Synthesis of 3,4-dihydropyrimidin-2-ones (DHPMs) using mesoporous aluminosilicate (AlKIT-5) catalyst with cage type pore structure

Article abstract of DOI:10.1016/j.tet.2009.10.074

Here we demonstrate on the synthesis of 3,4-dihydropyrimidin-2-ones (DHPMs) and their derivatives through a three-component condensation reactions of aldehyde, β-ketoester and urea or thiourea using mesoporous aluminosilicate (AlKIT-5) nanocage as catalyst and acetonitrile as solvent under reflux conditions. The catalyst was found to be highly active and selective, affording a high yield of DHPMs. Compared to the classical Biginelli reaction conditions, this new approach consistently has the advantage of excellent yields (80-96%) and short reaction times, 3.0-4.0 h. The effect of the acidity and the concentration of the catalyst on the above process was investigated. We also demonstrate the synthesis of various multifunctional Biginelli compounds using the highly active AlKIT-5 catalysts.

Full text of DOI:10.1016/j.tet.2009.10.074

Tetrahedron 65 (2009) 10608–10611
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Tetrahedron
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Synthesis of 3,4-dihydropyrimidin-2-ones (DHPMs) using mesoporous
aluminosilicate (AlKIT-5) catalyst with cage type pore structure
,
D. Shobha a, M.A. Chari b, A. Mano b, S.T. Selvan b, K. Mukkanti a, A. Vinu b
*
a Centre for Pharmaceutical Science, Jawaharlal Nehru Technological University, Kukatpally, Hyderabad, Andhra Pradesh 500-072, India
b International Center for Materials Nanoarchitectonics, World Premier International Research Center, National Institute for Materials Science, 1-1, Namiki, Tsukuba,
Ibaraki 305-0044, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Here we demonstrate on the synthesis of 3,4-dihydropyrimidin-2-ones (DHPMs) and their derivatives
Received 2 September 2009
Received in revised form
21 October 2009
Accepted 21 October 2009
Available online 25 October 2009
through a three-component condensation reactions of aldehyde, b-ketoester and urea or thiourea using
mesoporous aluminosilicate (AlKIT-5) nanocage as catalyst and acetonitrile as solvent under reflux
conditions. The catalyst was found to be highly active and selective, affording a high yield of DHPMs.
Compared to the classical Biginelli reaction conditions, this new approach consistently has the advantage
of excellent yields (80–96%) and short reaction times, 3.0–4.0 h. The effect of the acidity and the con-
centration of the catalyst on the above process was investigated. We also demonstrate the synthesis of
various multifunctional Biginelli compounds using the highly active AlKIT-5 catalysts.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
DHPMs
Mesoporous
Catalysis
Acidity
Adsorption
Cage
1. Introduction
occurrence of several side reactions, drastic reaction conditions and
tedious workup procedure. In addition, the solid oxide catalyst used
Aryl substituted 3,4-dihydropyrimidin-2-ones (DHPMs) and
their derivatives have been receiving much attention in the recent
years owing to their enormous application in the field of drugs and
pharmaceuticals.1 They also exhibit a wide range of biological ac-
tivities2 and are extensively used in the pharmaceutical industry as
previously had poor textural parameters such as low surface area
and pore volume, which do not support a better performance in the
synthesis of DHPMs. These factors stimulate us to search for a better
catalyst, which has to offer a high activity for the synthesis of
DHPMs under mild reaction conditions.
calcium channel blockers, antihypertensive,
a
-antagonist, antibac-
Recently, the use of heterogeneous catalysts26–31 has received
considerable importance in organic synthesis because of their ease
of handling, enhanced reaction rates, greater selectivity, simple
workup and recoverability of catalysts. Especially, mesoporous
heterogeneous catalysts have been receiving much attention in the
field of organic syntheses and catalysis owing to their excellent
textural characteristics and well-ordered mesostructure with uni-
form pores.29,32–37 Among the mesoporous solid acid catalysts,
materials with three-dimensional (3D) mesopore structures are
found to be more advantageous than the catalysts with one-di-
mensional (1D) mesoporous structure as the former can offer more
resistant to pore locking and allow faster diffusion of reactants,
which are highly necessary to obtain a stable and a high catalytic
activity.36,38–40 Dubey et al. reported the synthesis of 3,4-dihy-
dropyrimidine-2(1H)-ones in the liquid phase using SBA-15
impregnated with Al as catalyst, which was prepared by post-
synthetic grafting method.41 As the catalyst was prepared by post-
synthesis grafting method, there is a possibility that the Al species
terial, antiviral, antitumour, antiinflammatory and HIV agents.3,4
DHPMs are generally synthesized by the Biginelli reaction pathway,
which involves the one-pot condensation of an aldehyde,
b
-ketoester and urea or thiourea5 using acidic catalysts. Several
reports are available on the synthesis of DHPMs. In most of the
cases, homogenous catalysts such as concentrated HCl, BF3$OEt2,
clays, InCl3, LaCl3, lanthanide triflate, H2SO4, ceric ammonium ni-
trate, Mn(OAc)3, ion-exchange resin, 1-n-butyl-3-methyl imidazo-
lium tetra fluoroborate, BiCl3, LiClO4, InBr3, FeCl3, ZrCl4, Cu(OTf)2,
Bi(OTf)3, LiBr, ytterbium triflates, NH4Cl, MgBr2 and other reagents
have been used for this transformation.6–25 Homogenous catalyst
supported on the solid matrix has also been used for the synthesis
of DPHMs.21 Unfortunately, many of these catalysts suffer from one
or more limitations, such as long reaction times, low yields,
* Corresponding author. Tel.: þ81 29 860 4563; fax: þ81 29 860 4706.
E-mail address: vinu.ajayan@nims.go.jp (A. Vinu).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.10.074

D. Shobha et al. / Tetrahedron 65 (2009) 10608–10611
10609
may be leached out during the reaction. Recently, Vinu et al.
reported the direct synthesis of aluminium incorporated meso-
porous KIT-5 material (AlKIT-5), which possesses 3D mesostructure
with Fm3m symmetry and a high acidity and a large pore di-
ameter.39,40 Although these materials possess interesting textural
and catalytic properties, unfortunately, with the best of our
knowledge, there has been no report available on the synthesis of
DHPMs using such materials as catalysts in the open literature so
far. Here, we demonstrate a simple, convenient and efficient
method for the synthesis of DHPMs under acetonitrile solvent using
AlKIT-5 catalyst through one-pot condensation reaction of alde-
reaction conditions. It has been also found that the activity of our
catalyst is much better than the reported catalysts such as AlSBA-
15, Amberlyst-70 and MCM-41-R-SO3H.30,31,41
The effect of the catalyst concentration on the synthesis of
DHPMs was also investigated over different amounts of AlKIT-5(10)
at reflux temperature for 3.0 h and the results are presented in
Table 2. It has been found that the concentration of the catalyst
significantly alters the outcome of the final product. The yield of the
final product increases from 40 to 96% with increasing the weight of
the catalyst from 50 to 200 mg, respectively. This could be mainly
hyde, b-ketoester and urea or thiourea.
Table 2
Effect of the weight of AlKIT-5(10) on the synthesis of DHPMs
2. Results and discussion
Weight of AlKIT-5(10) (mg)
Reaction time (h)
Yield (%)
50
3.0
3.0
3.0
3.0
40
72
96
96
Initially we performed the Bignelli’s one-pot condensation
reaction of benzaldehyde (106 mg, 1.0 mmol) with ethyl acetoace-
tate (156 mg, 1.2 mmol) and urea (72 mg, 1.2 mmol) using AlKIT-
5(10)42,43 catalyst (150 mg) under reflux and acetonitrile solvent
conditions for 3 h (Scheme 1).
100
150
200
Reaction conditions: substrate¼aldehydes, ethyl acetoacetate, urea or thiourea,
reaction temperature¼reflux, solvent¼acetonitrile.
O
R
X
O
O
AlKIT-5(10)
R2
NH
+
+
RCHO
H2N
NH2
R1
R2
R1
N
H
O
CH3CN, Reflux
3
2
1
4
R1= Me, Ph
R2= OMe, OEt
X = O,S
Scheme 1. Synthesis of 3,4-dihydropyrimidin-2-ones.
The catalyst was found to be highly active, affording 96% isolated
yield of 4a in 3 h. It must be noted that no product was obtained
when the reaction was carried out without any catalyst. In order to
understand the role of acidity of AlKIT-5 on the yield of the final
product, we carried out the synthesis of DPHMs using AlKIT-5 with
different acidity. The acidity of the materials was controlled by
simple adjustment of the amount of Al content in the silica
framework of KIT-5. As can be seen in Table 1, the acidity of the
materials increases with increasing the Al content in the silica
matrix. Table 1 also shows the textural parameters including spe-
cific surface area, pore volume and pore diameter of the AlKIT-5
samples with different Al contents. The specific surface area, pore
volume, pore diameter, cage diameter and the acidity of the AlKIT-
5(10) are found to be 989 m2/g, 0.68 cm3/g, 6 nm, 12 nm, and
0.51 mmol of NH3/g, respectively. The detailed characterization
results of the materials and their discussion can be found in our
earlier reports.39,40 As expected, the activity of the catalyst in-
creases with increasing the amount of Al content in AlKIT-5, con-
firming the role of acidity of the catalyst in this transformation.
Among the AlKIT-5 catalysts studied, AlKIT-5(10) was found to be
highly active, which exhibits better textural parameters and higher
acidity than those of other materials used in the study and has been
used for the remaining catalytic studies under the optimized
due to the availability of huge number of surface acidic sites in the
reactant mixture as the weight of the catalyst is increased.
The synthesis43,44 of various DHPMs using several aromatic and
aliphatic aldehydes under the optimized conditions was also car-
ried out using AlKIT-5(10) catalyst (150 mg) and results are sum-
marized in Table 3. The reaction proceeded very smoothly in
refluxing conditions with the AlKIT-5(10) catalyst and all the
reactions were almost completed within 3–4 h of reaction time. The
catalyst showed an excellent activity in all the cases, showing 80–
96% isolated yield of the corresponding derivatives of DHPMs.
Another important feature of this procedure is the stability of
a variety of functional groups such as ether, hydroxy, halides, nitro,
etc., under these reaction conditions. This procedure not only
preserves the simplicity of Biginelli reaction but also produces
DHPMs in excellent yields. Thus this procedure offers an easy access
to substituted DHPMs with a variety of substitution patterns.
The effect of solvents on the synthesis of DPHMs was also in-
vestigated. Among various solvents like acetonitrile, methanol,
methylene chloride and THF studied, methanol and acetonitrile
were found to be the excellent solvent for this transformation.
Thiourea has also been used to obtain the corresponding thio de-
rivatives of dihydropyrimidinones, which were reported to have
good biological activities.3 Thiophene, furfural, cinnamal aldehydes
Table 1
Textural parameters, acidity and the catalytic activity of the AlKIT-5 catalysts with different Al contents
Catalyst
a0 (nm)
nSi/nAl
SBET (m2/g)
Vp (cm3/g)
Dpads, BJH
(nm)
Cage diameter
(nm)
Acidity
(mmol/g)
Yield
(%)
Gel
Product
AlKIT-5(10)
AlKIT-5(28)
AlKIT-5(44)
18.44
17.76
16.97
7
10
12
10
28
44
989
815
713
0.68
0.56
0.45
6.0
5.6
5.2
12.0
11.2
10.3
0.50
0.32
0.14
96
81
60
ao unit cell constant; SBET specific surface area; Vp specific pore volume; Dp pore diameter; reaction conditions: substrate¼benzaldehyde, ethyl acetoacetate and urea, weight
of the catalyst¼150 mg, reaction temperature¼reflux, solvent¼acetonitrile.

10610
D. Shobha et al. / Tetrahedron 65 (2009) 10608–10611
Table 3
Community Scheme and World Premier International Research
Center (WPI) Initiative on Materials Nanoarchitectonics, MEXT,
Japan.
Mesoporous aluminosilicate-AlKIT-5(10) catalyzed synthesis of dihydropyr-
imidinones and thio derivatives
Entry
Aldehyde
X
R1
R2
Product
Time
(h)
Yield
(%)
1
2
3
4
5
6
7
8
C6H5CHO
O
O
O
O
O
O
O
O
O
O
O
O
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
4a
4b
4c
4d
4e
4f
4g
4h
4i
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
96
96
93
86
88
89
84
88
83
82
88
92
References and notes
o-NO2C6H4CHO
p-NO2C6H4CHO
m-NO2C6H4CHO
p-ClC6H4CHO
p-CH3OC6H4CHO
m-(C6H5O)C6H4CHO
2-OHC6H4CHO
3-OHC6H4CHO
5-Cl-2-OHC6H4CHO
C6H4CH]CHCHO
2-Thiophene
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10
11
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4j
4k
4l
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Furfuraldehyde
C6H5CHO
C6H5CHO
C6H5CHO
o-NO2C6H4CHO
p-NO2C6H4CHO
m-NO2C6H4CHO
p-ClC6H4CHO
p-CH3OC6H4CHO
m-(C6H5O)C6H4CHO
2-OHC6H4CHO
3-OHC6H4CHO
5-Cl-2-OHC6H4CHO
C6H4CH]CHCHO
2-Thiophene
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13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
O
O
O
S
S
S
S
S
S
S
S
S
S
S
S
Me
Me
Ph
OEt
OMe
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
4m
4n
4o
4p
4q
4r
3.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
92
86
90
91
91
88
80
88
82
84
84
82
82
86
90
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
4s
4t
4u
4v
4w
4x
4y
4z
4
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carboxaldehyde
Furfuraldehyde
C6H5CHO
28
29
30
S
S
S
Me
Me
Ph
OEt
OMe
OEt
4
4
4
4.0
4.0
4.0
90
82
88
C6H5CHO
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the references cited therein.
and meta-phenoxy benzaldehyde also worked well to synthesize
multifunctionalised DHPMs using AlKIT-5(10).
It is also important to note that the workup of the reaction
mixture is very simple. The catalyst can be filtered out easily and
the solvent was evaporated. Recycling experiments were conducted
to find out the stability of the catalyst after the reaction. The cat-
alyst was easily separated by centrifugation and reused after acti-
vation at 500 ꢀC for 3–4 h. The efficiency of the recovered catalyst
was verified with the Biginelli reaction (entry 1). Using the fresh
catalyst, the yield of product (4a) was 96%, while the recovered
catalyst in the three subsequent recycling experiments gave the
yields of 95, 92 and 90%, respectively. These results reveal that the
catalyst can be recycled several times without losing much activity.
In summary, we have developed a simple, convenient and
effective method for the synthesis of DPHMs and their derivatives
21. (a) Amini, M. M.; Shaabani, A.; Bazgir, A. Catal. Commun. 2006, 7, 843; (b) Chen,
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using substituted aldehydes, b-ketoester, urea or thiourea at reflux
temperature using 3D mesoporous aluminosilicate catalyst with
cage type pore. This method is applicable to a wide range of sub-
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strates including aromatic, aliphatic, a,b-unsaturated and hetero-
cyclic aldehydes. The catalyst gave a high isolated yield of the
DHPMs in a shorter reaction time at reflux temperature and can be
recycled several times. The mesoporous AlKIT-5 catalysts are
promising heterogeneous catalysts in all circumstances where the
aluminosilicate matrix is highly stable and we strongly hope that
this catalyst could also be used for other acid catalyzed organic
transformation and help to replace the existing toxic, corrosive and
expensive homogenous catalysts.
42. Experimental section: all chemicals and solvents were obtained from Aldrich
and used without further purification. Column chromatographic separations
were carried out on silica gel 100–200 mesh size. The 1H NMR spectra of
samples were recorded on a JEOL 300 MHz NMR spectrometer using TMS as an
internal standard in CDCl3. Mass spectra were recorded on a MALDI-MS. FT-IR
Acknowledgement
This work was financially supported by the Ministry of Educa-
tion, Culture, Sports, Science and Technology (MEXT) under the
Strategic Program for Building an Asian Science and Technology
spectra of all the final products were recorded on
a Perkin Elmer 100
instrument by averaging 50 scans with a resolution of 2 cmꢁ1 measuring in
absorbance mode by using the KBr self-supported pellet technique.

D. Shobha et al. / Tetrahedron 65 (2009) 10608–10611
10611
43. Preparation of the catalyst: the AlKIT-5 materials with different nSi/nAl ratios
were synthesized using polymeric Pluronic F127 as a template, and tetraethyl
orthosilicate (TEOS) and aluminium isopropoxide as the sources of silicon and
aluminium, respectively. In a typical synthesis, pluronic F127 (5 g) was dis-
solved in concd HCl (3 g, 35 wt %) and distilled water (240 g). To this mixture,
TEOS (24 g) and the required amount of the aluminium source were added, and
the resulting mixture was stirred for 24 h at 45 ꢀC. Subsequently, the reaction
mixture was heated for 24 h at 100 ꢀC under static condition for hydrothermal
treatment. After hydrothermal treatment, the final solid product was filtered
off and then dried at 100 ꢀC without washing. The white coloured product was
calcined at 540 ꢀC for 10 h. The samples are denoted as AlKIT-5(x) where x
denotes the nSi/nAl ratio in the final product. The molar gel composition of the
reaction mixture was 1.0:0.041–0.071:0.0035:0.25:116.6 SiO2–Al2O3–F127–
HCl–H2O.39,40
TLC. The reaction mixture was then poured onto crushed ice and the solid
product separated was filtered and recrystallized from methanol. All products
were characterized by spectral (NMR and IR) data and by comparison with
those of authentic samples and also by the melting points of the samples mixed
with the authentic ones18. The spectral data of some of the compounds are
given below. Compound (4g): solid, mp 193–194 ꢀC. 1H NMR (DMSO-d6):
d 1.15
(t, 3H, J¼6.8 Hz), 2.37 (s, 3H), 4.10 (q, 2H, J¼6.8 Hz),5.35 (s, 1H), 5.82 (br s, NH),
6.84 (m, 1H), 7.05–7.10 (m, 5H),7.45 (m, 3H), 8.40 (br s, NH). EIMS: m/z 352
(Mþ), 323, 279,183, 155, 137, 91, 69. IR (KBr):
n 3242, 3112, 2981, 1712,1654,
1582, 1487, 1245, 1097, 786. Anal. Calcd for C20H22N2O4 (354.16): C, 67.78; H,
6.26; N, 7.90; O, 18.06. Found: C, 67.79; H, 6.26; N, 7.94; O, 18.10. Compound
(4k): solid, mp 229–231 ꢀC (lit. 232–235 ꢀC). 1H NMR (DMSO-d6):
d 1.06 (t, 3H,
J¼7.0 Hz), 2.50 (s, 3H), 3.95(q, 2H, J¼7.0 Hz), 4.24 (d, 1H, J¼6.0 Hz), 6.0 (d, 1H,
J¼16.4 Hz), 6.2 (d, 1H, J¼16.4 Hz), 7.20–7.25 (m, 5H), 7.45 (d, NH, J¼1.7 Hz), 8.95
44. General procedure for the synthesis of DHPMs: a solution of aldehyde (1.0 mmol),
ethyl acetoacetate (156 mg, 1.2 mmol), and urea (72 mg, 1.2 mmol) in aceto-
nitrile (6 ml) was heated under reflux conditions in the presence of AlKIT-5(10)
catalyst (150 mg) for 3.0–4.0 h. Completion of the reaction was monitored by
(br s, NH). EIMS: m/z 286 (Mþ), 252, 224,196, 149, 84. IR (KBr):
n 3335, 3242,
3098, 2978, 1689, 1642,1492, 1373, 1218, 1121, 785. Anal. Calcd for C16H20N2O3
(288.15): C, 66.65; H, 6.99; N, 9.72; O, 16.65. Found: C, 66.68; H, 6.99; N, 9.75; O,
16.67.