Punica granatum peel: an organocatalyst for green and rapid synthesis of 3,4-dihydropyrimidin-2 (1H)-ones/thiones under solvent-free condition

Article abstract of DOI:10.1007/s11164-016-2828-9

A novel and green approach was adopted for the synthesis of 3,4-dihydropyrimidin-2(1H)-one/thiones derivatives using Punica granatum peel as an inexpensive, efficient and mild catalyst under solvent-free condition. The methodology is characterized by high

Full text of DOI:10.1007/s11164-016-2828-9

Res Chem Intermed
DOI 10.1007/s11164-016-2828-9
Punica granatum peel: an organocatalyst for green
and rapid synthesis of 3,4-dihydropyrimidin-2
(1H)-ones/thiones under solvent-free condition
Narges Mohammadian1 Batool Akhlaghinia1
•
Received: 6 August 2016 / Accepted: 5 December 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract A novel and green approach was adopted for the synthesis of 3,4-dihy-
dropyrimidin-2(1H)-one/thiones derivatives using Punica granatum peel as an
inexpensive, efficient and mild catalyst under solvent-free condition. The method-
ology is characterized by high efficiency, short reaction time, high yields, simple
experimental procedure, availability of catalyst and environmentally friendly
reaction conditions. Further, the catalyst can be reused and recovered seven times
without significant decrease in its activity.
Keywords Biginelli reaction Á Pomegranate peel Á 3,4-dihydropyrimidin-
2(1H)ones/thiones Á Solvent-free green chemistry Á Aldehydes Á Urea Á Thiourea
Introduction
Dihydropyrimidinones and dihydropyrimidine thiones derivatives as Biginelli
adducts have received great attention from synthetic and medicinal chemists due
to their various promising activities such as antihypertensive, potassium channel
antagonist, anti-epileptic, antimalarial, antimicrobial, antitumor, antibacterial,
anticancer, and anti-inflammatory properties [1, 2]. The first synthesis of
dihydropyrimidinones, which was originally reported by P. Biginelli in 1893,
involves heating a mixture of an aldehyde, ethyl acetoacetate and urea, though
yields are somewhat low [3]. The Biginelli reaction is remarkable for its simplicity
Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2828-
9) contains supplementary material, which is available to authorized users.
&
Batool Akhlaghinia
akhlaghinia@um.ac.ir
1
Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad,
Mashhad 9177948974, Iran
123

N. Mohammadian, B. Akhlaghinia
and also for the fact that it represents one of the early examples of a multicomponent
reaction (MCR) [4–6]. Since the 1990s, several new methods have been developed
to improve the reaction yield, lower the reaction time, and/or broaden the scope of
the Biginelli reaction by using microwave irradiation, ultrasound irradiation, Lewis
and protic acid promoters such as lanthanide triflate [3], H3BO3, VCl3, Sr(OTf)2,
PPh3, indium(III) halides, Mn(OAc)3Á2H2O, Y(NO3)3Á6H2O, In(OTf)3, TaBr5,
Ce(NO3)3Á6H2O, BF3EtOH/CuCl, LaCl3Á7H2O with a catalytic amount of concen-
trated HCl, CeCl3.7H2O, Cu(OTf)2, LiClO4, LiBr, ceric ammonium nitrate (CAN),
FeCl3.6H2O/HCl, Fe(HSO4)3, TMSI, CdCl2, PPE, LaCl3, 1-n-butyl-3-methyl
imidazolium tetrafluoroborate (BMImBF4), ZrCl4, H4PMo11VO40, MgBr2, ZrOCl2-
8H2O, CaF2, CuCl2, 12H2O supported on silica, silica chloride, H3PW12O40/SiO2,
covalently anchored sulfonic acid onto silica, silica triflate, KSF clay, Dowex-50 W,
natural HEU type zeolite [3], ionic liquids [3, 7], Zn(BF4)2 [8], NiCl2 [9],
Fe(OTs)3.6H2O [10], CAN/HCl [11], TCICA [12], [bmim]BF4-immobilized Cu(II)
acetylacetonate [13], [bmim][FeCl4] [14], Zn(OTf)2 [15], p-TsOH [16], ZnO [17],
KAl(SO4)2. silica sulfuric acid [3, 18], silica gel-supported L-pyrrolidine-2-
carboxylic acid-4-hydrogen sulphate [19], SBA-15 sulfonic acid [20], NaHSO4/
SiO2 [21], mercaptopropyl silica [22], PEG–SO3 [23], p-dodecylbenzenesulfonic
acid (DBSA) [24], Fe3O4@mesoporous SBA-15 [25], HCOOH [26], H2SO4 [27], L-
proline [28], carbon-based solid acid [29], and so on.
Although a handful of the catalytic methodologies (by using metal Lewis acids,
Brønsted acids or bases, heterogeneous catalysts, and nonconventional techniques,
such as microwave, ultrasound, high pressure, and grindstone chemistry) have been
promoted by environmentally friendly catalysts, many others at a practical level
require relatively harsh reaction conditions such as high reaction temperatures,
expensive, toxic or highly corrosive acidic catalysts, and prolonged reaction times.
In most of the cases, stoichiometric amounts of catalyst are required in order to
achieve good yields. Moreover, most of the reactions suffer from narrow substrate
scope, tedious work-up procedures, metal leaching, solubility of the catalyst in the
reaction medium, and column chromatography purification, which ultimately results
in diminished yields [3, 30–35].
Catalysis lies at the heart of countless chemical protocols, from academic research
laboratories to the chemical industry. In recent years, in the field of chemical and
materials research, there has been increasing awareness of the right approach for the
maintenance of ‘‘greenness’’ in the catalyst design and catalytic processes, which have
encouraged chemists to design greener reaction pathways and methodologies that
reduce and prohibit the pollution of nature and ensure perpetual life on the earth
[36–40]. In the field of synthetic organic chemistry, metal-free organocatalysis is one
of the green catalytic methodological approaches. As separation of homogeneous
organocatalysts from the reaction mixture is very difficult, the use of a heterogeneous
organocatalyst is a smart choice which brought the reusability of the catalyst and
improved efficiency. Also, heterogeneous catalysis, in particular, addresses the goals
of green chemistry by providing the ease of separation of the product and catalyst,
thereby eliminating the need for separation through distillation or extraction.
Punicagranatum as an ancient fruit cultivated in Iran, Spain, Egypt, Russia, France,
Argentina, China, Japan, USA and India [41]. Modern science shows that Punica
123

Punica granatum peel: an organocatalyst for green and…
granatum contains anticarcinogenic [42], antimicrobial [43], antiviral [44], anti-
cancer, potent anti-oxidant and antimutagenic compounds [45, 46]. Punica granatum
peel (pericarp) is well known for its astringent properties and is rich in ellagitannins
(ETs) (such as punicalagin (A) and its isomers), as well as lesser amounts of punicalin
(B), gallagic acid, ellagic acid (EA) and EA-glycosides [47] (Scheme 1). Ellagitan-
nins (ETs) are esters of hexahydroxydiphenic acid and a polyol, usually glucose or
quinic acid [48]. Punicalagin (A) as a part of ellagitannins family is derived
biosynthetically from gallic acid and glucose. Also, punicalagin (A) is unique to
Punica granatum peel and includes the minor tannins called punicalin (B) and gallic
acid, which are characterized by good water solubility. Another important class of
phenolic natural products in Punica granatum peel is anthocyanins. These are water-
soluble polyphenolic compounds that are derivatives of anthocyanidins. Punica
granatum peel has been used for the direct removal of blue dye [49], 2,4-
dichlorophenol from aqueous solutions [50] and also the removal of metals from
wastewater such as lead, copper [51], chromium [52, 53], iron [54] and nickel [55].
In continuation of our green chemistry program [56–71], we present a simple and
economic method to synthesize a library of 3,4-dihydropyrimidin-2(1H)ones/
thiones derivatives performing the Biginelli reaction under solvent-free conditions
in the presence of Punica granatum peel (an organocatalyst) as an efficient and low
cost environmentally benign catalyst.
Experimental
General
All chemical reagents and solvents were purchased from Merck and Sigma-Aldrich
and were used as received without further purification. The purity determinations of
Scheme 1 Chemical structure of Punica granatum peel components
123

N. Mohammadian, B. Akhlaghinia
the products were accomplished by TLC on silica gel polygram STL G/UV 254
plates. The melting points of products were determined with an Electrothermal Type
9100 melting point apparatus. The FT-IR spectra were provided on pressed KBr
pellets using an AVATAR 370 FT-IR spectrometer (Therma Nicolet, USA) at room
temperature in the range between 4000 and 400 cm-1 with a resolution of 4 cm-1
.
TGA analysis was carried out on a Shimadzu Thermogravimetric Analyzer (TG-50)
in the temperature range of 50–592 °C at a heating rate of 10 °C min-1 under air
atmosphere. Elemental compositions were determined with a Leo 1450 VP scanning
electron microscope equipped with an SC7620 energy dispersive spectrometer
(SEM–EDS) presenting a 133-eV resolution at 20 kV. The NMR spectra were
obtained in Brucker Avance 300 MHz instruments in CDCl3 and DMSO-d6. Mass
spectra were recorded with a CH7A Varianmat Bremem instrument at 70-eV
electron impact ionization, in m/z (rel%). All the products were known compounds
and they were characterized by FT-IR, 1H NMR, 13C NMR, and mass spectrometry,
and comparison of their melting points with known compounds. All yields refer to
isolated products after purification by recrystallization.
Pre-preparation of Punica granatum peel
In order to remove pollution on the surface of the catalyst, the Punica granatum peel
was washed with distilled water, dried in an oven for 2 h at 90 °C, ground in a ball
mill and sieved to particle size range 0.3–0.6 mm.
Typical procedure for preparation of ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-
tetrahydropyrimidine-5-carboxylate in the presence of Punica granatum
peel
To a mixture of benzaldehyde (1 mmol, 0.106 g), ethyl acetoacetate (1 mmol,
0.130 g) and Punica granatum peel (0.03 g) at 100 °C, urea (1 mmol, 0.060 g) was
added with stirring. The progress of the reaction was monitored by thin layer
chromatography (TLC). After completion of the reaction, the reaction mixture was
cooled to room temperature. Then, cold distilled water (5 mL) was poured into the
reaction flask, and the resultant mixture was decanted. The brown precipitate was
dissolved in hot EtOH (3 mL) and the catalyst was separated by filtration. Then, the
filtrate was distilled under reduced pressure and finally the crude product was
recrystallized by EtOH to give the pure product (0.247 g, 95%).
Spectral data
Ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate [72]
(Table 2, 4a) White solid; yield 95%; mp 202–204 °C (Lit. 203–205 °C); FT-IR
(KBr): mmax/cm-1 3243.96 (NH str.), 3116.42 (aromatic CH str.), 2979.04 (aliphatic
1
CH str.), 1725.42 (C=O str.), 1648.50 and 1464.45 (aromatic C=C str.); H NMR
(300 MHz, CDCl3, ppm) d: 8.49 (s, 1H, NH), 7.34–7.27 (m, 5H, ArH), 5.99 (s, 1H,
NH), 5.42 (d, J = 2.7 Hz, 1H, CH), 4.10 (q, J = 8.0 Hz, 2H, OCH2CH3), 2.36 (s,
3H, CH3), 1.18 (t, J = 7.2 Hz, 3H, OCH2CH3); 13C NMR (75 MHz, CDCl3, ppm)
123

Punica granatum peel: an organocatalyst for green and…
d: 165.68, 153.62, 146.45, 143.75, 128.71, 127.94, 126.61, 101.30, 60.01, 55.68,
18.61, 14.15; MS (EI): m/z (%) 260 (5) [M?], 258 (70) [M?–2H], 182 (100) [M?–
C6H6], 171 (60) [M?–C7H5], 110 (60) [M?–C5H6N2O], 77 (65) [M?–C8H11N2O3],
28 (65) [M?–C12H12N2O3].
Ethyl 6-methyl-2-oxo-4-(p-tolyl)-1,2,3,4-tetrahydropyrimidine-5-carboxylate [72]
1
(Table 2, 4b) White solid; yield 95%; mp 214–216 °C (Lit. 215–216 °C); H
NMR (300 MHz, DMSO-d6, ppm) d: 9.19 (s, 1H, NH), 7.72 (s, 1H, NH), 7.13 (s,
4H, ArH), 5.12 (d, J = 2.7 Hz, 1H, CH), 3.99 (q, J = 7.1 Hz, 2H, OCH2CH3), 2.52
(s, 3H, CH3), 1.11 (t, J = 7.1 Hz, 3H, OCH2CH3); MS (EI): m/z (%) 274 (5) [M?],
271 (85) [M?–3H], 182 (100) [M?–C7H8], 154 (80) [M?–C9H12], 110 (95) [M?–
C10H12O2], 91 (80) [M?–C8H11N2O3], 28 (85) [M?–C12H12N2O3].
Ethyl
4-(4-methoxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate [73] (Table 2, 4c) White solid; yield 97%; mp 201–202 °C (Lit.
200–202 °C); FT-IR (KBr): mmax/cm-1 3240.68 (NH str.), 3112.59 (aromatic CH
str.), 2956.35 (aliphatic CH str.), 1727.34 (C=O str.), 1651.51 and 1461.28
(aromatic C=C str.); 1H NMR (300 MHz, DMSO-d6, ppm) d: 9.17 (s, 1H, NH), 7.68
(s, 1H, NH), 7.15 (d, J = 8.4 Hz, 2H, ArH), 6.88 (d, J = 8.7 Hz, 2H, ArH), 5.10 (d,
J = 3.0 Hz, 1H, CH), 3.99 (q, J = 7.1 Hz, 2H, OCH2CH3), 3.73 (s, 3H, OCH3),
2.25 (s, 3H, CH3), 1.11 (t, J = 7.2 Hz, 3H, OCH2CH3); 13C NMR (75 MHz,
DMSO-d6, ppm) d: 165.84, 158.90, 152.61, 148.49, 137.52, 127.86, 114.17, 100.02,
59.62, 55.53, 53.78, 18.22, 14.58; MS (EI): m/z (%) 290 (5) [M?], 287 (85) [M?–
3H], 258 (100) [M?–CH4O], 182 (90) [M?–C7H8O], 154 (85) [M?–C9H12O], 136
(85) [M?–C8H10NO], 110 (82) [M?–C10H12O3], 28 (85) [M?–C13H14N2O4].
Ethyl 4-(4-hydroxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxy-
late [72] (Table 2, 4d) White solid; yield 95%; mp 226–227 °C (Lit.
1
227–228 °C); H NMR (300 MHz, DMSO-d6, ppm) d: 9.41 (br s, 1H, OH), 9.13
(s, 1H, NH), 7.64 (s, 1H, NH), 7.04 (d, J = 8.7 Hz, 2H, ArH), 6.71 (d, J = 8.4 Hz,
2H, ArH), 5.06 (d, J = 3.0 Hz, 1H, CH), 3.98 (q, J = 7.0 Hz, 2H, OCH2CH3), 3.39
(s, 3H, OCH3), 2.25 (s, 3H, CH3), 1.11 (t, J = 7.1 Hz, 3H, OCH2CH3); 13C NMR
(75 MHz, DMSO-d6, ppm) d: 165.89, 157.03, 152.66, 148.21, 135.88, 127.86,
115.45, 100.21, 59.57, 53.90, 18.21, 14.57; MS (EI): m/z (%) 276 (5) [M?], 273 (85)
[M?–3H], 258 (45) [M?–H2O], 201 (100) [M?–C3H7O2], 182 (100) [M?–C6H6O],
110 (80) [M?–C9H10O3], 30 (80) [M?–C12H10N2O4].
Ethyl 4-(2-hydroxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxy-
late [74] (Table 2, 4e) White solid; yield 96%; mp 202–203 °C (Lit. 201–203 °C);
MS (EI): m/z (%) 276 (0) [M?], 273 (100) [M?–3H], 201 (100) [M?–C3H7O2], 182
(100) [M?–C6H6O], 159 (55) [M?–C4H9N2O2], 111 (100) [M?–C9H9O3], 28 (100)
[M?–C12H12N2O4].
Ethyl 4-(4-(dimethylamino)phenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5
carboxylate [75] (Table 2, 4f) White solid; yield 80%; mp 231–232 °C (Lit.
230–232 °C); MS (EI): m/z (%) 303 (5) [M?], 300 (100) [M?–3H], 257 (25) [M?–
123

N. Mohammadian, B. Akhlaghinia
C2H6O], 228 (100) [M?–C3H7O2], 174 (45) [M?–C4H5N2O3], 154 (40) [M?–
C10H15N], 120 (90) [M?–C8H11N2O3], 29 (85) [M?–C14H16N3O3].
Ethyl 4-(4-chlorophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxy-
late [72] (Table 2, 4g) White solid; yield 95%; mp 207–209 °C (Lit.
208–210 °C); MS (EI): m/z (%) 294 (50) [M?], 291 (75) [M?–3H], 182 (100)
[M?–C6H5Cl], 154 (75) [M?–C8H9Cl], 136 (70) [M?–C6H11N2O3], 110 (68) [M?–
C9H9ClO2], 28 (70) [M?–C12H11ClN2O3].
Ethyl 4-(2-chlorophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxy-
late [72] (Table 2, 4h) White solid; yield 90%; mp 214–215 °C (Lit.
214–216 °C); FT-IR (KBr): mmax/cm-1 3353.04 and 3228.55 (NH str.), 3113.46
(aromatic CH str.), 2977.10 (aliphatic CH str.), 1702.46 (C=O str.), 1642.23 and
1454.87 (aromatic C=C str.); 1H NMR (300 MHz, CDCl3, ppm) d: 8.89 (s, 1H, NH),
7.40–7.22 (m, 4H, ArH), 5.90 (s, 2H, NH and CH), 4.03 (q, J = 7.1 Hz, 2H,
OCH2CH3), 2.44 (s, 3H, CH3), 1.08 (t, J = 7.1 Hz, 3H, OCH2CH3); 13C NMR
(75 MHz, CDCl3, ppm) d: 165.35, 153.28, 148.51, 139.57, 132.59, 129.80, 129.29,
128.04, 127.56, 98.87, 59.99, 52.13, 18.31, 14.00; MS (EI): m/z (%) 294 (25) [M?],
292 (78) [M?–2H], 220 (85) [M?–C3H6O2], 182 (100) [M?–C6H5Cl], 154 (85)
[M?–C8H9Cl], 136 (82) [M?–C6H11N2O3], 110 (65) [M?–C9H9ClO2], 28 (85)
[M?–C12H11ClN2O3].
Ethyl 4-(3-bromophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxy-
late [73] (Table 2, 4i) White solid; yield 85%; mp 193–194 °C (Lit.
192–194 °C); MS (EI): m/z (%) 338 (65) [M?], 309 (70) [M?–C2H5], 263 (70)
[M?–C3H7O2], 182 (100) [M?–C6H5Br], 136 (72) [M?–C8H11BrO], 110 (70) [M?–
C9H9BrO2], 28 (70) [M?–C12H11BrN2O3].
Ethyl 4-(4-fluorophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxy-
late [75] (Table 2, 4j) White solid; yield 85%; mp 183–185 °C (Lit.
182–186 °C); FT-IR (KBr): mmax/cm-1 3243.64 (NH str.), 3117.56 (aromatic CH
str.), 2979.18 (aliphatic CH str.), 1729.31 (C=O str.), 1647.80 and 1468.83
(aromatic C=C str.); 1H NMR (300 MHz, DMSO-d6, ppm) d: 9.23 (s, 1H, NH), 7.75
(s, 1H, NH), 7.28–7.11 (m, 4H, ArH), 5.15 (d, J = 2.7 Hz, 1H, CH), 3.97 (q,
J = 7.0 Hz, 2H, OCH2CH3), 2.25 (s, 3H, CH3), 1.08 (t, J = 7.1 Hz, 3H,
OCH2CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d: 170.47, 168.14, 164.93,
157.21, 153.74, 146.33, 133.52, 120.47, 120.19, 104.34, 64.43, 58.56, 23.00, 19.27;
MS (EI): m/z (%) 278 (5) [M?], 275 (85) [M?–3H], 231 (70) [M?–C2H7O], 203
(90) [M?–C3H7O2], 182 (100) [M?–C6H5F], 154 (80) [M?–C8H9F], 121 (70) [M?–
C6H10N2O3], 95 (70) [M?–C8H11N2O3], 29 (85) [M?–C12H10FN2O3].
Ethyl 6-methyl-4-(4-nitrophenyl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate
[72] (Table 2, 4k) White solid; yield 98%; mp 210–211 °C (Lit. 210–211 °C); MS
(EI): m/z (%) 305 (0) [M?], 303 (10) [M?–2H], 230 (10) [M?–C3H7O2], 182 (35)
[M?–C6H5NO2], 149 (15) [M?–C7H10NO3], 77 (10) [M?–C8H10N3O5], 28 (100)
[M?–C12H11N3O5].
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Punica granatum peel: an organocatalyst for green and…
Ethyl 6-methyl-2-oxo-4-(thiophen-2-yl)-1,2,3,4-tetrahydropyrimidine-5-carboxylate
[74] (Table 2, 4m) White solid; yield 70%; mp 215–216 °C (Lit. 215–217 °C);
MS (EI): m/z (%) 266 (10) [M?], 263 (100) [M?–3H], 219 (80) [M?–C2H7O], 192
(100) [M?–C3H6O2], 182 (85) [M?–C4H4S], 154 (85) [M?–C6H8S], 136 (85) [M?–
C6H10SO], 110 (90) [M?–C7H8SO2], 84 (75) [M?–C8H10N2O3], 28 (85) [M?–
C10H10N2O3S].
Ethyl 6-methyl-4-phenyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate [72]
1
(Table 2, 5a) Yellow solid; yield 90%; mp 209–210 °C (Lit. 208–210 °C); H
NMR (300 MHz, DMSO-d6, ppm) d: 10.36 (s, 1H, NH), 9.68 (s, 1H, NH),
7.44–7.23 (m, 5H, ArH), 5.20 (d, J = 3.6 Hz, 1H, CH), 4.02 (q, J = 7.0 Hz, 2H,
OCH2CH3), 2.31 (s, 3H, CH3), 1.11 (t, J = 3.4 Hz, 3H, OCH2CH3); 13C NMR
(75 MHz, DMSO-d6, ppm) d: 174.71, 165.60, 145.50, 143.97, 129.03, 128.15,
126.86, 101.19, 60.06, 54.52, 17.63, 14.47; MS (EI): m/z (%) 276 (5) [M?], 273 (95)
[M?–3H], 202 (90) [M?–C3H6O2], 198 (100) [M?–C6H6], 170 (90) [M?–C8H10],
152 (60) [M?–C8H12O], 130 (60) [M?–C5H10N2OS], 77 (90) [M?–C8H11N2O2S],
29 (100) [M?–C12H11N2O2S].
Ethyl 6-methyl-2-thioxo-4-(p-tolyl)-1,2,3,4-tetrahydropyrimidine-5 -carboxylate
[72] (Table 2, 5b) Yellow solid; yield 90%; mp 191–192 °C (Lit. 190–192 °C);
MS (EI): m/z (%) 290 (5) [M?], 287 (95) [M?–3H], 243 (20) [M?–C2H7O], 215
(100) [M?–C3H7O2], 198 (95) [M?–C7H8], 170 (35) [M?–C9H12], 91 (40) [M?–
C8H11N2O2S], 76 (95) [M?–C9H14N2O2S], 29 (100) [M?–C13H13N2O2S].
Ethyl 4-(4-hydroxyphenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate [76] (Table 2, 5d) White solid; yield 95%; mp 204–205 °C (Lit.
1
203–205 °C); H NMR (300 MHz, DMSO-d6, ppm) d: 10.26 (s, 1H, NH), 9.57 (s,
1H, NH), 9.47 (br s, 1H, OH), 7.02 (d, J = 8.4 Hz, 2H, ArH), 6.73 (d, J = 8.4 Hz,
2H, ArH), 5.08 (d, J = 3.3 Hz, 1H, CH), 4.01 (q, J = 7.0 Hz, 2H, OCH2CH3), 2.29
(s, 3H, CH3), 1.11 (t, J = 7.1 Hz, 3H, OCH2CH3); 13C NMR (75 MHz, DMSO-d6,
ppm) d: 174.31, 165.69, 157.39, 144.97, 134.56, 128.11, 115.62, 101.60, 59.99,
54.03, 17.59, 14.49; MS (EI): m/z (%) 292 (10) [M?], 289 (85) [M?–3H], 245 (70)
[M?–C2H7O], 217 (100) [M?–C3H7O2], 198 (75) [M?–C6H6O], 170 (55) [M?–
C8H10O], 91 (35) [M?–C8H13N2O2S], 76 (70) [M?–C8H12N2O3S], 29 (75) [M?–
C12H11N2O3S].
Ethyl 4-(2-hydroxyphenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate [77] (Table 2, 5e) White solid; yield 90%; mp 207–208 °C (Lit.
206–209 °C); MS (EI): m/z (%) 292 (0) [M?], 276 (25) [M?–CH4], 245 (90)
[M?–C2H7O], 229 (50) [M?–C2H7O2], 202 (90) [M?–C3H6O3], 198 (100) [M?–
C6H6O], 170 (85) [M?–C8H10O], 152 (40) [M?–C8H12O2], 128 (65) [M?–C9H8O3],
77 (85) [M?–C8H11N2O3S], 29 (95) [M?–C12H11N2O3S].
Ethyl
4-(4-chlorophenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate [72] (Table 2, 5g) White solid; yield 95%; mp 196–198 °C (Lit.
197–199 °C); MS (EI): m/z (%) 310 (30) [M?], 308 (75) [M?–2H], 251 (80) [M?–
123

N. Mohammadian, B. Akhlaghinia
CHNS], 236 (80) [M?–C3H6O2], 199 (80) [M?–C6H4Cl], 112 (75) [M?–C8H10N2-
O2S], 77 (100) [M?–C8H10ClN2O2S], 29 (80) [M?–C12H10ClN2O2S].
Ethyl
4-(2-chlorophenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate [78] (Table 2, 5h) Yellow solid; yield 85%; mp 218–219 °C (Lit.
218–220 °C); MS (EI): m/z (%) 310 (10) [M?], 308 (30) [M?–2H], 250 (25) [M?–
CH2NS], 198 (50) [M?–C6H5Cl], 170 (15) [M?–C8H9Cl], 76 (100) [M?–C6H4], 29
(75) [M?–C12H10ClN2O2S].
Ethyl
4-(3-bromophenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate [79] (Table 2, 5i) Yellow solid; yield 90%); mp 182–183 °C (Lit.
182–184 °C); MS (EI): m/z (%) 354 (90) [M?], 325 (90) [M?–C2H4], 307 (30)
[M?–C2H6O], 281 (95) [M?–C3H4O2], 250 (100) [M?–C3H7N2S], 223 (75) [M?–
C5H10N2S], 198 (95) [M?–C6H5Br], 170 (85) [M?–C8H9Br], 154 (55) [M?–
C8H9BrO], 76 (90) [M?–C8H11BrN2O2S], 29 (90) [M?–C12H10BrN2O2S].
Ethyl
4-(4-fluorophenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate [80] (Table 2, 5j) Yellow solid; yield 80%; mp 186–187 °C (Lit.
1
186–187 °C); H NMR (300 MHz, DMSO-d6, ppm) d: 10.39 (s, 1H, NH), 9.69 (s,
1H, NH), 7.28–7.07 (m, 4H, ArH), 5.18 (d, J = 3.3 Hz, 1H, CH), 4.02 (q,
J = 7.0 Hz, 2H, OCH2CH3), 2.31 (s, 3H, CH3), 1.09 (t, J = 7.1 Hz, 3H,
OCH2CH3); MS (EI): m/z (%) 294 (5) [M?], 291 (65) [M?–3H], 247 (55) [M?–
C2H7O], 219 (100) [M?–C3H7O2], 198 (65) [M?–C6H5F], 152 (55) [M?–
C8H11FO], 95 (40) [M?–C6H4F], 28 (70) [M?–C12H11FN2O2S].
Ethyl 6-methyl-4-(4-nitrophenyl)-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxy-
late [76] (Table 2, 5k) Yellow solid; yield 95%; mp 110–111 °C (Lit.
110–112 °C); MS (EI): m/z (%) 321 (5) [M?], 319 (15) [M?–2H], 248 (20)
[M?–C3H5O2], 198 (25) [M?–C6H5NO2], 76 (100) [M?–C8H11N3O4S], 28 (95)
[M?–C12H11N3O4S].
Ethyl
4-(4-cyanophenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate [81] (Table 2, 5l) Yellow solid; yield 95%; mp 239–241 °C (Lit.
240–242 °C); FT-IR (KBr): mmax/cm-1 3374.80 and 3274.87 (NH str.), 3174.54
(aromatic CH str.), 2980.07 (aliphatic CH str.), 2229.04 (CN str.), 1688.69 (C=O
str.), 1608.96 and 1462.86 (aromatic C=C str.), 1183.47 (C=S str.); 1H NMR
(300 MHz, DMSO-d6, ppm) d: 10.48 (s, 1H, NH), 9.75 (s, 1H, NH), 7.87–7.33 (m,
4H, ArH), 5.25 (d, J = 3.6 Hz, 1H, CH), 4.02 (q, J = 3.3 Hz, 2H, OCH2CH3), 2.52
(s, 3H, CH3), 1.13 (t, J = 7.5 Hz, 3H, OCH2CH3); 13C NMR (75 MHz, DMSO-d6,
ppm) d: 184.30, 174.90, 165.36, 148.95, 146.35, 133.21, 127.92, 119.12, 110.97,
100.22, 60.23, 17.70, 14.45; MS (EI): m/z (%) 301 (5) [M?], 299 (50) [M?–2H],
254 (25) [M?–C2H7O], 226 (90) [M?–C3H7O2], 198 (30) [M?–C7H5N], 127 (34)
[M?–C10H9NO2], 76 (100) [M?–C9H11N3O2S], 28 (75) [M?–C13H11N3O2S].
Ethyl 6-methyl-4-(thiophen-2-yl)-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxy-
late [74] (Table 2, 5m) Yellow solid; yield 75%; mp 216–217 °C (Lit.
218–217 °C); MS (EI): m/z (%) 282 (30) [M?], 279 (100) [M?–3H], 235 (55)
123

Punica granatum peel: an organocatalyst for green and…
[M?–C2H7O], 207 (100) [M?–C3H7O2], 170 (40) [M?–C6H8S], 136 (65) [M?–
C5H10N2OS], 109 (65) [M?–C6H10N2O2S] 28 (80) [M?–C10H10N2O2S2].
5-Acetyl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one
[82]
(Table 2,
6a) Yellow solid; yield 95%; mp 264–265 °C (Lit. 264–265 °C); 1H NMR
(300 MHz, DMSO-d6, ppm) d: 9.22 (s, 1H, NH), 7.86 (s, 1H, NH), 7.36–7.23 (m,
5H, ArH), 5.28 (d, J = 3.3 Hz, 1H, CH), 2.31 (s, 3H, CH3), 2.12 (s, 3H, CH3); 13
C
NMR (75 MHz, DMSO-d6, ppm) d: 194.74, 152.64, 148.60, 144.72, 128.99, 127.82,
126.91, 110.06, 54.30, 30.79, 19.39; MS (EI): m/z (%) 230 (70) [M?], 228 (90) [M?–
2H], 186 (80) [M?–C2H4O], 152 (100) [M?–C6H6], 143 (70) [M?–C3H7N2O], 130
(50) [M?–C3H4N2O2], 110 (70) [M?–C8H8O], 29 (80) [M?–C11H9N2O2].
5-Acetyl-4-(4-methoxyphenyl)-6-methyl-3,4-dihydropyrimidin-2(1H)-one
[82]
1
(Table 2, 6b) White solid; yield 90%; mp 200–202 °C (Lit. 201–202 °C); H
NMR (300 MHz, DMSO-d6, ppm) d: 9.20 (s, 1H, NH), 7.81 (s, 1H, NH), 7.20 (d,
J = 8.4 Hz, 2H, ArH), 6.90 (d, J = 8.4 Hz, 2H, ArH), 5.24 (d, J = 2.7 Hz, 1H,
CH), 3.73 (s, 3H, OCH3), 2.31 (s, 3H, CH3), 2.09 (s, 3H, CH3); 13C NMR (75 MHz,
DMSO-d6, ppm) d: 194.87, 159.00, 152.64, 148.26, 136.84, 128.13, 114.32, 110.10,
55.51, 53.84, 30.61, 19.31; MS (EI): m/z (%) 260 (5) [M?], 258 (100) [M?–2H],
215 (100) [M?–CH3NO], 152 (100) [M?–C7H8O], 109 (20) [M?–C8H9O], 29 (70)
[M?–C12H11N2O3].
5-Acetyl-4-(4-chlorophenyl)-6-methyl-3,4-dihydropyrimidin-2(1H)-one
[82]
1
(Table 2, 6c) White solid; yield 98%; mp 258–259 °C (Lit. 258–260 °C); H
NMR (300 MHz, DMSO-d6, ppm) d: 9.25 (s, 1H, NH), 7.88 (s, 1H, NH), 7.40 (d,
J = 8.1 Hz, 2H, ArH), 7.27 (d, J = 8.4 Hz, 2H, ArH), 5.27 (d, J = 2.4 Hz, 1H,
CH), 2.30 (s, 3H, CH3), 2.14 (s, 3H, CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d:
194.58, 152.53, 148.94, 143.68, 132.31, 128.94, 128.78, 109.98, 53.54, 30.90,
19.45; MS (EI): m/z (%) 264 (50) [M?], 262 (100) [M?–2H], 219 (95) [M?–
C2H5O], 152 (100) [M?–C6H4Cl], 110 (40) [M?–C8H7ClO], 29 (100) [M?–
C11H8ClN2O2].
1-(6-Methyl-4-phenyl-2-thioxo-1,2,3,4-tetrahydropyrimidin-5-yl)ethanone
[83]
(Table 2, 7a) White solid; yield 90%; mp 230–231 °C (Lit. 230–231 °C; 1H
NMR (300 MHz, DMSO-d6, ppm) d: 10.29 (s, 1H, NH), 9.78 (s, 1H, NH),
7.39–7.23 (m, 5H, ArH), 5.31 (d, J = 3.9 Hz, 1H, CH), 2.35 (s, 3H, CH3), 2.17 (s,
3H, CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d: 195.26, 174.55, 145.05, 143.38,
129.11, 128.17, 127.03, 110.94, 54.23, 30.90, 18.73; MS (EI): m/z (%) 246 (60)
[M?], 244 (100) [M?–2H], 201 (85) [M?–C2H5O], 185 (65) [M?–CH3NS], 168
(100) [M?–C6H6], 143 (70) [M?–C3H7N2S], 110 (70) [M?–C9H12O], 91 (60) [M?–
C6H7N2OS2], 77 (70) [M?–C7H9N2OS], 29 (60) [M?–C11H9N2OS].
1-(4-(4-Methoxyphenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyri midin-5-yl)etha-
none [84] (Table 2, 7b) White solid; yield 90%; mp 168–170 °C (Lit.
1
169–170 °C); H NMR (300 MHz, DMSO-d6, ppm) d: 10.25 (s, 1H, NH), 9.72
(s, 1H, NH), 7.18–6.89 (m, 4H, ArH), 5.25 (d, J = 3.6 Hz, 1H, CH), 3.73 (s, 3H,
CH3), 2.34 (s, 3H, CH3), 2.13 (s, 3H, CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d:
123

N. Mohammadian, B. Akhlaghinia
195.36, 174.29, 159.25, 144.72, 135.54, 128.33, 114.45, 110.92, 55.57, 53.81,
30.73, 18.66; MS (EI): m/z (%) 276 (10) [M?], 273 (100) [M?–3H], 243 (80) [M?–
CH5O], 231 (95) [M?–C2H5O], 168 (80) [M?–C7H8O], 110 (80) [M?–C10H14O2],
29 (80) [M?–C12H11N2O2S].
Spectral data of intermediates II and II0
Ethyl 2-(hydroxy(phenyl)methyl)-3-oxobutanoate (II) [85] Yield 70%; Oil; FT-IR
(KBr): mmax/cm-1 3440.18 (OH str.), 3063.60 (aromatic CH str.), 2926.21 (aliphatic
CH str.), 1724.74 (C=O str.), 1642.22 and 1450.14 (aromatic C=C str.); MS (EI): m/
z (%) 236 (2) [M?], 209 (22) [M?–C2H3], 166 (35) [M?–C4H6O], 142 (45) [M?–
C6H6O], 130 (65) [M?–C8H10], 122 (70) [M?–C56H11O3], 105 (100) [M?–
C6H11O3], 77 (70) [M?–C7H11O4], 28 (65) [M?–C11H12O4].
1-Benzylideneurea (II0) [86] White solid; yield 80%; mp 224–226 °C (Lit.
225–226 °C); FT-IR (KBr): mmax/cm-1 3615.89 and 3314.90 (NH2 str.), 3064.25
(aromatic CH str.), 1647.31 (C=O str.), 1596.71 and 1448.99 (aromatic C=C str.); MS
(EI): m/z (%) 148 (10) [M?], 147 (40) [M?–H], 131 (80) [M?–NH3], 104 (100) [M?–
CH2NO], 77 (85) [M?–C2H3N2O], 60 (62) [M?–CH4N2O], 29 (65) [M?–C6H3N2O].
Results and discussion
Characterization of catalyst
FT-IR spectroscopy was carried out to identify the structure of Punica granatum
peel. As shown in Fig. 1a, the broad stretching and bending vibrations of the OH
140
C-H
bending
(a)
(b)
C-O stretching
C=O
stretching
120
100
80
60
40
20
0
C-H
O-H
bending
stretching
O-H
stretching
3900
3400
2900
2400
1900
1400
900
400
Wavenumber (cm-1)
Fig. 1 FT-IR spectra of a Punica granatum peel, b 7th recovered Punica granatum peel
123

Punica granatum peel: an organocatalyst for green and…
Fig. 2 TGA/DTG thermogram of Punica granatum peel
groups in Punica granatum peel were detected around 3700–3000 and 1360 cm-1
,
respectively (polyphenolic, alcoholic and acidic groups). Also, the alkyl C–H
groups of punicalagin (A) appeared at 2970–2800 cm-1. An absorption band at
1740 cm-1 is due to the C=O groups of ester and acid. Furthermore, the appearance
of two absorption bands at 1620 and 1430 cm-1 is attributed to the stretching
frequencies of the C=C aromatic rings and the strong absorption band at 1052 cm-1
is ascribed to the C–OH stretching vibration. The absorption bands at 1229 and
637 cm-1 are known to be associated to the C–O stretching bond of ester and
aromatic C–H bending frequencies, respectively.
Thermogravimetric analysis (TGA) of the Punica granatum peel was also
performed to investigate the thermal stability of the catalyst. As is obvious in Fig. 2,
the TGA thermogram showed three major weight loss stages. The first stage of
degradation represents the loss of water (weight loss 5.0%, from 50 to 200 °C). The
major weight loss took place in the second step (weight loss 90.0%, from 200 to
445 °C) which was followed by a further weight loss in the third step (weight loss
98.0%, from 445–592 °C). The second stage represents some chain scission of
Punica granatum peel. In the third stage, complete decomposition of the Punica
granatum peel main chains occurred.
The energy-dispersive X-ray analysis (EDX) of catalyst indicates the presence of
C, O, Fe, Na, K and Ca as the main components of the Punica granatum peel
(Fig. 3).
123

N. Mohammadian, B. Akhlaghinia
Fig. 3 EDX analysis of Punica granatum peel
Fig. 4 SEM micrographs of Punica granatum peel
The scanning electron microscopy (SEM) images were recorded to determine the
exact size and shape of the Punica granatum peel (Fig. 4). The SEM analysis proved
the porous surface of Punica granatum peel with particle size of around 10–20 lm.
123

Punica granatum peel: an organocatalyst for green and…
Catalytic synthesis of 3,4-dihydropyrimidin-2(1H)ones/thiones derivatives
The present study as a part of our ongoing research program [56–71] on the
exploration of green transformations and domino/sequential multicomponent
reactions reports the synthesis of a library of 3,4-dihydropyrimidin-2(1H)ones/
thiones derivatives by performing the Biginelli reaction under solvent-free
conditions in the presence of an environmentally benign organocatalyst (Scheme 2).
Organocatalysis offers many advantages for synthetic organic chemistry. In contrast
to many transition metal catalysts, most organocatalysts are stable to air and water,
easily handled, non-toxic and robust compounds and most of them are readily
separated from the crude reaction mixture. In general, a large number of them are
commercially available and/or easily synthesized.
The results of optimization experiments for the three-component Biginelli
condensation reaction involving benzaldehyde, ethyl acetoacetate and urea in the
presence of Punica granatum peel as catalyst are presented in Table 1. One
important aspect of green chemistry is the elimination of solvents in the chemical
processes or the replacement of hazardous solvents with relatively benign solvents
[87]. Thus, our initial work started by performing the condensation reaction in
solvent-free condition. It could be seen that, in the presence of 0.1 g of Punica
granatum peel ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-car-
boxylate was obtained rapidly in high isolated yield, whereas in the absence of
Punica granatum peel and under the same reaction conditions, the condensation
reaction does not proceed even after a long period of time (Table 1, compare entries
1 and 2). In order to improve the performance of the reaction, the influence of
temperature on the yield and reaction time was investigated. It was found that at
100 °C a higher yield of desired product was rapidly obtained (Table 1, entries
3–6). In order to fine-tune the reaction conditions, we also examined the effect of
molar ratio of reactants on the reaction rate. Interestingly, it was observed that, by
applying a 1/1/1 molar ratio of aldedyde/ethylacetoactate/urea, the desired product
was obtained in a short reaction time and in high yield (Table 1, entry 7). The
catalytic activity of Punica granatum peel in condensation reaction was then studied
in different solvents (Table 1, entries 8–14). The findings indicate that there is no
Scheme 2 Synthesis of different structurally 3,4-dihydropyrimidin-2(1H)-one/thiones in the presence of
Punica granatum peel under solvent-free condition
123

N. Mohammadian, B. Akhlaghinia
Table 1 Optimization of various reaction parameters for the synthesis of ethyl 6-methyl-2-oxo-4-phe-
nyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate in the presence of Punica granatum peel
Entry Molar ratio
1a:2a:3a
Catalyst
(g)
Solvent
Temperature
(°C)
Time
(min)
Isolated yield
(%)
1
1:1:1.5
1:1:1.5
1:1:1.5
1:1:1.5
1:1:1.5
1:1:1.5
1:1:1
–
–
120
120
110
100
95
24(h)
5
Trace
95
2
0.1
–
3
0.1
–
5
95
4
0.1
–
5
95
5
0.1
–
18
82
6
0.1
–
90
25
75
7
0.1
–
100
100
100
100
100
100
5
95
8
1:1:1
0.1
H2O
EtOH
PEG
DMSO
DMF
20(h)
20(h)
20(h)
20(h)
20(h)
20(h)
20(h)
5
Trace
50
9
1:1:1
0.1
10
11
12
13
14
15
16
17
18
19
20
21
1:1:1
0.1
20
1:1:1
0.1
Trace
Trace
Trace
Trace
95
1:1:1
0.1
1:1:1
0.1
Toluene 100
Glycerol 100
1:1:1
0.1
1:1:1
0.08
0.06
0.05
0.04
0.03
0.02
0.025
–
–
–
–
–
–
–
100
100
100
100
100
100
100
1:1:1
5
95
1:1:1
5
95
1:1:1
5
95
1:1:1
5
95
1:1:1
15
83
1:1:1
10
89
crucial outcome in H2O, EtOH, PEG, DMSO, DMF, toluene and glycerol. Then, the
condensation reaction occurs more efficiently in solvent-free conditions than it does
in solution since the reactants and catalyst are arranged more tightly when a solvent
is not used. Therefore, without a solvent, the reactions usually need shorter reaction
times, simpler reactors, simple and efficient workup procedures, and are often more
environmentally friendly. We further found that the yields are obviously affected by
the amount of catalyst. Punica granatum peel (0.03 g) was found to be effective in
stitching of all starting substrates to ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-
tetrahydropyrimidine-5-carboxylate with high yield (Table 1, entries 15–21). It is
remarkable to note that higher amounts of catalyst did not boost the yields, while
lower amounts were proved to be less effective.
123

Punica granatum peel: an organocatalyst for green and…
Encouraged by these results, we studied the Biginelli condensation reaction of
several aromatic aldehydes with 1,3-dicarbonyl compounds and urea/thiourea in the
presence of Punica granatum peel (Table 2). In all cases, the three-component
reaction proceeded smoothly to give the corresponding 3,4-dihydropyrimidin-
2(1H)-ones/thiones in good to excellent yields. Various substituted aldehydes
bearing electron-donating and electron-withdrawing groups at different positions of
aromatic rings have been employed for the one-pot three-component condensation
reactions under solvent-free conditions. According to the results of Table 2, the
nature and position of substitution on the aromatic ring have little effect on the
reaction rate or on the final yield of 3,4-dihydropyrimidin-2(1H)-ones/thiones. In
comparison, the condensation reaction with thiourea required relatively more time
for completion than did urea. This was probably due to the lower electronegativity
of sulfur compared with oxygen which caused weak hydrogen bonding with the
catalyst and then rendered slow cyclization of intermediate III (Scheme 3) due to
the more weakened nucleophile(–NH2).
The yields of condensation reactions are measured by weighing the final products
which were purified by recrystallization from ethanol. All the products were known
compounds and they were characterized by comparison of their physical (color,
melting points) and spectral (mass spectrometry) data with those of authentic
1
compounds. The selected compounds were further identified by FT-IR, H NMR
and13C NMR spectroscopy which compared them with literature data.
Key features in the FT-IR spectra of the products include the absorption bands at
3353–3228 cm-1 (related to the N–H stretching vibration), 1729–1702 cm-1 and
1183–1050 cm-1 (due to the C=O and C=S stretching vibrations). In all cases, the
formation of 3,4-dihydropyrimidin-2(1H)-one/thiones was established by the
disappearance of two sharp absorption bands at 2850 and 2750 cm-1 (related to
the –CHO stretching vibrations of aldehyde). The 1HNMR spectra of 3,4-
dihydropyrimidin-2(1H)-one/thiones exhibited a singlet resonating at around
10.48–8.49 (due to the NH proton at position 1) and 9.78–5.99 ppm (due to NH
proton at position 3). In addition, click condensations were confirmed by the
appearance of a doublet resonating at around 5.42–5.06 ppm in the 1H NMR
spectra, which corresponds to the hydrogen on position 4 of the dihydropyrimidin
ring and confirms the regioselective synthesis of 4-disubstituted dihydropyrimidin
regioisomers. Also in the 13C NMR spectra, a signal at 195–165 ppm corresponds to
the carbonyl carbon at position 5 and another signal at 164–152/184–174 ppm to the
C = X at position 2 (X = O/S) of 3,4-dihydropyrimidin-2(1H)-one/thiones, which
can be beneficial for further confirming the structure of the desired products.
On the basis of the above observations and the literature reports, we have
proposed a reaction mechanism for the Punica granatum peel-catalyzed Biginelli
condensation reaction under solvent-free condition in Scheme 3. The catalytic
activity of Punica granatum peel in the Biginelli condensation reaction was
established by performing the reaction in the absence of Punica granatum peel.
After a long reaction time, a lower yield of product (trace) was obtained (Table 1,
entry 1). Although the role of Punica granatum peel in the Biginelli condensation
reaction is not definitively clear, as shown in Scheme 3, it is speculated that the
phenolic hydroxyl groups of punicalagin (A) and punicalin (B) (two essential
123

N. Mohammadian, B. Akhlaghinia
Table 2 Synthesis of different structurally 3,4-dihydropyrimidin-2(1H)-one/thiones in the presence of
Punica granatum peel under solvent-free condition
Entry
R1
1,3 dicarbonyl
compound
Product
X
Time (min)/ Isolated
Yield (%)
O, 4a
S, 5a
5/95
1
C6H5
Ethyl acetoacetate
Ethyl acetoacetate
Ethyl acetoacetate
Ethyl acetoacetate
Ethyl acetoacetate
Ethyl acetoacetate
Ethyl acetoacetate
15/90
O, 4b
S, 5b
10/95
20/90
2
3
4
5
6
7
4-CH3-C6H4
4-CH3O-C6H4
4-HO-C6H4
2-HO-C6H4
O, 4c
S, 5c
5/97
15/98
O, 4d
S, 5d
5/95
15/95
O, 4e
S, 5e
10/96
15/90
O, 4f
S, 5f
10/80
20/75
4-(CH3)2N-C6H4
O, 4g
S, 5g
5/95
4-Cl-C6H4
15/95
123

Punica granatum peel: an organocatalyst for green and…
Table 2 continued
Entry
R1
1,3 dicarbonyl
compound
Product
X
Time (min)/ Isolated
Yield (%)
O, 4h
S, 5h
5/90
8
2-Cl-C6H4
3-Br-C6H4
Ethyl acetoacetate
Ethyl acetoacetate
15/85
O, 4i
S, 5i
10/85
20/90
9
O, 4j
S, 5j
10/85
15/80
10
11
12
13
14
15
16
4-F-C6H4
4-O2N-C6H4
4-CN-C6H4
2-thienyl
Ethyl acetoacetate
Ethyl acetoacetate
Ethyl acetoacetate
Ethyl acetoacetate
Acetylacetone
O, 4k
S, 5k
5/98
10/95
O, 4l
S, 5l
5/96
15/95
O, 4m
S, 5m
15/70
20/75
O, 6a
S, 7a
10/95
15/90
C6H5
O, 6b
S, 7b
10/90
15/90
4-CH3O-C6H4
Acetylacetone
O, 6c
S, 7c
10/98
15/95
4-Cl-C6H4
Acetylacetone
123

N. Mohammadian, B. Akhlaghinia
Scheme 3 Proposed reaction mechanism for the synthesis of 3,4-dihydropyrimidin-2(1H)-one/thiones
derivatives in the presence of Punica granatum peel
components of Punica granatum peel) through hydrogen bonding activate the
carbonyl group of aldehyde towards the nucleophilic attack of I (enolic form of 1,3-
dicarbonyl compound which was produced upon treatment with catalyst) and urea.
The condensed product II was produced more quickly than II0, but in a reversible
manner. To understand which component (ethylacetoacetate or urea) is more
reactive toward aldehyde, benzaldehyde was treated in two separate flasks by ethyl
acetoacetate and urea under optimized reaction conditions. Subsequently, addition
123

Punica granatum peel: an organocatalyst for green and…
of urea/thiourea to II, while forwarding the equilibrium to the right and to more
formation of II, led to the formation of III. On the other hand, addition of I to II0
produced III which upon dehydration led to the corresponding 3,4-dihydropyrim-
idin-2(1H)-one/thiones as IV. Further investigation on the elucidation of the
mechanism was undertaken in our laboratory by performing the simultaneous
reaction of aldehyde with the 1,3-dicarbonyl compound and urea/thiourea under
optimized reaction conditions. When the progress of the reaction was followed
precisely, intermediate II was produced as the major product in the first step of the
Biginelli condensation reaction along with trace amounts of II0. According to the
results obtained from Table 2, as condensation of II with urea was completed faster
than condensation with thiourea, cyclization of III may be referred to as a rate-
determining step in the Biginelli condensation reaction. So, we can conclude that
3,4-dihydropyrimidin-2(1H)-one/thiones derivatives in the presence of Punica
granatum peel were produced through the formation of intermediate II (pathway a),
and the re-generated catalyst re-enters the catalytic cycle. The structure of
intermediates II and II0 were confirmed by FT-IR spectroscopy, mass spectrometry
and comparison of their melting points with known compounds [85, 86]. FT-IR
spectroscopy of intermediate II revealed two absorption bands at 3440 and
1724 cm-1 due to vibration stretching of the hydroxyl (OH) and carbonyl groups
(C=O), respectively. The presence of the NH2 group of II0 was established by two
strong absorption bands at 3615 and 3314 cm-1 (due to asymmetric and symmetric
stretching vibration of NH2), and C=O vibration stretching was revealed as a strong
absorption band at 1647 cm-1. Also, the existence of a molecular ion peak at m/
z 236 and 148 in the mass spectra confirmed the formation of intermediates II and
II0, respectively (see Supporting Information, pages 75–78).
The relationship between the number of cycles of the model reaction and the
catalytic activity in terms of conversion and isolated yield of product is presented in
Fig. 5. Upon completion of the reaction in the specified time, the mixture was
washed with water (15 mL). After decantation of the washing water, the solid
mixture was dissolved in hot EtOH (15 mL) and the catalyst was separated, washed
with ethanol and finally dried at 90 °C for 2 h prior to the next run. During the
recycling experiment with fresh reactants, under the same reaction conditions, no
considerable change in the activity of the Punica granatum peel was observed for at
least 7 consecutive runs, which clearly demonstrates the stability of the catalyst for
these conditions in the Biginelli reaction (Fig. 5). The identity of the recovered
catalyst was checked by FT-IR spectroscopy (Fig. 1b), and it was observed that
there were no considerable changes in the chemical structure of the functional
groups and the hydrogen bonding network of the catalyst as compared to fresh
catalyst (Fig. 1a).
A comparative study was performed for the use of Punica granatum peel with
some of the reported catalysts for the Biginelli condensation reaction (Table 3). The
reaction with different catalysts required long reaction times for completion
compared with Punica granatum peel which afforded the desired product rapidly.
Moreover, in most methods, the reaction was performed in solvents such as H2O,
acetic acid, ethanol, methanol, acetonitrile, dioxane and toluene. The Punica
granatum peel promoted the reaction more effectively under mild conditions than
123

N. Mohammadian, B. Akhlaghinia
98
98
98
98
95
95
95
100
80
60
40
20
95
95
95
90
90
90
85
0
First
Second
Third
Fourth
Fifth
Sixth
Seventh
Isolated yield
Conversion
Fig. 5 Synthesis of ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5- carboxylate in the
presence of reused Punica granatum peel
Table 3 Comparison between the efficiency of Punica granatum peel and some other catalysts for the
synthesis of ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate
Entry Catalyst
Solvent
Temperature
(°C)
Time
(h)
Yield
(%)
Refs.
1
2
3
Imidazol-1-yl-acetic acid
H2O
H2O
Reflux
100
0.35
5
92
80
76
[88]
[78]
[89]
Cellulose sulfuric acid
Ytterbium(III) triflate
H2O/acetic
acid
95
3
4
5
6
7
Trichloroisocyanuric acid
Copper(II) triflate
EtOH
Reflux
100
12
1
94
65
90
94
[3]
EtOH
[90]
[91]
[3]
Zirconium(IV) chloride
EtOH
Reflux
Reflux
4
Indium(III)
Trifluoromethanesulfonate
EtOH/N2
6.5
8
Silica-bonded N-propyl
sulfamic acid
EtOH
Reflux
4
95
[92]
9
Nafion-H
EtOH
EtOH
Reflux
Reflux
Sonication
Reflux
Reflux
Reflux
Reflux
80
4
94
81
98
92
81
92
84
92
86
79
90
[3]
10
11
12
13
14
15
16
17
18
19
p-Sulfonic acid calixarenes
Calcium fluoride
Ceric ammonium nitrate
[Al(H2O)6](BF4)3
Lithium bromide
Zeolite-supported HPA
MPMCM-41a
EtOH
8
[93]
[3]
EtOH
2
MeOH
CH3CN
CH3CN
CH3CN
Toluene
Dioxane
Acetic acid
–
3.5
20
3
[3]
[3]
[3]
10
6
[94]
[95]
[3]
PS-PEG-SO3H
10
6
Copper(II) Sulfamate
Fe3O4/PAA-SO3H
100
[79]
[96]
r.t
2
123

Punica granatum peel: an organocatalyst for green and…
Table 3 continued
Entry Catalyst
Solvent
Temperature
(°C)
Time
(h)
Yield
(%)
Refs.
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Pineapple Juice
–
–
–
–
–
–
–
–
–
–
–
–
–
–
r.t
3.5
1
60
84
85
90
97
90
70
90
95
80
88
94
[97]
[3]
Ca(NO3)2Á4H2O
NH4H2PO4 or 4H2PO4/SiO2
Co(NO3)2.6H2O
Sr(OTf)2
80
100
80
2
[98]
[99]
[3]
0.6
4
70
NH4Cl
100
100
100
60
3
[3]
Triphenylphosphine
TiCl4-MgCl2
10
3
[3]
[3]
nanoZnO
10
48
1
[77]
[3]
Yb(III)-resin
120
90
Zr(H2PO4)2
DBSAb
[100]
[101]
[72]
80
3
[Et3N–SO3H]HSO4
Punica granatum peel
70
40 min 98
5 min 95
100
Present
study
a
3-mercaptopropyl MCM-41
b
p-dodecylbenzenesulfonic acid
the other catalysts, and it can be considered as one of the best choices for selecting
an environmentally benign and user-friendly catalyst.
Conclusion
Here, we have elaborated a new green and rapid Biginelli condensation reaction in
the presence of Punica granatum under solvent-free condition. Punica granatum is
shown to be an effective heterogeneous organocatalyst for the multicomponent one-
pot condensation of aldehydes,1,3-dicarbonyl compounds and urea/thiourea to
produce 3,4-dihydropyrimidin-2(1H)-one/thiones in high to excellent yields, which
could be regenerated up to seven cycles without any considerable loss of efficiency.
The noteworthy merits of this protocol are the simple operation, short reaction time,
high yields, mild and clean reaction conditions, avoiding hazardous catalysts or
corrosive or toxic solvents, easy work-up procedure and green sustainable
conditions. We believe that these features will enable this protocol to find
widespread applications in the field of organic synthesis.
Acknowledgement The authors gratefully acknowledge the partial support of this study by Ferdowsi
University of Mashhad Research Council.
References
1. D.L. da Silva, F.S. Reis, D.R. Muniz, A.L.T.G. Ruiz, J.E. de Carvalho, A.A. Sabino, L.V. Modolo,
A. de Fatima, Bioorg. Med. Chem. 20, 2645 (2012)
123

N. Mohammadian, B. Akhlaghinia
2. C.O. Kappe, Eur. J. Med. Chem. 35, 1043 (2000)
3. K. Singh, K. Singh, Adv. Heterocycl. Chem. 105, 223 (2012)
4. B.B. Tour, D.G. Hall, Chem. Rev. 109, 4439 (2009)
5. L.F. Tietze, Chem. Rev. 96, 115 (1996)
6. A. Dmling, I. Ugi, Angew. Chem. Int. Ed. Engl. 32, 563 (1993)
7. A. Hasaninejad, A. Zare, M. Shekouly, J.A. Rad, J. Comb. Chem. 12, 844 (2010)
8. S.K. Kundu, A. Majee, A. Hajra, Indian J. Chem. 48B, 408 (2009)
9. U.B. More, Asian J. Chem. 24, 1906 (2012)
10. J.T. Starcevich, T.J. Laughlin, R.S. Mohan, Tetrahedron Lett. 54, 983 (2013)
11. H.N. Karade, J. Acharya, M.P. Kaushik, Tetrahedron Lett. 53, 5541 (2012)
12. F. Shirini, M.A. Zolfigol, E. Mollarazi, Lett. Org. Chem. 2, 718 (2005)
13. S.L. Jain, J.K. Joseph, B. Sain, Catal. Lett. 115, 52 (2007)
14. X. Chen, Y. Peng, Catal. Lett. 122, 310 (2008)
15. X. Hui, W. Yan-Guang, Chin. J. Chem. 21, 327 (2003)
16. R.H. Shoar, G. Rahimzadeh, F. Derikvand, M. Farzaneh, Synth. Commun. 40, 1270 (2010)
17. K. Bahrami, M.M. Khodaei, A. Nejati, Monatsh. Chem. 142, 159 (2011)
18. S. Rostamnia, K. Lamei, Chin. Chem. Lett. 23, 930 (2012)
19. A.G. Choghamarani, P. Zamani, Chin. Chem. Lett. 24, 804 (2013)
20. S. Rostamnia, F. Pourhassan, Chin. Chem. Lett. 24, 401 (2013)
21. M.A. Chari, K. Syamasundar, J. Mol. Catal. A Chem. 221, 137 (2004)
22. C. Mukhopadhyay, P.K. Tapaswi, M.G.B. Drew, Tetrahedron Lett. 51, 3944 (2010)
23. X.C. Wang, L.J. Zhang, Z. Zhang, Z.J. Quan, Chem. Lett. 23, 423 (2012)
24. M.A. Bigdeli, G. Gholami, E. Sheikhhosseini, Chem. Lett. 22, 903 (2011)
25. J. Mondal, T. Sen, A. Bhaumik, Dalton Trans. 41, 6173 (2012)
26. J. Cheng, D.Y. Qi, Chin. Chem. Lett. 18, 647 (2007)
27. K. Folkers, T.B. Johnson, J. Am. Chem. Soc. 55, 2886 (1933)
28. S. Samai, G.C. Nandi, P. Singh, M.S. Singh, Tetrahedron 65, 10155 (2009)
29. T.H. Niloofar, D. Abolghasem, Chin. J. Chem. 29, 203 (2011)
30. S. Tu, X. Zhu, F. Shi, J. Zhang, Y. Zhang, J. Heterocycl. Chem. 44, 837 (2007)
31. H. Sachdeva, R. Saroj, S. Khaturia, H.L. Singh, J. Chil. Chem. Soc. 57, 1012 (2012)
32. Y. Wang, H. Yang, J. Yu, Z. Miao, R. Chena, Adv. Synth. Catal. 351, 3057 (2009)
33. R.S. Bhosale, S.V. Bhosale, S.V. Bhosale, T. Wang, P.K. Zubaidha, Tetrahedron Lett. 45, 9111
(2004)
34. S.E. Hankari, B. Motos-Perez, P. Hesemann, A. Bouhaouss, J.J.E. Moreau, Chem. Commun. 47,
6704 (2011)
35. N. Prosa, R. Turgis, R. Piccardi, M.C. Scherrmann, Eur. J. Org. Chem. 11, 2188 (2012)
36. D. Tejedor, F. Garcia-Tellado, Chem. Soc. Rev. 36, 484 (2007)
37. L. Weber, Drug Discov. Today 7, 143 (2002)
38. C. Hulme, V. Gore, Curr. Med. Chem. 10, 51 (2003)
39. S.D. Sharma, P. Gogoi, D. Konwar, Green Chem. 9, 153 (2007)
40. A.R. Gholap, K. Venkatesan, T. Daniel, R.J. Lahoti, K.V. Srinivasan, Green Chem. 6, 147 (2004)
41. A.V. Patil, A.R. Karade, In T.K. Bose and S.K. Mitra (Eds.), Fruits: Tropical, Subtropical (Naya
Prakash, Calcutta, 1996)
42. C. Bell, S. Hawthorne, J. Pharm. Pharmacol. 60, 139 (2008)
43. M.K. Reddy, S.K. Gupta, M.R. Jacob, S.I. Khan, D. Ferreira, Planta Med. 73, 461 (2007)
44. G.J. Kotwal, Vaccine 26, 3055 (2007)
45. N.P. Seeram, L.S. Adams, S.M. Henning, Y. Niu, Y. Zhang, M.G. Nair, D. Heber, J. Nut. Biochem.
16, 360 (2005)
46. P.S. Negi, G.K. Jayaprakash, B.S. Jena, Food Chem. 80, 393 (2003)
47. N. Seeram, R. Lee, M. Hardy, D. Heber, Separ. Purif. Technol. 41, 49 (2005)
48. M.N. Clifford, A. Scalbert, J. Sci. Food Agric. 80, 1118 (2000)
49. N. Kamal, Amin. J. Hazard. Mater. 165, 52 (2009)
50. A. Bhatnagar, A.K. Minocha, J. Hazard. Mater. 168, 1111 (2009)
51. E.S.Z. El-Ashtoukhya, N.K. Amina, O. Abdelwahab, Desalination 223, 162 (2008)
52. A. El Nemr, Chem. Ecol. 23, 409 (2007)
53. A. El Nemr, J. Hazard. Mater. 161, 132 (2009)
54. M. Rohani Moghadam, N. Nasirizadeh, Z. Dashti, E. Babanezhad, Int. J. Ind. Chem. 4, 19 (2013)
55. A. Bhatnagar, A.K. Minocha, Colloids Surf. B Biointerfaces 76, 544 (2010)
123

Punica granatum peel: an organocatalyst for green and…
56. N. Razavi, B. Akhlaghinia, RSC Adv. 5, 12372 (2015)
57. S.S.E. Ghodsinia, B. Akhlaghinia, RSC Adv. 5, 49849 (2015)
58. M. Zarghani, B. Akhlaghinia, Appl. Organomet. Chem. 29, 683 (2015)
59. Z. Zarei, B. Akhlaghinia, Chem. Pap. 69, 1421 (2015)
60. M. Zarghani, B. Akhlaghinia, RSC Adv. 5, 87769 (2015)
61. N. Razavi, B. Akhlaghinia, New J. Chem. 40, 477 (2016)
62. R. Jahanshahi, B. Akhlaghinia, RSC Adv. 5, 104087 (2015)
63. N. Yousefi Siavashi, B. Akhlaghinia, M. Zarghani, Res. Chem. Intermed. 42, 5789 (2016)
64. E. Karimian, B. Akhlaghinia, S.S.E. Ghodsinia, J. Chem. Sci. 128, 429 (2016)
65. R. Jahanshahi, B. Akhlaghinia, RSC Adv. 6, 29210 (2016)
66. M. Zarghani, B. Akhlaghinia, RSC Adv. 6, 31850 (2016)
67. M. Zarghani, B. Akhlaghinia, RSC Adv. 6, 38592 (2016)
68. S.S.E. Ghodsinia, B. Akhlaghinia, RSC Adv. 6, 63613 (2016)
69. M. Zarghani, B. Akhlaghinia, Bull. Chem. Soc. Jpn 89, 1192 (2016)
70. S. Memar Masjed, B. Akhlaghinia, M. Zarghani, N. Razavi, Aust. J. Chem. (2016). doi:10.1071/
CH16126
71. Z. Zarei, B. Akhlaghinia, RSC Adv. 6, 106473 (2016)
72. M. Abbasi, Res. Chem. Intermed. 42, 3303 (2016)
73. A. Zare, Z. Nasouri, J. Mol. Liq. 216, 364 (2016)
74. J. Safari, S. Gandomi-Ravandi, S. Ashiri, New J. Chem. 40, 512 (2016)
75. Q. Song, X. An, F. Che, T. Shen, J. Heterocycl. Chem 52, 1496 (2015)
76. H. Kiyani, M. Ghiasi, Res. Chem. Intermed. 41, 5177 (2015)
77. F. Tamaddon, S. Moradi, J. Mol. Catal. A Chem. 370, 117 (2013)
78. A. Rajack, K. Yuvaraju, Ch. Praveen, Y.L.N. Murthy, J. Mol. Catal. A Chem. 370, 197 (2013)
79. C.J. Liu, J.D. Wang, Molecules 14, 763 (2009)
80. S. Nagarajan, T.M. Sheikh, E. Kandasamy, J. Chem. Sci. 127, 1539 (2015)
81. W. Li, G. Zhou, P. Zhang, Y. Lai, S. Xu, Heterocycles 83, 2067 (2011)
82. F. Shaghayeghi Toosi, A. Maghsoodi, F.S. Toosi, Synth. React. Inorg. M. 46, 168 (2016)
83. K. Akhter, K. Jahan, U.K.R. Romman, M.G. Ahmed, M.S. Rahman, M. Al-Amin, Asian J. Chem.
27, 2624 (2015)
84. J. Safari, Z. Zarnegar, RSC Adv. 3, 17962 (2013)
85. R.O.M.A. De Souza, E.T. Da Penha, H.M.S. Milagre, S.J. Garden, P.M. Esteves, M.N. Eberlin,
O.A.C. Antunes, Chem. Eur. J. 15, 9799 (2009)
86. P.K. Sahu, P.K. Sahu, D.D. Agarwal, RSC Adv. 3, 9854 (2013)
87. J. Safari, Z. Zarnegar, M. Heydarian, J. Taibah Univ. Sci. 7, 17 (2013)
88. M. Kargar, R. Hekmatshoar, A. Mostashari, Z. Hashemi, Catal. Commun. 15, 123 (2011)
89. F. Damkaci, A. Szymaniak, J. Chem. Educ. 91, 943 (2014)
90. X.W. Liu, K.K. Pasunooti, H. Chai, C.N. Jensen, B.K. Gorityala, S. Wang, Tetrahedron Lett. 52, 80
(2011)
91. ChV Reddy, M. Mahesh, P.V.K. Raju, T.R. Babu, V.V.N. Reddy, Tetrahedron Lett. 43, 2657 (2002)
92. S. Rao Jetti, A. Bhatewara, T. Kadre, S. Jain, Chin. Chem. Lett. 25, 469 (2014)
93. D.L. da Silva, S.A. Fernandes, A.A. Sabino, A. de Fatima, Tetrahedron Lett. 52, 6328 (2011)
94. M. Moosavifar, C. R. Chim. 15, 444 (2012)
95. G.H. Mahdavinia, H. Sepehrian, Chin. Chem. Lett. 19, 1435 (2008)
96. F. Zamani, E. Izadi, Catal. Commun. 42, 104 (2013)
97. S. Patil, S.D. Jadhav, S.Y. Mane, Int. J. Org. Chem. 1, 125 (2011)
98. R. Tayebee, B. Maleki, M. Ghadamgahi, Chin. J. Catal. 33, 659 (2012)
99. M. Nasr-Esfahani, M. Montazerozohori, M. Aghel-Mirrezaee, H. Kashi, J. Chil. Chem. Soc. 59,
2311 (2014)
100. S. Besoluk, M. Kukukislamoglu, M. Zengin, M. Arsalan, M. Nebioglu, Turk. J. Chem. 34, 411
(2010)
101. K. Aswin, S.S. Mansoor, K. Logaiya, P.N. Sudhan, R.N. Ahmed, J. Taibah Univ. Sci. 8, 236 (2014)
123