Sulfonated carbon catalyzed Biginelli reaction for one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones

Article abstract of DOI:10.1016/S1872-2067(11)60377-X

A sulfonated carbon material was shown to be a highly efficient, eco-friendly, and recyclable solid acid catalyst for the Biginelli reaction of β-ketoester, aldehyde, and urea or thiourea under solvent-free conditions. It gave 3,4-dihydropyrimidin-2(1H)-ones and -thiones in good to excellent yields. This method has the advantages of a simple procedure with easy work-up, short reaction time, and high yields. The catalyst can be recycled after a simple work-up and was reused four times without substantial reduction in activity.

Full text of DOI:10.1016/S1872-2067(11)60377-X

CHINESE JOURNAL OF CATALYSIS
Volume 33, Issue 4, 2012
Online English edition of the Chinese language journal
Cite this article as: Chin. J. Catal., 2012, 33: 706–710.
ARTICLE
Sulfonated Carbon Catalyzed Biginelli Reaction for One-Pot
Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and -thiones
Maryam MOGHADDAS1, Abolghasem DAVOODNIA1,*, Majid M. HERAVI2,
Niloofar TAVAKOLI-HOSEINI1
1Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
2Department of Chemistry, School of Sciences, Alzahra University, Vanak, Tehran, Iran
Abstract: A sulfonated carbon material was shown to be a highly efficient, eco-friendly, and recyclable solid acid catalyst for the Biginelli
reaction of ꢀ-ketoester, aldehyde, and urea or thiourea under solvent-free conditions. It gave 3,4-dihydropyrimidin-2(1H)-ones and -thiones
in good to excellent yields. This method has the advantages of a simple procedure with easy work-up, short reaction time, and high yields.
The catalyst can be recycled after a simple work-up and was reused four times without substantial reduction in activity.
Key words: sulfonated carbon; solid acid; Biginelli reaction; heterogeneous catalysis; solvent-free condition
The Biginelli synthesis is an easy and useful multicompo-
nent reaction that is gaining increasing importance in organic
and medicinal chemistry for its generation of multifunctional-
ized products, including 3,4-dihydropyrimidin-2(1H)-ones and
their thione analogs and other related heterocyclic compounds
[1,2]. Dihydropyrimidinones and thiones are important for
their therapeutic and pharmacological properties. They are
used in several calcium channel blockers [3], antihypertensive
drugs [4], ꢀ1a-adrenergic antagonists [5], and neuropeptide
antagonists [6]. Recently, dihydropyrimidinones have also
been considered for the development of new anticancer drugs
[7]. In addition, their special structure has been found in natural
marine alkaloid batzelladines, which are the first low molecular
weight natural products reported in the literature that inhibits
the binding of HIVgp-120 to CD4 cell. This could be a new
path for the development of AIDS therapy [8,9]. Thus, the
efficient synthesis of these heterocyclic compounds has been of
great interest in recent years.
acid (TCCA) [15], M(NTf)2 (M = Ni, Cu, Yb) [16], Fe(ClO4)3
[17], RuCl3 [18], ZrCl4 [19,20], ZrOCl2 [20], H3PMo12O40 [21],
and H3PW12O40 [21,22]. However, many of the reported
one-pot protocols involved long reaction time and have unsat-
isfactory yields, cumbersome product isolation procedures, use
of harmful organic solvents, expensive reagents, stoichiometric
amounts of catalysts, strongly acidic conditions, and envi-
ronmental pollution. Due to the importance of the Biginelli
reaction, the introduction of milder, faster, and greener meth-
ods with higher yields is needed.
The replacement of conventional toxic and polluting Brøn-
sted and Lewis acid catalysts with environmentally benign and
reusable solid catalysts is an active area of research. Solid acid
catalysts have the advantages of ease of product separation,
recycling of the catalyst, and environmental compatibility as
compared to liquid acid catalysts [23–26]. Sulfonated carbon
materials (SCMs) as solid acid catalysts have many advantages.
They are insoluble in common organic solvents, hardly cause
corrosion, and have environmental compatibility. Also, the
products can be easily separated from the reaction mixture and
the catalyst is recoverable without loss in activity. They have
been successfully used to replace sulfuric acid as catalysts
[27–31].
The most straightforward procedure for the preparation of
dihydropyrimidinones and thiones is by condensation of
ꢀ-dicarbonyl compounds with an aromatic aldehyde and urea
or thiourea in the presence of Lewis and Brønsted acid pro-
moters such as concentrated H2SO4 [10], HEU type zeolite [11],
InBr3 [12], CuI [13], [bmim][FeCl4] [14], trichloroisocyanuric
There is no example on the use of SCMs as catalyst for the
Received 19 October 2011. Accepted 17 February 2012.
*Corresponding author. Tel: +98-511-8435000; Fax: +98-511-8424020; E-mail: adavoodnia@mshdiau.ac.ir, adavoodnia@yahoo.com
This work was supported by Islamic Azad University, Mashhad Branch.
Copyright © 2012, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved.
DOI: 10.1016/S1872-2067(11)60377-X

Maryam MOGHADDAS et al. / Chinese Journal of Catalysis, 2012, 33: 706–710
The separated catalyst was washed with cold ethanol, dried at
R'
60 °C under vacuum for 1 h, and was reused. The product was
collected from the filtrate after cooling to room temperature
and recrystallized from the ethanol to give compounds 4a–4t.
Melting points were recorded with an electrothermal Type
9100 melting point apparatus. The infrared (IR) spectra were
obtained using a 4300 Shimadzu spectrophotometer and KBr
O
R
R'
O
H
O
R
EtO
NH
2
NH2
X
EtO
N
H
4a 4t
X
+
H2N
ꢀ
O
3
1
1
disks. The H NMR (500 MHz) spectra were recorded with a
Solvent-free
140 oC
Bruker DRX500 spectrometer.
4a (R = Me, R' = 3-BrC6H4, X = O). H NMR (500 MHz,
1
DMSO-d6): ꢀ 1.10 (t, 3H, J = 7.0 Hz, CH3), 2.25 (s, 3H, CH3),
3.95–4.05 (m, 2H, CH2), 5.14 (d, 1H, J = 3.2 Hz, CH), 7.23 (d,
1H, J = 7.7 Hz, arom-H), 7.31 (t, 1H, J = 7.8 Hz, arom-H), 7.39
(s, 1H, arom-H), 7.45 (dt, 1H, J = 7.9, 0.9 Hz, arom-H), 7.77 (s,
1H, NH), 9.25 (s, 1H, NH); IR (KBr, cm–1): ꢁ 3238 (NH), 3114
(NH), 1706 (C=O), 1654 (C=O).
SO3H
Scheme 1. Biginelli reaction catalyzed by SCM.
1
4c (R = Me, R' = 4-ClC6H4, X = O). H NMR (500 MHz,
synthesis of dihydropyrimidinones and thiones. In a continua-
tion of our previous works on the applications of reusable
catalysts in the synthesis of organic compounds [32–41], we
report here a novel, heavy metal-free, and recyclable catalyst
SCM for the efficiently synthesis of 3,4-dihydropyrimidin-
2(1H)-ones and -thiones (Scheme 1).
DMSO-d6): ꢀ 1.09 (t, 3H, J = 7.1 Hz, CH3), 2.25 (s, 3H, CH3),
3.95–4.05 (m, 2H, CH2), 5.15 (d, 1H, J = 3.2 Hz, CH), 7.25 (d,
2H, J = 7.7 Hz, arom-H), 7.39 (d, 2H, J = 7.7 Hz, arom-H),
7.75 (s, 1H, NH), 9.22 (s, 1H, NH); IR (KBr, cm–1): ꢁ 3233
(NH), 3114 (NH), 1703 (C=O), 1650 (C=O).
1
4d (R = Me, R' = 4-FC6H4, X = O). H NMR (500 MHz,
DMSO-d6): ꢀ 1.09 (t, 3H, J = 7.2 Hz, CH3), 2.25 (s, 3H, CH3),
3.95–4.00 (m, 2H, CH2), 5.14 (d, 1H, J = 3.2 Hz, CH),
7.10–7.30 (m, 4H, arom-H), 7.73 (s, 1H, NH), 9.20 (s, 1H, NH);
IR (KBr, cm–1): ꢁ 3238 (NH), 3079 (NH), 1703 (C=O), 1650
(C=O).
1 Experimental
1.1 Preparation of SCM
4g (R = Me, R' = 4-MeOC6H4, X = O). 1H NMR (500 MHz,
CDCl3): ꢀ 1.10 (t, 3H, J = 7.1 Hz, CH3), 2.27 (s, 3H, CH3), 3.72
(s, 3H, CH3O), 3.99 (q, 2H, J = 7.1 Hz, CH2), 5.25 (d, 1H, J =
2.4 Hz, CH), 6.20 (s, 1H, NH), 6.75 (d, 2H, J = 8.7 Hz,
arom-H), 7.18 (d, 2H, J = 8.7 Hz, arom-H), 8.38 (s, 1H, NH);
IR (KBr, cm–1): ꢁ 3247 (NH), 3118 (NH), 1703 (C=O), 1649
(C=O).
The SCM was prepared according to the procedure reported
by Hara et al. [31]. Naphthalene (20 g) was heated in concen-
trated sulfuric acid (> 96%, 200 ml) at 250 °C under a flow of
N2. After heating for 15 h, excess sulfuric acid was removed
from the dark brown tar by vacuum distillation at 250 °C for 5 h,
which resulted in a black solid. The solid was then ground to a
powder and was washed repeatedly in boiling water until im-
purities such as sulfate ions were no longer detected in the
wash water. The density of the SO3H groups was measured
using NaOH (0.01 mol/L) as titrant by acid-base potentiomet-
ric titration. The amount of SO3H attached to the polycyclic
aromatic carbon was 2.84 mmol/g. The resulting black powder
was insoluble in solvents such as water, methanol, ethanol,
benzene, and hexane even at their boiling temperatures.
1
4k (R = Me, R' = 4-ClC6H4, X = S). H NMR (500 MHz,
DMSO-d6): ꢀ 1.10 (t, 3H, J = 7.1 Hz, CH3), 2.29 (s, 3H, CH3),
3.95–4.05 (m, 2H, CH2), 5.17 (s, 1H, CH), 7.22 (d, 2H, J = 8.3
Hz, arom-H), 7.42 (d, 2H, J = 8.3 Hz, arom-H), 9.65 (s.br., 1H,
NH), 10.36 (s.br., 1H, NH); IR (KBr, cm–1): ꢁ 3328 (NH), 3175
(NH), 1673 (C=O).
4m (R = Me, R' = 4-MeOC6H4, X = S). 1H NMR (500 MHz,
DMSO-d6): ꢀ 1.11 (t, 3H, J = 7.1 Hz, CH3), 2.28 (s, 3H, CH3),
3.72 (s, 3H, CH3O), 4.00 (q, 2H, J = 7.1 Hz, CH2), 5.11 (d, 1H,
J = 3.6 Hz, CH), 6.89 (d, 2H, J = 8.6 Hz, arom-H), 7.12 (d, 2H,
J = 8.6 Hz, arom-H), 9.57 (s, 1H, NH), 10.26 (s, 1H, NH); IR
(KBr, cm–1): ꢁ 3314 (NH), 3171 (NH), 1667 (C=O).
1.2 General procedure for the synthesis of
3,4-dihydropyrimidin-2(1H)-ones and -thiones
A mixture of ꢁ-ketoester (1, 4 mmol), an aldehyde (2, 4
mmol), urea or thiourea (3, 5 mmol), and SCM (0.1 g) was
heated in the oil bath at 140 °C for the appropriate time. The
progress of the reaction was monitored by TLC. Upon com-
pletion, the reaction mixture was cooled to room temperature
and hot ethanol was added. The catalyst was insoluble in hot
ethanol and it could therefore be recycled by simple filtration.
2 Results and discussion
Solvent-free conditions are especially important for pro-
viding an eco-friendly system. The number of publications
reporting solvent-free conditions for heterocyclic synthesis has

Maryam MOGHADDAS et al. / Chinese Journal of Catalysis, 2012, 33: 706–710
Table 1 Effect of SCM amount and temperature on the synthesis of
compound 4c under solvent-free conditions
Table 2 Synthesis of compound 4c in the presence of SCM in different
solvents
Entry
1
2
3
4
5
6
7
8
Catalyst (g) Temperature (oC) Time (min) Yield* (%)
Solvent
EtOH
CH3CN
CHCl3
THF
Solvent-free
Temperature (oC)
reflux
Time (h)
Yield* (%)
—
140
140
140
140
140
140
25
180
30
30
30
30
40
30
30
30
30
30
40
—
63
6
8
10
12
0.5
38
25
15
10
92
0.05
0.08
0.10
0.15
0.20
0.10
0.10
0.10
0.10
0.10
0.10
reflux
reflux
reflux
140
78
92
85
72
none
21
63
78
92
Other conditions: ethyl acetoacetate 4 mmol, 4-chlorobenzaldehyde 4
mmol, urea 5 mmol, SCM 0.1 g. *Isolated yields.
60
4-chlorobenzaldehyde, and urea in the presence of SCM. The
efficiency of the reaction was affected by the amount of SCM
(Table 1, entries 1–6)). No product was obtained in the absence
of the catalyst (entry 1), indicating that the catalyst was nec-
essary for the reaction. The optimal amount of the catalyst was
0.1 g (entry 4). Larger amounts of the catalyst were found to
have an inhibitory effect on formation of the product (entries 5
and 6).
The same reaction in the presence of 0.1 g of the catalyst was
carried out at different temperatures under solvent-free condi-
tions to assess the effect of temperature on the reaction yield.
The yield increased as the reaction temperature was raised. At
140 ºC, product 4c was obtained in high yield within 30 min. A
further increase in temperature and time did not improve the
product yield (entries 11 and 12).
9
100
120
150
150
10
11
12
92
Other conditions: ethyl acetoacetate 4 mmol, 4-chlorobenzaldehyde 4
mmol, urea 5 mmol. *Isolated yields.
increased rapidly in recent years [42]. One advantage of sol-
vent-free reactions, in comparison to reactions in solvents, is
that the compounds formed are often pure enough to circum-
vent the need for purification using chromatography. Further,
the use of a heterogeneous catalyst is an environmentally clean
technique for the synthesis of organic compounds. Therefore,
we investigated the efficiency of a SCM as a solid acid catalyst
for the synthesis of dihydropyrimidinones and thiones under
solvent-free conditions.
For showing the effect of the solvent, the same reaction was
also carried out in different solvents including EtOH, CH3CN,
CHCl3, and tetrahydrofuran (THF) in the presence of 0.1 g of
the catalyst. As shown in Table 2, the yield under solvent-free
To find the optimal conditions, the synthesis of compound 4c
was used as a model reaction (Table 1). The reaction was car-
ried out by heating a mixture of ethyl acetoacetate,
Table 3 SCM catalyzed synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones 4a–4t
Melting point (oC)
Entry
R
R'
X
Product
Time (min)
Yield* (%)
Found
Reported
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Ph
3-BrC6H4
2-ClC6H4
4-ClC6H4
4-FC6H4
3-HOC6H4
4-HOC6H4
4-MeOC6H4
4-MeC6H4
3-NO2C6H4
4-NO2C6H4
4-ClC6H4
4-HOC6H4
4-MeOC6H4
4-MeC6H4
Me
O
O
O
O
O
O
O
O
O
O
S
S
S
S
O
O
O
O
S
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
30
30
30
30
30
30
25
15
30
30
20
20
20
20
30
30
30
30
30
30
85
86
92
88
82
88
83
89
85
82
88
86
82
85
88
90
88
81
80
85
195–197
220–222
215–217
178–180
168–170
236–238
203–205
210–212
223–225
208–210
192–193
200–202
158–160
212–214
192–194
170–172
153–155
152–154
185–187
150–152
195–196 [14]
222–224 [12]
212–214 [12]
173–176 [19]
163–165 [12]
230–232 [12]
198–200 [19]
216–218 [14]
232–234 [14]
206–208 [19]
192–194 [12]
193-194 [19]
150–152 [12]
192–194 [12]
194–195 [12]
171–174 [17]
152–154 [17]
152–155 [15]
183–185 [20]
151–152 [20]
Et
n-Pr
Ph
Ph
Ph
Ph
4-MeOC6H4
S
4t
Other conditions: ꢁ-ketoester 4 mmol, aldehyde 4 mmol, urea or thiourea 5 mmol, SCM 0.1 g, 140 ºC. *Isolated yields.

Maryam MOGHADDAS et al. / Chinese Journal of Catalysis, 2012, 33: 706–710
Table 4 Comparison of the efficiency of various catalysts in the synthe-
sis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones
94
92
90
88
86
84
82
80
Conditions
Solvent
Time
(h)
Yield
(%)
Catalyst
Ref.
T/oC
100
HEU type zeolite
InBr3
CuI
CuI
[bmim][FeCl4]
TCCA
M(NTf)2
RuCl3
H3PMo12O40
H3PW12O40
SCM
AcOH
EtOH
4–12
7–36
0.75–2
4–6
2–3
8–12
24
0.5–1.5
3.5–9
6–7
44–87
68–98
70–87
65–73
68–92
46–95
25–80
74–93
63–97
40–75
[11]
[12]
[13]
[13]
[14]
[15]
[16]
[18]
[21]
[22]
reflux
CH3CN reflux
H2O
—
reflux
90
EtOH
H2O, HCl
—
reflux
r.t.
100
CH3CN reflux
1
2
3
4
5
Reaction cycle
AcOH
—
reflux
140
0.25–0.5 80–92 this work
Fig. 1. Reusability of SCM for the synthesis of compound 4c.
conditions was more, and the reaction time was considerably
shorter.
tions in a solvent.
The reusability of the catalyst was also investigated with the
same model reaction again studied under the optimized condi-
tions. After the completion of the reaction, the catalyst was
recovered according to the procedure described in the experi-
mental section and reused. As shown in Fig. 1, the catalyst
could be reused at least four times with only a slight reduction
in activity.
A reaction mechanism is proposed in Scheme 2. SCM ꢂ HA
facilitates the formation of the intermediate I by Knoevenagel
condensation of ꢁ-ketoester 1 and aldehydes 2, and I after
dehydration gives the olefin II. Nucleophilic attack of the
amino group in urea or thiourea at the ꢁ-carbon of the
ꢀ,ꢁ-unsaturated carbonyl group followed by cyclization yields
the products 4a–4t. Under these conditions, attempts to isolate
the intermediates I and II failed even after careful monitoring
of the reactions.
To show the generality of this model reaction, a range of
dihydropyrimidinones and thiones were prepared by the reac-
tion of different ꢁ-ketoesters, including ethyl acetoacetate and
ethyl benzoylacetate, different aliphatic and aromatic alde-
hydes, and urea or thiourea under optimized reaction condi-
tions. In all cases, the reactions proceeded successfully and
gave the expected products in good to high yields in short
reaction time (Table 3). The type of ꢁ-ketoesters and aliphatic
or aromatic aldehydes had no significant effect on the reaction
time and yield.
Compared to other methods reported for the synthesis of
dihydropyrimidinones and thiones, the present method offers
more suitable conditions with good yields. Some of the results
are summarized in Table 4, which shows that the reactions
under solvent-free conditions gave better results than the reac-
HA
O
R'
HO
R'
O
R
R'
H
H
O
O
R'
O
2
HA
EtO
EtO
EtO
OH
O
H
R
O
EtO
HA
EtO
II
I
R
O
R
OH
HA
1
X
O
R
O
R
R'
R'
O
R
R'
H
N
H
N
X
X
H2N
NH2
EtO
EtO
NH2
NH2
3
OH
O
OH
HA
O
R
HO
HA
R'
O
R'
O
R'
N
H
H
N
X
EtO
NH
EtO
EtO
NH
NH2
N
H
X
R
OH
R
X
H
ꢀ
4a 4t
Scheme 2. Mechanism for the formation of 3,4-dihydropyrimidin-2(1H)-ones and -thiones in the presence of SCM ꢂ HA as catalyst.

Maryam MOGHADDAS et al. / Chinese Journal of Catalysis, 2012, 33: 706–710
7861
3 Conclusions
17 Heravi M M, Behbahani F K, Oskooie H A. Chin J Chem,
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We developed a very simple and efficient method for the
synthesis of dihydropyrimidin-2(1H)-ones and -thiones by a
three-component reaction of ꢁ-ketoesters, aldehydes, and urea
or thiourea in the presence of a SCM as catalyst under sol-
vent-free conditions. The catalyst can be recycled after a sim-
ple work-up, and was reused at least four times without sub-
stantial reduction in activity. High yields, short reaction time,
easy work-up, and absence of a volatile and hazardous organic
solvent are a few advantages of this procedure.
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