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. 2026 May 2;21(1):156. doi: 10.1186/s11671-026-04601-x

L-glutamine-functionalized magnetic polystyrene for highly efficient synthesis of 2-amino-4H-pyrans

Fatemeh Zahra Hajian 1, Sakineh Asghari 1,✉, Ghasem Firouzzadeh Pasha 1,✉, Taraneh Abbaspour 1, Mahmood Tajbakhsh 1, Fatemeh Zare 1
PMCID: PMC13135607  PMID: 42068488

Abstract

In this study, we reported the synthesis and characterization of a novel magnetic polystyrene nanocatalyst functionalized with L-glutamine (L-Glu-MPS) and evaluation of its catalytic performance in a multicomponent organic reaction for the preparation of 2-amino-4 H-pyrans. The catalyst was prepared through magnetization of chloromethylated polystyrene (PS-Cl) using FeCl2·4H2O and FeCl3·6H2O, followed by covalent attachment of L-glutamine. The characteristics of the samples were meticulously analyzed by applying TGA, FT-IR, XRD, VSM, EDS-mapping, SEM, EDS, and elemental analysis, confirming effective surface modification and satisfactory stability. The catalytic performance of L-Glu-MPS was examined in the three-component condensation reaction involving aromatic aldehydes, malononitrile, and ethyl acetoacetate, aimed at synthesizing 2-amino-4 H-pyran derivatives. The results demonstrated high efficiency of the nanocatalyst, providing excellent yields (88–98%) under mild, room-temperature conditions with short reaction times (25 min). Moreover, the catalyst demonstrated remarkable reusability, with at least 6 consecutive runs without significant loss in activity or structural integrity. These findings highlight L-Glu-MPS as a green, efficient, and reusable catalytic system for the sustainable synthesis of heterocyclic compounds.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11671-026-04601-x.

Keywords: Magnetic polystyrene, L-Glutamine, Multicomponent reaction, 4H-pyran, Green chemistry

Introduction

Due to the environmental impact of industrialization and population growth, “green chemistry” has gained attention in recent years [1, 2]. Heterogeneous catalysis plays a key role in advancing technological processes for synthesizing sustainable chemicals with a focus on environmentally friendly methods that lead to increased yields [3–5]. In the context of environmentally friendly organic synthesis, the development of reusable and highly active immobilized catalysts has garnered significant interest among chemists [6, 7]. In the interim, nanomaterials possessing unique physicochemical properties, including a high surface-to-volume ratio, tunable surface chemistry, and pronounced size-dependent catalytic behavior—have attracted considerable attention as efficient catalytic platforms [8]. The interest in magnetic heterogeneous catalysts has been increasing, mainly because of their wide range of uses in medicine and drug delivery. Their notable advantages include easy separation and recyclability, which surpass the efficiency of centrifugation and filtration [9]. Due to their high surface-to-volume ratio, magnetic nanoparticles (MNPs) exhibit high surface energy, which promotes van der Waals interactions and leads to aggregation. Such agglomeration reduces the accessibility of active sites and catalytic efficiency. Therefore, surface functionalization is essential to enhance stability, prevent aggregation, and provide suitable anchoring sites for the immobilization of active catalytic species [10, 11]. Among them, natural and synthetic polymers are recognized as one of the best options among the various available modifying agents. Polystyrene is one of the most commonly used polymer bases in synthetic organic chemistry due to its availability, low cost, ease of functionalization, and chemical inertness. Functionalizing the surface of the polystyrene with organic ligands improves its catalytic performance. Consequently, amino acids, which serve as neutral and nitrogen-containing ligands, have attracted considerable interest owing to their distinctive characteristics, such as remarkable biocompatibility, enhanced stability, affordability, and extensive availability [12–15].

L-Glutamine (L-Glu) is an essential, non-corrosive amino acid renowned for its affordability, efficiency, and eco-friendly properties, making it the subject of extensive research. This amino acid contains a primary amine group and an amide side chain, rendering it an attractive bifunctional ligand for heterogeneous catalysis. Unlike simple amine-based ligands, L-glutamine can provide cooperative catalytic activation through basic amine sites coupled with hydrogen-bond donor/acceptor interactions mediated by the amide functionality [16]. Such dual activation may facilitate key steps in multicomponent reactions, including the Knoevenagel condensation and subsequent Michael addition [17]. Functionalization of magnetic supports with amino acids has been widely explored to enhance catalytic activity and recyclability. For example, L-Proline was immobilized onto Fe3O4@SiO2 magnetic nanoparticles and successfully applied in the synthesis of 2,4,6-triarylpyridines, demonstrating high yields and easy magnetic recovery [18]. Additionally, L-Aspartic acid grafted onto Fe3O4@SiO2 served as a bifunctional acid–base catalytic system for the efficient synthesis of benzo[b]pyran and pyrano[3,2–c] chromene derivatives [19]. Also, multifunctional systems incorporating various amino acids such as L-tryptophan, L-serine, L-proline, and L-cysteine on magnetic supports have been explored for biomedical applications, highlighting the versatility of amino acid surface modification. Although amino acid-functionalized magnetic catalysts have been reported [20], studies employing L-glutamine immobilized on polymeric magnetic supports remain limited. This provides an opportunity to investigate its potential as an environmentally benign ligand for surface modification in the synthesis of heterocyclic compounds, offering a promising approach in this field.

Multi-component reactions (MCRs) are an efficient method for synthesizing diverse, drug-like compounds. They provide advantages such as high yields, faster reaction times, better atom economy, and lower solvent and energy consumption [19–21]. Oxygen-based heterocyclic compounds have attracted considerable attention in recent years due to their broad range of applications. Tetrahydrobenzopyrans, or tetrahydro-4H-chromenes, are valuable fused oxygen-containing heterocycles with diverse applications in synthetic organic and medicinal chemistry [22–24]. They exhibit various biological activities including anticancer [25], anti-inflammatory [26], anti-HIV [27], antibacterial [28], anticoagulant [29], and antioxidant effects [30]. Various methods have been reported for developing 2-amino-4H-pyran using heterogeneous and homogeneous catalysts [31–33]. Therefore, it is essential to create eco-friendly and efficient catalysts for synthesizing 2-amino-4H-pyran under mild reaction conditions.

Due to the exceptional attributes of nanoparticles, characterized by their nanoscale dimensions and significant surface-to-volume ratio, we aimed to synthesize magnetic polystyrene modified with L-Glu as a novel catalyst with easy separation and recycling capabilities. This modified material will be used as a proficient nanocatalyst for the synthesis of 4H-pyran through a three-component condensation reaction involving aromatic aldehydes 1a-i, malononitrile 2, and ethyl acetoacetate 3 or dimedone 4 (Scheme 1). Additionally, the incorporation of L-Glu onto the surface of the magnetic polystyrene improves both the uniformity and catalytic efficiency of the catalyst within the reaction medium.

Scheme 1.

Scheme 1

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Synthesis of 2-amino-4H-pyran with nanocatalyst L-Glu-MPS

Materials & methods

Chemicals and reagents

All materials employed in this study, including the primary substances for the reaction and catalyst preparation, as well as solvents, were of high purity and sourced from Merck and Sigma-Aldrich, Germany. Detailed information about the analytical instruments and materials used can be found in the supporting file.

Preparation of nanocatalyst

Synthesis of nanomagnetic polystyrene functionalized with L-glutamine (L-Glu-MPS)

The synthesis of magnetic polystyrene (MPS) was carried out as described in our previous report [34]. Briefly, a mixture consisting of chloromethylated polystyrene (PS-Cl, 1 g, with a Cl content of 1.8 mmol Cl/g), FeCl3·6 H₂O (1.5 g), and FeCl2·4 H₂O (0.6 g) was prepared by dispersing the ingredients in ethanol and sonicated until uniform. The mixture was then subjected to reflux heating for 1 h, after which NH3·H2O 25% (10 ml) was introduced and stirred for an additional hour. Upon cooling, the resulting black precipitate was extracted using an external magnet. Ultimately, the solution was washed multiple times with deionized water and ethanol to ensure neutralization. The resultant MPS was subsequently dried in an oven at 60 °C, yielding a black powder.

To synthesize L-Glu-MPS, a mixture of 1 g of MPS and 2.24 g of L-Glu (20 mmol) was refluxed in toluene for two days. After cooling to 25 °C, L-Glu-MPS was extracted using a strong magnet, washed with ethanol and dichloromethane. The non-bonded glutamine amino acid was removed using a Soxhlet extractor with absolute ethanol for 24 h. The L-Glu-functionalized MPS (L-Glu-MPS) was collected in its pure form and then dried in a vacuum oven at 60 °C, yielding a brown powder.

General experimental procedure for synthesis of 2‑amino‑4H‑pyrans

A mixture of benzaldehyde derivatives (1 mmol), dimedone or ethyl acetoacetate (1 mmol), and malononitrile (1 mmol) in 10 mL of ethanol was stirred in the presence of 20 mg of L-Glu-MPS nanocatalyst for 20 min at room temperature. The reaction was monitored by TLC using a ratio of 3:1 hexane to ethyl acetate. After completion of the reaction, the catalyst was extracted from the mixture using a supermagnet and washed with ethanol. The solvent was then evaporated, and the resulting precipitate was purified through recrystallization in hot ethanol. The product structures were verified through melting point analysis and verified by FT-IR, and NMR analyses. Spectra data for all compounds are presented in the supporting section in Figures S1–S20.

Result & discussion

Our study focused on the development of a novel, reusable, and recoverable solid catalyst by attaching the amino acid L-Glutamine to magnetized chloromethylated polystyrene and evaluating its effectiveness in facilitating organic transformations (Scheme 2). MPS was initially synthesized by reacting PS-Cl with FeCl2·4H2O and FeCl3.6H2O in refluxing ethanol. Subsequently, the surface of the MPS was functionalized with glutamine’s amino group via nucleophilic addition in refluxed toluene for two days. The structure of the synthesized catalysts was established utilizing several analytical techniques, including TGA, FT-IR, XRD, VSM, EDS-mapping, SEM, EDS and elemental analysis.

Scheme 2.

Scheme 2

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Synthesis of L-Glu-MPS nanocatalyst

In Fig. 1, the FT-IR spectra for all samples are illustrated. The spectrum of PS-Cl displays main vibrational bands associated with H-C-Cl and C-Cl bonds, appearing at 1262 cm− 1 and 752 cm− 1, respectively [35]. Furthermore, the appearance of a new peak around 560 cm− 1 in the MPS spectrum, associated with the Fe-O stretching vibration, confirms that the magnetization of the PS-Cl surface was successfully achieved using Fe3O4 NPs. The spectrum of L-Glu-MPS, the disappearance of the broad O-H band, and the appearance of a sharp peak at 3406 cm⁻¹, which is attributed to N-H stretching vibrations, confirm the successful bonding of L-glutamine on the surface of MPS [36].

Fig. 1.

Fig. 1

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FT-IR spectrum of PS-Cl, MPS, and L-Glu-MPS

Thermogravimetric analysis (TGA) of PS-Cl, MPS, and L-Glu-MPS was performed from 50 to 600 °C at a heating rate of 10 °C/min (Fig. 2). All samples show a minor weight loss below 250 °C due to the removal of adsorbed moisture. A more pronounced weight loss appears between 300 and 450 °C, corresponding to the decomposition of polymeric and organic components [37].

Fig. 2.

Fig. 2

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TGA graph of PS-Cl, MPS and L-Glu-MPS

Compared to MPS, L-Glu-MPS exhibits an additional weight loss of approximately 20% in this region, attributed to the decomposition of immobilized L-glutamine moieties. This moderate increase in organic content indicates controlled surface grafting rather than the presence of excessive free acid. The reduced thermal stability and char residue of L-Glu-MPS further confirm successful surface functionalization. As the non-grafted L-Glu amino acid has been removed using a Soxhlet extractor, there is no unusual organic weight loss in the TGA profile of the L-Glu-MPS, which further verifies that L-Glu covalently bonded onto the MPS surface.

The elemental analysis of CHN for PS-Cl and L-Glu-MPS is presented in Table 1. The results show a nitrogen content of approximately 12%, confirming the successful incorporation of nitrogen-containing L-glutamine moieties onto the polymer surface (the amount of amine groups grafted onto the PS-Cl surface is approximately 4.47 mmol/g). The relatively high nitrogen percentage indicates efficient surface functionalization and a high density of active sites.

Table 1.

Elemental analysis of the catalysts

Samples C (W %) N (W %) H (W %)
PS-Cl 84.78 – 6.93
L-Glu-MPS 42.20 12.53 5.99
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The SEM images of PS-Cl, MPS, and L-Glu-MPS are presented in Fig. 3 to evaluate the morphology changes during the stepwise modification process. The initial PS-Cl particles display a relatively smooth and uniform spherical shape. After the immobilization of Fe3O4 nanoparticles, the particles maintain their spherical structure but exhibit a significantly rougher surface, which confirms successful magnetic coating. Further functionalization with L-glutamine results in a more irregular and slightly larger surface texture, indicating effective immobilization of the organic ligand [38].

Fig. 3.

Fig. 3

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SEM of PS-Cl, MPS, and L-Glu-MPS

To quantitatively evaluate the size change, particle size distribution histograms were constructed from the SEM images (Fig. 4). The results show a gradual increase in the average particle size from PS-Cl (⁓48 nm) to MPS (⁓61 nm) and finally to L-Glu-MPS (⁓72 nm), confirming the successful stepwise surface modification. The observed size enlargement is attributed to the precipitation of magnetic nanoparticles and subsequent organic functionalization.

Fig. 4.

Fig. 4

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Histogram of particle size distributions of PS-Cl, MPS, and L-Glu-MPS

The EDS mapping analyses for all the samples are presented in Figs. 5 and 6, and 7 respectively, demonstrating a uniform distribution of all elements across the sample surfaces. According to the compositional maps in Fig. 5, the expected elements C and Cl of the polystyrene substrate are evident.

Fig. 5.

Fig. 5

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EDS Mapping of PS-Cl

Fig. 6.

Fig. 6

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EDS and EDS Mapping of MPS

Fig. 7.

Fig. 7

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EDS and EDS Mapping of L-Glu-MPS

After magnetization, the presence of iron and oxygen elements along with the parent elements in the structure of the PS-Cl confirms the successful magnetization of the polystyrene surface (Fig. 6).

The EDS-mapping and EDS analyses of the L-Glu-MPS are shown in Fig. 7. As can be seen, the presence of N element in the EDS-mapping image and EDS profile, as well as the disappearance of the Cl element, confirms the successful bonding of the Glu onto the MPS surface. Based on EDS results, the nitrogen amount supported on the MPS surface is about 16%, which is in good agreement with CHN analysis (12%). The findings obtained from the TGA, CHN, SEM, and EDS analyses, along with the removal of the unreacted Glu using a Soxhlet extractor, strongly support the hypothesis of MPS surface covalently modified with L-Glu rather than mere physical incorporation.

To examine the crystal structures of the samples, X-ray diffraction analysis was performed. The XRD patterns of PS-Cl, MPS, and L-Glu-MPS are shown in Fig. 8, which show a broad peak in the region of 2θ = 19–25, indicating PS-Cl [39]. In the XRD pattern of MPS, distinctive peaks at 30.1°, 35.5°, 43.1°, 53.4°, 57.0°, and 62.6° are attributed to the (220), (311), (400), (422), (511), and (440) planes confirming the successful modification of the PS-Cl surface with iron oxide NPs. In the case of MPS and L-Glu-MPS, their XRD patterns exhibit a remarkable similarity, indicating that the surface modification of MPS with L-Glu has a minimal impact on the catalyst’s surface structure.

Fig. 8.

Fig. 8

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XRD spectrum of PS-Cl, MPS, and L-Glu-MPS

The Vibrating Sample Magnetometer (VSM) was employed to examine the magnetic properties of the magnetic catalysts under ambient temperature conditions. Figure 9 shows VSM curves for MPS and L-Glu-MPS. The VSM data indicate that MPS exhibits strong magnetization, demonstrating its effectiveness as a magnetic catalyst. In contrast, L-Glu-MPS exhibits a lower level of magnetization, which is attributed to the presence of non-magnetic materials on the coating of the MPS surface that interfere with its overall magnetic response. While the presence of the L-Glu amino acid coating is beneficial for enhancing catalytic activity and stability, it appears to reduce the magnetic interactions within the material.

Fig. 9.

Fig. 9

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VSM curve of MPS and L-Glu-MPS

Building on our earlier research aimed at enhancing green synthesis methods for the preparation of 4H-pyran compounds [31–33], we have now explored the catalytic activity of the synthesized L-Glu-MPS in the environmentally friendly and efficient synthesis of 2-amino-4H-pyran derivatives 5 and 6. These derivatives are obtained via the reaction of aromatic aldehydes 1a-i, malononitrile 2, and ethyl acetoacetate 3 or dimedone 4, in the presence of a catalytic amount of synthesized modified polystyrene L-Glu-MPS.

The reaction of dimedone (1mmol), 4-chlorobenzaldehyde (1mmol), and ethyl acetoacetate (1mmol) was used as a model to optimize reaction conditions, testing PS-Cl, MPS, and L-Glu-MPS catalysts, and a catalyst-free control (Table 2). The catalyst-free reaction (entry 1) and reactions with PS-Cl and MPS (entries 2 and 3) yielded only trace amounts of product 5a after 2 h. The results show that the model reaction achieved 85% yield in the presence of non-bonded L-Glu as a homogeneous catalyst (entry 4). Also, the model reaction was performed in the presence of various amino acids, including alanine (Ala), glycine (Gly), proline (Pro), and serine (Ser) (entries 5–8). The results show that the catalytic effect of the Glu amino acid is better than that of other amino acids. The model reaction was tested using L-Glu-MPS as a heterogeneous, magnetic, and reusable catalyst, yielding compound 5a with a 75% success rate (entry 9). L-Glu-MPS was selected as the optimal catalyst due to its excellent properties, including high reusability and easy separation. The reaction was conducted using varying amounts of L-Glu-MPS catalyst (5, 10, 15, 20, and 25 mg) (entries 9–13). Results indicated that the optimal catalyst amount was 20 mg (entry 12), while increasing the catalyst beyond this quantity did not enhance the outcome (entries 12). The model reaction was studied with different solvents, yielding the best results with Ethanol (entry 12 in comparison to entries 14–18). Additionally, increasing the reaction temperature did not enhance the yield or decrease the reaction time (entries 19 and 20).

Table 2.

Determination of the optimized reaction conditions for the synthesis of compounds 5a

Entry Catalyst Solvent Temperature (oC) Time (min) Yield %a, b
1 -c EtOH r.t 120 Trace
2 PS-Cl (10 mg) EtOH r.t 120 Trace
3 MPS (10 mg) EtOH r.t 20 Trace
4 L-Glu (10 mol%) EtOH r.t 20 85
5 Ala (10 mol%) EtOH r.t 20 69
6 Gly (10 mol%) EtOH r.t 20 67
7 Pro (10 mol%) EtOH r.t 20 78
8 Ser (10 mol%) EtOH r.t 20 65
9 L-Glu-MPS (10 mg) EtOH r.t 20 75
10 L-Glu-MPS (5 mg) EtOH r.t 20 82
11 L-Glu-MPS (15 mg) EtOH r.t 20 89
12 L-Glu-MPS (20mg) EtOH r.t 20 98
13 L-Glu-MPS (25 mg) EtOH r.t 20 98
14 L-Glu-MPS (20 mg) MeOH r.t 20 73
15 L-Glu-MPS (20 mg) H2O r.t 20 67
16 L-Glu-MPS (20 mg) EtOH: H2O r.t 20 82
17 L-Glu-MPS (20 mg) DMF r.t 20 81
18 L-Glu-MPS (20 mg) CH2Cl2 r.t 20 52
19 L-Glu-MPS (20 mg) EtOH 40 20 98
20 L-Glu-MPS (20 mg) EtOH Reflux 20 98
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Reaction conditions: 4-chlorobenzaldehyde (1 mmol), dimedone (1 mmol), and ethyl acetoacetate (1 mmol) in the presence of the L-Glu-MPS catalyst in a 10 mL solvent

b Isolated yields. c Catalyst-free conditions

After determining the optimal reaction conditions, the performance of the L-Glu-MPS catalyst in synthesizing other 2-amino-4H-pyran derivatives through reactions involving aromatic aldehydes and dimedone or ethyl acetoacetate was examined. As shown in Table 3, aromatic aldehydes containing electron-donating and electron-withdrawing substituents resulted in the formation of compounds 5a-i and 6a-g, which were obtained in good to excellent yields ranging from 88% to 98% under mild conditions (at room temperature for 20 min). The validation of the structures for compounds 5a-i and 6a-g was achieved by comparing their melting points and the 1H and 13C NMR spectral data with the documented references in the literature.

Table 3.

Synthesis of 2-amino-4H- pyran derivates a

graphic file with name 11671_2026_4601_Figa_HTML.gif
Entry Product Structure Time (min) M.P (OC) [Refs] Yield b
1 5a graphic file with name 11671_2026_4601_Figb_HTML.gif 25 175–177 [40] 96
2 5b graphic file with name 11671_2026_4601_Figc_HTML.gif 35 173–175 [40] 97
3 5c graphic file with name 11671_2026_4601_Figd_HTML.gif 30 190 − 188 [40] 98
4 5d graphic file with name 11671_2026_4601_Fige_HTML.gif 30 132 − 130 [41] 95
5 5e graphic file with name 11671_2026_4601_Figf_HTML.gif 25 134 − 132 [40] 96
6 5f graphic file with name 11671_2026_4601_Figg_HTML.gif 40 192 − 188 [40] 97
7 5 g graphic file with name 11671_2026_4601_Figh_HTML.gif 25 136 − 134 [42] 98
8 5 h graphic file with name 11671_2026_4601_Figi_HTML.gif 30 192 − 190 [42] 90
9 5i graphic file with name 11671_2026_4601_Figj_HTML.gif 25 170 − 168 [43] 96
10 6a graphic file with name 11671_2026_4601_Figk_HTML.gif 25 229 − 227 [32] 95
11 6b graphic file with name 11671_2026_4601_Figl_HTML.gif 10 210 − 208 [31] 90
12 6c graphic file with name 11671_2026_4601_Figm_HTML.gif 30 191 − 189 [32] 96
13 6d graphic file with name 11671_2026_4601_Fign_HTML.gif 40 139 − 137 [32] 88
14 6e graphic file with name 11671_2026_4601_Figo_HTML.gif 25 120 − 118 [32] 98
15 6f graphic file with name 11671_2026_4601_Figp_HTML.gif 25 242 − 240 [32] 94
16 6 g graphic file with name 11671_2026_4601_Figq_HTML.gif 25 230 − 228 [44] 96
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a: Aldehydes (1 mmol), dimedone (1 mmol), and ethyl acetoacetate (1 mmol), in the presence of the L-Glu-MPS (20 mg) in EtOH (10 ml). b Isolated yield,

A possible bifunctional catalytic mechanism for the synthesis of 2-amino-4H-pyrans is shown in Scheme 3. The catalytic activity of L-Glu-MPS is due to the cooperative action of its amine and amide/carboxyl functional groups immobilized on a magnetic polystyrene support. In the first step, aldehyde 1 is activated via hydrogen bonding and/or iminium-type interaction with the amine functional group of L-glutamine, while malononitrile 2 is simultaneously activated via hydrogen bonding with the amide/carboxyl groups. This dual activation facilitates the Knoevenagel condensation and leads to the formation of the malononitrile arylidene intermediate A, which subsequently undergoes Michael addition with the activated dicarbonyl compound. The catalyst drives this step by hydrogen-bonding stabilization of the carbanion/enolate species, generating intermediate B. Finally, intramolecular cyclization occurs via nucleophilic attack of the enolate oxygen on the cyano group, followed by proton transfer and tautomerization to produce the desired 2-amino-4H-pyran derivatives (5a-i and 6a-g). The heterogeneous nature of the catalyst allows for efficient recovery without significant loss of active sites [31].

Scheme 3.

Scheme 3

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A plausible mechanism of synthesis of 2-amino-4H-pyran

The efficiency of the L-Glu-MPS catalyst in synthesizing 5a is highlighted in Table 4, alongside a comparison with several previously reported methods. The model reaction with different catalytic systems has some drawbacks, such as higher temperatures (entries 1–7), lower yields (entries 1, 5–9), high catalyst ratios (entries 1, 4, 5, 7, and 9), and longer reaction times (entries 6 and 8). Nevertheless, the catalytic method demonstrated effective performance for the model reaction at 25 °C in ethanol, yielding product 5a with an impressive 98% after just 20 min (entry 10). These results suggest that the L-Glu-MPS catalyst is a promising alternative for the synthesis of pyrans.

Table 4.

Comparison of the catalytic synthesis of 5a

Entry Catalyst Condition Time Yield [Refs]
1 Zr@IL-Fe3O4/ 20 mg solvent-free /100 °C 15 min 96 [45]
2 Al2O3/V2O5/ 2 mg solvent-free/80°C 5 min 98 [46]
3 BaFe12O19@IM/ 12 mg EtOH /80 °C 10 min 97 [47]
4 Fe3O4@Ph-PMO-NaHSO4/ 20 mg EtOH: H2O (1:1)/80 °C 12 min 98 [48]
5 SBPPSP/ 26 mg H2O: Ethanol (1:1)/reflux 15 min 94 [49]
6 sodium alginate/ 20 mg EtOH /Reflux 50 min 93 [50]
7 ChCl/AA (23 mg) Solvent-free/80°C 5 min 97 [51]
8 SiO2 NPs (5 mg) EtOH/r.t 20 min 98 [52]
9 MNPs-BPAT (30 mg) EtOH/r.t 20 min 93 [53]
10 L-Glu-MPS (20 mg) EtOH/ r.t 20 min 98a
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a This work

The reuse and recovery of catalysts from reaction media are critical components of chemical processes. Consequently, these issues present ongoing challenges that engage numerous scientists. In this context, the recyclability of the L-Glu-MPS catalyst was examined under model reaction conditions. As illustrated in Fig. 10, the L-Glu-MPS catalyst can be successfully recovered and reused for six successive cycles without any notable decline in activity. The investigation into the L-Glu-MPS catalyst’s ability to be reused six times consecutively without any significant alteration in its surface morphology was conducted using back-recycling analyses, SEM, and FT-IR, which collectively demonstrate its stability and recyclability (Fig. 11).

Fig. 10.

Fig. 10

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Reusability of the L-Glu-MPS catalyst in the model reaction

Fig. 11.

Fig. 11

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(A): FT-IR images of (left) and SEM images (right) of the fresh and reused L-Glu-MPS after six cycles

Conclusion

Due to the growing demand for green organic synthesis and industrial needs, we report a straightforward method for synthesizing a new high-performance catalytic system using functionalized magnetic polystyrene with L-glutamine. To verify the structure of the synthesized catalysts, several analytical techniques were employed, including TGA, FT-IR, XRD, VSM, EDS- mapping, SEM, EDS and elemental analysis. The catalytic efficiency of the L-Glu-MPS catalyst was assessed through a three-component reaction involving aromatic aldehydes, active methylene, and either ethyl acetoacetate or dimedone for the synthesis of pyrans. This catalytic system offers several advantages, including straightforward separation from the reaction mixture, reusability without significant loss of activity over six cycles, room-temperature, excellent yields of up to 98%, and remarkably short reaction times of just 20 min. The results indicated that the proposed catalytic method holds potential for efficiently synthesizing various valuable heterocycles under environmentally friendly reaction conditions.

Supplementary Information

Below is the link to the electronic supplementary material.

Supplementary Material 1 (8.1MB, docx)

Acknowledgements

The authors are thankful to the University of Mazandaran for partial support of this project.

Author contributions

Fatemeh Zahra Hajian performed the experimental work, including catalyst synthesis, characterization, and organic reactions, and contributed to data analysis.Sakineh Asghari and Ghasem Firouzzadeh Pasha supervised the project, contributed to the study design, data interpretation, and critically revised the manuscript.Taraneh Abbaspour Wrote and drafted the Manuscript, characterized the catalyst, and interpreted the data.Mahmood Tajbakhsh provided scientific advice.Fatemeh Zare performed organic reactions and contributed to data analysis.All authors have read and approved the final version of the manuscript.

Funding

Not applicable.

Data availability

The data that support the findings of this study are available in the supplementary material of this article.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent to publish

Not applicable.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Contributor Information

Sakineh Asghari, Email: s.asghari@umz.ac.ir.

Ghasem Firouzzadeh Pasha, Email: ghasemf.pasha@umail.umz.ac.ir, Email: ghasempasha@yahoo.com.

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