ketones can
participate in this reaction affording unconventional Biginelli com-
pounds in excellent yields [7]. The first Biginelli-like reaction,
reported by Wang et al. [8] was conducted in CH CN by using alde-
3
hydes, ketones, and urea, which remarkably broadened the Biginelli
reaction. In recent years, several synthetic procedures for prepar-
ing DHPMs via a Biginelli-like reaction have been reported. Recent
publications on Biginelli-type reactions describe the use of different
catalysts, [9,10] microwave, [11] and ultrasound [12] irradiations.
In spite of their potential utility, some of these methods involve
long reaction times (12 h), stoichiometric amounts of catalysts, and
unsatisfactory yields.
reaction using MnO –CNT nanocomposites as an efficient catalyst
2
for the synthesis of DHPMs by a three-component one-pot con-
densation of aromatic aldehyde, ketone and urea. To the best of
our knowledge, there was no report for the synthesis of DHPMs
catalyzed by MnO –CNT nanocomposites under microwave irradi-
2
ation (Scheme 1).
2. Experimental
∗ Corresponding author. Tel.: +98 0361 591 2320; fax: +98 0361 591 2397.
E-mail address: Safari@kashanu.ac.ir (J. Safari).
All reagents were purchased from Merck and Fluka and
used without further purification. MWNTs were purchased from
1
381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.02.021

J. Safari, S. Gandomi-Ravandi / Journal of Molecular Catalysis A: Chemical 373 (2013) 72–77
73
R
R
MnO -CNTs
2
NH
H
O
O
1
NH2
MW, Solvent free
N
H
X
H N
X
2
R'
R'
2
3
4
Scheme 1. Microwave-assisted MnO2–CNT nanocomposites-catalyzed Biginelli-like reaction.
Nanotech Port Co. (Taiwan). These MWNTs were produced via the
chemical vapor deposition (CVD) method. The outer diameter of
CNT was between 20 and 40 nm. IR spectra were recorded on KBr
DMSO-d ): ı 8.57 (s, 1H, NH), 7.54–7.28 (m, 10H, Ar–H), 5.18 (d, 1H,
6
J = 3.6 Hz, CH), 5.13 (d, 1H, J = 3.6 Hz, CH), 3.43 (br, 1H, NH); C NMR
13
(100 MHz, DMSO-d ): ı 153.5, 145.2, 134.1, 128.5, 128.3, 128.4,
6
1
pellets on a Perkin Elmer FT-IR 550 spectrophotometer. H and
127.2, 126.2, 125.3, 135.4, 98.7, 54.9; Anal. Calcd. for C16H14N O:
2
13
C NMR spectra were obtained in CDCl3 solution on a Bruker DRX
C, 76.78; H, 5.64; N, 11.19. Found C, 76.23; H, 5.54; N, 11.20; HRMS
(ESI) for [M+H] found (expected): 250.1102 (250.1106).
4
00 MHz spectrometer; chemical shifts (ı) are given in ppm using
TMS as internal reference. The CEM-Discover Focused Monomode
Microwave reactor (2450 MHz, 300 W) was used for microwave
irradiation. Microwave-mediated reactions were performed in
sealed process vials under air with magnetic stirring. ESI-MS was
recorded on a MICROMASS QUATTRO II triple quadrupole mass
spectrometer. Elemental analysis was recorded on a Heraeus CHN-
O-RAPID elemental analyzer. The course of the reactions and the
purity of the synthesized compounds were monitored by TLC.
2
2
.2.2. 4-(2,4-Dichlorophenyl)-3,4-dihydro-6-phenylpyrimidin-
(1H)-one 4b
◦
White solid; Mp 272–274 C; IR (KBr) ꢁmax: 3279 (NH), 2952
−1
1
(NH), 1655 (C O), 1587 (C C), 1415 (C C) cm
;
H NMR
(400 MHz, DMSO-d ): ı 8.91 (s, 1H, NH), 7.62–6.76 (m, 8H, Ar–H),
6
6
.26 (d, J = 6.4 Hz, 1H, CH), 5.62 (s, 1H, NH), 5.31 (d, J = 6.4 Hz, 1H,
13
CH); C NMR (100 MHz, DMSO-d ): ı 154.2, 142.7, 135.3, 134.4,
133.2, 129.3, 128.4, 127.4, 127.1, 126.3, 125.4, 95.3, 43.1; Anal.
Calcd. for C16H12Cl N O: C, 60.20; H, 3.79; N, 8.78; Cl, 22.21. Found
6
The morphologies of the synthesized MnO /CNTs composites were
2
studied by scanning electron microscopy (SEM, FEI Quanta 200
scanning electron microscope). X-ray diffraction patterns (XRD)
were obtained with a Holland Philips Xpert X-ray powder diffrac-
tion (XRD) diffractometer (CuK, radiation, ␭ = 0.154056 nm), at a
2
2
C, 60.37; H, 3.68; N, 9.00; Cl, 21.87; HRMS (ESI) for [M+H] found
expected): 318.0324 (318.0327).
(
◦
◦
◦
scanning speed of 2 /min from 10 to 100 (2ꢀ).
.1. The preparation of MnO2 supported CNT nanocomposites
MnO –CNT nanocomposites were prepared as reported in the
2
(
.2.3. 3,4-Dihydro-4-(4-methoxyphenyl)-6-phenylpyrimidin-2
1H)-one 4c
White solid; Mp 259–262 C; IR (KBr) ꢁmax: 3381 (NH), 2932
2
◦
−1
1
(NH), 1613 (C O), 1515 (C C), 1402 (C C) cm
;
H NMR
2
(400 MHz, DMSO-d ): ı 11.91 (s, 1H, NH), 9.33 (s, 1H, NH), 8.33–7.24
6
literature [27]. Briefly, the CNTs were activated by stirring in nitric
(m, 9H, Ar–H), 6.96 (d, J = 8.8 Hz, 1H, CH), 5.44 (d, J = 8.8 Hz, 1H, CH),
◦
acid at 110 C for 3 h. The acid-treatment CNTs were obtained by
13
3
1
5
.77 (s, 3H, OCH ); C NMR (100 MHz, DMSO-d ): ı 162.1, 159.4,
3
6
◦
rinsing with deionized water and drying in the air at 100 C, then
52.8, 133.2, 131.4, 129.4, 128.7, 127.4, 114.2, 113.8, 79.2, 62.4,
5.5; Anal. Calcd. for C17H16N O : C, 72.84; H, 5.75; N, 10.00. Found
in a direct redox reaction, 100 mg of modified CNT was mixed with
2
2
1
3
00 ml aqueous solution of KMnO4 under ultrasonic vibration for
C, 72.57; H, 5.76; N, 10.11; HRMS (ESI) for [M+H] found (expected):
2
0 min, and then acetic acid (10 ml) was added into the mixture
80.1208 (280.1211).
◦
until pH 2. The resulting suspension was refluxed at 70 C for 3 h.
At last, the mixture was separated by filtration and then washed
several times with deionized water and acetone. After that, the solid
2.2.4. 4-(2-Chlorophenyl)-3,4-dihydro-6-phenylpyrimidin-
2(1H)-one 4d
◦
precipitate dried at 70 C for 12 h in a vacuum oven.
◦
White solid; Mp 261–263 C; IR (KBr) ꢁmax: 3289 (NH), 2942
−1
1
(NH), 1654 (C O), 1589 (C C), 1418 (C C) cm
;
H NMR
2
4
.2. Typical procedure for the synthesis of
,6-diaryl-3,4-dihydropyrimidine-2(1H)-ones
(400 MHz, DMSO-d ): ı 8.60 (s, 1H, NH), 8.15 (s, 1H, NH), 7.42–7.15
6
(m, 9H, Ar–H), 5.45 (d, J = 4.4 Hz, 1H, CH), 5.12 (d, 1H, J = 2.8 Hz,
CH); 13C NMR (100 MHz, DMSO-d ): ı 154.7, 145.7, 138.3, 135.8,
6
To a 50 ml flame dried round-bottom flask was added benz-
aldehyde (1 mmol), acetophenone (1 mmol), urea (1.5 mmol) and
131.6, 129.5, 128.8, 128.6, 128.4, 128.1, 127.5, 125.5, 94.1, 54.3;
Anal. Calcd. for C16H12Cl N O: C, 60.21; H, 3.79; N, 8.78; Cl, 22.21.
2
2
MnO –CNT nanocomposites (0.03 g). The resulting mixture was
placed into the microwave reactor. After completion of the reaction
Found C, 60.31; H, 3.71; N, 9.00; Cl, 21.96; HRMS (ESI) for [M+H]
found (expected): 318.0324 (318.0327).
2
(
monitored by TLC), it was allowed to cool to room temperature,
then distilled water (10 ml) was added into the beaker and stirred
for several minutes. The precipitate thus obtained was filtered off.
The crude product purified by recrystallization from ethanol and
dried to give powder compounds 4a–j.
2
.2.5. 3,4-Dihydro-6-phenyl-4-p-tolylpyrimidin-2(1H)-one 4e
◦
White solid; mp 249–251 C; IR (KBr) ␯max: 3235 (NH), 2920
−1
1
(
(
(
NH), 1650 (C O), 1570 (C C), 1402 (C C) cm
400 MHz, DMSO-d ): ı 9.24 (s, 1H, NH), 8.48 (s, 1H, NH), 7.84–6.00
m, 9H, Ar–H), 5.56 (d, J = 6.8 Hz, 1H, CH), 5.31 (d, J = 6.8 Hz, 1H, CH),
;
H NMR
6
13
2
.2.1. 3,4-Dihydro-4,6-diphenylpyrimidin-2(1H)-one 4a
2.42 (s, 3H, CH ); C NMR (100 MHz, DMSO-d ): ı 157.5, 136.4,
133.4, 133.1, 132.5, 129.3, 128.4, 126.2, 125.6, 120.3, 111.1, 110.1,
99.3, 23.1; Anal. Calcd. for C17H16N O: C, 77.25; H, 6.10; N, 10.60.
3
6
◦
White solid; Mp 229–231 C; IR (KBr) ꢁmax: 3225 (NH),
2
922 (NH), 1687 (C O), 1602 (C C) cm ; 1H NMR (400 MHz,
−1
2

7
4
J. Safari, S. Gandomi-Ravandi / Journal of Molecular Catalysis A: Chemical 373 (2013) 72–77
Found C, 77.32; H, 5.99; N, 10.61; HRMS (ESI) for [M+H] found
expected): 264.1258 (264.1262).
(
2.2.6. 4-(2,6-Dichlorophenyl)-3,4-dihydro-6-phenyl-pyrimidin-
2
(1H)-one 4f
◦
White solid; Mp 275–277 C; IR (KBr) ꢁmax: 3235 (NH), 2920
−
1
1
(
(
(
NH), 1650 (C O), 1570 (C C), 1402 (C C) cm
400 MHz, DMSO-d ): ı 8.57 (s, 1H, NH), 8.20 (s, 1H, NH), 8.16–7.28
m, 8H, Ar–H), 5.89 (d, J = 4 Hz, 1H,CH), 5.56 (d, J = 4 Hz, 1H,
;
H NMR
6
13
CH); C NMR (100 MHz, DMSO-d ): ı 153.3, 142.2, 137.6, 132.3,
6
1
31.7, 128.7, 127.7, 126.3, 126.4, 125.6, 96.4, 32.1; Anal. Calcd. for
C16H12Cl N O: C, 60.20; H, 3.79; N, 8.78; Cl, 22.21. Found C, 59.82;
2
2
H, 4.00; N, 8.67; Cl, 21.94; HRMS (ESI) for [M+H] found (expected):
3
18.0324 (318.0327).
Fig. 2. Optimization of time reaction of 4a using various amounts of catalyst.
2.2.7. 3,4-Dihydro-4-(3-methoxyphenyl)-6-phenylpyrimidin-2
(
1H)-one 4g
White solid; Mp 257–259 C; IR (KBr) ꢁmax: 3209 (NH), 2933
◦
−
1
1
(
NH), 1689 (C O), 1598 (C C), 1402 (C C) cm
;
H NMR
(
400 MHz, DMSO-d ): ı 8.55 (s, 1H, NH), 7.58–6.83 (m, 9H, Ar–H),
6
5
.18 (d, 1H, J = 4.4 Hz, CH), 5.10 (d, 1H, J = 4.4 Hz, CH), 3.43 (br, 1H,
13
NH); C NMR (100 MHz, DMSO-d ): ı 146.7, 159.4, 135.5, 134.0,
6
1
5
29.6, 128.5, 128.4, 118.3, 113.7, 112.4, 112.0, 143.1, 98.6, 55.0,
4.8; Anal. Calcd. for C17H16N O : C, 72.84; H, 5.75; N, 9.99. Found
2
2
C, 72.04; H, 5.63; N, 10.00; HRMS (ESI) for [M+H] found (expected):
2
80.1209 (280.1211).
2.2.8. 3,4-Dihydro-4-(3,4-dimethoxyphenyl)-6-phenylpyrimidin-
2
(1H)-one 4h
◦
Yellow solid; Mp 242–244 C; IR (KBr) ꢁmax: 3275 (NH), 2933
−
1
1
(
NH), 1614 (C O), 1512 (C C), 1459 (C C) cm
;
H NMR
(
400 MHz, DMSO-d ): ı 11.95 (s, 1H, NH), 8.58 (s, 1H, NH), 8.58–7.44
6
Fig. 3. Study of reusability of the catalyst in model reaction.
(m, 8H, Ar–H), 7.82 (d, J = 8.4 Hz, 1H, CH), 7.06 (d, J = 8.4 Hz, 1H, CH),
13
3
.91 (s, 3H, OCH ), 3.89 (s, 3H, OCH ); C NMR (100 MHz, DMSO-
3
3
2
[
4.27. Found C, 57.84; H, 4.12; N, 8.49; Br, 24.12; HRMS (ESI) for
M+H] found (expected): 328.0208 (328.0211).
d6): ı 159.3, 151.8, 148.7, 131.3, 128.7, 127.5, 121.2, 111.4, 110.4,
7
1
9.1, 55.7, 55.6; Anal. Calcd. for C18H18N O : C, 69.66; H, 5.85; N,
2 3
5.50. Found C, 69.65; H, 5.84; N, 9.01; HRMS (ESI) for [M+H] found
(
expected): 310.1313 (310.1317).
2.2.10. 3,4-Dihydro-4-(4-hydroxyphenyl)-6-phenylpyrimidin-2
(
1H)-one 4j
Yellow solid; mp 255–257 C; IR (KBr) ꢁmax: 3389 (NH), 2922
◦
2
(
.2.9. 4-(3-Bromophenyl)-3,4-dihydro-6-phenylpyrimidin-2
1H)-one 4i
White solid; Mp 256–258 C; IR (KBr) ꢁmax: 3122 (NH), 2923
−
1
1
(NH), 1631 (C O), 1515 (C C), 1450 (C C) cm
;
H NMR
◦
(400 MHz, DMSO-d ): ı 9.26 (s, 1H, NH), 8.17–7.53 (m, 9H, Ar–H),
6
−
1
1
(
NH), 1693 (C O), 1572 (C C), 1401 (C C) cm
;
H NMR
7.38–7.36 (s, 1H, NH), 7.23 (d, J = 8.8 Hz, 1H, CH), 5.50 (s, 1H, OH),
(
400 MHz, DMSO-d ): ı 9.16 (s, 1H, NH), 8.32–7.30 (m, 9H, Ar–H),
5.13 (d, J = 8.8 Hz, 1H, CH); 13C NMR (100 MHz, DMSO-d ): ı 156.8,
6
6
7
.12 (s, 1H, NH), 5.52 (d, J = 5.6 Hz, 1H, CH), 5.14 (d, J = 5.6 Hz, 1H,
141.6, 131.4, 129.4, 128.9, 127.6, 127.5, 127.3, 124.1, 123.8, 124.9,
13
CH); C NMR (100 MHz, DMSO-d ): ı 152.9, 147.4, 135.8, 133.7,
96.6, 55.4; Anal. Calcd. for C16H14N O : C, 72.17; H, 5.30; N, 10.52.
6
2 2
1
5
30.3, 129.7, 128.7, 128.5, 128.0, 125.1, 124.9, 121.4, 121.3, 97.6,
Found C, 72.00; H, 5.31; N, 10.34; HRMS (ESI) for [M+H] found
(expected): 266.1051 (266.1055).
4.2; Anal. Calcd. for C16H13BrN O: C, 58.38; H, 3.98; N, 8.51; Br,
2
3. Results and discussion
Biginelli-type three-component condensation of building blocks
aromatic ketone, urea and substituted benzaldehyde (Scheme 1)
leads to the formation of 4,6-diaryl-3,4-dihydropyrimidin-2(1H)-
one under microwave irradiation and solvent free conditions. The
Table 1
Effects of the microwave power and the irradiation time on the formation of 4a.
Entry
P (w)
Time (min)
25
20
14
5
Yield (%)
1
2
3
4
5
6
30
50
75
80
90
69
87
94
97
94
90
4
4
100
Fig. 1. Optimization of amount of catalyst in the synthesis of 4a.

J. Safari, S. Gandomi-Ravandi / Journal of Molecular Catalysis A: Chemical 373 (2013) 72–77
75
Fig. 4. SEM images of acid-treated CNTs (a), MnO2/CNT (b), and TEM pattern of MnO2/CNT (c).
reaction occurs more efficiently in solvent-free conditions than
does in solution since the catalyst and reagents are arranged more
tightly when solvent is not used. Therefore, without solvent, reac-
tions usually need shorter reaction time, simpler reactors, simple
and efficient workup procedures, and often more environmen-
conditions was attempted. Further, the reaction was carried out
with varied concentrations of MnO –CNT nanocomposites and it
2
was found that the catalyst equivalent to 0.03 g was sufficient
for the reaction to proceed in quantitative yield. The results are
shown in Figs. 1 and 2. As shown in Fig. 2, greater amounts of
tally friendly. The use of MnO –CNT nanocomposites catalyst,
MnO /CNT conforms oxidative conditions rather than catalytic
2
2
substrates, and solvent-free conditions in conjunction with
microwave heating is a standard technology used in this con-
text. We have tested a variety of reaction conditions with a
model reaction using benzaldehyde, urea, and acetophenone as
the starting materials that the best result was achieved with
a molar ratio of 1:1.5:1. Further optimization of the reaction
conditions. Therefore the reaction time is enhanced. These find-
ings demonstrate the effectiveness of using this nanocatalyst. The
reusability of the catalyst then was investigated. The MnO /CNT
2
nanocomposites were recovered by filtration, rinsed with mini-
mum sodium bicarbonate dissolved in distilled water up to neutral
◦
pH and dried at 100 C in autoclave for 1 h. The obtained results
Table 2
a
Catalytic cyclocondensation of aromatic aldehydes, ketone, and urea under microwave irradiation.
ꢀ
◦
Entry
R
R
X
Product
MnO2–CNTs
MnO2
M.p ( C)
Time (min)/yield (%)
Time (min)/yield (%)
Found
Reported
1
2
3
4
5
6
7
8
9
0
H
H
H
H
H
H
H
H
H
H
H
O
O
O
O
O
O
O
O
O
O
4a
4b
4c
4d
4e
4f
4g
4h
4i
5/97
38/70
46/65
41/68
40/70
49/61
55/58
45/72
62/54
53/73
80/50
229–231
272–274
259–262
261–263
249–251
275–277
257–259
242–244
256–258
255–257
228–230 [28]
271–274 [29]
259–261 [29]
264–265 [29]
248–250 [29]
274–276 [29]
257–258 [29]
243–245 [29]
258–259 [28]
257–258 [28]
2,4-Cl2
4-OMe
2-Cl
13/93
10/94
10/96
15/90
20/89
12/95
23/88
17/96
25/87
4-Me
2,6-Cl2
3-OMe
3,4-(OMe)2
3-Br
1
4-OH
4j
a
Microwave power 80 w.

7
6
J. Safari, S. Gandomi-Ravandi / Journal of Molecular Catalysis A: Chemical 373 (2013) 72–77
O -CNT
2
O -CNT
2
H
Mn
Mn
H
O
O
O
O
O
O
+
Ar
CH3
Ar
H
Ar
CH2
Ar
Ar
C
Ar
H
2
-
H O
2
Ar
Ar
Ar
O
MnO -CNT
NH
2
2
HC
H
NH
O
NH
HC
CX(NH2)2
-
H O
X
2
H N
2
X
Ar
O
Ar
N
H
X
Ar
C
H
Ar
H N
Ar
2
MnO -CNT
2
MnO -CNT
2
I
II
Scheme 2. Proposed reaction mechanism for the synthesis of dihydropyrimidinones.
◦
◦
◦
show that the catalyst activity slightly decreases for each run
Fig. 3).
Based on the above optimized results, we further examined
(Fig. 6b) at 12.54 , 37.19 and 65.71 of 2␪ can be perfectly indexed
(
as (0 0 1), (1 1 1) and (0 2 0) planes of MnO2 [32,33]. Furthermore,
the peaks corresponding to the structure of pristine CNTs at 26.16
becomes weak and the peak at 44.32 of 2ꢀ has disappeared simul-
taneously after the deposition of MnO , indicating that the surfaces
◦
◦
the effect of microwave power, and the irradiation time (Table 1)
on the Biginelli-like reaction, involving aromatic aldehyde, ketone
and urea to afford DHPM 4a, as shown in Scheme 1. When higher
powers are used degradation product is occurred that it lead to
the decrease in yields (Table 1, entries 5 and 6). In order to
examine the scope and generality of this procedure, we extended
the methodology to different aromatic aldehydes. Electron-rich
as well as electron- deficient aldehydes proved to be excellent
substrates for the cyclocondensation reaction. Table 2 shows that
various aromatic aldehydes and several aromatic ketones were
converted to the corresponding products in good yields and in short
time.
2
of CNTs are uniformly covered by MnO2.
The proposed mechanism in Scheme 2 illustrates that the
reaction may proceed through the activation of the carbonyl
functions by metal atom, so make the methyl group readily eno-
lisable for cross-aldol condensation of aldehyde and ketone to
form chalcone I. Then chalcone I react with urea in a Michael
type step to produce ureide II. Finally, intramolecular cycliza-
tion with loss of H O molecule, produce the corresponding
dihydropyriminones.
Compared to other commonly employed methods for the prepa-
ration of dihydropyrimidinones, the methodology presented herein
also provided a novel, convenient and efficient access to a wide
variety of 4,6-diaryl-3,4-dihydropyrimidine-2(1H)-ones in a one-
2
Fig. 4 shows the SEM and TEM images of acid-treated CNTs and
MnO -supported CNTs. It can be seen that the purified CNTs exhibit
2
regular morphology and smooth walls, as shown in Fig. 4a the mor-
phology of MnO -supported CNTs (in Fig. 4b and c) showed that
pot manner. However, we found that the addition of MnO –CNT
2
2
thin nanoscale MnO2 supporting uniformly shaped on the surface
of CNTs. No aggregations of MnO2 nanoparticles were observed in
nanocomposites accelerated the Biginelli-like reaction and gave a
good result. These results not only provide a new aspect of catalytic
the composite, indicating that the nucleation of MnO was predom-
organic reaction catalyzed by MnO –CNT nanocomposites, but also
2
2
inantly on the CNT surface.
extend the utility of ketones in Biginelli reactions. The structures
of the products were confirmed by IR, 1H NMR, mass spectral data
and comparison with authentic samples prepared according to the
literature methods.
FTIR spectra confirm the formation of MnO /CNTs composite.
Fig. 5 shows FTIR patterns of the pristine CNTs and the as-prepared
CNTs/MnO2 samples. It can be obviously found that a broad band
at low frequency region (around 500 cm ) in the composite is
revealed to the Mn O and Mn Mn vibrations [30].
2
−
1
O
XRD analysis can provide more information of the sample and
was further performed to illustrate the structure of the MnO –CNTs
2
composite. As shown in Fig. 6a, there are two diffraction peaks at 2ꢀ
◦
◦
values of 26.16 , 44.32 which can be well assigned to the (0 0 2) and
(
1 0 1) planes of graphite carbon [31]. Three broad diffraction peaks
Fig. 5. FT-IR spectra of (a) pristine CNTs and (b) MnO2/CNTs composite.
Fig. 6. XRD patterns of (a) pristine CNTs and (b) MnO2-supported CNTs composite.

J. Safari, S. Gandomi-Ravandi / Journal of Molecular Catalysis A: Chemical 373 (2013) 72–77
77
4
. Conclusions
[5] S.J. Haggarty, T.U. Mayer, D.T. Miyamoto, R. Fathi, R.W. King, T.J. Mitchison, S.L.
Schreiber, Chem. Biol. 7 (2000) 275–286.
[
[
6] C.O. Kappe, Eur. J. Med. Chem. 35 (2000) 1043–1052.
7] P.P. Baruah, S. Gadhwal, D. Prajapati, J.S. Sandhu, Chem. Lett. 10 (2002)
1038–1039.
8] Z. Wang, L. Xu, C. Xia, H. Wang, Tetrahedron Lett. 45 (2004) 7951–7953.
9] D. Russowsky, E.V. Benvenutti, G.S. Roxo, F. Grasel, Lett. Org. Chem. 4 (2007)
In conclusion, we successfully developed a simple, solventless
and efficient method for the synthesis of dihydropyrimidinone
derivatives by the rapid condensation of various aromatic alde-
hydes, ketones and urea using efficient and readily obtainable
[
[
39–42.
MnO –CNT nanocomposites as catalyst under microwave irradia-
[10] M. Gopalakrishnan, P. Sureshkumar, J. Thanusu, V. Kanagarajan, M.R. Ezhilarasi,
Lett. Org. Chem. 5 (2008) 142–147.
11] A. Arfan, L. Paquin, J. Bazureau, Russ. J. Org. Chem. 43 (2007) 1058–1064.
12] J.S. Wang, J.T. Li, Z.P. Lin, Lett. Org. Chem. 3 (2006) 523–525.
[13] L. Yang, X. Ren, F. Tang, L. Zhang, Biosens. Bioelectron. 25 (2009) 889–895.
[14] G. Yuan, J. Zheng, C. Lin, X. Chang, H. Jiang, Mater. Chem. Phys. 130 (2011)
2
tion. This simple procedure is efficient and can be applied to the
synthesis of a wide variety of dihydropyrimidinones in good to
excellent yields. The present work opens a new window towards
potential application nanocomposites in the field of catalysis and
developing various reactions.
[
[
387–391.
[
15] N. Bouazza, M. Ouzzine, M.A. Lillo-Ródenas, D. Eder, A. Linares-Solano, Appl.
Catal. B. 92 (2009) 377–383.
Acknowledgment
[16] J.L.G. Fierro, L.L.G. Fierro, Metal Oxides: Chemistry and Applications, CRC, Taylor
Francis, Boca Raton, 2006.
&
[
[
17] H.Y. Lee, J. Solid State Chem. 144 (1999) 220–223.
18] S.C. Pang, M.A. Anderson, T.W. Chapman, J. Electrochem. Soc. 147 (2000)
444–450.
We are grateful to University of Kashan for financial support by
grant no. 159198/16.
[
19] V. Subramanian, H.W. Zhu, B.Q. Wei, Electrochem. Commun. 8 (2006) 827–832.
20] S.L. Chou, J.Z. Wang, S.Y. Chew, H.K. Liu, S.X. Dou, Electrochem. Commun. 10
[
Appendix A. Supplementary data
(
2008) 1724–1727.
[
21] Z. Fan, J.H. Chen, M.Y. Wang, K.Z. Cui, H.H. Zhou, W. Kuang, Diamond Relat.
Mater. 15 (2006) 1478–1483.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
[
[
22] W. Chen, Z. Fan, L. Gu, X. Bao, C. Wang, Chem. Commun. 46 (2010) 3905–3907.
23] A.L.M. Reddy, M.M. Shaijumon, S.R. Gowda, P.M. Ajayan, J. Phys. Chem. C 114
(2010) 658–663.
2
013.02.021.
[
24] F. Teng, S. Santhanagopalan, Y. Wang, D.D. Meng, J. Alloys Compd. 499 (2010)
2
59–264.
References
[
[
25] G. Zhu, H. Li, L. Deng, Z.H. Liu, Mater. Lett. 64 (2010) 1763–1765.
26] L. Gong, L. Su, H. Jiang, Mater. Lett. 65 (2011) 1588–1590.
[
[
1] C.O. Kappe, Tetrahedron 49 (1993) 6937–6963.
2] K.S. Atwal, B.N. Swanson, S.E. Unger, D.M. Floyd, S. Moreland, A. Hedberg, B.C.
O’Reilly, J. Med. Chem. 34 (1991) 806–811.
[27] H. Wang, C. Peng, F. Peng, H. Yu, J. Yang, Mater. Sci. Eng. B 176 (2011) 1073–1078.
[28] Y.M. Ren, C. Cai, Monatsh. Chem. 140 (2009) 49–52.
[29] B. Liang, X. Wang, J.X. Wang, Z. Du, Tetrahedron 63 (2007) 1981–1986.
[30] X.F. Xie, L. Gao, Carbon 45 (2007) 2365–2373.
[31] H.J. Wang, L.L. Zhu, S. Peng, F. Peng, H. Yu, J. Yang, Renew. Energy 37 (2012)
192–196.
[32] Q.T. Qu, L. Li, S. Tian, W.L. Guo, Y.P. Wu, R. Holze, J. Power Sources 195 (2010)
2789–2794.
[33] Y.P. Lin, C.B. Tsai, W.H. Ho, N.L. Wu, Mater. Chem. Phys. 130 (2011) 367–372.
[
3] G.J. Grover, S. Dzwonczyk, D.M. McMullen, D.E. Normandin, C.S. Parham, P.G.
Sleph, S. Moreland, J. Cardiovasc. Pharmacol. 26 (1995) 289–294.
4] D. Nagarathnam, S.W. Miao, B. Lagu, G. Chiu, J. Fang, T.G.M. Dhar, J. Zhang, S.
Tyagarajan, M.R. Marzabadi, F.Q. Zhang, W.C. Wong, W.Y. Sun, D. Tian, J.M.
Wetzel, C. Forray, R.S.L. Chang, T.P. Broten, R.W. Ransom, T.W. Schorn, T.B.
Chen, S. O’Malley, P. Kling, K. Schneck, R. Benedesky, C.M. Harrell, K.P. Vyas,
C. Gluchowski, J. Med. Chem. 42 (1999) 4764–4777.
[