JBCS

INTRODUCTION

Recently, to decrease waste and atom economy in the using raw materials, the purpose of technology and science has been modified toward more environmentally friendly, reusable catalysts and sustainable resources.¹ During the last decades, magnetic nanoparticles (MNPs) have been intensively investigated because of their broad applications such as ferrofluids, digital media recording, targeted drug delivery, magnetic hyperthermia, magnetic resonance imaging, etc.^2,3

Magnetite Fe₃O₄ nanoparticles (Fe₃O₄ NPs) as a class of nano-sized materials have received great attention due to their wide range of usages in various fields such as medical applications, drug delivery, remediation, catalyst, industry.^4-6 The salient and significant property of magnetite nanoparticles is simple and facile separation of these catalysts from the reaction mixture using an external magnet. Coating magnetite nanoparticles with an amorphous silica layer is a useful and important approach in the growth of magnetite nanoparticle in various fields.⁷ Silica shell in nanostructures is chemically inert and has high stability against aggregation. In addition, the existing of silanol parts on the surfaces can easily be functionalized via the appropriate surface modifications which causing to attach of different functionalities.⁸ Furthermore, silanol groups on the surfaces of nanoparticles cause to protect of the related core toward oxidation and also various groups including guanidine,⁹ proline,¹⁰ sulfamic acid¹¹ and sulfonic acid¹² can attach to the outer shell.

In recent years, nano-Fe₃O₄ encapsulated-silica particles bearing sulfonic acid (Fe₃O₄@SiO₂-OSO₃H) nanocomposites were applied as an effective nanocatalyst in the synthesis of 1,8-dioxo-octahydroxanthene,¹³ indazolo[2,1-b]phthalazine-triones and pyrazolo[1,2-b]phthalazine-diones,¹⁴ functionalized pyrimido[4,5-b]quinolines and indeno fused pyrido[2,3-d]pyrimidines¹⁵ and 3,4-dihydropyrimidinones/thiones.¹⁶

The multi-component coupling reactions (MCRs) are emerging as a valuable versatile for affording diverse organic structures for potential applications in medicinal and pharmaceutical chemistry.¹⁷ MCRs often adapt to the goals of green chemistry connected to economy of reaction approaches as well as the many particular principles of favorable chemical transformations.^18-20 Due to of their benefits such as facile performance, environmentally friendly, fast and atom economic, MCRs interested great attention related to combinatorial chemistry.²¹

Tricarboxamide derivatives are a class of nitrogen heterocyclic compounds which have significant and well-reported biological activities that include neuroprotective,²² anti-diabetic,²³ anti-bacterial,²⁴ anti-carcinogenic²⁵ and anti-tumor activities.²⁶

Therefore, the importance of these constitutions has prompted researchers to develop more efficient pathways for the synthesis of these heterocycles compounds due to their significant biological and pharmaceutical properties.

In continuation of our attempts on using heterogeneous nanocatalysts in multi-component reactions,^27-31 herein we describe an efficient synthesis of functionalized tricarboxamide derivatives via five-component condensation reactions of isocyanides, aldehydes, Meldrum's acid and amines in the presence of magnetic Fe₃O₄@SiO₂-OSO₃H nanocomposites as catalyst under solvent-free conditions.

 

EXPERIMENTAL

General

Chemicals were purchased from the Sigma-Aldrich and Merck in high purity. All melting points are uncorrected and were determined in capillary tube on Boetius melting point microscope.¹H NMR and ¹³C NMR spectra were obtained on Bruker 400 MHz spectrometer with DMSO-d₆ as solvent using TMS as an internal standard. FT-IR spectrum was recorded on Magna-IR, spectrometer 550. The elemental analyses (C, H, N) were obtained from a Carlo ERBA Model EA 1108 analyzer. Powder X-ray diffraction (XRD) was carried out on a Philips diffractometer of X'pert Company with mono chromatized Cu Kα radiation (λ = 1.5406 Å). Microscopic morphology of products was visualized by SEM (LEO 1455VP). The mass spectra were recorded on a Joel D-30 instrument at an ionization potential of 70 eV. Transmission electron microscopy (TEM) was performed with a Jeol JEM-2100UHR, operated at 200 kV. Magnetic properties were obtained on a BHV-55 vibrating sample magnetometer (VSM) made by MDK-I.R.Iran. The compositional analysis was done by energy dispersive analysis of X-ray (EDX, Kevex, Delta Class I).

Preparation of Fe₃O₄ nanoparticles

Fe₃O₄ nanoparticles were prepared according to the procedure reported by Zhang et al.³² To a solution of FeCl₂.4H₂O (2.5 g) and FeCl₃.6H₂O (6 g) in 30 mL deionized water was added dropwise 1.0 mL of concentrated hydrochloric acid at room temperature. The solution was added in to 300 mL of 1.5 mol L^-1 NaOH and then the solution was stirred vigorously at 80 ºC until precipitation. Afterwards, the prepared magnetic nanoparticles were separated magnetically, washed with deionized water and then dried at 70 ºC for 8 h.

Preparation of Fe₃O₄@SiO₂ nanocomposite

The core-shell Fe₃O₄@SiO₂ nanocomposite were prepared according to the previously reported method.³³ Briefly 1g of Fe₃O₄ nanoparticles was treated with 0.5 mol L^-1 HCl aqueous solution (25 mL) by sonication. After the treatment for 10 min, The magnetite particles were separated and washed with deionized water, and then homogeneously dispersed in the mixture of ethanol (60 mL), deionized water (100 mL) and concentrated ammonia aqueous solution (10 mL, 28 wt. %), followed by the addition of tetraethylorthosilicate (TEOS, 0.22 g, 0.144 mmol). After stirring at room temperature for 2 h, the Fe₃O₄@SiO₂ nanocomposite were separated using an external magnet and washed with ethanol and water.

Preparation of Fe₃O₄@SiO₂-OSO₃H nanocomposite

Fe₃O₄@SiO₂-SO₃H MNPs were prepared according to a previously reported procedure by Kiasat and Davarpanah (Scheme 1).¹⁴ A suction flask equipped with a constant-pressure dropping funnel. The gas outlet was connected to a vacuum system through an adsorbing solution of alkali trap. Firstly, Fe₃O₄@SiO₂ (1 g) was added to the flask and dispersed in dry CH₂Cl₂ (10 ml) by ultrasonic for 30 min. Subsequently, chlorosulfonic acid (1 ml) was added drop-wise to a cooled (ice-bath) solution of Fe₃O₄@SiO₂ (1 g) over a period of 30 min at room temperature. After completion of the addition, the mixture was stirred for a further 6 h until to allow for the complete dissipation of HCl from the reaction vessel. The resulted MNPs were separated using an external magnet and washed with ethanol and water before been dried in an oven at 70 ºC to give Fe₃O₄@SiO₂-OSO₃H as a brown powder.

 

 

General procedure for the preparation of tricarboxamide derivatives

A mixture of isocyanide (1 mmol), aromatic aldehyde (1 mmol), Meldrum's acid (1 mmol), aromatic amine (2 mmol) and Fe₃O₄@SiO₂-OSO₃H nanocomposite (0.003 g) were heated in a sealed tube at 50 ºC for appropriate times. Progress of the reaction was continuously monitored by TLC. After completion of the reaction, the mixture was cooled to room temperature and then was dissolved in methanol and then the nanocatalyst was separated using an external magnet. The solvent was evaporated under vacuum and the solid obtained recrystallized from EtOH to afford the pure tricarboxamides.

All of the products were characterized and identified with m.p., ¹H NMR, ¹³C NMR and FT-IR spectroscopy techniques.

Spectral data of new compounds

N²-cyclohexyl-2-(4-fluorophenyl)-N¹,N^'1-diphenylethane-1,1,2-tricarboxamide (5f): White solid; m.p 303-304 ºC; FT- IR (KBr): 3314 (NH), 3291 (NH), 1673 (CO), 1615 (C=C), 1462 (C=C) cm^-1; ¹H NMR (400 MHz, DMSO-d₆) δ/ppm : 0.99-1.32 (m, 10 H, 5CH₂), 3.27 (m, 1H, NCH), 4.01 (d, 1H, CH), 4.11 (d, 1H, CH), 6.91-7.63 (m, 14H, Ar), 8.41 (bs, 1H, NH), 10.12 (s, 2H, 2 NH); ¹³C NMR (100 MHz, DMSO-d₆) δ/ppm : 173.1 (C=O), 169.4 (C=O), 149.1, 147.9, 144.6, 143.2, 131.3, 127.4, 121.2, 118.1, 64.3, 52.1, 48.1, 31.5, 30.4, 27.8. MS (EI) (m/z): 487 (M⁺); Anal. Calcd. mass fraction of elements, w/% for C₂₉H₃₀FN₃O₃ (M_r = 487.23) are: C 71.44; H 6.20; N 8.62; Found: C 71.32; H 6.26; N 8.69.

2-(4-cyanophenyl)-N²-cyclohexyl-N¹,N^'1-diphenylethane-1,1,2-tricarboxamide (5g): White solid; m.p 312-315 ºC; FT- IR (KBr): 3325 (NH), 3286 (NH), 2211 (CN), 1668 (CO), 1584 (C=C), 1453 (C=C) cm^-1; ¹H NMR (400 MHz, DMSO-d₆) δ/ppm : 1.01-1.29 (m, 10 H, 5CH₂), 3.31 (m, 1H, NCH), 4.03 (d, 1H, CH), 4.10 (d, 1H, CH), 6.95-7.42 (m, 14H, Ar), 8.38 (bs, 1H, NH), 10.09 (s, 2H, 2 NH); ¹³C NMR (100 MHz, DMSO-d₆) δ/ppm : 172.8 (C=O), 168.1 (C=O), 149.2, 147.9, 145.1, 143.6, 131.3, 127.4, 120.8, 119.2, 116.5, 62.1, 51.9, 48.3, 30.8, 29.2, 27.6. MS (EI) (m/z): 494 (M⁺); Anal. Calcd. mass fraction of elements, w/% for C₃₀H₃₀N₄O₃ (M_r = 494.23) are: C 72.85; H 6.11; N 11.33; Found: C 72.97; H 6.16; N 11.19.

N²-(tert-butyl)-2-(4-fluorophenyl)-N¹,N^'1-diphenylethane-1,1,2-tricarboxamide (5m): White solid; m.p 285-287 ºC; FT- IR (KBr): 3303 (NH), 3278 (NH), 1675 (CO), 1606 (C=C), 1458 (C=C) cm^-1; ¹H NMR (400 MHz, DMSO-d₆) δ/ppm : 0.98-1.22 (s, 9 H, 3CH₃), 3.87 (d, 1H, CH), 4.11 (d, 1H, CH), 7.07-7.64 (m, 14H, Ar), 8.27 (bs, 1H, NH), 10.23 (s, 2H, 2 NH); ¹³C NMR (100 MHz, DMSO-d₆) δ/ppm : 176.2 (C=O), 172.5 (C=O), 151.2, 149.8, 144.1, 143.2, 131.1, 128.1, 120.7, 118.6, 64.1, 50.8, 42.9, 28.1. MS (EI) (m/z): 461 (M⁺); Anal. Calcd. mass fraction of elements, w/% for C₂₇H₂₈FN₃O₃ (M_r = 461.21) are: C 70.26; H 6.12; N 9.10; Found: C 70.42; H 5.98; N 9.03.

N²-(tert-butyl)-2-(4-cyanophenyl)-N¹,N^'1-diphenylethane-1,1,2-tricarboxamide (5n): White solid; m.p 293-295 ºC; FT- IR (KBr): 3341 (NH), 3291 (NH), 2216 (CN), 1678 (CO), 1603 (C=C), 1483 (C=C) cm^-1; ¹H NMR (400 MHz, DMSO-d₆) δ/ppm : 1.02-1.33 (m, 9 H, 3CH₃), 3.91 (D, 1H, CH), 4.11 (d, 1H, CH), 6.98-7.53 (m, 14H, Ar), 8.22 (bs, 1H, NH), 10.14 (s, 2H, 2 NH); ¹³C NMR (100 MHz, DMSO-d₆) δ/ppm : 171.1 (C=O), 168.4 (C=O), 148.8, 147.5, 145.1, 142.4, 129.1, 128.6, 123.7, 111.4, 115.1, 63.9, 51.1, 38.8, 28.2. MS (EI) (m/z): 468 (M⁺); Anal. Calcd. mass fraction of elements, w/% for C₂₈H₂₈N₄O₃ (M_r = 468.22) are: C 71.78; H 6.02; N 11.96; Found: C 71.67; H 5.92; N 12.14.

Recycling and Reusing of the Catalyst

After completion of the reaction, the obtained product was dissolved in methanol and then the nanocatalyst was separated by an external magnet, then the nanocatalyst were washed three to four times with methanol and ethyl acetate and then dried overnight in an oven at 50 ºC. To investigate lifetime and level of recoverability of the Fe₃O₄@SiO₂-OSO₃H MNPs, the model study was carried out several times using recycled magnetite nanocomposite. The summarized results of Table 1 show that the recovered catalyst could be used for five successive runs with a slightly decreased in activity.

 

 

RESULTS AND DISCUSSION

In the initial experiments Fe₃O₄@SiO₂-SO₃H nanocomposites was prepared and characterized by EDX, SEM XRD, FT-IR VSM and TEM analysis.

The chemical purity of the samples as well as their stoichiometry was tested by EDX studies. The EDX spectrum given in Figure 1a shows the presence of Fe and O as the only elementary components of Fe₃O₄ NPs. EDX spectrum Fe₃O₄@SiO₂ (Figure 1b) shows the elemental compositions are (Fe, O and Si) of core-shell nanocomposites. EDX spectrum of Fe₃O₄@SiO₂-OSO₃H (Figure 1c) shows the elemental compositions are (Fe, Si, O and S) of magnetic nanocomposites.

 

 

Scanning electron microscopy (SEM) is a useful tool for determining the size distribution, particles shape, and porosity. It has been a primary tool for characterizing the surface morphology and fundamental physical properties of the surface. According to Figure 2b, Fe₃O₄@SiO₂ nanocomposites still keep the morphological properties of Fe₃O₄ (Figure 2a) except for a slightly larger particle size and smoother surface, while silica are uniformly coated on the Fe₃O₄ particles to form silica shell compared to the Fe₃O₄@SiO₂, The SEM image shown in Figure 2c demonstrates that Fe₃O₄@SiO₂-OSO₃H nanocomposite are nearly spherical with about 30 nm in size.

 

 

The structure of Fe₃O₄ (a), Fe₃O₄@SiO₂ (b) and Fe₃O₄@SiO₂ sulfonic acid (c) were analyzed by X-ray diffraction (XRD) spectroscopy (Figure 3). XRD diagram of the bare Fe₃O₄ NPs displayed patterns consistent with the patterns of spinel ferrites described in the literature (Figure 3).¹¹ The same peaks were observed in the both of the Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂ sulfonic acid XRD patterns, indicating retention of the crystalline spinel ferrite core structure during the silica-coating process. The average MNPs core diameter of Fe₃O₄, Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂ sulfonic acid were calculated to be about 18, 25 and 32 nm, respectively from the XRD results by Scherrer's equation.

 

 

The FT-IR spectra of Fe₃O₄ nanoparticles, Fe₃O₄@SiO₂, and Fe₃O₄@SiO₂ sulfonic acid are shown in Figure 4. The FT-IR analysis of the Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂ sulfonic acid exhibits two basic characteristic peaks at ~3300 cm^-1 (O-H stretching) and 580 cm^-1 (Fe-O vibration).³⁴ The band at 1081 cm^-1 comes from the Si-O-Si group. The presence of the sulfonyl group of Fe₃O₄@Silica sulfonic acid is confirmed by 1217 cm^-1 and 1124 cm^-1 bands, which were covered by a stronger absorption of Si-O bonds at 1081 cm^-1.¹¹ A wide bond at 2500-3409 cm^-1 is due to the stretching of OH groups in the SO₃H.

 

 

The magnetic properties of the uncoated magnetic iron oxide (Fe₃O₄), Fe₃O₄@SiO₂, and Fe₃O₄@SiO₂-SO₃H were measured by vibrating sample magnetometer, VSM, at room temperature (Figure 5). In Figure 5, the hysteresis loops that are characteristic of superparamagnetic behavior can be clearly observed for all the nanoparticles. Superparamagnetism is the responsiveness to an applied magnetic field without retaining any magnetism after removal of the applied magnetic field. From M versus H curves, the saturation magnetization value (Ms) of uncoated Fe₃O₄ NPs was found to be 48.12 emu g^-1. For Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂-SO₃H, the magnetization obtained at the same field were 38.16 and 35.82 emu g^-1, respectively, lower than that of uncoated Fe₃O₄. These results indicated that the magnetization of Fe₃O₄ decreased considerably with the increase of SiO₂ and SO₃H. This is mainly attributed to the existence of nonmagnetic materials on the surface of the nanoparticles.

 

 

The size and morphology of Fe₃O₄@SiO₂-SO₃H nanocomposites were analyzed by Transmission electron microscopy (TEM) (Figure 6). The results show that these nanocatalysts consist of spherical particles with the crystallite size about 30 nm, confirming the results calculated from Scherrer's formula based on the XRD pattern.

 

 

Initially, to optimize the reaction conditions, the reaction of 4-bromobenzaldehyde, Meldrum's acid, tert-butyl isocyanide and aniline was selected as a model reaction (Scheme 2).

 

 

The reaction conditions were optimized on the basis of the solvent, catalyst, and different temperatures for synthesis of tricarboxamide (5a).

To show the advantage of the current approach in comparison to other catalysts, the model reaction was carried out using various nanocatalysts such as ZnO, MgO, CuO, AgI, Co₃O₄ and Fe₃O₄@SiO₂-SO₃H. From the results provided in Table 2, it was clear that nano-Fe₃O₄ encapsulated-silica particles bearing sulfonic acid afforded the corresponding tricarboxamide (5a) in excellent yield and short reaction time (60 min in 95 % yield).

 

 

During the optimization of reaction conditions the influence of solvent was studied when the model reaction was carried out using Fe₃O₄@SiO₂-OSO₃H MNPs by different solvents and also solvent-free conditions.

We found that the best result was obtained when the reaction was carried out under solvent-free conditions at 50 ºC. Increasing temperature showed unsatisfactory effect on the yield and reaction time (Table 3).

 

 

The reaction conditions were also investigated with different catalyst loading, revealing that 0.003 g of the catalyst provided the best results in terms of reaction time, economy of catalyst charge, and reaction yield (Table 3, entry 5). As shown in Table 3 increasing the amount of catalyst does not improve the yield of the product any further, whereas decreasing the amount of catalyst leads to decrease in the product yield. Hence, the optimum concentration of Fe₃O₄@SiO₂-OSO₃H was chosen 0.003 g in the model reaction.

 

 

To study the scope and limitations of multi-component synthesis of tricarboxamide, we next utilized a diversity of aldehydes and amines to investigate five-component reactions under the optimized conditions (Scheme 3). As shown in Table 4, aldehydes with both electron-withdrawing and electron donating groups were effectively produced the corresponding products. In addition aryl amines with various substituents afforded tricarboxamide derivatives in excellent yields and short reaction times. Comparison between tert-butyl isocyanide and cyclohexyl isocyanide shows that multi-component reactions of isocyanides, aldehydes Meldrum's acid and amines was smoothly proceed using tert-butyl isocyanide.

 

 

CONCLUSIONS

In summary, we have described a highly effective, mild and green approach for the preparation of tricarboxamide using Fe₃O₄@SiO₂-OSO₃H nanocomposites under solvent-free conditions at 50 ºC. The products were obtained in excellent yields and short reaction times via one-pot pseudo-five component reactions of isocyanides, aldehydes Meldrum's acid and 2 equiv. of amines. The salient properties of the applied nanocatalyst are simple work-up procedure, ease of separation, and recyclability of the magnetic nanocatalyst.

 

ACKNOWLEDGEMENTS

This work is funded by the Research Affairs Office of the Islamic Azad University, Qom Branch, Qom, I. R. Iran [grant number 2014-13929].

 

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