Boehmite nanoparticle catalyst for the one-pot multicomponent synthesis of 3,4-dihydropyrimidin-2-(1H)-ones and thiones under solvent-free conditions

Article abstract of DOI:10.1016/S1872-2067(12)60759-1

A simple, green, and efficient synthesis protocol for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones using boehmite nanoparticles as catalyst was developed. It did not use any toxic metal catalysts or corrosive acidic reagents. The method gave good to excellent yields and has short reaction time, operational simplicity, and a recyclable catalyst.

Full text of DOI:10.1016/S1872-2067(12)60759-1

Chinese Journal of Catalysis 35 (2014) 362–367
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Boehmite nanoparticle catalyst for the one‐pot multicomponent
synthesis of 3,4‐dihydropyrimidin‐2‐(1H)‐ones and thiones under
solvent‐free conditions
Ali Keivanloo*, Mahdi Mirzaee, Mohammad Bakherad, Atena Soozani
School of Chemistry, Shahrood University of Technology, Shahrood, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
A simple, green, and efficient synthesis protocol for the synthesis of 3,4‐dihydropyrimidin‐2‐(1H)‐
ones using boehmite nanoparticles as catalyst was developed. It did not use any toxic metal cata‐
lysts or corrosive acidic reagents. The method gave good to excellent yields and has short reaction
time, operational simplicity, and a recyclable catalyst.
Received 22 August 2013
Accepted 25 November 2013
Published 20 March 2014
© 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Keywords:
Boehmite nanoparticle
One‐pot synthesis
Multicomponent synthesis
Dihydropyrimidine
Solvent‐free
1. Introduction
calcium channel blockers [9,10]. The anti‐cancer agent monas‐
trol is the only cell‐permeable molecule currently known to
Multicomponent reactions (MCRs) are powerful, versatile,
and popular tools for the synthesis of novel and complex mo‐
lecular structures that have advantages over a conventional
multistep synthesis [1–3]. The major advantages of MCRs in‐
clude lower cost, shorter reaction time, high atom economy,
energy saving, and avoidance of time consuming and expensive
purification [4–6]. MCRs are generally much more environ‐
mentally friendly, provide synthetic access to large compound
libraries with diverse functionalities, and do not need protec‐
tion and deprotection steps [7].
specifically inhibit mitotic kinesin Eg5 [11].
DHPMs are also prominent in SQ32547 and SWO2, which
have been identified as potent oral active anti‐hypertensive
agents [12]. In addition, several alkaloids isolated from marine
sources that contain the dihydropyrimidine core unit have
shown interesting biological properties [13]. In particular, Bat‐
zelladine alkaloids have been found to be potent HIV
gp‐120‐CD4 inhibitors [14]. Therefore, the synthesis of DHPM
derivatives has gained prominence in synthetic organic as well
as medicinal chemistry.
One of the most important MCRs is the Biginelli reaction.
This reaction allows the synthesis of dihydropyrimidinones
(DHPMs), which are compounds with anti‐viral, anti‐tumor,
anti‐bacterial, cytotoxic, and anti‐flammatory properties [8].
DHPMs possess remarkable pharmacological efficiency, which
is demonstrated by their utility as the integral backbones of
The Biginelli reaction, first described by the Italian chemist
Pietro Biginelli [15] in 1893, involves the one‐pot condensation
of an aldehyde, a β‐ketoester, and urea or thiourea under
strongly acidic conditions. The harsh reaction conditions, long
reaction time, and low yields when using substituted aromatic
and aliphatic aldehydes are its main drawbacks. Hence the
* Corresponding author. Tel/Fax: +98‐273‐3395441; E‐mail: akeivanloo@yahoo.com; keivanloo@shahroodut.ac.ir
DOI: 10.1016/S1872‐2067(12)60759‐1 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 35, No. 3, March 2014

Ali Keivanloo et al. / Chinese Journal of Catalysis 35 (2014) 362–367
original Biginelli condensation was not suitable for compounds
with sensitive functional groups.
mol%). The resulting mixture was heated with stirring at 120
°C for an appropriate time. The progress of reaction was moni‐
tored by TLC. At the end of the reaction, after cooling, the reac‐
tion mixture was washed with water to remove excess urea or
thiourea. The crude product was dried and an execess amount
of hot ethanol was added to it, and it was filtered to remove the
catalyst. After evaporation of the solvent, the residue was crys‐
tallized from ethanol to afford the pure product.
The structures of the compounds were characterized by
spectroscopic data and elemental analysis by the comparison of
their spectroscopic data and physical properties with those
reported in the literature. The characterization data for the
synthesized compounds are given below.
5‐Acetyl‐6‐methyl‐4‐(2,6‐dichlorophenyl)‐3,4‐dihydropyri‐
midin‐2(1H)‐thione (4n). mp = 226–228 °C. 1H NMR (400 MHz,
d6‐DMSO): δ 2.10 (s, 3H, CH3), 2.22 (s, 3H, CH3), 6.17 (s, 1H, CH),
7.29 (t, J = 8 Hz, 1H, CH), 7.42 (d, J = 8 Hz, 2H, 2CH), 9.49 (s, 1H,
NH), 10.23 (s, 1H, NH); 13C NMR (100 MHz, d6‐DMSO): δ 18.29,
30.90, 52.67, 107.96, 129.34, 129.67, 135.51, 136.30, 144.40,
173.52, 194.57. IR (KBr): 3168, 1632, 1571, 1433, 1321, 1117,
777 cm–1. Anal Calcd. for C13H12Cl2N2OS: C, 49.53; H, 3.84; N,
8.89; S, 10.17; Found: C, 49.45; H, 3.80; N, 8.97; S, 10.22.
5‐Acetyl‐6‐methyl‐4‐(2‐fluorophenyl)‐3,4‐dihydropyrimidin
‐2(1H)‐thione (4s). mp = 208–210 °C. 1H NMR (400 MHz,
d6‐DMSO): δ 2.18 (s, 3H, CH3), 2.30 (s, 3H, CH3), 5.52 (s, 1H, CH),
7.12–7.25 (m, 3H, 3CH), 7.28–7.30 (m, 1H, CH), 9.62 (s, 1H, NH),
10.28 (s, 1H, NH); 13C NMR (100 MHz, d6‐DMSO): δ 18.89,
32.15, 50.21, 108.04, 116.53, 126.16, 130.05, 131.17, 132.76,
148.65, 153.67, 175.21, 194.95. IR (KBr): 3312, 3200, 1615,
1580, 1480, 1450, 1320, 1180, 759 cm–1. Anal. Calcd. for
C13H13FN2OS: C, 59.07; H, 4.96; N, 10.60; S, 12.13; Found: C,
59.19; H, 4.90; N, 10.50; S, 12.22.
Over the past few years, significant efforts have been made
to find new procedures to produce DHPMs in good yields.
However, most of the reported procedures have low reaction
yields [16]. A large number of optimized procedures have been
reported where most of the protocols employ catalytic meth‐
ods in order to synthesize DHPMs [17–22]. These protocols
utilize Lewis acids or metal‐based catalysts such as NiCl2·6H2O,
p‐TsOH, LaCl3·7H2O, BF3·OEt2, InBr3, LiClO4, FeCl3, InCl3, and
metal triflates [23–31]. However, these often require relatively
harsh reaction conditions such as high reaction temperature,
expensive or highly acidic catalysts, and prolonged reaction
time. In most cases, a stoichiometric amount of the catalyst is
required to achieve good yields. In addition, most of the reac‐
tions require tedious work‐up procedures and column purifica‐
tion, which ultimately result in diminished yields. Hence, the
development of a new method that gives substituted DHPMs by
an efficient and convenient procedure is of interest.
2. Experimental
All the reagents used were general reagent grade. The IR
spectra were obtained with potassium bromide pellets or sol‐
vent in the range of 400–4000 cm–1 on a Shimadzu Model 460
pectrometer. The 1H NMR spectra were recorded on a Brucker
BRX 400 AVANCE spectrometer. The elemental analyses were
performed on a Thermo Finnigan Flash EA microanalyzer.
Powder X‐ray diffraction (XRD) was carried out on a Philips
PW1800 diffractometer.
2.1. Preparation of the catalyst
Boehmite nanoparticles were prepared according to Refs.
[32–34] by the following procedure. Aluminum‐2‐butoxide (2
mol/L, 10 mL) in 2‐butanol was placed in a 300 mL stainless
steel autoclave that contained 50 mL of deionized water. The
autoclave was heated for 5 h at 100 °C in an oven. After cooling
the autoclave, the powder produced was filtered off and dried
at 100 °C overnight. This powder was used as the catalyst in the
organic reactions.
3. Results and discussion
In this continuation of our studies on the synthesis of heter‐
ocyclic compounds [35–38] and its methodology [39–42], we
investigated the synthesis of DHPMs and thiones by the use of a
solid catalyst under thermal or microwave and solvent‐free
conditions. Here, we report a mild and efficient one‐pot proto‐
col for the synthesis of substituted 3,4‐dihydropyrimidin‐2‐
(1H)‐ one and thione derivatives by a multicomponent reaction
involving a 1,3‐dicarbonyl compound, an aldehyde, and urea or
thiourea using boehmite nanoparticles as the catalyst under
solvent‐free conditions (Scheme 1).
2.2. General procedure for the synthesis of 3,4‐dihydropyrimi‐
din‐2‐(1H)‐ones and thiones under solvent‐free conditions
To
a
mixture of aromatic aldehyde (1 mmol),
a
Boehmite is an aluminum oxide hydroxide (γ‐AlOOH) min‐
eral. It is a component of the aluminium ore bauxite and con‐
tains extra hydroxyl groups on its surface. Among the different
1,3‐dicarbonyl compound (1 mmol) and urea or thiourea (1.5
mmol) in a test tube was added the boehmite nanoparticles (10
O
Ar
X
O
O
O
R
NH
Boehmite NPs
120 oC
solvent free
+
+
H2N
NH2
H3C
R
H
Ar
H3C
N
H
X
X = O, S
R = CH3, OC2H5
18 examples
78%-98%
Scheme 1. Synthesis of substituted 3,4‐dihydropyrimidin‐2(1H)‐ones or thions by a multicomponent reaction of aldehydes, 1,3‐dicarbonyl com‐
pounds, and urea or thiourea in the presence of boehmite nanoparticles under solvent‐free conditions.

Ali Keivanloo et al. / Chinese Journal of Catalysis 35 (2014) 362–367
methods used for the preparation of boehmite nanoparticles,
AlOH sites
the hydrothermal sol‐gel technique has the advantages of
preparation in a one‐pot process and low temperature pro‐
cessing. The most promising property of this hydrothermally
produced nanoboehmite is the formation of it as a highly crys‐
talline single phase product with no organic residue [32–34].
This was shown by its IR spectrum and XRD pattern, shown in
Figs. 1 and 2, respectively.
The acidic sites of boehmite are shown in Fig. 3. The bridged
and terminal surface hydroxyl groups of boehmite give two
different stretching vibrations at 3280 and 3075 cm–1 in the IR
spectrum. Boehmite also has some Al–O related vibrations at
1150, 1075, 740, 610, and 480 cm–1.
H
H
O
O
H
O
O
O
Al
Al
O
Al
O
H
H
O
O
O
Al2OH sites
The XRD pattern of the catalyst prepared also confirmed the
crystallization as a single phase boehmite. The calculation of
the particle size from the XRD pattern using the Scherer equa‐
tion showed 10 nm particles. The surface area of the boehmite
nanoparticles was 326 m2/g.
In order to optimize the reaction conditions for the synthe‐
sis of DHPMs and thiones, the reaction of benzaldehydes with
ethyl acetoacetate and urea was used as a model reaction. Re‐
actions in different solvents, at different temperatures, and
with various amounts of catalyst revealed that the best condi‐
tions were solvent‐free at 120 °C and 10 mol% of boehmite
nanoparticles (enry 8, Table 1).
Fig. 3. Bridged and terminal hydroxyl groups of boehmite.
and a library of substituted DHPMs was obtained (Table 2).
Both electron‐withdrawing and electron‐donating substit‐
uents on the aldehyde aryl ring were tolerated well. Methyl‐,
methoxy‐, nitro‐, fluoro‐, chloro‐, and dichlorobenzaldehydes
produced the desired products in high yields. The position of
the substituent had no significant effect on the yield.
Next we replaced ethyl acetoacetate with acetylacetone, and
we were pleased to find that the boehmite nanoparticles also
catalyzed these reactions and afforded the DHPMs in quantita‐
tive yield. When we used thiourea instead of urea, 3,4‐dihy‐
dropyrimidin‐2‐(1H)‐thiones were formed in high yields alt‐
hough the reaction time was prolonged.
To study the scope of the method, the reactions of a variety
of aldehydes with ethyl acetoacetate and urea were performed,
Table 1
Condensation of benzaldehyde, ethylacetoacetate, and urea using dif‐
ferent amounts of boehmite nanoparticles and solvents under thermal
or microwave conditions.
O
O
O
O
O
Boehmite NPs
EtO
NH
+
+
H
H N
2
NH
2
H C
OEt
3
H C
N
H
O
3
Catalyst loading Time Temperature
Yeild a
(%)
10
8
21
17
5
Entry Solvent
Condition
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm1)
(mol%)
10
20
10
20
10
20
10
10
10
5
(min)
300
300
300
300
300
300
20
5
(°C)
80
80
80
80
100
100
100
120
140
120
120
120
—
1
2
3
4
EtOH
EtOH
CH3CN
CH3CN
H2O
Thermal
Thermal
Thermal
Thermal
Thermal
Thermal
Thermal
Thermal
Thermal
Thermal
Thermal
Thermal
Fig. 1. IR spectrum of the boehmite nanoparticles prepared by a hy‐
drothermal sol‐gel process at 100 °C.
5
6
H2O
7
7
8
9
10
11
11
12
Neat
Neat
Neat
Neat
Neat
Neat
Neat
71
94
90
75
70
65
5
5
3
5
20
10
3
4
Microwave 42
(400 W)
13
14
Neat
Neat
10
10
6
8
—
—
Microwave 75
(600 W)
Microwave 53
(700 W)
10
20
30
2/(o )
40
50
60
Reaction conditions: aldehyde (1.0 mmol), 1,3‐dicarbonyl compound
(1.0 mmol), urea/thiourea (1.5 mmol), catalyst and solvent (10 mL).
Fig. 2. XRD pattern of the boehmite nanoparticles prepared by a hy‐
a Isolated yield.
drothermal sol‐gel process at 100 °C.

Ali Keivanloo et al. / Chinese Journal of Catalysis 35 (2014) 362–367
Table 2
Synthesis of 3,4‐dihydropyrimidin‐2‐(1H)‐ones and thiones under solvent‐free conditions catalyzed by boehmite nanoparticles.
Dicarbonyl
compound
Time Yeild a
(min) (%)
Dicarbonyl
compound
Time Yeild a
(min) (%)
Entry Aldehyde Amine
Product
Ref. Entry Aldehyde Amine
Product
Ref.
CHO
O
CHO
O
O
Cl
O
O
O
O
O
Cl
1
4a
4b
5
94 [43] 10
4j 45
85 [49]
95 [50]
EtO
H3C
NH
EtO
OEt
NH
H3C
OEt
H3C
NH2
H2N
NH2
H2N
N
H
O
H3C
N
H
O
F
CHO
CHO
CHO
O
O
O
O
O
O
O
O
2
3
4
6
90 [44] 11
98 [28] 12
87 [45] 13
4k 50
EtO
OEt
NH
H3C
OEt
H3C
NH2
H2N
NH2
H2N
EtO
NH
F
H3C
N
H
S
H C
3
N
H
O
CHO
O
O
O
O
O
O
O
O
4c 10
4l 60
97 [51]
H C
3
NH
H3C
NH
H2N
NH2 H C
3
CH
3
H N
2
NH H C
CH
3
2
3
H C
3
N
H
O
H3C
N
H
S
Cl
CH
3
CHO
CH3
CHO
Cl
O
O
O
O
O
O
O
O
4d 40
4m 120 95 [51]
H2N
NH2 H3C
CH3
H N
2
NH H C
CH
3
2
3
H C
NH
H C
NH
3
3
H C
N
H
O
H C
3
N
H
S
3
F
CHO
Cl
O
CHO
Cl
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Cl
Cl
O
5
6
7
4e 40
4f 50
4g 10
91 [46] 14
97 [47] 15
96 [48] 16
4n 100 90
—
H3C
CH3
NH
H2N
H2N
H2N
NH2 H3C
CH3
H2N
NH2 H3C
H3C
H3C
NH
F
H3C
N
H
S
N
H
O
NO2
CH3
CHO
CHO
NO2
O
O
4p 100 88 [48]
NH2 H C
CH
H N
2
NH H C
CH
3
3
3
2
3
H3C
H3C
NH
H3C
NH
CH3
N
H
O
H3C
O
N
S
H
NO
CH3
CHO
CHO
F
O
H C
NH
3
4q 80
85 [52]
78 [53]
NH2 H C
CH
H N
2
NH H C
CH
3
3
3
2
3
H3C
H3C
NH
NO
H C
N
S
2
3
H
N
O
H
F
CHO
F
CHO
O
OH
O
O
O
O
O
O
OH
O
8
9
4h
8
91 [43] 17
78 [48] 18
4r 90
EtO
H3C
NH
H3C
OEt
H3C
NH
2
OEt
H2N
NH2
H N
2
EtO
NH
N
O
H
H C
3
N
H
S
CHO
CHO
O
OCH3
O
F
O
O
O
O
O
O
F
OH3
4i 15
4s 60
83
—
H3C
NH
H3C
NH
H2N
NH2 H C
CH
H N
2
NH H C
CH
3
3
3
2
3
H3C
N
O
H3C
N
H
S
H
Reaction conditions: aldehyde (1.0 mmol), 1,3‐dicarbonyl compound (1.0 mmol), urea/thiourea (1.5 mmol), boehmite NPs (10 mol%), 120 °C.
a Isolated yield.
The mechanism for the synthesis of DHPMs in the presence
of the boehmite nanoparticle catalyst is shown in Scheme 2.
The reaction proceeds via the acyl imine intermediate, which is
formed by the reaction of aromatic aldehyde with urea or thio‐
urea, with the aldehydic carbonyl group being activated by the
acidic hydroxyl groups on the surface of boehmite nanoparti‐
cles by intermolecular hydrogen bonding. The reaction of this
imine intermediate with ethyl acetoacetate produces an open
chain ureide [30], which subsequently cyclizes to form the de‐
sired product.
Each compound can be isolated by crystallization, which
avoids tedious work‐up and column purification. The products
were characterized by spectroscopic data and elemental analy‐
sis.
The reusability of the catalyst was also examined (Table 3).
After each run, DMF was added, and the product was filtered.
The residue (catalyst) was washed with CHCl3 and reused. The
treatment with CHCl3 removed tars more efficiently from the
catalyst surface. This catalyst was reusable, although a gradual
decline in its activity was observed.

Ali Keivanloo et al. / Chinese Journal of Catalysis 35 (2014) 362–367
X
X
AlOO-H
AlOO-H
H2N NH2
O
O
N
NH2
AlOOH
- H2O
Ar
H
Ar
H
Ar
H
O
O
O
X
O
H3C
R
H3C
R
O
Ar
H2N
HN
H3C
X
H
R
H3C
NH
O
O
Ar
O
+
N
NH2
N
H
X
H3C
R
R
Ar
O
Scheme 2. Mechanism for the formation of 3,4‐dihydropyrimidin‐2(1H)‐ones/thions by a multicomponent reaction of aldehydes, 1,3‐dicarbonyl
compounds, and urea or thiourea in the presence of boehmite nanoparticles.
Table 3
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Condensation of benzaldehyde, ethylacetoacetate and urea using recy‐
cled catalysts.
Number of cycles
Time (min)
Yeild a (%)
1
2
3
5
10
20
30
30
92
88
85
80
Reaction conditions: aldehyde (1.0 mmol), ethylacetoacetate (1.0
mmol), urea (1.5 mmol), boehmite NPs (10 mol%), 120 °C.
a Isolated yield.
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We developed an efficient, clean, and environmentally
friendly procedure to produce DHPMs and thiones in good to
high yields using MCRs. The protocol utilizes boehmite nano‐
particles as the catalyst, uses mild reaction conditions, and does
not require work‐up or column purification. This green meth‐
odology can synthesize new substituted DHPM and thione
scaffolds with biological applications.
Acknowledgements
The authors would like to thank the Research Council of
Shahrood University of Technology for the financial support of
this work.
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Ali Keivanloo et al. / Chinese Journal of Catalysis 35 (2014) 362–367
Graphical Abstract
Chin. J. Catal., 2014, 35: 362–367 doi: 10.1016/S1872‐2067(12)60759‐1
Boehmite nanoparticle catalyst for the one‐pot multicomponent
synthesis of 3,4‐dihydropyrimidin‐2‐(1H)‐ones and thiones
under solvent‐free conditions
Ali Keivanloo*, Mahdi Mirzaee, Mohammad Bakherad, Atena Soozani
Shahrood University of Technology, Iran
Boehmite nanoparticles are a highly active and green catalyst for the
synthesis of highly substituted 3,4‐dihydropyrimidin‐2‐(1H)‐ones
and thiones under solvent‐free conditions.
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