XRD analysis of Cu@MNPs
The energy dispersive X-ray analysis (EDX) spectrum of the Fe3O4, Fe3O4@Gu@TSH and Cu@Fe3O4 MNPs (Fig. 6) had six characteristic peaks at 2θ = 30.29, 35.34, 43.73, 54.45, 57.51, 63.19, and 74.58 were indexed to the (220), (311), (400), (422), (511), and (440) planes, respectively, which have a good accordance with the spinel phase of magnetic iron oxide nanoparticles. These indicated that the surface modification of the Fe3O4 magnetic nanoparticles with functional groups did lead to retention of the crystalline structure.
Herein, we reported our outcomes for the effective and rapid preparation of tetrahydrobenzimidazo[2,1-b]quinazolin-1(2H)-ones and 2H-indazolo[2,1-b]-phthalazine-triones using an effective and reusable heterogeneous nanomagnetic catalyst, Cu@Fe3O4 MNPs, under solvent-free conditions (Scheme 2).
After synthesizing and identifying the Cu@Fe3O4 MNPs, in order to screen the reaction conditions for synthesizing tetrahydrobenzimidazo[2,1-b]quinazolin-1(2H)-ones, the impact of the solvents, the reaction temperature, and the concentrations of catalyst were explored using the reaction of 2-aminobenzimidazole (1 mmol), 4-chlorobenzaldehyde (1 mmol) and dimedone (1 mmol) (molar ratio: 1 : 1 : 1) as a model reaction. The outcomes are listed in Table 1. To attain the optimal reaction solvent, different solvents such as CH3CN, n-hexane, H2O, and EtOH in the existence of a certain concentrations of catalyst were examined (Table 1, entries 1-4) and most favorable conditions in terms of rate and yield were found under solvent-free conditions for the reaction (Table 1, entry 8). To explore the impact of reaction temperature, different temperatures (25, 80, 90, 100, and 110 °C) were used for comparing the reaction efficiency (Table 1, entries 5-9). In the absence of temperature, the reaction speed was very slow and the yield was negligible (Table 1, entry 5). The product yield was increased at higher temperatures (Table 1, entries 6-9). At 100 °C, under solvent-free conditions, the reaction rate was the maximum (Table 1, entry 8); however, a further increase in temperature did not indicate any sign of the enhancement (Table 1, entry 9). In the following phase of the study, the impact of catalyst loading on the completion of the reaction was investigated (Table 1, entries 8 and 10-11). The outcomes indicated that the reaction using 0.38 mol% of the Cu@Fe3O4 MNPs as the catalyst at 100 °C under solvent-free conditions proceeded with the highest yield at the short reaction time (Table 1, entry 8). Finally, when the model reaction was performed in the presence of 0.38 mol% of Fe3O4, Fe3O4@SiO2, Fe3O4@PC, Fe3O4@Gu, and Fe3O4@Gu@TSH, under the optimized conditions, the yield of the product were 43, 51, 59, 71 and 83%, respectively (Table 1, entries 12-16). The favourable comparison of the product yields for inputs 8 and 12-16 accurately exhibits that the catalyst activity increases when Fe3O4@Gu@TSH is coordinate to the CuCl2 through the nitrogen lone pair.
Encouraged by these results, the scope and generality of the developed protocol regarding diverse aromatic and heterocyclic aldehydes were surveyed in the existence of 0.38 mol% of Cu@Fe3O4 MNPs at 100 °C under solvent-free conditions. The outcomes are presented in Table 2.
We also report a rapid and efficient one-pot three-component preparation of some 2H-indazolo[2,1-b]phthalazine-triones via the reaction of phthalhydrazide, aromatic aldehydes, and dimedone in the existence of Cu@Fe3O4 MNPs (Table 3). To identify the best conditions, we carried out the reaction between 4-chlorobenzaldehyde (1 mmol), dimedone (1 mmol) and phthalhydrazide (1 mmol) (molar ratio: 1 : 1 : 1) in the existence of 0.38 mol% of Cu@Fe3O4 MNPs at 100 °C under solvent-free conditions. We found that the desired product with a very high yield (96%) within 15 min (Table 3, entry 8).
After optimization of the conditions for the model reaction, a range of different tetrahydrobenzimidazo[2,1-b]quinazolin-1(2H)-ones was synthesized with array of arylaldehydes bearing either electron-withdrawing or electron-donating substituents and aliphatic aldehyde by this protocol (Table 4).
A possible mechanism for the creation of tetrahydrobenzimidazo[2,1-b]quinazolin-1(2H)-ones and 2H-indazolo[2,1-b]phthalazine-triones is proposed in Scheme 3. The reaction occurs via initial formation of the heterodyne 7 by nucleophilic addition of dimedone 3 to aldehyde 2 followed by dehydration. The second step involves initial formation of intermediates 8 and 9 by Michael-type addition of the 2-aminobenzimidazole 1 and phthalhydrazide 5 with heterodyne 7, followed by cyclization of the corresponding products 4 and 6.
To obtain the degree of leaching of the copper from the heterogeneous catalyst, in a typical experiment, phthalhydrazide (1 mmol), 4-chlorobenzaldehyde (1 mmol), dimedone (1 mmol), and Cu@Fe3O4 MNPs (0.38 mol%) and 3 mL of EtOH were placed in a round bottom flask and stirred at 100 °C for 30 min. Then, the catalyst was separated by a prominent magnetic field and allowed to the residue solution to be stirred at 100 °C for further 60 min. This experiment illustrated only a little progress in the yield of the product (GC) in the absence of Cu@Fe3O4 MNPs, which corroborates little leaching of copper and confirms responsibility of the heterogeneous Cu@Fe3O4 MNPs in catalyzing the desired reaction.
To evaluate the recycled Cu@Fe3O4MNPs performance, this nanocatalyst was reused in the reaction of 2-aminobenzimidazole/phthalhydrazide with 4-hydroxycoumarin, 4-chlorobenzaldehyde, and dimedone for at least seven runs under the optimal reaction conditions (Fig. 7). To achieve this purpose, at the end of the reaction, the mixture was dissolved in a hot mixture of ethyl acetate and ethanol (4 : 10 ratio) and then the catalyst was removed using an appropriate magnet. The recovered Cu@Fe3O4 MNPs were washed with chloroform, dried, and reused with a negligible reduction of its activity.
Table 5 shows the efficiency of Cu@Fe3O4 MNPs as the catalyst in the preparation of tetrahydrobenzimidazo[2,1-b]quinazolin-1(2H)-ones and 2H-indazolo[2,1-b]phthalazine-triones compared with several of the previously mentioned homogeneous and heterogeneous catalysts. As clearly shown in Table 5, although all the reported catalysts are suitable for certain synthetic conditions, the catalytic behavior of the present catalytic system is remarkable in terms of low reaction times, easy work-up procedures, low catalyst loading, and simple recovery of the catalyst.
Nguồn: https://capquangvnpt.edu.vn
Danh mục: Hóa
