Ultrasound-mediated synthesis of 3,4-dihydropyrimidin-2-(1H)-ones (or Thiones) with NaHSO4·H 2O

Article abstract of DOI:10.1080/10426507.2013.777725

A fast and efficient Biginelli synthesis of 3,4-dihydropyrimidin-2-(1H)- ones (or thiones) by the reaction of aromatic aldehydes, β-dicarbonyls, and urea/thiourea using NaHSO₄·H₂O/ultrasound system is presented. The reactions were ca

Full text of DOI:10.1080/10426507.2013.777725

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Phosphorus, Sulfur, and Silicon and the
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Ultrasound-Mediated Synthesis of 3,4-
Dihydropyrimidin-2-(1H)-Ones (or
Thiones) with NaHSO4·H2O
Karim Akbari Dilmaghani a , Behzad Zeynizadeh a & Maryam
Amirpoor a
a Department of Chemistry, Faculty of Sciences , Urmia University ,
Urmia , 57159-165 , Iran
Accepted author version posted online: 05 Apr 2013.Published
online: 20 Sep 2013.
To cite this article: Karim Akbari Dilmaghani , Behzad Zeynizadeh & Maryam Amirpoor
(2013) Ultrasound-Mediated Synthesis of 3,4-Dihydropyrimidin-2-(1H)-Ones (or Thiones) with
NaHSO4·H2O, Phosphorus, Sulfur, and Silicon and the Related Elements, 188:11, 1634-1642, DOI:
10.1080/10426507.2013.777725
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Phosphorus, Sulfur, and Silicon, 188:1634–1642, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2013.777725
ULTRASOUND-MEDIATED SYNTHESIS OF
3,4-DIHYDROPYRIMIDIN-2-(1H)-ONES (OR THIONES)
WITH NaHSO4·H2O
Karim Akbari Dilmaghani, Behzad Zeynizadeh,
and Maryam Amirpoor
Department of Chemistry, Faculty of Sciences, Urmia University, Urmia
57159-165, Iran
GRAPHICAL ABSTRACT
Abstract A fast and efficient Biginelli synthesis of 3,4-dihydropyrimidin-2-(1H)-ones (or
thiones) by the reaction of aromatic aldehydes, β-dicarbonyls, and urea/thiourea using
NaHSO4·H2O/ultrasound system is presented. The reactions were carried out in refluxing
n-hexane/CH3CN (2.5:0.5 mL) to afford the products in excellent yields.
Keywords 3,4-Dihydropyrimidin-2-(1H)-ones; aldehydes; β-dicarbonyls; NaHSO4·H2O;
ultrasound
INTRODUCTION
A simple and straightforward procedure for synthesis of 3,4-dihydropyrimidin-
2-(1H)-ones (DHPMs) by three-component condensation of aromatic aldehydes, β-
dicarbonyl compounds, and urea/thiourea was first reported by an Italian chemist Biginelli
in 1893.1 DHPMs have attracted increasing interest due to their diverse therapeutic and phar-
macological properties such as antiviral, antibacterial, antihypertensive agents, and antitu-
mor effects.2 Moreover, some marine natural products containing the dihydropyrimidinone-
5-carboxylate core, such as Batzelladine B alkaloid, have been found to be potent HIV
gp-120-CD4 inhibitors.3
Received 26 November 2012; accepted 15 February 2013.
The authors gratefully appreciate the financial support of this work by the Research Council of Urmia
University.
Address correspondence to Professor Behzad Zeynizadeh, Department of Chemistry, Faculty of Science,
Urmia University, Urmia, Islamic Republic of Iran. E-mail: bzeynizadeh@gmail.com
1634

SYNTHESIS OF 3,4-DIHYDROPYRIMID INONES
1635
The original one-pot protocol often suffers from the drawbacks including longer
reaction times, harsh reaction conditions, and lower yields. In recent years, several
modified procedures aimed to improve the efficiency of Biginelli synthesis of 3,4-
dihydropyrimidinones have been reported. ZrCl4,4 ZrOCl2·8H2O,5 sulfated zirconia,6
InBr3,7 InCl3,8 CeCl3·7H2O,9 CuCl2·2H2O,10 SnCl2·2H2O,11 BiCl3,12 Bi(OTf)3,13
Cu(OTf)2,14 Fe(OTf)3 and Fe(O2CCF3),15 Mn(OAc)3·2H2O,16 I2,17 NH4Cl,18 B(OH)3,19
Al(HSO4)3,20 NaHSO4·H2O,21 H2SO4/SiO2,22 H2SO4/charcoal,23 silica sulfuric acid
(SiO2-OSO3H),24 MeSO3H/Al2O3,25 p-TsOH,26 montmorillonite KSF,27 H3PMo12O40,28
reusable Wells-Dawson29 and doped keggin30 heteropolyacids, baker yeast,31 and
ionic liquid32 are some of the reagents which have been reported for synthesis of
3,4-dihydropyrimidinones.
Nowadays, acceleration of reactions using ultrasound irradiation is an interesting
strategy in organic synthesis; numerous reviews and papers have demonstrated its impor-
tance.33 Sonic conditions not only accelerate chemical reactions but also reduce the number
of steps which are required using normal conditions. In addition, cruder reagents can be
used and reactions can be initiated without any additives. The chemical effects of ultrasound
are due to the phenomena of acoustic cavitations, and the primary chemical reactions result
from a transient state of higher temperatures and pressures.34 A literature review shows that
ultrasound-mediated Biginelli synthesis of 3,4-dihydropyrimidinones has been reported in
the presence of HCl,35 TFA,35 [Hbim]BF4,35 NH2SO3H,36 NH4Cl,37 Sm(ClO4)3,38 I2,39
CAN,40 and SiO2.41 In these methods, using strong acidic conditions, expensive or toxic
reagents and moderate yields of the products are the main disadvantages.
On the other hand, hydrated sodium hydrogen sulfate, as a cheap and mineral-
weak acidic reagent, has been found to have some useful applications in organic syn-
thesis.42 Recently, we used NaHSO4·H2O in n-hexane for Biginelli synthesis of 3,4-
dihydropyrimidinones.21a In this report, synthesis of 3,4-dihydropyrimidinones was carried
out efficiently under mild conditions; however, performing the reactions in long reaction
times puts a restriction to use this method for any practical applications. So, in order to
run the reactions under greener conditions and to save energy and costs, we decided to
incorporate sonic conditions with NaHSO4·H2O as a new promoter system for Biginelli
synthesis of 3,4-dihydropyrimidin-2-(1H)-ones (or thiones) (4–69) by cyclocondensation
reaction of aromatic aldehydes (1), β-dicarbonyls (2) and urea/thiourea (3) (Scheme 1).
Scheme 1
RESULTS AND DISCUSSION
Reaction conditions were initially optimized by the promotion of a one-pot cyclo-
condensation reaction of benzaldehyde, ethyl acetoacetate, and urea with NaHSO4·H2O in
the presence or absence of ultrasound irradiation to afford 3,4-dihydropyrimidinone (4).

1636
K. A. DILMAGHANI ET AL.
Table 1 Optimization experiments for synthesis of DHPM (4) with NaHSO4·H2O in the presence or absence of
ultrasound irradiationa
NaHSO4·H2O
Ultrasound
(W)
Solvent
(mL)
Time
(h)
Conversion
(%)b
Entry
(mmol)
1
2
3
4
5
6
7
8
2
2
2
3
3
—
3
3
—
—
—
—
—
240
240
200
CH3CN (3 mL)
THF (3 mL)
n-Hexane (3 mL)
n-Hexane (3 mL)
n-Hexane-CH3CN (2.5:0.5 mL)
n-Hexane-CH3CN (2.5:0.5 mL)
n-Hexane-CH3CN (2.5:0.5 mL)
n-Hexane-CH3CN (2.5:0.5 mL)
10
10
7
7
6
6
2
3
30
35
90
100
100
15
100
100
aAll reactions were carried out with 1 mmol of benzaldehyde in a molar ratio of aldehyde/ethyl acetoacetate/urea
(1:1:1.2) under reflux conditions.
bConversions less than 100% were determined on the basis of recovered aldehyde.
The effect of variant solvents, amount of NaHSO4·H2O, and power of ultrasound were
investigated on the typical experiment (Table 1). The results showed that a mixture of
n-hexane/CH3CN (2.5:0.5 mL) was the best solvent choice to run the multicomponent re-
action. Moreover, three molar equivalents of NaHSO4·H2O were sufficient to complete the
reaction within 6 h in refluxing n-hexane/CH3CN (2.5:0.5 mL) system (Entry 5). However,
irradiation of the reaction by ultrasound (240 W) dramatically accelerated the rate, and con-
sequently the reaction was completed within 2 h at reflux conditions (Entry 7) (Scheme 2).
Me
NaHSO4·H2O (3 mmol)
Ph
O
CO2Et
CHO
n-Hexane/CH3CN (2.5:0.5 mL), 6 h, 100%
EtO2C
Me
NH
H2NCONH2
+
N
H
O
NaHSO4·H2O (3 mmol), Ultrasound (240 W)
n-Hexane/CH3CN (2.5:0.5 mL), 2 h, 100%
4
Scheme 2
Table 1 also shows that the irradiation of ultrasound (240 W) in the absence of
NaHSO4·H2O was not efficient and the experiment had only 15% conversion within 6 h
(Entry 6). These results definitely exhibit a synergic influence of sonic and heating (re-
flux) conditions for catalysis of the one-pot reaction by NaHSO4·H2O. Therefore, using
NaHSO4·H2O (3 mmol) in refluxing n-hexane/CH3CN (2.5:0.5 mL) and under ultrasonic
conditions (240 W) was selected as the optimum to afford the best yield of DHPM (4) from
the reaction of benzaldehyde (1 mmol), ethyl acetoacetate (1 mmol), and urea (1.2 mmol)
(Entry 7).
Next, the potential and synthetic utility of NaHSO4·H2O/ultrasound system was
further studied by cyclocondensation reaction of aromatic aldehydes with various func-
tionalities, β-dicarbonyls (ethyl/methyl acetoacetate and acetylacetone), and urea at the
optimized reaction conditions. Table 2 summarizes the results of this investigation. As can
be seen, all reactions were carried out successfully within 0.5–2.8 h to afford DHPMs
(5–36) in excellent yields. The electronic effects of substituents on aromatic rings also

SYNTHESIS OF 3,4-DIHYDROPYRIMID INONES
1637
Table 2 Synthesis of 3, 4-dihydropyrimidin-2-(1H)-ones with NaHSO4·H2O/ultrasound systema
M.p. (◦C)
R
Rꢁ
X
DHPMs
Time (h)
Yield (%)b
Found
Reported
C6H5
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
Me
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
O
O
O
O
O
O
4
5
6
7
8
9
2
95
95
94
96
92
96
97
94
95
97
96
95
97
94
95
91
96
95
94
93
94
95
95
97
95
94
95
94
95
95
94
93
95
202–203
200–202
163–164
200–201
225–226
207–208
212–214
201–202
204–206
232–234
233–234
210–212
182–185
157–160
230–231
280–281
234–236
202–204
192–194
215–216
176–178
251–253
230–231
198–200
200–203
220–224
231–233
231 (dec)
227–228
168–170
211–213
202–203
215–217
200–20221a
200–20221a
164–16621a
199–20021a
226–22723
207–20921a
214–21621a
200–20121a
203–20521a
232–23521a
233–23543
209–21221a
—
2-HOC6H4
3-HOC6H4
4-HOC6H4
3-NO2C6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
2-Furyl
1.8
0.7
1
0.5
1
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
36
2.5
2.2
1.3
0.6
0.9
1.4
2.3
0.9
0.8
0.5
0.8
2
2.8
1.4
0.7
1.2
1.4
2.5
0.7
0.8
0.5
0.8
2.6
2.3
0.9
1.9
1.5
Ph-CH CH
4-HO-3-MeOC6H3
C6H5
2-HOC6H4
3-HOC6H4
4-HOC6H4
3-NO2C6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
2-Furyl
—
229–23044
279–28023
235–23721a
204–20621a
192–19421a
214–21644
—
Ph-CH CH
4-HO-3-MeOC6H3
C6H5
252–25423
229–23124
—
2-HOC6H4
3-HOC6H4
4-HOC6H4
3-NO2C6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
2-Furyl
Me
Me
Me
Me
Me
Me
Me
Me
—
—
—
230 (dec)21a
228–22923
168–17021a
210–21221a
—
Ph-CH CH
4-HO-3-MeOC6H3
Me
Me
—
aAll reactions were carried out with the molar ratio of aldehyde/β-dicarbonyl/urea/NaHSO4·H2O (1:1:1.2:3)
in refluxing n-hexane-CH3CN (2.5:0.5 mL) accompanied with ultrasound irradiation (240 W).
bYields refer to isolated pure products.
influenced the rate of reactions: electron-withdrawing groups accelerated the rates, and
electron-releasing ones prolonged the times of reactions. Moreover, under the experimental
conditions, furfural and cinnamaldehyde as the acid-sensitive compounds reacted smoothly
and gave the corresponding DHPMs (12, 13, 23, 24, 34 and 35) in 93–97% yields without
formation of any side products.
Thiourea has also been used to provide the corresponding sulfur analogs of 3,4-
dihydropyrimidinones which are also of much interest because of their biological activ-
ities.2 Similarly, the reaction of substituted aromatic aldehydes (1 mmol), β-dicarbonyl
compounds (1 mmol), and thiourea (1.2 mmol) with 3 mmol NaHSO4·H2O under ul-
trasonic conditions (240 W) afforded 3,4-dihydropyrimidin-2(1H)-thiones (37–69) within

1638
K. A. DILMAGHANI ET AL.
Table 3 Synthesis of 3, 4-dihydropyrimidin-2-(1H)-thiones with NaHSO4·H2O/ultrasound systema
M.p. (◦C)
R
Rꢁ
X
DHPMs
Time (h)
Yield (%)b
Found
Reported
C6H5
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
Me
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
1.3
2.5
0.5
0.9
0.9
1.2
2.2
2
1.2
0.9
1
1.6
1.5
1
1.5
0.7
1.3
2.2
3.1
0.9
0.6
1.3
1.4
2
0.6
1.2
0.8
1.2
2.5
2.5
0.8
1.5
1.2
96
95
96
98
95
94
92
94
93
95
94
91
91
95
94
92
90
92
94
96
93
92
94
92
95
95
96
97
92
97
92
91
96
208–209
171–173
185–187
192–193
207–208
108–110
192–193
149–151
182–183
243–244
146–149
227–228
150–153
221–223
201–203
206–207
108–110
164–165
149–150
163–164
218–221
257–258
185 (dec)
172–173
251–252
253–254
158–160
255–256
228–229
182–183
215–218
231–233
231–233
208–21021a
—
2-HOC6H4
3-HOC6H4
4-HOC6H4
3-NO2C6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
2-Furyl
184–18621a
193–19421a
206–20724
109–11121a
192–19421a
150–15221a
183–18443
243–24543
147–14943
228–22923
—
Ph-CH CH
4-HO-3-MeOC6H3
C6H5
2-HOC6H4
3-HOC6H4
4-HOC6H4
3-NO2C6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
2-Furyl
222–22323
202–20345
206–20745
—
165–16623
149–15044
—
Ph-CH CH
4-HO-3-MeOC6H3
C6H5
—
257–25823
185 (dec)24
—
2-HOC6H4
3-HOC6H4
4-HOC6H4
3-NO2C6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
2-Furyl
Me
Me
Me
Me
Me
Me
Me
Me
250–25123
252–25323
—
256–25823
228–22923
183–18423
—
Ph-CH CH
4-HO-3-MeOC6H3
Me
Me
—
232–23423
aAll reactions were carried out with the molar ratio of aldehyde/β-dicarbonyl/thiourea/NaHSO4·H2O (1:1:1.2:3)
in refluxing n-hexane-CH3CN (2.5:0.5 mL) accompanied with ultrasound irradiation (240 W).
bYields refer to isolated pure products.
0.6–3.1 h in 91–98% yields (Table 3). It is notable that in these cases, again, the combination
system of ultrasound and heating conditions was essential for catalysis of the condensation
reactions with NaHSO4·H2O.
As previously mentioned, the Biginelli synthesis of 3,4-dihydropyrimidinone has
been reported by modified sulfuric acid systems such as NaHSO4·H2O,21a H2SO4/SiO2,22
H2SO4/charcoal,23 and silica sulfuric acid.24 So, in order to highlight the advantages of
NaHSO4·H2O/ultrasound system, we compared some of our results with those of reported
methods (Table 4). Comparison of the results shows that due to the phenomena of acoustic
cavitations, the combination system of ultrasound with hydrated sodium hydrogen sulfate

1639

1640
K. A. DILMAGHANI ET AL.
exhibited the more or comparable rates and efficiency than the other hydrogen sulfate-
mediated protocols.
In summary, we have shown that NaHSO4·H2O under ultrasonic conditions dra-
matically accelerates the Biginelli synthesis of 3,4-dihydropyrimidinones (or thiones)
through one-pot cyclocondensation reaction of aromatic aldehydes, β-dicarbonyls, and
urea/thiourea in refluxing n-hexane/CH3CN system. All reactions were completed within
0.5–3.1 h to afford the products in 91–98% yields. Using available low-cost reagents, short
reaction times, excellent yields, and formation of variant DHPMs are the main advantages
which make this protocol a useful addition to the present methodologies.
EXPERIMENTAL
General
All solvents and reagents were purchased from commercial sources with the best
quality, and they were used without further purification. 1H, 13C NMR and IR spectra were
recorded on 300 MHz Bruker Avance and Thermo Nicolet Nexus 670 FT-IR spectrometers,
respectively. Irradiations of ultrasound were carried out by Cole-Parmer high-intensity
power ultrasound (600 W, 20 KHz) at 40% power amplitude. Melting points were measured
by a Philip-Harris melting point apparatus and were uncorrected. All products are known
and were characterized by their spectral data. Yields refer to isolated pure products. TLC
was applied for monitoring of the reactions over silica gel 60 F254 aluminum sheet.
Synthesis of 3,4-Dihydropyrimidin-2-(1H)-Ones and Their 2-Thioxo
Derivatives with NaHSO4· H2O/Ultrasound System: A General Procedure
To a solution of an aldehyde (1 mmol), ethyl/methyl acetoacetate or acetylacetone
(1 mmol) and urea/thiourea (1.2 mmol) in n-hexane/CH3CN (2.5:0.5 mL), NaHSO4·H2O
(3 mmol) was added. The reaction mixture was then heated to reflux and synchronously
irradiated by ultrasound (240 W) via a micro-tip probe for an appropriate time. Progress
of the reactions was monitored by TLC (n-hexane/EtOAc: 5/3). After completion of the
reaction, the solution was cooled to room temperature and H2O (5 mL) was then added
followed by stirring for 5 min. The mixture was extracted with EtOAc (3 × 8 mL) and
dried over anhydrous Na2SO4. Evaporation of the solvent and recrystallization of the crude
product in hot MeOH affords the pure DHPM (4–69) in 91–98% yield (Tables 2 and 3).
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