Green Synthesis of New Category of Pyrano[3,2-c]Chromene-Diones Catalyzed by Nanocomposite as Fe3O4@SiO2-Propyl Covalented Dapsone-Copper Complex

Nanomagnetic dapsone-Cu supported on the silica-coated Fe3O4 (Fe3O4@SiO2-pr@dapsone-Cu) nanocomposite was synthesized and characterized by Fourier transform infrared (FT-IR), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), zeta potential, vibrating sample magnetometer (VSM), and thermogravimetric analysis (TGA). This newly synthesized nanocomposite was chosen to act as a green, efficient, and recyclable Lewis acid for the multicomponent synthesis of new derivatives of pyrano[3,2-c]chromene-diones through the reaction of aromatic aldehydes, indandione, and 4-hydroxycoumarin in water. All of the synthesized compounds are new and are recognized by FT-IR, NMR, and elemental analysis; this avenue is new and has advantages such as short reaction times, high productivity, economical synthesis, and use of green solvent, H2O, as a medium. The catalyst is magnetically recoverable and can be used after six runs without a decrease in the efficiency.


INTRODUCTION
Multicomponent reactions (MCRs) are useful avenue for the synthesis of organic compounds. This reaction is a combination of at least three components in a one-pot domino (Li and Chan, 1997;Grieco, 1998;Dömling and Uzi, 2000;Dömling, 2002;Hosseini-Zare et al., 2012). MCRs have benefits such as higher atom economy and selectivity and production of complex molecules with low by-products. Nowadays, MCRs have attracted a lot of interest in organic transformation (Bienaymé et al., 2000;Kandhasamy and Gnanasambandam, 2009;Müller 2014).
To the best of our knowledge, there are no reports on the use of Fe3O4@SiO2-propyl-loaded dapsone-copper as a catalyst for the synthesis of pyrano[3,2-c]chromenes via multicomponent reactions of aldehydes, indandione, and 4-hydroxycoumarin results.

Synthesis of Fe3O4@SiO2-Cl
Fe 3 O 4 @SiO 2 NPs were prepared by Zare Fekri (Nikpassand et al., 2017;. Synthesis of Fe 3 O 4 @SiO 2 @dapsone 500 mg Fe 3 O 4 @SiO 2 -Cl MNPs in 50 ml distilled water were irradiated under ultrasound for 30 min. Then, dapsone 0.5 g was added. The mixture was refluxed at 110°C for 14 h. The Fe 3 O 4 @SiO 2 @dapsone was filtered in the presence of an enormous magnet and washed with chloroform several times and dried at 80°C for 4 h. Synthesis of Fe 3 O 4 @SiO 2 @dapsone-Cu 500 mg Fe 3 O 4 @SiO 2 @dapsone MNPs in 50 ml EtOH-H 2 O (1:1) were irradiated under ultrasonic bath for 30 min. Then, 20 ml aqueous solution of copper chloride (I) (0.1 g; 0.001 mol) was added to the Fe 3 O 4 @SiO 2 @dapsone and stirred for 48 h. The Fe 3 O 4 @SiO 2 @dapsone-Cu MNPs were filtered in the presence of a magnetic bar and washed using ethanol and water subsequently, to separate the nanoparticles.
General Procedure for the Synthesis of Pyrano[3,2-c]chromene-Dione A mixture of aldehyde (1.0 mmol), indan-1,3-dione (2.0 mmol), 4-hydroxycoumarin (1 mmol), and 0.05 g Fe 3 O 4 @SiO 2 @ dapsone-Cu MNPs was stirred at room temperature in 10 ml distilled water for the required reaction time as indicated by TLC (TLC silica gel 60 F250, ethyl acetate : n-hexane 1 : 4). After completion of the reaction, the resulting mixture was filtered in the presence of an efficient magnetic bar to separate the catalyst. The catalyst was washed with 10 ml ethanol and reused. The crude products were collected and dried.

Synthesis and Characterization
In order to prepare nanocatalyst, initially, Fe3O4 MNPs were modified with silica and then with chloropropyl silane via chemical bonds to obtain Fe3O4@SiO2-pr. In the next step, Fe3O4@SiO2-propyl was covalented by substitution reaction by dapsone to prepare Fe3O4@SiO2-propyl loaded dapsone.
This nanocatalyst was treated with copper chloride to produce Fe3O4@SiO2-propyl@dapsone-Cu (Scheme 1). The structure of the prepared nanocatalyst was studied and fully characterized using FT-IR, energy-dispersive X-ray (EDX), XRD, zeta potential, TEM, and field emission scanning electron microscope (FE-SEM) analysis. As shown in Figure 1 (FE-SEM and TEM), the magnetic nanoparticles have a spherical shape with an average diameter of 14-38 nm. The synthesized nanoparticles have aggregated well.   (Figure 3A), which indicate that the MNPs have highly crystalline cubic spinel structure of the magnetite and matched with the diffraction patterns of the standard Fe 3 O 4 (JCPD 19-0629). This confirmed the stability of the crystalline phase of the magnetite core in the structure after silica coating, condensation, and complexation process. The absence of an amorphous peak in pattern confirmed the crystalline structure. Using Debye-Scherrer equation, the mean size of crystallite was calculated as 12.1 nm from the XRD pattern (crystallite shape factor: 0.9 and λ CuKa1 1.54060 Å). This value is lower than the size obtained by FE-SEM and TEM due to the fact that some crystallite forms a particle. Also, the d-spacing and full width at half maximum   Figure 3B revealed the TGA analysis of synthesized nanoparticles. Two weight losses are observed. The first decrease is related to a temperature below 333°C because of desorption of water and the second weight-loss step at 524°C is due to decomposition of organic compound as dapsone.
As shown in Figure 4A, the zeta potential was scanned. The large zeta potential obtained revealed a more stable dispersion of synthesized MNPs. The zeta potential value of dispersed synthesized in deionized water in absence of any electrolyte was +25.1 mV.
The presence of iron, oxygen, nitrogen, carbon, silica, sulfur, and copper, in EDX, revealed the successful synthesis of these nanoparticles.
The magnetic properties of synthesized nanoparticles are shown in Figure 5. The results approve the superparamagneticity behavior.
To complete our assessment, we checked the effect of different conditions in the sample reaction. For example, we treated 4nitrobenzaldehyde, indandione, and 4-hydroxycoumarin under stirring at room temperature and refluxing in EtOH. The satisfactory results were obtained via the reaction of 4nitrobenzaldehyde, indandione, and 4-hydroxycoumarin in the presence of 0.05 g of Fe 3 O 4 @SiO 2 -propyl@dapsone-Cu in aqueous media under stirring ( Table 1).
To expand the generality and efficiency of this avenue, some aldehydes with electron-donating or electronwithdrawing substituents were treated with indan-1,3dione and 4-hydroxycoumarin. The results are summarized in Table 2.
As a proposed mechanistic pathway, initially, aldehyde was activated by the nanocatalyst, followed by nucleophilic attack of C-H acid of indan-1,3-diones, together with the departure of water, and chalcone was produced. Nucleophilic attack of 4hydroxycoumarin to chalcone as Michael addition and then intramolecular cyclization followed by elimination of water lead to product 4 (Scheme 3).
Furthermore, the magnetic nanoparticles are magnetically recoverable and can be reused for six runs. Appearance SCHEME 2 | Multicomponent synthesis of pyrano[3,2-c]chromene-diones.  features of the catalyst were not changed after several uses ( Figure 6).
To better understand the stability of catalyst after five cycles under these reaction conditions, FE-SEM and TEM analyses were carried out. The results are summarized in Figure 7.

CONCLUSION
In conclusion, a new catalytic method for the synthesis of pyrano [3,2-c]chromene-diones has been developed. This method offers several advantages, such as simple workup and purification procedure without the use of any chromatographic method, FIGURE 6 | The recyclability of nanocatalyst. SCHEME 3 | Proposed mechanism for the synthesis of pyranochromene-diones.
Frontiers in Chemistry | www.frontiersin.org September 2021 | Volume 9 | Article 720555 9 mild reaction conditions, use of inexpensive and commercially available starting materials, recyclability and reusability of the catalyst, high product yields, and short reaction time. So we think that this procedure could be considered a new and useful addition to the present methodologies in this area.

DATA AVAILABILITY STATEMENT
The original contributions presented in the study are included in the article/supplementary files, further inquiries can be directed to the corresponding author.

AUTHOR CONTRIBUTIONS
LZ carried out experimental studies, wrote the original draft, and analyzed spectral characterization of synthesized molecules and project planning, proofreading, and editing.

ACKNOWLEDGMENTS
Financial support from the Research Council of Payame Noor University of Rasht branch is sincerely acknowledged.