Three component reaction: An efficient synthesis of 3,4-dihydropyrimidin-2(1H)-ones and thiones using heterogeneous catalyst

Article abstract of DOI:10.1002/cjoc.201090084

Fluoroboric acid supported on silica gel (HBF₄-SiO₂) catalyzes efficiently the three component condensation of an aldehyde, a 1,3-dicarbonyl compound and urea or thiourea to afford the corresponding 3,4-dihydropyrimidin-2(1H)-ones an

Full text of DOI:10.1002/cjoc.201090084

FULL PAPER
Three Component Reaction: An Efficient Synthesis of
3,4-Dihydropyrimidin-2(1H)-ones and Thiones
Using Heterogeneous Catalyst
Kamble, Vinod Tribhuvannathji*
Atkore, Sandeep Tukaram
Muley, Dnyanoba Baburao
Dakore, Sharad Digambarrao
Organic Chemistry Research Laboratory, School of Chemical Sciences, Swami Ramananad Teerth Marathwada
University, Nanded-431 606, M. S., India
Fluoroboric acid supported on silica gel (HBF4-SiO2) catalyzes efficiently the three component condensation of
an aldehyde, a 1,3-dicarbonyl compound and urea or thiourea to afford the corresponding 3,4-dihydropyrimidin-
2(1H)-ones and thiones in high yields. The ambient conditions, fast reaction rates, and excellent product yields are
the important characteristics of this reaction.
Keywords aldehyde, urea, ethyl acetoacetate, dihydropyrimidinone, fluoroboric acid supported on silica gel
(HBF4-SiO2)2
Introduction
dropyrimidinones attention has been mainly paid to us-
ing open-chained 1,3-dicarbonyl compounds, while the
use of cyclic 1,3-dicarbonyl compounds has been sel-
dom reported.26,28 Therefore, the development of a
milder, faster, eco-friendly and high-yielding protocol
using cyclic 1,3-dicarbonyl compounds is still of great
importance.
Since the pioneering work reported more than a
century ago by Biginelli,1 dihydropyrimidinones
(DHPM) and their derivatives have attracted growing
interest in the last few years and particularly in the last
six years, and much efforts have paved the way for new
synthetic methodologies for their preparation, due to
their therapeutic and pharmacological properties.2-4 Di-
hydropyrimidinones are an important class of bioactive
molecules and are widely used as anti-viral, anti-tumor,
anti-bacterial and anti-inflammatory agents.5,6 They are
also used as calcium channel blockers, anti-hypertensive
Solid-supported reagents48-59 have recently attracted
much attention due to their low toxicity, high catalytic
activity, moisture and air tolerance, ease of separation,
recyclability and low price. This fact has prompted us to
initiate an investigation to explore the catalytic activity
of solid-supported fluoroboric acid (HBF4-SiO2) for
useful organic transformations.
agents, neuropeptide Y (NPY) antagonists and α -
1a
adrenergic antagonists.7,8 The biological activity of
some alkaloids isolated recently has been attributed to
the dihydropyrimidinone moiety.9 Dihydropyrimidi-
nones have been prepared by employing protic ac-
ids,10-12 Lewis acids,13-28 triflates,29,30 microwave irra-
diation,31-34 ionic liquids35,36 and clays.37,38 Unfortu-
nately, many of these processes suffer major or minor
limitations, such as drastic reaction conditions, low
yields, expensive and toxic reagents, stoichiometric
amounts of catalysts, strongly acidic conditions, long
reaction time, and incompatibility with other functional
groups. Very recently, Sr(NO3)2,39 polyoxometalate
catalysts,40 12-molybdophosphoric acid,41 silica-sup-
ported heteropoly acid,42 Dowex-50W,43 modified zeo-
lite-type E4a,44 and natural HEU type zeolite,45 aqueous
HBF4,46 and polyaniline-HBF4-dodecyl hydrogensul-
fate,47 have been used for Biginelli cyclocondensation to
give dihydropyrimidinones. For the synthesis of dihy-
The present work describes our endeavors to develop
a very simple, economic and highly efficient strategy
for the synthesis of dihydropyrimidinones and thiones
through the three-component one-pot condensation of
an aldehyde, a 1,3-dicarbonyl compound and urea/thio-
urea by using silica-supported fluoroboric acid as a
catalyst in ethanol at room temperature [Eqs. (1) and
(2)].
*
E-mail: vtkd@rediffmail.com
Received September 27, 2008; revised August 26, 2009; accepted November 13, 2009.
388
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 388— 392

An Efficient Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Thiones
aldehydes such as furfural worked well without the
formation of any side products (Table 2, Entry 15). For
aliphatic and α,β-unsaturated aldehydes, which normally
show low conversion in the Biginelli reaction, the cor-
responding dihydropyrimidinones could be obtained in
83%—87% yields (Table 2, Entries 1—4, 14). Notably,
3,4-dihydropyrimidin-2(1H)-thiones which are also im-
portant due to their biological activities, were also ob-
tained in high yields (Table 2, Entries 28—35). In addi-
tion, in order to increase diversity of the present proto-
col, we employed cyclic 1,3-dicarbonyl compounds and
found that these compounds reacted with different al-
dehydes and urea with equal ease to afford the corre-
sponding dihydropyrimidinones in high yields (Table 3).
The high catalytic ability of HBF4-SiO2 can be attrib-
uted to larger surface area and better selectivity.
The feasibility of the reusability and recycling of the
catalyst HBF4-SiO2 was examined through a series of
sequential condensations of ethyl acetoacetate and ben-
zaldehyde with urea as a model reaction. In a typical
reaction, the catalyst was recovered by simple filtration
from the reaction mixture and reused for five cycles.
The reaction proceeded smoothly with a yield of
94%—89% and this result shows that the catalyst does
not lose its activity even after five runs (Table 1, Entry
6).
While comparing the effect of catalysts on the syn-
thesis of 5-ethoxycarbonyl-4-phenyl-3,4-dihydro-pyri-
midin-2(1H)-one from the reaction of benzaldehyde,
ethyl aceoacetate, and urea, we found that, HBF4-SiO2
was more efficient than some of the recently reported
catalysts in terms of the amount of catalyst, yields and
reaction time (Table 4).
A proposed reaction mechanism of Biginelli con-
densation via an acylimine intermediate is presented in
Scheme 1. This intermediate is formed by the reaction
of the aldehyde and urea or thiourea and then stabilized
by followed HBF4-SiO2. Subsequent addition of ethyl
acetoacetate enolate to the acylimine, followed by cy-
clization and dehydration, afforded the corresponding
3,4-dihydropyrimidin-2(1H)-ones or thiones.
We started our study on one-pot Biginelli condensa-
tion by examining the conditions for the reaction in-
volving ethyl acetoacetate, benzaldehyde, and urea to
afford the corresponding DHPM (4d). The results pre-
sented in Table 1 indicate the optimization experiments.
Entries 1—6 show the effect of various solvents on the
reaction. Benzene (Entry 1, 88%), CH3CN (Entry 2,
90%), THF (Entry 3, 82%), and 95% ethanol (Entry 6,
94%) gave the highest yields. Ethanol was chosen as the
solvent with the consideration to the environmental as-
pect and reaction yields. The optimum amount of cata-
lyst (5 mol%) was determined from the experiments
corresponding to Entries 6—10.
Table 1 HBF4-SiO2 catalyzed synthesis of 4a under different
reaction conditions
HBF4-SiO2/
Entry Solvent
Time/h
Yielda/%
mol%
1
2
3
4
5
6
7
8
9
Benzene
CH3CN
THF
5
5
3.5
2.5
2.5
3
88
90
5
82
CH2Cl2
Water
5
77
5
3.5
2
15
Ethanol
Ethanol
Ethanol
Ethanol
5
94, 93, 93, 92, 89b
2
3
62
88
93
94
4
2.5
2.5
2.5
7
10 Ethanol
10
Scheme 1
a Isolated yields. b Catalyst was resused for five times.
Table 2 indicates the scope and generality of the
present protocol, which is equally effective for urea and
thiourea. The reaction conditions are very comfortable
for the variation in all three components. Thus, this
procedure offers easy access to substituted dihydro-
pyrimidinones with a variety of substitution patterns.
Aromatic aldehydes carrying either electron donating or
withdrawing substituents afforded the corresponding
dihydropyrimidinones in good to excellent yields with
high purity (Table 2, Entries 4—27). The important fea-
ture of this procedure is the ability to tolerate the variety
of functional groups such as ether, nitro, olefin, hydroxy
and halide under the reaction conditions. Acid sensitive
In conclusion, HBF4-SiO2 is a highly efficient and
practical catalyst for the synthesis of 3,4-dihydropyri-
midin-2(1H)-ones and 3,4-dihydropyrimidin-2(1H)-
thiones. The advantages include the low cost, ease of
catalyst handling, mild reaction conditions, and short
Chin. J. Chem. 2010, 28, 388— 392
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
389

Kamble et al.
Table 2 HBF4-SiO2 catalyzed synthesis of dihydropyrimidinones and thiones from open chained 1,3-dicarbonyl compounds
FULL PAPER
Entry
1
Product
4a
R1
R2
X
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
S
Time/h
1.5
2
Yielda,b/%
91
92
90
94
93
90
91
93
95
94
86
89
92
93
91
89
88
92
91
92
92
93
92
85
88
90
91
92
90
88
90
92
91
90
89
Ref.
19
21
15
18
18
21
—
21
21
21
17
17
—
39
39
39
39
41
41
29
18
21
21
42
29
29
18
7d
21
47
39
21
47
—
—
Me2CH
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OMe
OMe
OMe
OMe
OMe
Me
2
4b
4c
CH3(CH2)4
CH3(CH2)5
C6H5
3
2
4
4d
4e
2
5
4-FC6H4
2.5
2.5
2.5
3
6
4f
4-ClC6H4
7
4g
4-BrC6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
2-OHC6H4
3,4-(OCH2O)C6H3
2,5-(OMe)2C6H3
C6H5CH＝CH
2-Furyl
8
4h
4i
9
2.5
2.5
3.5
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
4j
4k
4l
4m
4n
4o
3.5
3
2.5
4
4p
4q
5r
3-OMe-4-OHC6H3
4-OHC6H4
3-NO2C6H4
2-NO2C6H4
C6H5
3.5
3
4s
3
4t
2
4u
4v
4-ClC6H4
2.5
3
4-NO2C6H4
4-OMeC6H4
4-NMe2C6H4
4-OMeC6H4
C6H5
4w
4x
3
4.5
2.5
2
4y
4z
Me
4aa
4bb
4cc
4dd
4ee
4ff
4gg
4hh
4ii
4-ClC6H4
Me
2.5
3
4-NO2C6H4
4-OMeC6H4
3-OHC6H4
C6H5
Me
OEt
OEt
OEt
OEt
Me
S
3
S
3.5
2.5
3.5
2.5
2.5
3
S
4-ClC6H4
S
C6H5
S
Me2CH
OMe
OEt
S
C5H11
S
a Yields are of pure isolated products. b Products are characterized by their physical constants and spectral analysis.
Table 3 HBF4-SiO2 catalyzed synthesis of dihydropyrimidinones from open chained 1,3-dicarbonyl compounds 1a and 1b
Entry
Product
5a
R1
C6H5
X
O
O
O
O
O
O
O
O
Time/h
Yielda,b/%
Ref.
28
28
28
28
28
26
26
26
1
2
3
4
5
6
7
8
3
89
87
90
89
88
94
93
93
5b
4-FC6H4
4
5c
4-OMeC6H4
4-NO2C6H4
4-OHC6H4
4-CLC6H4
2-CLC6H4
3-NO2C6H4
4
5d
4.5
4
5e
6a
5
6b
4.5
6c
4
a Yields are of pure isolated products. b Products are characterized by their physical constants and spectral analysis.
390 Chin. J. Chem. 2010, 28, 388— 392
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© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

An Efficient Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Thiones
Table 4 Comparison of catalytic efficiency of HBF4-SiO2 against recently reported catalysts for the reaction of benzaldehyde, ethyl
acetoacetate and urea
Entry
Catalyst
Solvent
AcOH
AcOH
CH3CN
Neat
Condition
Reflux
Reflux
80 ℃
130 ℃
80 ℃
100 ℃
45 ℃
Reflux
r.t.
Catalyst
5 mol/%
2 mol/%
9 mol/%
0.1 g
Time/h
Yield/% Ref.
1
2
3
4
5
6
7
8
9
Sr(NO3)2
5
77.8
80
95
92
93
75
95
97
94
39
41
42
43
44
45
46
47
—
12-Molybdophosphoric acid
Silica supported heteropoly acid
Dowex-50W
5
1
3
Modified zeolite type E4a
Natural HEU type zeolite
HBF4
Ethanol
AcOH
—
0.1 g
8
0.2 g
4—5
0.6
6
10 mol/%
5 wt%
PANI-HBF4-DHS
Ethanol
Ethanol
Silica-supported HBF4
5 mol/%
2
reaction time.
(s, 3H), 3.80 (s, 3H), 4.10 (q, J＝7.0 Hz, 2H), 5.45 (s,
1H), 5.90 (br s, 1H), 6.55 (d, J＝8.2 Hz, 1H), 6.69 (dd,
J＝2.8, 8.2 Hz, 1H), 6.76 (d, J＝8.2 Hz, 1H), 8.85 (brs,
Experimental
－1
1H); IR (KBr) ν: 1650, 1710, 3000, 3190, 3250 cm ;
EIMS m/z: 320 (M＋). Anal. calcd for C16H20N2O5: C
59.99, H 3.46, N 8.74; found C 59.92, H 3.49, N 8.70.
4hh: Solid; m.p. 175—177 ℃; 1H NMR (DMSO-d6,
300 MHz) δ: 0.90 (d, J＝6.2 Hz, 3H), 1.02 (d, J＝6.0
Hz, 3H), 1.76—1.80 (m, 1H), 2.25 (s, 3H), 3.60 (s, 3H),
4.20 (d, J＝3.0 Hz, 1H), 6.75 (br s, 1H)－, 8.65 (br s, 1H);
Melting points were measured using a Buchi R-535
apparatus. IR spectra were recorded on a Bomem MB
FT-IR spectrometer. H NMR spectra were recorded on
a Varian Gemini-200 spectrometer. Mass spectra were
recorded on a VG Micromass-7000 H instrument (70
eV). CHN analyses were performed on a Vario EL ana-
lyser. The catalyst (HBF4-SiO2) was prepared by an es-
tablished procedure.58,59
1
1
IR ＋(KBr) ν: 50, 1705, 3110, 3235 cm ; IMS m/z: 28
(M ). Anal. calcd for C10H16N2O2S: C 52.60, H 7.06, N
12.26; found C 52.56, H 7.10, N 12.22.
Preparation of catalyst
1
4ii: Solid; m.p. 165—167 ℃; H NMR (DMSO-d6,
HBF4 (1.65 g, as a 40% aqueous solution) was added
to the suspension of silica gel (13.35 g, 230—400 mesh)
in diethyl ether (40 mL). The mixture was concentrated
and the residue dried under vaccum at 100 ℃ for 72 h
300 MHz) δ: 0.95 (t, J＝7.2 Hz, 3H), 1.20—1.60 (m,
11H), 2.30 (s, 3H), 4.10—4.40 (m,＋3H), 5.75 (br s, 1H),
8.20 (br s, 1H); EIMS m/z: 70 (M ); IR (KBr) ν: 625,
－1
1685, 3060, 3275 cm . Anal. calcd for C13H22N2O2S: C
－1
to afford HBF4-SiO2 (0.5 mmol•g ) as a free flowing
57.14, H 8.19, N 10.35; found C 57.10, H 8.22, N 10.32.
powder.
References
General experimental procedure
A mixture of aldehyde (1mmol), β-keto ester (1
mmol), urea or thiourea (1.5 mmol) and HBF4-SiO2 (5
mol%) in ethanol (10 mL) was stirred at room tempera-
ture for a certain period of time as required to complete
the reaction. The progress of the reaction was monitored
by TLC. On completion, the reaction mixture was di-
luted with ethanol (10 mL×2) and filtered to separate
catalyst. The solvent was removed under reduced pres-
sure and the resulting product recrystallized from hot
ethanol to afford pure dihydropyrimidinone.
1
2
3
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Chin. J. Chem. 2010, 28, 388— 392
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
391

Kamble et al.
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