Chemicals and reagentThe Merck Corporation provided the chemicals employed in this investigation, which included nickel nitrate, ethanol, sodium hydroxide, dimedone, aryl aldehydes, and aniline. Since all reagents are of analytical grade, no additional purification is required. Water that has been double-distilled was utilized to prepare the solution.Material characterizationEvery XRD result was gathered using a Philips PC-APD X-ray diffractometer (XRD, Netherlands). Energy Dispersive Spectroscopy (SEM–EDS analysis; EM 3200 SEM and KYKY; China) was utilized to analyze the heterogeneous catalyst. A thermoanalyzer (TG 209F3 NETZSCH) was used to analyze thermal behavior in N2 between ambient temperature and 350 °C. A TriStar II Plus surface area and porosity analyzer operating at 77 K was used to quantify N2 adsorption–desorption isotherms (BET). Magnetization measurements were carried out with a Lakeshore (model 7407) under magnetic fields at room temperature. The reaction progress and purity of the materials were investigated by thin-layer chromatography (TLC). Melting points were measured and uncorrected by Electro thermal 9100 apparatus. IR spectra were recorded on a Perkin-Elmer 240-C spectrophotometer operating with KBr discs. 1H and 13C NMR spectra were also provided with a Bruker AC (250 MHz for 1H NMR and 62.5 MHz for 13C NMR) in DMSO-d6 as solvents and tetramethylsilane (TMS) as the internal standard.Fabrication of nanocatalystFabrication of NiO nanoparticlesTo prevent the creation of contaminants in the finished product, an aqueous solution of nickel nitrate (0.5 M) (100 mL) in deionized distilled water was used as the solvent to prepare NiO nanoparticles. Then an appropriate amount of NaOH solution with a concentration of 0.1 M was added dropwise in the aforementioned solution until the pH value of the mixture reached 9–10 and the obtained mixture was stirred for two hours. Following the completion of the reaction, the precursor was centrifuged for 15 min at 3000 rpm, cleaned several times with distilled water and ethanol, dried for 8 h at 80 °C, and then calcined for 4 h at 400 °C48.Fabrication of NiO@Bentonite nanocatalysts as heterogeneous catalyst2.0 mmol (0.149 g) of the NiO nanoparticles and 0.593 g of the bentonite have been dispersed in deionized water under ultra-sonication for 30 min. The mixture was transferred to a glass vial to be irradiated in the microwave. Subsequently, the glassy vial was placed straight into the 180 W microwave oven and was exposed to microwave radiation for 90 min. After that, the finished product was washed with distilled water and was dried for ten hours at 80 °C.General procedure for synthesizing 1,8-dioxo-decahydroacridine derivativesIn a round-bottom flask, the three-component reaction of aromatic aldehyde (4 mmol), aniline (4 mmol), and at 40 °C, dimedone (8 mmol) was used in a solvent of water: ethanol (1:1) with a 15-weight percent NiO@Bentonite catalysis. Thin-layer chromatography (TLC) was used to examine the reaction’s progress in ethyl acetate: solvent n-hexane (3:7). Following the end of the reaction, to washout the produced precipitates, appropriate amount of ethanol was introduced into the flask and stirred on a magnetic stirrer for a couple of minutes to separate the product from the insoluble catalyst particles, Then, the obtained mixture was filtered to have the product pass through the paper filter while keeping the catalyst on the paper. The catalyst was several times washed with ethanol and then dried in an oven at 40 °C. Following the dehydration, the recycled catalyst was used for the next reactions. The pure product could be obtained following the evaporation of the ethanol in the mixture and washing the precipitates with another 15 mL of ethanol.Selected spectral data3,3,6,6-tetramethyl-9-(3-nitrophenyl)-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4a): Yield: 97%, m.p: 193–196 °C; IR (KBr, cm−1): 3087, 2961, 2872, 1597, 1527, 1460, 1378, 1042–1347, 703–893; 1H NMR (250 MHz, DMSO-d6, ppm) δ: 1.03 (s, 6H, 2CH3), 1.10 (S, 6H, 2CH3), 2.33 (brs, 8H, 4CH2), 5.41 (s, 1H, CH), 7.40–7.53 (m, 5H, H-Ar), 7.77 (brs, 1H, H-Ar), 7.94 (brs, 3H, H-Ar); 13C NMR (62.5 MHz, DMSO-d6) δ: 27.8, 29.2, 32.8, 33.7, 43.6, 48.0, 50.2, 51.7, 101.8, 102.7, 115.17, 121.7, 122.4, 124.2, 130.1, 130.8, 134.8, 136.5, 137.5, 145.7, 148.6, 148.7, 149.2, 188.8, 197.3 ppm.9-(4-hydroxy-3-methoxyphenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4b): m.p.: 221–225 °C; Yield: 94%; 1H NMR (250 MHz, DMSO-d6) δ: 1.03 (s, 12H, 4CH3), 2.30 (brs, 8H, 4CH2), 3.61 (s, 3H, OCH3), 5.75 (s, 1H, CH), 6.33–6.63 (m, 8H, H-Ar), 8.61 (brs, 1H, OH).9-(4-chlorophenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4c): m.p.: 148–149 °C; Yield: 92%; 1H NMR (250 MHz, DMSO-d6) δ: 1.00 (s, 12H, 4CH3), 2.30 (brs, 8H, 4CH2), 5.91 (s, 1H, CH), 6.84–7.21 (m, 9H, H-Ar).9-(4-hydroxyphenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4d): m.p.: 282–284 °C; Yield: 95%; 1H NMR (250 MHz, DMSO-d6) δ: 0.69 (s, 6H, 2CH3), 0.84 (s, 6H, 2CH3), 1.68–2.48 (m, 8H, 4CH2), 4.92 (s, 1H, CH), 6.58–7.56 (m, 9H, H-Ar), 9.05 (brs, 1H, OH).9-(4-methoxyphenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4e): m.p.: 217–218 °C; Yield: 98%; 1H NMR (250 MHz, DMSO-d6) δ: 1.04 (s, 6H, 2CH3), 1.08 (s, 6H, 2CH3), 2.17–2.62 (m, 8H, 4CH2), 3.68 (s, 3H, OCH3), 6.78 (d, J = 7.5 Hz, 2H, H-Ar), 6.98 (d, J = 7.5 Hz, 2H, H-Ar), 7.16–7.40 (m, 5H, H-Ar).9-(5-bromo-2-hydroxyphenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4f.): m.p.: 247–251 °C; Yield: 98%; 1H NMR (250 MHz, DMSO-d6) δ: 0.94 (s, 6H, 2CH3), 1.01 (s, 6H, 2CH3), 1.97–2.55 (m, 8H, 4CH2), 5.00 (s, 1H, CH), 6.90–7.26 (m, 8H, H-Ar), 10.62 (brs, 1H, OH).9-(2-hydroxynaphthalen-1-yl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4g): m.p.: 288–290 °C; Yield: 99%; 1H NMR (250 MHz, DMSO-d6) δ: 0.96 (s, 6H, 2CH3), 1.05 (s, 6H, 2CH3), 2.55–2.65 (m, 8H, 4CH2), 5.33 (s, 1H, CH), 7.19 (dd, J1 = 5 Hz, J2 = 2.5 Hz, 2H, H-Ar), 7.38 (brs, 4H, H-Ar), 7.72 (d, J = 10 Hz, 2H, H-Ar), 7.81 (t, J = 3.7 Hz, 1H, H-Ar), 8.18 (dd, J1 = 3.7 Hz, J2 = 2.5 Hz, 2H, H-Ar), 10.48 (brs, 1H, OH).3,3,6,6-tetramethyl-9-(2-nitrophenyl)-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4h): m.p.: 188–190 °C; Yield: 97%; 1H NMR (250 MHz, DMSO-d6) δ: 1.01 (s, 6H, 2CH3), 1.05 (s, 6H, 2CH3), 2.05 (brs, 4H, 2CH2), 2.20 (brs, 4H, 2CH2), 5.71 (s, 1H, CH), 7.13 (d, J = 5 Hz, 1H, H-Ar), 7.33–7.45 (m, 5H, H-Ar), 7.60 (d, J = 7.5 Hz, 1H, H-Ar), 7.78 (d, J = 10 Hz, 1H, H-Ar), 7.87 (d, J = 7.5 Hz, 1H, H-Ar),9-(4-(dimethylamino)phenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4i): m.p.: 168–170 °C; Yield: 99%; 1H NMR (250 MHz, DMSO-d6) δ: 1.02 (s, 12H, 4CH3), 2.29 (brs, 8H, 4CH2), 2.79 (s, 6H, 2CH3), 5.73 (s, 1H, CH), 6.59 (brs, 5H, H-Ar), 6.77 (d, J = 5 Hz, 2H, H-Ar), 6.95 (d, J = 5 Hz, 2H, H-Ar).9-(2-hydroxy-3-methoxyphenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4j): m.p.: 228–229 °C; Yield: 94%; 1H NMR (250 MHz, DMSO-d6) δ: 0.96 (s, 6H, 2CH3), 1.02 (s, 6H, 2CH3), 1.97–2.47 (m, 8H, 4CH2), 3.75 (s, 3H, OCH3), 5.01 (s, 1H, CH), 6.50 (d, J = 5.7 Hz, 4H, H-Ar), 6.75–6.88 (m, 4H, H-Ar), 10.33 (brs, 1H, OH).9-(4-bromophenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4 k): m.p.: > 300 °C; Yield: 98%; 1H NMR (250 MHz, DMSO-d6) δ: 1.00 (s, 12H, 4CH3), 2.30 (brs, 8H, 4CH2), 5.90 (s, 1H, CH), 6.82–7.57 (m, 9H, H-Ar).9-(3-hydroxyphenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4l): m.p.: 231–233 °C; Yield: 94%; 1H NMR (250 MHz, DMSO-d6) δ: 0.92 (s, 6H, 2CH3), 1.04 (s, 6H, 2CH3), 2.30 (brs, 4H, 2CH2), 2.38–2.48 (m, 4H, 2CH2), 5.52 (s, 1H, CH), 6.52 (s, 1H, H-Ar), 6.99 (brs, 2H, H-Ar), 7.16–7.22 (m, 4H, H-Ar), 7.39 (d, J = 2.5 Hz, 2H, H-Ar).9-(2-chlorophenyl)-3,3,6,6-tetramethyl-10-phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4m): m.p.: 220–223 °C; Yield: 92%; 1H NMR (250 MHz, DMSO-d6) δ: 1.01 (s, 6H, 2CH3), 1.08 (s, 6H, 2CH3), 2.03–2.48 (m, 8H, 4CH2), 5.58 (s, 1H, CH), 6.88 (d, J = 3.7 Hz, 2H, H-Ar), 7.07 (brs, 5H, H-Ar), 7.28 (brs, 2H, OH).3,3,6,6-tetramethyl-10-phenyl-9-(3,4,5-trimethoxyphenyl)-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (4n): m.p.: 243–244 °C; Yield: 95%; 1H NMR (250 MHz, DMSO-d6) δ: 1.04 (s, 12H, 4CH3), 2.32 (brs, 8H, 4CH2), 3.62 (s, 9H, 3OCH3), 5.82 (s, 1H, CH), 6.23 (brs, 5H, H-Ar), 6.36–6.42 (m, 2H, H-Ar).
