# 1-Methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium Chloride as a New and Green Ionic Liquid Catalyst for One-Pot Synthesis of Dihydropyrimidinones under Solvent-Free Condition

Authors: Sami Sajjadifar; Eshagh Rezaee Nezhad; Ghasem Darvishi
Journal: Journal of Chemistry
 (2013)

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## Abstract

An efficient and simple method for the preparation of 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium chloride{(MSEI)Cl} as an acidic ionic liquid is described. One-pot multicomponent condensation of 1,3-dicarbonyl compounds, urea/thiourea and aldehydes at 80∘C affords the corresponding compounds in high yields and in short reaction times by using (MSEI)Cl.


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## Body

## 1. Introduction

First reported for multicomponent reaction involves a three-component, one-pot condensation of an aldehyde,α,β-ketoester, and urea under strongly acidic conditions discovered by Biginelli in 1893 [10]. In the past few decades, interest in this reaction has increased dramatically since dihydropyrimidinones have a wide range of biological activities, acting as calcium channel antagonists, anti-hypertensive, anti-bacterial and anti-inflammatory agents, while also possessing cytotoxic activity [11–17]. In order to improve the efficiency of Biginelli reaction, a variety of catalysts have been reported which of them H4PMo11VO40, [18], Dowex-50W [19], H3PW12O40/SiO2 [20], MgBr2 [21], polymer-supported 4-aminoformoyldiphenylammonium triflate [22], NaHSO4/SiO2 [23], FeCl3 [24], ZrCl4 [25], Cu(OTf)2 [26], Bi(OTf)3 [27], yutterbium triflate [28], NH2SO3H [29], 12-Molybdopho sphoric acid [30], natural HEU type zeolite [31], Sr(OTf)2 [32], covalently anchored sulfonic acid onto silica [33], ZrOCl2·8H2O [34], silica triflate [35], Fe(HSO4)3 [36], TCICA [37], PPh3 [38], CaF2 [39], [bmim]BF4-immobilized Cu(II) acetylacetonate [40], [bmim][FeCl4] [7], ionic liquidsunder ultrasound irradiation [41], and melamine trisulfonic acid [42] are examples. Ionic liquids (ILs), which have been widely promoted as green solvents, are attracting much attention for applications in many fields of chemistry and industry due to their chemical and thermal stability, low vapor pressure, and high-ionic-conductivity properties. Over the last few years, ILs have been popularly used as solvents for organic synthesis, catalysis,and also been used as media for extraction processes [43, 44]. But some of the mentioned methods encounter drawbacks such as the requiring expensive reagents, long reaction times, low yields of the products and tedious workup. The advantages of the present procedure are simplicity of operation, short reaction times, inexpensive reagents, green condition, and the high yields of products.We synthesized the bronsted acidic ionic liquid 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium chloride [45] as an efficient and reusable catalyst for the synthesis of DHPMs derivatives.


## 2. Experimental

IR spectra of the compounds were obtained on a PerkinElmer spectrometer version 10.03.06 using a KBr disk. The1H nuclear magnetic resonance (1H NMR) spectra were recorded on a Bruker AQS 400 Avance instrument at 400 MHz in dimethyl sulfoxide (DMSO-d6) using tetramethylsilane as an internal standard. The progress of reaction was followed with thin-layer chromatography (TLC) using silica gel SILG/UV 254 and 365 plates. All the products are known compounds and were characterized by comparing the IR, 1H NMR, and 13C NMR spectroscopic data and their melting points with the literature values.


### 2.1. Preparation of Bronsted Acidic Ionic Liquid

1-Methylimidazole1 (4.1 g, 50 mmol) and 2-chloroethanol 2 (4.02 g, 50 mmol) were added in a flask containing 10 mL of CHCl3, and the mixture was refluxed for 8 h and removed CHCl3 under vacuum. Unreacted 1-methylimidazole or 2-chloroehanol was extracted with ether (3 × 10 mL) to give 1-methyl-3-(2-hydroxylethyl) imidazolium chloride (yield 95%). IR spectrum of compound 3: OH (3200–3600 cm−1), C=C (1450, 1575 cm−1), and C=N (1643 cm−1) (Figure 2).A stoichiometric amount of 97% chlorosulfonic acid (3.4 mL, 50 mmol) in CCl4 (10 mL) was added dropwise to compound 3 over a period of 45–60 min at 0°C, and HCl gas was evolved in an alkali trap immediately (Scheme 1). The mixture was washed with CCl4 (3 × 10 mL) to remove the unreacted chlorosulfonic acid (yield 92%). IR spectrum of compound 4: OH (3200–3600 cm−1), C=C (1440, 1579 cm−1), C=N (1648 cm−1), S=O (1019 cm−1), and S–O (623 cm−1) (Figures 1 and 2) [44].Scheme 1
Synthesis of 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium chloride.Scheme 2
Synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones.Figure 1Figure 2
Comparison IR spectrum of ionic liquid3, bronsted acidic ionic liquid 4.


### 2.2. General Procedure for the Preparation of DHPMs

A mixture of an aromatic aldehyde (1 mmol),β-dicarbonyl (1 mmol), urea/thiourea (1.5 mmol), and catalyst (50 mg) was finely mixed together in a test tube at 80°C for the times reported in (Table 2). During the reaction process, a solid product spontaneously formed. The completion of the reaction was monitored by TLC. The reaction mixture was cooled to room temperature and then cold water (20 mL) was added to the reaction mixture and stirred for 10–15 min. During this time, crystals of the product formed which were collected by filtration and dried and then recrystallized from ethanol to afford the pure product. The results are summarized in Table 2. The aqueous layer (including BAIL) was separated, and its solvent was evaporated to obtain pure BAIL. The recycled catalyst was used for the next run under identical reaction conditions.


## 2.1. Preparation of Bronsted Acidic Ionic Liquid

1-Methylimidazole1 (4.1 g, 50 mmol) and 2-chloroethanol 2 (4.02 g, 50 mmol) were added in a flask containing 10 mL of CHCl3, and the mixture was refluxed for 8 h and removed CHCl3 under vacuum. Unreacted 1-methylimidazole or 2-chloroehanol was extracted with ether (3 × 10 mL) to give 1-methyl-3-(2-hydroxylethyl) imidazolium chloride (yield 95%). IR spectrum of compound 3: OH (3200–3600 cm−1), C=C (1450, 1575 cm−1), and C=N (1643 cm−1) (Figure 2).A stoichiometric amount of 97% chlorosulfonic acid (3.4 mL, 50 mmol) in CCl4 (10 mL) was added dropwise to compound 3 over a period of 45–60 min at 0°C, and HCl gas was evolved in an alkali trap immediately (Scheme 1). The mixture was washed with CCl4 (3 × 10 mL) to remove the unreacted chlorosulfonic acid (yield 92%). IR spectrum of compound 4: OH (3200–3600 cm−1), C=C (1440, 1579 cm−1), C=N (1648 cm−1), S=O (1019 cm−1), and S–O (623 cm−1) (Figures 1 and 2) [44].Scheme 1
Synthesis of 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium chloride.Scheme 2
Synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones.Figure 1Figure 2
Comparison IR spectrum of ionic liquid3, bronsted acidic ionic liquid 4.


## 2.2. General Procedure for the Preparation of DHPMs

A mixture of an aromatic aldehyde (1 mmol),β-dicarbonyl (1 mmol), urea/thiourea (1.5 mmol), and catalyst (50 mg) was finely mixed together in a test tube at 80°C for the times reported in (Table 2). During the reaction process, a solid product spontaneously formed. The completion of the reaction was monitored by TLC. The reaction mixture was cooled to room temperature and then cold water (20 mL) was added to the reaction mixture and stirred for 10–15 min. During this time, crystals of the product formed which were collected by filtration and dried and then recrystallized from ethanol to afford the pure product. The results are summarized in Table 2. The aqueous layer (including BAIL) was separated, and its solvent was evaporated to obtain pure BAIL. The recycled catalyst was used for the next run under identical reaction conditions.


## 3. Results and Discussion

The one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones was achieved by the three-component condensation of aldehydes, dicarbonyl, and urea or thiourea in presence of bronsted acidic ionic liquid is conducted at 80°C, and the results are summarized in Table1. The procedure gives products in good yields, short reaction times and avoids the use of organic solvents (handling, cost, safety, pollution) (Table 4). Environmental friendly ionic liquid afforded a valuable alternative to promote a numerous efficient catalytic systems that have already been proposed for the achievement of DHPMs. As long as, the reaction rate and the yields are depending on electron donating/withdrawing effect of the groups on the benzene ring in benzaldehydes. Aryl aldehydes containing electron-donating substituent gave excellent yields of the products in a shorter reaction time. The mechanism of the Biginelli reaction established by Kappe [6] proposed that the key step in this cyclocondensation process should involve the formation of N-acyliminium ion intermediate (Scheme 3).Table 1
Temperature and time effect on dihydropyrimidinones synthesis.
Entry
Temperature (°C)
Time (min)
Yield (%)
1
r.t.
90
36
2
50
90
45
3
80
30
93
4
100
30
91
5
120
30
90Table 2
Dihydropyrimidinones synthesis catalyzed by BrØnsted acidic ionic liquid (BAIL).
Entry
R1
R2
X
Time (min)
Yield (%)
M.p. (°C)
Found
Reported
1
Ph
Me
O
30
93
231–233
235-236 [1]
2
4-OH–C6H4
Me
O
30
95
254–256
256–258 [2]
3
4-Me–C6H4
Me
O
30
92
231-232
228-229 [1]
4
4-MeO–C6H4
Me
O
30
90
175–177
177–179 [2]
5
4-Cl–C6H4
Me
O
30
92
223-224
224–226 [3]
6
4-NO2–C6H4
Me
O
45
85
227 (dec)
229 (dec) [2]
7
3-NO2–C6H4
Me
O
45
82
246–248
248–250 [1]
8
Ph
OEt
O
45
88
203–205
201-202 [1]
9
2-OH–C6H4
OEt
O
45
92
200–202
201–203 [3]
10
4-Me–C6H4
OEt
O
45
90
170–172
170-171 [1]
11
4-MeO–C6H4
OEt
O
45
87
198–200
199–201 [4]
12
4-Cl–C6H4
OEt
O
45
86
211–213
209-210 [1]
13
3-NO2–C6H4
OEt
O
60
78
225–227
226-227 [4]
14
Ph
Me
S
75
81
230-231
232–233 [5]
15
2-OH–C6H4
Me
S
75
83
239–241
242-243 [3]
16
4-Me–C6H4
Me
S
75
80
221–223
222–224 [5]
17
4-NO2–C6H4
Me
S
90
73
106-107
108–110 [6]
18
Ph
OEt
S
105
75
206–208
208-209 [5]
19
4-Me–C6H4
OEt
S
105
72
193-194
193-194 [1]
20
4-NO2–C6H4
OEt
S
120
70
214–216
209–212 [3]Scheme 3
Mechanism of synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones.According at Table2 the using of thiourea and ethylacetoacetate increased reaction time, and also the using of thiourea reduces the efficiency of Biginelli reaction. Thiourea stability of negatively charged than urea and low nucleophiles property of thiourea than urea at intermediate State. The catalyst is reusable and can be applied several times without any decrease in the yield of the reaction. As it can be seen from Table 3, (MSEI)Cl as a catalyst afforded the good results with respect to the another ionic liquid catalysts.Table 3
Comparison of catalytic ability of catalysts.
Entry
Catalyst
Time (min)condition
Yield (%) (reference)
1
[BMIM]FeCl4
120
90
90°C, s.f.a
[7]
2
[HMIM]Tfa
45
90
50°C, s.f.
[4]
3
[BMIM]BF4
30
99
100°C, s.f.
[8]
4
[HMIM]HSO4
90
96
80°C, s.f.
[9]
5
[MSEI]Cl
30
93
80°C, s.f.
—
as.f.: solvent free condition.Table 4
Formation of DHMP in different solvents and comparison with solvent-free condition.
Entry
Solvent
Time (h)
Temperature (°C)
Yield (%)
1
Ethanol
4
Refluxing
81
2
H2O
4
Refluxing
<20
3
MeCN
4
Refluxing
70
4
CH2Cl2
8
Refluxing
38
5
Solvent-free
0.5
80
93


## 4. Conclusions

In summary, we have developed the use of bronsted acidic ionic liquid 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium chloride as an inexpensive, easy to handle, noncorrosive and environmentally benign catalyst for the Biginelli reaction from an aldehyde, aβ-dicarbonyl, and urea or thiourea. The advantages of the present procedure are simplicity of operation, very short reaction times compared with other procedures for the preparation of dihydropyrimidinones derivatives, and the high yields of products. In this reaction the catalyst can be were easily recyclable after removing starting materials and water (Table 5).Table 5
Recovery of catalyst.
Number
Reaction
Yield (%)
1
First
91
2
Second
91
3
Third
90
4
Forth
88



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*Source: 834656-2012-10-23.xml*