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Document Type : Original Article


1 Department of Chemistry, Faculty of Science, Ilam University, Ilam 69315516, Iran

2 Department of Chemistry, University of Zanjan, Zanjan, 45195-313, Iran


The primary objective of this study was to devise a straightforward and environmentally sustainable approach for creating Biginelli compounds. Accordingly, a p(AMPS) hydrogel served as an effective catalyst of diverse nature, facilitating the preparation of 3,4-dihydropyrimidine-2-(1H)-ones, commonly recognized as Biginelli compounds. The chemical process unfolded using an eco-friendly method, resulting in notably abundant product yields. Moreover, the catalyst exhibited remarkable reusability, maintaining its efficacy through four cycles without a substantial decline. The innovative Biginelli reaction technique achieves environmentally conscious synthesis, robust product generation, simplified isolation procedures, catalyst sustainability, and avoids harmful by-products.

Graphical Abstract

Synthesis of 3, 4-Dihydropyrimidin-2-(1H)-ones Using a Hydrogel as a Green and Reusable Catalyst


Main Subjects


Hydrogels, being three-dimensional hydrophilic polymer networks, offer distinct environments suitable for preparing and safeguarding metal nanoparticles. Their three-dimensional, water-swollen, and cross-linked structure of hydrophilic polymer chains makes them particularly ideal for this purpose. Polymer chains within hydrogel networks have hydrophilic properties that are caused by the functional groups SO3H, -COOH, -CONH2, -OH, and -NH2 present in them. Recently, hydrogels have received attention as an intriguing class of catalysts, motivated by the rising need to develop cost-effective, environmentally friendly, efficient, and reusable catalysts [1-3]. Green chemistry stands out as an efficient technology aimed at minimizing or preferably eliminating waste generation, avoiding toxic solvents and reagents, and maximizing the use of renewable raw materials whenever possible [4-9].

Multi-component reactions (MCRs) are highly efficient and versatile synthetic procedures that promote the production of unique and complex molecular structures. They offer advantages over typical multistep syntheses [10-15]. In the realm of organic synthesis, multicomponent reactions (MCRs) that specifically target the synthesis of heterocyclic molecules featuring the dihydropyrimidinone scaffold have earned considerable acclaim [16-20]. The recent surge of interest in exploiting the MCRs capabilities underscores their pivotal role in advancing innovative synthetic methodologies [21-23]. Among various MCRs, the Biginelli reaction holds paramount importance. This chemical pathway enables the production of dihydropyrimidinones (DHPMs), a technique initially published by the Italian chemist Pietro Biginelli over a century ago [24-28].

The use of environmentally friendly methods to produce multi-component compounds is widely favored. Sustainable techniques reduce the environmental impact of chemical processes [29-31]. Green synthesis uses non-toxic solvents, sustainable resources, and energy-saving techniques [32-35]. Researchers can improve chemical production by prioritizing these principles and developing synthetic routes that produce compounds. The synthesis of this multi-component green compound contributes to global efforts to reduce the environmental impact of chemical production [36-40].

Despite their potential advantages, several of the documented one-pot protocols have limitations, including the utilization of costly reagents, reliance on volatile strong acid conditions, and long reaction times. Consequently, there is a pressing need to introduce a more moderate and efficient method that not only avoids these drawbacks, but also ensures higher yields. To the best of our knowledge, there are no documented instances employing hydrogels as eco-friendly additive within a green solvent under reflux conditions. Consequently, this study introduces a novel methodology for synthesizing substituted DHPM, employing a straightforward and suitable approach under green conditions, as exhibited in Scheme 1.


Scheme 1: DHPMs synthesis using hydrogel


Materials and Methods

Merck, Fluka, and Aldrich supplied starting materials used without purification.

Preparation of Catalytic Hydrogel

The process detailed in [41] was followed to create Poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (p(AMPS)) hydrogel. This involved radical polymerization using a redox initiator. Specifically, 0.0217 mol of AMPS (C7H13NO4S) was mixed with 0.5 mol% of Bis (C7H10N2O2) in 3.5 mL water along with 100 mL TEMED (C6H16N2). A 1 mL aqueous initiator solution (5 wt%) of APS ( (NH4)2S2O8) (1 mol% in relation to the monomer) was added to the hydrogel precursors.

The mixture was then poured into plastic pipettes with a 4 mm diameter and allowed to undergo polymerization and crosslinking for 24 h at room temperature. The resulting p(AMPS) hydrogel was cut into cylindrical shapes measuring 4-5 mm in length. These pieces were cleaned by immersing them in water for three days, with water changed per 12 h to remove residues like monomer, polymer, crosslinker, and unreacted initiator. Post-cleaning, the hydrogel was dried in an oven at 45 °C until reaching a constant weight. Finally, it was stored in an airtight container for future use.

General Method for the Synthesis of DHPMs Derivatives

A mixture of urea (2 mmol), aldehyde 2a-u (1 mmol) and hydrogel (0.15 mg) in ethanol (5 mL) was subjected to magnetic stirring at room temperature. After adding 1.5 mmol of ethyl acetoacetate, the mixture was stirred under reflux conditions for a specified time until the reaction was completed.

The reaction was monitored by TLC (n-hexane:EtOAc, 10:6). At the end of the reaction, the solid product was filtered and purified through recrystallization in hot ethanol. All identified products, recognized as known compounds, underwent characterization including analysis of melting points, IR, 1H-NMR, and 13C-NMR spectra.

The Selected Spectral Data

Sample 4b: mp 212-214 °C; IR: NH 3231, NH 3102, CO 1701, CO 1646, C–O 1122, and C–N 1091 cm-11H-NMR (250.13 MHz, CDCl3): δ 1.04 (t, 3J 7.5 Hz, 3H, CH3), 2.41 (s, 3H, CH3), 3.98 (q, 3J 7.5 Hz, 2H, CH2), 5.86 (s, 1H, CH), 7.18–7.37 (m, 4H, Ar–H), 5.86 (NH), and 8.92 (NH); 13C-NMR (62.90 MHz, CDCl3) δ 13.9, 18.3, 52.1, 59.9, 98.8, 127.5, 128.0, 129.8, 132.5, 139.5, 148.5, 153.3, and 165.3 ppm.

Results and Discussion

A practical and straightforward method was employed in this study to affirm the synthesis of DHPM. Various reaction setups were explored to establish optimal conditions for creating modified DHPM (4a-u), involving urea, ethyl acetoacetate, 4-chlorobenzaldehyde, and hydrogel as an eco-friendly element in ethanol solvent, serving as a model reaction. In our efforts to optimize these reaction conditions, we investigated the influence of solvents and the amount of additives. We initially experimented with different solvents include: H2O, C2H5OH, C2H5OH-H2O, CH3OH, CH3CN, and CH2Cl2 in the synthesis of 4c, a representative compound. The most favorable result was obtained from the reaction using 4-chlorobenzaldehyde, ethyl acetoacetate, urea, and hydrogel as a green additive in ethanol solvent, which provided 4c in 6 h with 94% yield (Table 1, Entry 2).

While H2O, C2H5OH-H2O, CH3OH, CH2Cl2, and CH3CN resulted in moderate yields of the desired products, C2H5OH proved to be the optimal solvent for all subsequent processes.

To determine the optimized quantity of the catalyst, the model reaction was conducted for the synthesis of compound 4c. The additive quantity was varied, as depicted in Table 2, entries 2-4. The highest yield of the desired product was attained with 0.15 mg of the additive. The summarized results are presented in Table 2. Under these optimized conditions, we extended our examination to the reaction of ethyl acetoacetate and urea with diverse aldehydes using hydrogel as an efficient and thermally stable catalyst.



Table 1: The effect of the solvents on the preparation of substituted 3,4-dihyrdopyrimidin-2-(1H)-ones

Yield a (%)





















aIsolated yield


The reactions progressed seamlessly in ethanol under reflux conditions, completing within 6 h. The results pertaining to the conversion of differently substituted aryl aldehydes into DHPM derivatives 4a–u are presented in Table 3.

The proposed mechanism for synthesizing substituted DHPM (4a-u) is depicted in Scheme 2. Given the established reflux chemistry of substituted DHPM, we propose an acid-catalysed condensation of urea (2) and an aromatic aldehyde (1) in EtOH. The hydrogel presence aids imine formation (4). Subsequently, ethyl acetoacetate (5) undergoes nucleophilic addition, generating an enol (6) that contributes to a 1, 3-dipolar intermediate. This intermediate reacts with the imine, followed by an intramolecular attack leading to the nitrogen-containing six-membered ring. Elimination of ethanol and hydrogel molecules yields the target product, as detailed in Scheme 2.

The catalyst's recyclability, reusability, and catalytic performance were evaluated. Post-filtration from the reaction mix, the catalyst underwent washing with diluted water, drying, and reuse in subsequent reactions multiple times. Remarkably, the hydrogel exhibited consistent reusability for at least four cycles, maintaining product yield without noticeable decline. The potential for reusability and recycling of the hydrogel was explored via sequential condensations involving ethyl acetoacetate and 4-chlorobenzaldehyde with urea. Recovering the catalyst involved washing the reaction mix with water. The catalyst extracts, obtained after water evaporation and concentration, were reused without purification in the subsequent run. Impressively, the reaction proceeded smoothly, yielding products at 85-94%, highlighting the catalyst's sustained activity even after four runs (Table 4).

In summary, this innovative procedure offers an efficient route to synthesizing target products with high yields and exceptional purities. It represents a simple and convenient method applicable to various substituted DHPM. The structural confirmation of sample was validated through FT-IR, 1H-NMR, and 13C-NMR analyses.



Table 2: Influence of varying catalyst quantities on the synthesis of 4d

             Yield (%) a

Time (h)

Catalyst (mg)






















aIsolated yield


 Table 3:  Hydrogel Catalyzed synthesis of 3,4-dihyrdopyrimidin-2-(1H)-ones a,b













































































4F- C6H4





3F- C6H4





























aReaction conditions: Aldehyde 1 (1 mmol), urea 2 (2 mmol), ethyl acetoacetate 3 (1.5 mmol) EtOH (5 mL), and hydrogel (0.15 mg), Reflux condition. b Isolated yield


Scheme 2: The proposed mechanistic pathway for the DHPMs preparation

Table 4: Reusability and recovery of the catalyst

Yield (%)a












aIsolated  yield



To sum up, a straightforward and effective method was introduced for producing a range of DHPMs. This method utilizes aryl aldehyde, β-ketoester, and urea as substrates, employing hydrogel as a catalyst. The approach boasts several benefits such as high yields, operational ease, straightforward product isolation via filtration, the use of an environmentally friendly solvent, and a significant reduction in yield after four reuses of the catalyst.

Disclosure statement

No potential conflict of interest was reported by the authors.


This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions

All authors contributed toward data analysis, drafting, and revising the paper and agreed to responsible for all the aspects of this work.

Conflict of interest

The authors declare that they have no conflicts of interest in this article.


Saeid Taghavi Fardood

Ali Ramazani


Saeid Taghavi Fardood, Zahra Hosseinzadeh, Ali Ramazani. Synthesis of 3,4-Dihydropyrimidin-2-(1H)-ones Using a Hydrogel as a Green and Reusable Catalyst. Chem. Methodol., 2024, 8(3) 154-163




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[1]. Manuel M., Jennifer A., A Review on Starch and Cellulose-Enhanced Superabsorbent Hydrogel, Journal of Chemical Reviews, 2023, 5:183 [Crossref], [Google Scholar], [Publisher]
[2]. Hakimi F., Taghvaee M., Golrasan E., Synthesis of benzoxazole derivatives using Fe3O4@SiO2-SO3H nanoparticles as a useful and reusable heterogeneous catalyst without using a solvent, Advanced Journal of Chemistry, Section A, 2023, 6:188 [Crossref], [Google Scholar], [Publisher]
[3]. Sattari Alamdar S., A Review on Synthesis of Carbohydrazide Derivatives, Asian Journal of Green Chemistry, 2023, 7:91 [Crossref], [Publisher]
[4]. Sheldon R.A., The E factor: fifteen years on, Green Chemistry, 2007, 9:1273 [Crossref], [Google Scholar], [Publisher]
[5]. Sheldon R.A., Chemicals from synthesis gas: catalytic reactions of CO and (Vol. 2). Springer Science & Business Media. 1983 [Google Scholar], [Publisher]
[6]. Ahankar H., Ramazani A., Ślepokura K., Lis T., Joo S.W., Synthesis of pyrrolidinone derivatives from aniline, an aldehyde and diethyl acetylenedicarboxylate in an ethanolic citric acid solution under ultrasound irradiation, Green Chemistry, 2016, 18:3582 [Crossref], [Google Scholar], [Publisher]
[7]. Hasan M.S., Sardar M.R.I., Shafin A.A., Rahman M.S., Mahmud M., Hossen M.M., A Brief Review on Applications of Lignin, Journal of Chemical Reviews, 2023, 5:56 [Crossref], [Google Scholar], [Publisher]
[8]. Katre S.D., Microwaves in Organic Synthetic Chemistry- A Greener Approach to Environmental Protection: An Overview, Asian Journal of Green Chemistry, 2024, 8:68 [Crossref], [Publisher]
[9]. Taghavi Fardood S., Moradnia, F., Mostafaei, M., Afshari, Z., Faramarzi, V.,Ganjkhanlu, S., Biosynthesis of MgFe2O4 magnetic nanoparticles and its application in photo-degradation of malachite green dye and kinetic study, Nanochemistry Research, 2019, 4:86 [Crossref], Publisher]
[10]. Moradnia F., Taghavi Fardood S., Ramazani A., Osali S., Abdolmaleki I., Green sol–gel synthesis of CoMnCrO4 spinel nanoparticles and their photocatalytic application. Micro & Nano Letters, 2020, 15:674 [Crossref], [Google Scholar], [Publisher]
[11]. Ahankar H., Taghavi Fardood S., Ramazani A., One-pot three-component synthesis of tetrahydrobenzo[b]pyrans in the presence of Ni0.5Cu0.5Fe2O4 magnetic nanoparticles under microwave irradiation in solvent-free conditions, Iranian Journal of Catalysis, 2020, 10:195 [Google Scholar], [Publisher]
[12]. Fardood S.T., Ramazani A., Ayubi M., Moradnia M., Abdpour S., Forootan, R., Microwave Assisted Solvent-free Synthesis of 1-phenyl-1,2-dihydro-3H-naphtho [1,2-e][1,3] oxazin-3-one Catalyzed by FeCl3, Chemical Methodologies, 2019, 3:519 [Crossref], [Google Scholar], [Publisher]
[13]. Fardood S.T., Ramazani A., Moradnia F., Afshari Z., Ganjkhanlu S., Zare F.Y., Green synthesis of ZnO nanoparticles via Sol-gel method and investigation of its application in solvent-free synthesis of 12-Aryl-tetrahydrobenzo[α] xanthene-11-one derivatives under microwave irradiation, Chemical Methodologies, 2019, 3: 632 [Crossref], [Google Scholar], [Publisher]
[14]. Taghavi Fardood S., Ramazani A., Azimzadeh Asiabi P., Bigdeli Fard Y., Ebadzadeha B., Microwave-assisted multicomponent reaction for the synthesis of 2-amino-4H-chromene derivatives using ilmenite (FeTiO3) as a magnetic catalyst under solvent-free conditions, Asian Journal of Green Chemistry, 2017, 1:34 [Crossref], [Google Scholar], [Publisher]
[15]. Abegunde S.M., Idowu K.S., Enhanced Adsorption of Methylene Blue Dye from Water by Alkali Treated Activated Carbon. Eurasian Journal of Science and Technology, 2023, 3:109 [Crossref], [Google Scholar], [Publisher]
[16]. Adole V.A., Computational Chemistry Approach for the Investigation of Structural, Electronic, Chemical and Quantum Chemical Facets of Twelve Biginelli Adducts, Journal of Applied Organometallic Chemistry, 2021, 1:29 [Crossref], [Google Scholar], [Publisher]
[17]. kidwai M., Dwivedi P., Jahan A., An Environmentally Friendly Strategy for One-pot Synthesis of Dithiocarbamates Using Ceric Ammonium Nitrate (CAN) and PEG: H2O Solvent System, Journal of Applied Organometallic Chemistry, 2023, 3:156 [Crossref], [Google Scholar], [Publisher]
[18]. Swami M., Nagargoje G., Mathapati S., Bondge A., Jadhav A., Panchgalle S., More V., A magnetically recoverable and highly effectual Fe3O4 encapsulated MWCNTs nano-composite for synthesis of 1,8-dioxo-octahydroxanthene derivatives, Journal of Applied Organometallic Chemistry, 2023, 3:184 [Crossref], [Google Scholar], [Publisher]
[19]. Das R., Mukherjee D., Reja S., Sarkar K., Kejriwal A., Copper Based N,N-Dimethyl-N-(1-Pyridinylmethylidene) Propane-1,3-Diamine Compound: Synthesis, Characterization, and Its Application toward Biocidal Activity, Journal of Applied Organometallic Chemistry, 2023, 3:73 [Crossref], [Google Scholar], [Publisher]
[20]. Mhaibes R. M., Arzehgar Z., Mirzaei Heydari M., Fatolahi L. ZnO Nanoparticles: A Highly Efficient and Recyclable Catalyst for Tandem Knoevenagel-Michael-Cyclocondensation Reaction, Asian Journal of Green Chemistry, 2023, 7:1 [Crossref], [Google Scholar], [Publisher]
[21]. Ezzatzadeh E., Sheikholeslami-Farahani F., Yadollahzadeh K., Rezayati S., Highly Efficient Reusable Carboxy Group Functionalized Imidazolium Salts for a Simple and Cost-effective Preparation of pyrano [2,3-d] pyrimidinone Derivatives, Combinatorial Chemistry & High Throughput Screening, 2021, 24:1465 [Crossref], [Google Scholar], [Publisher]
[22]. Rezanejade G., Ghavami S., Sadat S., A review on pH and temperature responsive gels in drug delivery, Journal of Chemical Reviews, 2020, 2:80 [Crossref], [Google Scholar], [Publisher]
[23]. Saeidian H., Mirjafary Z., Abdolmaleki E., Moradnia F., An expedient process for the synthesis of 2-(N-arylamino) benzaldehydes from 2-hydroxybenzaldehydes via Smiles rearrangement, Synlett, 2013, 24:2127 [Crossref], [Google Scholar], [Publisher]
[24]. Pouramiri B., Tavakolinejad Kermany E., Khajesamani H., Khabazzadeh H., An Efficient, Three-Component Synthesis of 3, 4-Di Hydropyrimidin-2 (1H)-Ones Using LaCl3/ClCH2COOH as Environmentally Benign and Green Catalytic System, Journal of Sciences, Islamic Republic of Iran, 2014, 25:323 [Google Scholar], [Publisher]
[25]. Ramazani A., Rouhani M., Joo S.W., Catalyst-free sonosynthesis of highly substituted propanamide derivatives in water, Ultrasonics Sonochemistry, 2016, 28:393 [Crossref], [Google Scholar], [Publisher]
[26]. Taghavi Fardood S., Ramazani A., Golfar Z., Joo S.W., Green synthesis of Ni‐Cu‐Zn ferrite nanoparticles using tragacanth gum and their use as an efficient catalyst for the synthesis of polyhydroquinoline derivatives. Applied Organometallic Chemistry, 2017, 31:e3823 [Crossref], [Google Scholar], [Publisher]
[27]. Ramazani A., Farshadi A., Mahyari A., Sadri F., Woo J.S., Azimzadeh A.P., Taghavi F.S., Dayyani N., Ahankar H., Synthesis of electron-poor N-Vinylimidazole derivatives catalyzed by Silica nanoparticles under solvent-free conditions, International Journal of Nano Dimension, 2016, 7:41 [Crossref], [Google Scholar], [Publisher]
[28]. Fardood S.T., Ramazani A., Moradi S., Green synthesis of Ni–Cu–Mg ferrite nanoparticles using tragacanth gum and their use as an efficient catalyst for the synthesis of polyhydroquinoline derivatives, Journal of Sol-Gel Science and Technology, 2017, 82:432 [Crossref], [Google Scholar], [Publisher]
[29]. Muhiebes R.M., Fatolahi L., Sajjadifar S., L-proline catalyzed multicomponent reaction for simple and efficient synthesis of tetrahydropyridines derivatives, Asian Journal of Green Chemistry, 2023, 7:121 [Crossref], [Google Scholar], [Publisher]
[30]. Mohammadzadeh Koumleh S., Rahmani S., Nasr-Isfahani H., Synthesis, characterization and comparative study of aromatic polyureas based on 2,3-dihydro-1,4-phthalazinedione with various aromatic and aliphatic diisocyanates, Asian Journal of Green Chemistry, 2022, 6:145 [Crossref], [Publisher]
[31]. Wijekoon S., Gunasekara C., Palliyaguru L., Fernando N., Jayaweera P., Kumarasinghe U., Solvent-free synthesis and antifungal activity of 3-alkenyl oxindole derivatives, Asian Journal of Green Chemistry, 2022, 6:297 [Crossref], [Google Scholar], [Publisher]
[32]. Ajormal F., Moradnia F., Taghavi Fardood S., Ramazani A., Zinc Ferrite Nanoparticles in Photo-Degradation of Dye: Mini-Review, Journal of Chemical Reviews, 2020, 2:90 [Crossref], [Google Scholar], [Publisher]
[33]. Fardood S.T., Moradnia F., Forootan R., Abbassi R., Jalalifar S., Ramazani A., Sillanpӓӓ M., Facile green synthesis, characterization and visible light photocatalytic activity of MgFe2O4@ CoCr2O4 magnetic nanocomposite, Journal of Photochemistry and Photobiology A: Chemistry, 2022, 423:113621 [Crossref], [Google Scholar], [Publisher]
[34]. Moradnia F., Fardood S.T., Ramazani A., Gupta V.K., Green synthesis of recyclable MgFeCrO4 spinel nanoparticles for rapid photodegradation of direct black 122 dye, Journal of Photochemistry and Photobiology A: Chemistry, 2020, 392:112433 [Crossref], [Google Scholar], [Publisher]
[35]. Taghavi Fardood S., Moradnia F., Heidarzadeh S., Naghipour A., Green synthesis, characterization, photocatalytic and antibacterial activities of copper oxide nanoparticles of copper oxide nanoparticles, Nanochemistry Research, 2023, 8:134 [Crossref], [Google Scholar], [Publisher]
[36]. Ramazani A., Moradnia F., Aghahosseini H., Abdolmaleki I., Several species of nucleophiles in the Smiles rearrangement, Current Organic Chemistry, 2017, 21:1612 [Crossref], [Google Scholar], [Publisher]
[37]. Taghavi Fardood S., Ramazani A., Joo S., Green chemistry approach for the synthesis of copper oxide nanoparticles using tragacanth gel and their structural characterization, Journal of Structural Chemistry, 2018, 59:482 [Crossref], [Google Scholar], [Publisher]
[38]. Taghavi Fardood S., Ramazani A., Golfar Z., Joo S., Green synthesis using tragacanth gum and characterization of Ni–Cu–Zn ferrite nanoparticles as a magnetically separable catalyst for the synthesis of hexabenzylhexaazaisowurtzitane under ultrasonic irradiation, Journal of Structural Chemistry, 2018, 59:1730 [Crossref], [Google Scholar], [Publisher]
[39]. Fardood S.T., Forootan R., Moradnia F., Afshari Z., Ramazani A., Green synthesis, characterization, and photocatalytic activity of cobalt chromite spinel nanoparticles, Materials Research Express, 2020, 7:015086 [Crossref], [Google Scholar], [Publisher]
[40]. Moradnia F., Taghavi Fardood S., Ramazani A., Osali S., Abdolmaleki I., Green sol–gel synthesis of CoMnCrO4 spinel nanoparticles and their photocatalytic application, Micro & Nano Letters, 2020, 15:674 [Crossref], [Google Scholar], [Publisher]
[41]. Sahiner N., Ozay H., Ozay O., Aktas N., A soft hydrogel reactor for cobalt nanoparticle preparation and use in the reduction of nitrophenols, Applied Catalysis B: Environmental, 2010, 101:137 [Crossref], [Google Scholar], [Publisher]
[42]. Rao G.D., Acharya B., Verma S., Kaushik M., N, N′-Dichlorobis (2,4,6-trichlorophenyl) urea (CC-2) as a new reagent for the synthesis of pyrimidone and pyrimidine derivatives via Biginelli reaction, Tetrahedron Letters, 2011, 52:809 [Crossref], [Google Scholar], [Publisher]
[43]. Murata H., Ishitani H., Iwamoto M., Synthesis of Biginelli dihydropyrimidinone derivatives with various substituents on aluminium-planted mesoporous silica catalyst, Organic & Biomolecular Chemistry, 2010, 8:1202 [Crossref], [Google Scholar], [Publisher]
[44]. Salehi P., Dabiri M., Zolfigol M.A., Fard M.A.B., Silica sulfuric acid: an efficient and reusable catalyst for the one-pot synthesis of 3, 4-dihydropyrimidin-2(1H)-ones, Tetrahedron Letters, 2003, 44:2889 [Crossref], [Google Scholar], [Publisher]
[45]. Safari J., Gandomi-Ravandi S., Titanium dioxide supported on MWCNTs as an eco-friendly catalyst in the synthesis of 3, 4-dihydropyrimidin-2-(1H)-ones accelerated under microwave irradiation, New Journal of Chemistry, 2014, 38:3514 [Crossref], [Google Scholar], [Publisher]
[46]. Khademinia S., Behzad M., Jahromi H.S., Solid state synthesis, characterization, optical properties and cooperative catalytic performance of bismuth vanadate nanocatalyst for Biginelli reactions, RSC Advances, 2015, 5:24313 [Crossref], [Google Scholar], [Publisher]
[47]. Javidi J., Esmaeilpour M., Dodeji F.N., Immobilization of phosphomolybdic acid nanoparticles on imidazole functionalized Fe3O4@SiO2: A novel and reusable nanocatalyst for one-pot synthesis of Biginelli-type 3, 4-dihydro-pyrimidine-2-(1H)-ones/thiones under solvent-free conditions, RSC Advances, 2015, 5:308 [Crossref], [Google Scholar], [Publisher]
[48]. Zhang Y., Wang B., Zhang X., Huang J., Liu C., An efficient synthesis of 3,4-dihydropyrimidin-2 (1 H)-ones and thiones catalyzed by a novel brønsted acidic ionic liquid under solvent-free conditions, Molecules, 2015, 20:3811 [Crossref], [Google Scholar], [Publisher]
[49]. Ma Y., Qian C., Wang L., Yang M., Lanthanide triflate catalyzed Biginelli reaction. One-pot synthesis of dihydropyrimidinones under solvent-free conditions, Journal of Organic Chemistry, 2000, 65:3864 [Crossref], [Google Scholar], [Publisher]
[50]. Yu J., Hu S., Wang J., Wong G.K.-S., Li S., Liu B., Deng Y., Dai L., Zhou Y., Zhang X., A draft sequence of the rice genome (Oryza sativa L. ssp. indica), Science, 2002, 296:79 [Crossref], [Google Scholar], [Publisher]
[51]. Lu J., Bai Y.J., Guo Y.H., Wang Z.J., Ma H.R., CoCl2·6H2O or LaCl3·7H2O catalyzed Biginelli reaction. One‐pot synthesis of 3, 4‐dihydropyrimidin‐2(1H)‐ones, Chinese Journal of Chemistry, 2002, 20:681 [Crossref], [Google Scholar], [Publisher]
[52]. Hu E.H., Sidler D.R., Dolling U.H., Unprecedented catalytic three component one-pot condensation reaction: an efficient synthesis of 5-alkoxycarbonyl-4-aryl-3, 4-dihydropyrimidin-2(1H)-ones, The Journal of Organic Chemistry, 1998, 63:3454 [Crossref], [Google Scholar], [Publisher]
[53]. Masoud N.E., Hoseini S.J., Mohammadi F., Fe3O4 nanoparticles as an efficient and magnetically recoverable catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones under solvent-free conditions, Chinese Journal of Catalysis, 2011, 32:1484 [Crossref], [Google Scholar], [Publisher]
[54]. Salehi H., Guo Q.X., A facile and efficient one‐pot synthesis of dihydropyrimidinones catalyzed by magnesium bromide under solvent‐free conditions, Synthetic Communications, 2004, 34:171 [Crossref], [Google Scholar], [Publisher]
[55]. Lu J., Bai Y., Catalysis of the Biginelli reaction by ferric and nickel chloride hexahydrates. One-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones, Synthesis, 2002, 2002:0466 [Crossref], [Google Scholar], [Publisher]
[56]. Prakash G.S., Lau H., Panja C., Bychinskaya I., Ganesh S.K., Zaro B., Mathew T., Olah G.A., Synthesis of dihydropyrimidinones/ thiopyrimidinones: Nafion-Ga, an efficient “green” lewis acid catalyst for the biginelli reaction, Catalysis Letters, 2014, 144:2012 [Crossref], [Google Scholar], [Publisher]
[57]. Zarnegar Z., Safari J., Magnetic nanoparticles supported imidazolium-based ionic liquids as nanocatalyst in microwave-mediated solvent-free Biginelli reaction. Journal of Nanoparticle Research, 2014, 16:1 [Crossref], [Google Scholar], [Publisher]
[58]. Salehi H., Ahmadi S.J., Firouz Z.M., Sadat K.S., Pakouian H., Tajik A.H., Green procedure for synthesis of 3, 4 dihydropyrimidinones using 12-molybdophosphoric acid, as a catalyst and solvent free condition under microwave irradiation. International Journal of Surgical Pathology, 2010, 18:5 [Crossref], [Google Scholar], [Publisher]