One-pot synthesis of dihydropyrimidine-thione derivatives using tungstate sulfuric acid (TSA) as a recyclable catalyst

Article abstract of DOI:10.1080/10426507.2011.616562

An efficient, simple, and environmentally benign procedure for the one-pot synthesis of 3,4-dihydropyrimidine-2-(1H) thione derivatives that entails the three-component condensation of appropriate aryl aldehydes, β-dicarbonyls, and thiourea in the presenc

Full text of DOI:10.1080/10426507.2011.616562

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One-Pot Synthesis of Dihydropyrimidine-
Thione Derivatives Using Tungstate
Sulfuric Acid (TSA) as a Recyclable
Catalyst
Bahador Karami a , Zahra Haghighijou a , Mahnaz Farahi a & Saeed
Khodabakhshi a
a Department of Chemistry , Yasouj University , Yasouj , Iran
Published online: 05 Apr 2012.
To cite this article: Bahador Karami , Zahra Haghighijou , Mahnaz Farahi & Saeed Khodabakhshi
(2012) One-Pot Synthesis of Dihydropyrimidine-Thione Derivatives Using Tungstate Sulfuric Acid (TSA)
as a Recyclable Catalyst, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:6, 754-761,
DOI: 10.1080/10426507.2011.616562
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Phosphorus, Sulfur, and Silicon, 187:754–761, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.616562
ONE-POT SYNTHESIS OF DIHYDROPYRIMIDINE-THIONE
DERIVATIVES USING TUNGSTATE SULFURIC ACID (TSA)
AS A RECYCLABLE CATALYST
Bahador Karami, Zahra Haghighijou, Mahnaz Farahi,
and Saeed Khodabakhshi
Department of Chemistry, Yasouj University, Yasouj, Iran
GRAPHICAL ABSTRACT
Abstract An efficient, simple, and environmentally benign procedure for the one-pot synthesis
of 3,4-dihydropyrimidine-2-(1H) thione derivatives that entails the three-component conden-
sation of appropriate aryl aldehydes, β-dicarbonyls, and thiourea in the presence of catalytic
amount of tungstate sulfuric acid under solvent-free conditions was reported. This method has
many advantages including excellent yields, short reaction time, and simple work-up procedure.
Supplemental materials are available for this article. Go to the publisher’s online edition
of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supple-
mental resource: 1H, 13C NMR and Mass Spectra for 5b, 5g, 5j, 5i, 5l (S2-S16). Additional
Characterization Data (S17-18).
Keywords Tungstate sulfuric acid; 3,4-dihydropyrimidine-2-(1H) thione; β-dicarbonyls;
thiourea
INTRODUCTION
The chemistry of molecules containing sulfur atom attracts continuous attention as a
consequence of the potential biological activity of this class of compounds.1 For instance,
Received 23 November 2010; accepted 18 August 2011.
We are thankful to the Yasouj University for partial support of this work.
Address correspondence to Bahador Karami, Department of Chemistry, Yasouj University, P.O. Box 353,
Yasouj 75918-74831, Iran. E-mail: karami@mail.yu.ac.ir
754

ONE-POT SYNTHESIS OF DIHYDROPYRIMIDINE-THIONE DERIVATIVES
755
OH
NO2
O
O
O
EtO
Me
NH
i-PrO
Me
(R)-SQ 32,926
N
NH2
N
H
S
N
S
H
Monastrol
Figure 1 Two types of biologically active dihydropyrimidine compounds.
Monastrol, as one of the most important dihydropyrimidine-thione derivatives, is a new
class of anticancer agents acting as cell division (mitosis) blockers and the (R)-SQ 32,926
has been identified as a potent orally active antihypertensive agent (Figure 1).2 Considering
the use of functionalized dihydropyrimidine-2(1H)-one/thione as potent calcium channel
blockers,3 antihypertensive agents,4 and neuropeptide Y antagonist5 and also, because of
their diversified activities such as antibacterial,6 antiviral,7 and antitumor properties,8 it
can be concluded that these heterocyclic compounds play a significant role in synthetic,
therapeutic, and bioorganic chemistry.
For preparing 3,4-dihydropyrimidine-2-(1H) one/thione derivatives, numerous meth-
ods are available in the literature. Generally, these compounds could be prepared via the
Biginelli condensation of aldehydes with β-diketones and urea or thiourea derivatives in
refluxing ethanolic HCl,9 but the major disadvantage in this protocol, particularly for sub-
stituted aromatic and aliphatic aldehydes, is low yield of the products.10,11 Due to the
importance of Biginelli reaction products, several kinds of improved routes including the
use of new catalysts, reagents, and techniques have been developed.12 However, some of
the reported methods have drawbacks such as unsatisfactory yield, long reaction time, and
the use of complex or expensive catalysts, organic solvents, and many heavy metallic salts
that can pollute the environment12c–g
.
RESULTS AND DISCUSSION
Recently, silica sulfuric acid and Nafion-H13 have been used for a wide variety of
reactions.14 Accordingly, we found that anhydrous sodium tungstate reacts with chlorosul-
fonic acid (1:2 mole ratio) to give tungstate sulfuric acid (TSA 1). The reaction is easy,
clean, and performed without any workup (Scheme 1). It is to be noted that there is no
gas production during the reaction. More details (particularly the synthetic method and
characterization) of this process have been fully described in our previous article.15a
O
O
2 ClSO3H
HO SO W OSO H
NaO W ONa
2 NaCl
+
3
3
O
O
1
Scheme 1
In connection with our previous programs on developing the TSA (1) in organic
transformations,15 in this work, we wish to report a simple and convenient route for the
condensation of aryl aldehydes (2) with β-dicarbonyls (3) and thiourea (4) using tungstate

756
B. KARAMI ET AL.
S
H2N
O
NH2
O
O
R1
4
R2
Me
NH
R1CHO
1
(5 mol %)
+
o
solvent-free, 80 C
N
H
S
2
Me
R2
5
3
Scheme 2
sulfuric acid as a catalyst under solvent-free conditions to afford the 3,4-dihydropyrimidine-
2-(1H) thione derivatives (5) (Scheme 2).
To exploit simple and suitable conditions for the preparation of (5) using (1) as a solid
acid catalyst, the treatment of benzaldehyde, ethyl acetoacetate, and thiourea was chosen as
a model reaction. At first, we found that in the absence of (1), the reaction did not proceed
even at a high temperature. After examining the various amounts of (1) according to Table 1
and a wide range of temperatures (Table 2), it was found that the condensation reaction
can be efficiently carried out by adding 5 mol% of the catalyst at 80 ◦C under solvent-free
conditions in a short time span of 60 min. The use of excessive amounts of the catalyst does
not increase the yield or reaction rate.
In comparison with previous methods, two parallel reactions series, one according
to classical Biginelli reaction (Method B) and another in our conditions (Method A),
were designed. As shown in Table 3, the product yields were moderate (40%–75%) after
370–660 min, when the reactions were carried out with HCl (aq.) alone (classical Biginelli
conditions), whereas the same reactions in the presence of tungstate sulfuric acid gave good
to excellent yields (73%–90%) after 45–75 min under solvent-free conditions.
In order to prove the versatility of this method (summarized in Table 3), we extended
these reaction conditions to a series of aryl aldehydes and two types of β-dicarbonyl com-
pounds such as ethyl acetoacetate and acetylacetone. Both electron-donating and electron-
withdrawing groups on the aryl aldehyde (R1) reacted well in this process to afford the
corresponding products (5) in good to excellent yields (Entries 1–13, Table 3).
The main advantages of the presented protocol over existing methods can be seen by
comparing our results with those of some recently reported procedures, as shown in Table 4.
In many cases, in order to achieve fast synthesis in organic process, a catalyst must be used.
The need to implement green chemistry principles (e.g., safer solvents, less hazardous
Table 1 Optimization of the amounts of TSA (1) under solvent-free conditions at 80 ◦C for the synthesis of (5k)
Entry
Catalyst amount (mol%)
Time (min)
Yield (%)a
1
2
3
4
5
6
—
1
2
5
10
20
300
300
300
60
70
100
10b
35b
40b
80
75
75
aIsolated yields.
bNot completed.

ONE-POT SYNTHESIS OF DIHYDROPYRIMIDINE-THIONE DERIVATIVES
757
Table 2 Optimization of the temperature under solvent-free using TSA (1) (5 mol%) for the synthesis of (5k)
Entry
Temperature (◦C)
Time (min)
Yield (%)a
1
2
3
4
25
60
80
360
360
60
10
25
80
75
120
55
aIsolated yields.
Table 3 Synthesis of (5) through our and classical Biginelli method
Yield (%)a
Time (min)
Entry
Product
R1
R2
Ab
Bc
Ab
Bc
mp (◦C) [L]
1
2
3
4
5
6
7
8
5a
5b
5c
5d
5e
5f
5g
5h
5i
C6H5
2-OH-C6H4
2-Cl-C6H4
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
OEt
OEt
OEt
80
80
73
76
88
87
82
76
87
90
86
80
85
55
40
75
75
65
65
70
68
64
70
50
45
65
60
60
45
45
75
75
45
45
60
60
60
60
75
660
660
600
480
600
370
460
390
600
420
600
600
490
223–22516a,b
224–226d
174–17516c
189–19116d
133–13516d
156–15816e
155–157d
4-Cl-C6H4
2,6-Cl2-C6H3
4-NO2-C6H4
2-OMe-C6H4
4-OMe-C6H4
3,4,5-OMe3-C6H2
4-Me-C6H4
C6H5
187–18916d
152–153d
9
10
11
12
13
5j
5k
5l
153–155d
206–20716d
221–22316f
206–20816g
2-OH-C6H4
3-NO2-C6H4
5m
aIsolated yields.
bMethod A: new reaction conditions under solvent-free (cat. tungstate sulfuric acid, 45–75 min) conditions.
cMethod B: classical Biginelli conditions (cat. HCl in EtOH, reflux).
dNovel compounds.
Table 4 Comparison of our method with other methods for the synthesis of (5k) based on the condensation of
aldehydes (1 mmol), ethylacetoacetate (1 mmol), and thiourea (1.5 mmol)
Time (h)/Yield
Entry
Catalyst
Catalyst amount
One drop
0.025 g
0.1 mmol
Aqueous solution (40% w/v)
(0.06 mmol)
0.5 mmol
1 g
0.2 mmol
Condition
Reflux
(%)/[Ref.]
1
2
3
4
HCl in EtOH
Na2SeO4
ClCH2CO2H
Zn(BF4)2
10/50/[This work]
1.5/77/17a
5/79–87/17b
6/65/17c
Solvent-free, 80 ◦C
Solvent-free, 90 ◦C
RT
5
6
7
9
Ca(HSO4)2
P2O5/SiO2
NaBF4
Solvent-free, 90 ◦C
Solvent-free, 80 ◦C
Ethanol/Reflux
2.5/74/17d
2.5/83/17e
4.5/89/17f
TSA
0.05 mmol
Solvent-free, 80 ◦C
1/86/[This work]

758
B. KARAMI ET AL.
Figure 2 Recyclability of TSA as a catalyst for the synthesis of (5k) on the condensation of aldehydes (1 mmol)
and ethylacetoacetate (1 mmol) under solvent-free conditions at 80 ◦C. Reaction time = 60–70 min.
chemical synthesis, atom economy, and catalysis) is a driving force toward the development
of recoverable and reusable catalysts and avoidance of the use of toxic organic solvents.
Not only the ecological profile (through helping to decrease hazardous industrial
waste) but also the economic profile (through the elimination of expensive organic solvent)
is further improved if the catalyst is recyclable and reaction conditions are solvent-free. In
this process, as indicated in Figure 2, the recycled catalyst was used for five cycles during
which a little appreciable loss was observed in the catalytic activities.
R
H
OH
NH2
O
S
R
OH2
NH2
HA
HA
-
+
+ A
R1
H
H2N
NH2
N
O
N
H
2
4
S
S
H
O
R1
R
H
O
R2
NH
R2
N
NH2
H3C
-H2O
H
S
H3C OH
S
NH2
6
7
R1
O
R1
O
H
R2
H3C
HO
NH
R2
H3C
NH
S
-H2O
-HA
N
S
N
H
H
O
5
HA: HO3SOWOSO3H
O
Scheme 3

ONE-POT SYNTHESIS OF DIHYDROPYRIMIDINE-THIONE DERIVATIVES
759
Considering the general mechanistic pathway, which was proposed in a previ-
ous report,18 the suggested mechanism for the formation of (5) using (1) is shown in
Scheme 3. Protonation of the carbonyl group by Brønsted acid (TSA) generates an elec-
trophilic center on the carbonyl carbon atom, which is easily attacked by the thiourea to
form minimum intermediate (6), which is the key rate-limiting step. Interception of this
minimum intermediate (6) by β-dicarbonyl produces an open chain thioureide (7), which
subsequently cyclizes through dehydration process yielding compounds (5a–n).
CONCLUSION
In this study, we presented a powerful and modified method for the one-pot reaction
of aldehydes, β-dicarbonyls, and thiourea by employing the tungstate sulfuric acid as
commercially available, inexpensive, and reusable solid acid catalyst under solvent-free
conditions. Higher yields and shorter reaction times than the classical Biginelli method,
and simple work-up procedure are the appealing attributes of this project. Moreover, the
use of the nonhygroscopic and ecofriendly catalyst such as TSA (1) is another advantage
that makes this method a valid contribution to the existing methodologies.
EXPERIMENTAL
General
All chemicals were purchased from Merck, Fluka, and Aldrich. The reactions were
monitored by thin layer chromatography (TLC; silica-gel 60 F254, n-hexane: ethyl acetate).
IR spectra were recorded on a FT-IR JASCO-680 and the 1H NMR spectra were obtained on
a Bruker-Instrument DPX-400 MHz Avance 2 model. The varioEl CHNS Isfahan Industrial
University was used for elemental analysis. Mass spectra were recorded on a Shimadzu
Gc-MS QP 100 Ex spectrometer.
General procedure for the preparation of 3,4-dihdropyrimidine-
2(1H)-thiones (5)
A mixture of aryl aldehyde 2 (1 mmol), β-dicarbonyl compound 3 (1 mmol), thiourea
4 (1.5 mmol), and TSA 1 (5 mol%) was stirred and heated at 80 ◦C in a preheated oil bath
for the appropriate time (Table 3). After completing the reaction as indicated by TLC,
the reaction mixture was cooled to room temperature and filtered, then washed with cold
water, and recrystallized from ethanol to afford the pure product (5). Many of the products
were identified by comparing their spectral and physical data with those for authentic
samples.18 1H, 13C NMR, and mass spectra for 5b, 5g, 5i, 5j, and 5l can be found in the
Supplemental Materials (Figures S 1–S 15).
Spectral and physical data for novel compounds
5-Acetyl-6-methyl-4-(2-hydroxyphenyl)-3,4-dihydropyrimidine-2(1H)-thione
1
(5b): FT-IR (KBr) cm−1: 3229, 3146, 1609, 1588, 1195, 760, 719; H NMR (400 MHz,
DMSO-d6): δH (ppm) 9.06 (s, 1H), 9.01 (s, 1H), 7.23–7.18 (m, 2H), 6.94 (t, J = 7.2 Hz,
1H), 6.82 (d, J = 8 Hz, 1H), 4.74 (d, J = 2.4 Hz, 1H), 3.42 (s, 1H), 2.27 (s, 1H), 1.67
(s, 3H); 13C NMR (100 MHz): δc (ppm) 176.93, 151.06, 130.09, 129.40, 124.72, 121.13,

760
B. KARAMI ET AL.
116.86, 48.47, 47.89, 29.62, 23.24; Anal. Calcd. for C13H14N2O2S: C, 59.52; H, 5.38; N,
10.88; S, 12.22. Found: C, 60.83; H, 5.53; N, 10.72; S, 12.34; MS (m/z: 262).
5-Acetyl-6-methyl-4-(2-methoxylphenyl)-3,4-dihydropyrimidine-2(1H)-thione
1
(5g): FT-IR (KBr) cm−1: 3325, 3184, 1671, 1592, 1387, 754; H NMR (400 MHz,
DMSO-d6): δH (ppm) 10.21 (s, 1H), 9.35 (s, 1H), 7.26 (d, J = 8 Hz, 1H), 7.03–6.92
(m, 2H), 6.89 (d, J = 8 Hz, 1H), 5.58 (d, J = 3.6 Hz, 1H), 3.76 (s, 3H), 2.27 (s, 3H),
2.07 (s, 3H); 13C NMR (100 MHz): δc (ppm) 195.57, 174.61, 156.65, 144.35, 130.51,
129.74, 127.76, 120.91, 111.83, 109.61, 55.91, 49.54, 30.10, 18.30; Anal. Calcd. for
C14H16N2O2S: C, 60.85; H, 5.84; N, 10.14; S, 11.60. Found: C, 59.98; H, 5.58; N, 9.37;
S, 12.10; MS (m/z: 276).
5-Acetyl-6-methyl-4-(3,4,5-trimethoxyphenyl)-3,4-dihydropyrimidine-2(1H)-
thione (5i): FT-IR (KBr) cm−1: 3297, 3002, 1613, 1593, 1567, 1187, 1124, 1018, 685; 1H
NMR (400 MHz, DMSO-d6): δH (ppm) 10.28 (s, 1H), 9.71 (s, 1H), 6.51 (s, 2H), 5.25 (s,
1H), 3.71 (s, 6H), 3.62 (s, 3H), 2.33 (s, 3H), 2.16 (s, 3H); 13C NMR (100 MHz): δc (ppm)
195.47, 174.56, 153.38, 145.06, 138.86, 137.48, 110.51, 104.23, 60.43, 56.28, 54.23,
30.84, 18.65; Anal. Calcd. for C16H20N2O4S: C, 57.12; H, 5.99; N, 8.33; S, 9.53. Found:
C, 57.45; H, 5.98; N, 8.33; S, 10.44; MS (m/z: 336).
5-Acetyl-6-methyl-4-(4-metheylphenyl)-3,4-dihydropyrimidine-2(1H)-thione
1
(5j): FT-IR (KBr) cm−1: 3329, 3177, 1671, 1571, 1454, 1341, 749; HNMR (400 MHz,
DMSO-d6): δH (ppm) 10.24 (s, 1H), 9.71 (s, 1H), 7.14–7.08 (2d Jc = 7,6 and 7,6 Hz, 4H),
5.23 (s, 1H), 2.31 (s, 3H), 2.25 (s, 3H), 2.12 (s, 3H); 13C NMR (100 MHz): δc (ppm) 195,
28, 174.42, 144.84, 140.45, 137.43, 129.62, 126.96, 110.86, 54.02, 30.78, 21.13, 18.67;
Anal. Calcd. for C14H16N2OS: C, 64.58; H, 6.19; N, 10.76; S, 12.32. Found: C, 65.97; H,
6.33; N, 10.84; S, 13.02; MS (m/z: 260).
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