Synthesis of the first nano ionic liquid 1-methylimidazolium trinitromethanide {[HMIM]C(NO₂)₃} and its catalytic use for Hanztsch four-component condensation

Abstract

A novel, green and reusable nano ionic liquid and catalyst, namely 1-methylimidazolium trinitromethanide {[HMIM]C(NO₂)₃}, was designed and fully characterized by ¹H NMR, ¹³C NMR, IR, mass, X-ray diffraction patterns (XRD) and Transmission electron microscopy (TEM) analysis. The catalytic application of the presented catalyst was successfully tested on the Hantzsch four-component reaction of various aromatic aldehydes, 1,3-dione, β-ketoester and ammonium acetate at room temperature under solvent-free and mild conditions to give the polyhydroquinoline derivatives in good to excellent yields. In the presented work, some products have been reported for the first time.

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Introduction

Ionic liquids (ILs) have received considerable attention in the last decade, due to their specific properties¹ and their applications in chemistry² including liquid–liquid separations,³ nano materials synthesis,⁴ biocatalysis,⁵ polymerization reactions,⁶ extraction⁷ and dissolution processes,⁸ catalysis⁹ and electrochemistry.¹⁰ Ionic liquids mainly have low vapour pressure, non-volatility, high polarity, solubility with certain organic solvents and/or water and good solubility in organic and inorganic materials.¹¹

Multi-component reactions (MCRs) play an important role in combinatorial chemistry due of their capability to preparation of target molecules with atomic economy and high efficiency by the reaction of three or more starting materials together in a single step. Furthermore, this technique increases synthetic efficacy and simplicity of the reaction with respect to the conventional organic transformations.^12,13

Recently, much attention has been focused on the multi-component synthesis of 1,4-dihydropyridine compounds (1,4-DHP) because of their variation in biological activities such as Ca²⁺ channel blockers.¹⁴ Furthermore, they also have communal types of several bio active compounds such as bronchodilators, hepatoprotective, vasodilators, anti-tumor, anti-atherosclerotic and anti-diabetic agents for the behavior of cardiovascular diseases including hypertension.¹⁵ The recent investigations reveal that 1,4-DHP exhibit ions some medicinal applications which contain cerebral anti chemic activity in the treatment of Alzheimer's disease,¹⁶ platelet anti aggregators activity,¹⁷ neuro protectant¹⁸ and chemo sensitizer acting in tumor therapy.¹⁹ Recently, these compounds have been synthesized in the presence of [pyridine-SO₃H]Cl,²⁰ [Dsim]HSO₄,²¹ TiO₂ NPs,²² SnO₂ NPs,²³ [2-MPyH]OTf,²⁴ Ni-nanoparticle,²⁵ Baker's yeast,²⁶ L-proline,²⁷ [bmim]BF₄,²⁸ solvent-free conditions on grinding,²⁹ 1-vinyl-3-ethylimidazolium iodide.³⁰ Although several catalysts for this transformation are known, newer catalysts continue to attract attention for their difference with the others, high novelty and effectiveness.

In continuation to our studies involving the synthesis of 1,4-dihydropyridine,^31–34 preparation and applications of ionic liquids in organic synthesis,^13,20,35,36 we have prepared a novel ionic liquid and catalyst namely 1-methylimidazolium trinitromethanide {[HMIM]C(NO₂)₃} and employed it for the preparation of polyhydroquinoline derivatives under solvent-free reaction conditions (Schemes 1 and 2).

Scheme 1 The synthesis of 1-methylimidazolium trinitromethanide as a nano ionic liquid and catalyst.

Scheme 2 The synthesis of polyhydroquinoline derivatives catalyzed by {[HMIM]C(NO₂)₃} as a novel nano ionic liquid and catalyst.

Results and discussion

Characterization of 1-methylimidazolium trinitromethanide {[HMIM]C(NO₂)₃}

The structure of 1-methylimidazolium trinitromethanide as a novel nano ionic liquid and catalyst was prepared and identified by FT-IR, ¹H NMR, ¹³C NMR, mass, TG, DTG, XRD and TEM analysis.

The IR spectrum of the nano ionic liquid indicated an abroad peak at 3144 cm⁻¹ which can be related to N–H stretching group on imidazolium ring. Additionally, the two peaks observed at 1584 cm⁻¹ and 1383 cm⁻¹ correspond to vibrational modes of NO₂ bonds (Fig. 1).

Fig. 1 The IR spectrum of 1-methylimidazolium trinitromethanide (a); trinitromethane (b); 1-methylimidazole (c).

Furthermore, the ¹H NMR and ¹³C NMR spectra of the 1-methylimidazolium trinitromethanide in DMSO-d₆ are displayed in Fig. 2 and 3. As Fig. 2 and 3, indicates that, the important peak of ¹H NMR spectra of nano ionic liquid catalyst is linked to the acidic hydrogen (NH group on imidazolium ring) which is observed in δ = 14.30 ppm.

Fig. 2 The ¹H NMR spectrum of the novel nano ionic liquid as a catalyst.

Fig. 3 The ¹³C NMR spectrum of the 1-methylimidazolium trinitromethanide as an ionic liquid catalyst.

Thermal gravimetric analysis (TGA) of 1-methylimidazolium trinitromethanide as a novel nano ionic liquid catalyst was also studied. The constant illustrations are revealed in Fig. 4 and 5. The thermo gravimetry (TG) and derivative thermo gravimetry (DTG) illustrations of the ionic liquid catalyst exhibited weight losses in one step, and decomposition after about 150 °C.

Fig. 4 The thermogravimetry (TG) illustrations of nano ionic liquid catalyst.

Fig. 5 The derivative thermogravimetry (DTG) illustrations of nano ionic liquid catalyst.

Size, shape and morphology of the nano ionic liquid catalyst were investigated using X-ray diffraction (XRD) pattern sand transmission electron microscopy (TEM) imaging techniques. XRD patterns of the catalyst {[HMIM]C(NO₂)₃} was studied in a domain of 10–90 degree (Fig. 6). As shown at Fig. 6, XRD patterns exhibited diffraction lines of a high crystalline nature at 2θ ≈ 16.70°, 19.70°, 26.60°, 29.70°, 37.10° and 40.00°. Peak width (FWHM), size and inter planer distance studies of the catalyst could be worked out in the 16.70 to 40.00 degree and results have been summarized in Table 1. As example, calculations for the highest diffraction line 19.70° confirmed that an FWHM of 0.22 a crystallite size of the catalyst of ca. 36.67 nm via the Scherrer equation [D = Kλ/(β cos θ)] and an inter planer distance of 0.450109 nm (sing the same highest diffraction line at 19.70°) was calculated to be via the Bragg equation: dhkl = λ/(2 sin θ), (λ: Cu radiation (0.154178 nm)) were obtained. Most importantly, crystallite sizes as obtained from the various diffraction lines using the Scherrer equation were found to be in the nanometer range (36.67–62.45 nm), which is fundamentally in a good accordance with the transmission electron microscopy (TEM) (Fig. 7).

Fig. 6 The XRD pattern of the nano ionic liquid catalyst.

Table 1 XRD data for the nano ionic liquid catalyst

Entry	2θ	Peak width [FWHM] (degree)	Size [nm]	Inter planer distance [nm]
1	17.60	0.18	44.68	0.503314
2	19.70	0.22	36.67	0.450109
3	26.60	0.18	45.37	0.334710
4	29.70	0.25	62.45	0.089457
5	37.10	0.21	39.51	0.242037
6	40.00	0.19	44.68	0.225132

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Fig. 7 Transmission electron microscopy (TEM) of the nano ionic liquid catalyst.

Application of 1-methylimidazolium trinitromethanide as an ionic liquid catalyst

After the synthesis of 1-methylimidazolium trinitromethanide as a novel nano ionic liquid catalyst, to optimize the reaction conditions, we have tested the efficiency of the catalyst in the synthesis of polyhydroquinoline derivatives (Scheme 2). For this purpose, as a model, the condensation reaction of 2,5-dimethoxybenzaldehyde, dimedone, methyl acetoacetate and ammonium acetate was investigated using different amounts of the catalyst at range of 25–125 °C under solvent-free conditions (Table 2). As Table 2, indicates that, the best results were obtained when the reaction was achieved in the presence of 0.5 mol% of nano ionic liquid catalyst at room temperature (Table 2, entry 3). No improvement in the reaction results was observed by increasing the amount of the catalysts and the temperature (Table 2, entries 4–11).

Table 2 The effect of amount of the catalyst and temperature on the condensation of between 2,5-dimethoxybenzaldehyde, dimedone, methyl acetoacetate and ammonium acetate under solvent-free conditions

Entry	Catalyst amount (mol%)	Temperature (°C)	Time (min)	Yield (%)
1	—	25	60	—
2	0.2	25	30	53
3	0.5	25	7	97
4	0.5	50	7	97
5	0.5	75	7	97
6	0.5	100	10	87
7	0.5	125	15	81
8	1	25	7	97
9	2	25	7	97
10	5	25	10	95
11	10	25	10	95

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To compare the efficiency of the solution versus solvent-free conditions, a mixture of 2,5-dimethoxybenzaldehyde, dimedone, methyl acetoacetate and ammonium acetate, as model reaction, in the presence of 0.5 mol% of nano ionic liquid catalyst in some various solvents such as C₂H₅OH, H₂O, CH₂Cl₂, CH₃CN and CH₃CO₂Et was studied at room temperature. The results are summarized in Table 3. As it can be realized in Table 3, solvent-free condition was the best conditions in this reaction.

Table 3 The effect of various solvents on the reaction of between 2,5-dimethoxybenzaldehyde, dimedone, methyl acetoacetate and ammonium acetate catalyzed by 0.5 mol% of nano ionic liquid at room temperature

Entry	Solvent	Time (min)	Yield (%)
1	—	7	97
2	H2O	10	95
3	C2H5OH	12	95
4	CH3CN	20	92
5	CH2Cl2	33	87
6	CH3CO2Et	45	82

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Stimulated by the significant results, and in order to confirmation of generalization and scope of this new procedure, various polyhydroquinoline derivatives were synthesized from the Hantzsch four-component condensation reaction of different aromatic aldehydes, 1,3-dione, β-ketoester and ammonium acetate in the presence of a catalytic amount of 1-methylimidazolium trinitromethanide {[HMIM]C(NO₂)₃} as a nano ionic liquid catalyst under solvent-free reaction conditions. The results have been depicted in Table 4. All aromatic aldehydes including benzaldehyde and aldehydes containing electron-releasing substituents, electron-withdrawing substituents and halogens on their aromatic ring afforded the analogous products in high to excellent yields in short reaction times. The reaction times of aromatic aldehydes having electron withdrawing groups were rather faster than electron donating groups. However meta- and para- substituted aromatic aldehydes offered excellent results, ortho-substituted aromatic aldehydes provided slightly lower yields due to the steric effects.

Table 4 Synthesis of polyhydroquinoline derivatives using 1-methylimidazolium trinitromethanide

Entry	Aldehyde	R^1	Time (min)	Yield (%)	M.p (°C)
5a	2,5-Dimethoxybenzaldehyde	H	10	96	238–240
5b	4-Hydroxy-3-methoxybenzaldeyhe	H	20	94	224–226 (ref. 30)
5c	4-N,N-Dimethylaminobenzaldehyde	H	15	95	253–255
5d	Biphenyl-4-carbaldehyde	Me	5	98	256–258
5e	Terephthaldehyde	Me	18	92	343–345
5f	2,5-Dimethoxybenzaldehyde	Me	7	97	193–195
5g	α-Methylcinnamaldehyde	Me	23	91	193–195
5h	4-Hydroxy-3-methoxybenzaldeyhe	Me	15	95	273–275
5i	4-N,N-Dimethylaminobenzaldehyde	Me	12	95	228–230 (ref. 29)
6a	2,5-Dimethoxybenzaldehyde	H	13	95	197–199
6b	Biphenyl-4-carbaldehyde	Me	8	98	196–198
6c	Terephthaldehyde	Me	25	92	367–369 (ref. 20)
6d	2,5-Dimethoxybenzaldehyde	Me	9	96	191–193
6e	α-Methylcinnamaldehyde	Me	27	90	218–220
7a	2,4-Dinirobenzaldehyde	H	10	98	247–249
7b	4-Hydroxy-3-methoxybenzaldeyhe	H	25	93	211–213
7c	4-N,N-Dimethylaminobenzaldehyde	H	18	93	259–261
7d	Biphenyl-4-carbaldehyde	Me	11	97	191–193
7e	Terephthaldehyde	Me	31	91	248–250
7f	2,5-Dimethoxybenzaldehyde	Me	12	96	182–184
7g	α-Methylcinnamaldehyde	Me	33	90	127–129
7h	4-Hydroxy-3-methoxybenzaldeyhe	Me	18	94	281–283

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In a proposed mechanism (Scheme 3), we suggest that at first dimedone is converted to its enol form using {[HMIM]C(NO₂)₃} and reacted to activated aldehyde by {[HMIM]C(NO₂)₃} to give intermediate I. On the other hand, the activated β-ketoester (by the catalyst) and ammonia (resulted from ammonium acetate) affords enamine II. Afterward, the intermediate I and enamine II react with each other to give intermediate III. III is converted to IV by tautomerization, and intermediate IV affords V by intramolecular nucleophilic attack of the NH₂ group to the activated carbonyl group. Finally, polyhydroquinonine forms by removing one molecule H₂O. It should be mentioned that in the mentioned steps, {[HMIM]C(NO₂)₃} gives a proton for the activation of carbonyl groups and then the proton is transferred to the catalyst in another steps. The mechanism is confirmed by the literature.^20,21

Scheme 3 The suggested mechanism for the synthesis of polyhydroquinoline in the presence of 1-methylimidazolium trinitromethanide as a nano ionic liquid and catalyst.

Additionally, recyclability of the catalyst was tested upon the condensation of between 2,5-dimethoxybenzaldehyde, dimedone, methyl acetoacetate and ammonium acetate. At the end of the reaction, ethyl acetate was added to the reaction mixture and heated to extract product and remained starting materials. This solution was washed with water to separate catalyst from the other materials (the product is soluble in hot ethyl acetate and nano ionic liquid catalyst is soluble in water). The aqueous layer was decanted, separated and used for alternative reaction after removing of water. We have been observed that the catalytic activity of the catalyst was restored within the limits of the experimental errors for six continuous runs (Fig. 8).

Fig. 8 Reusability of the nano ionic liquid catalyst in 7 minutes.

The reused catalyst was also characterized by ¹H NMR and ¹³C NMR spectra after its application in the reaction. These spectra were same as those of the fresh catalyst (Fig. S4 and S5†). Also the size of the catalyst was studied after the recovery process by transmission electron microscopy (TEM) analysis. This study was showed that the catalyst was recovered in nano size. The related pictures were added in Fig. S6.†

Conclusions

In this work, a novel, green and reusable catalyst namely 1-methylimidazolium trinitromethanide {[HMIM]C(NO₂)₃} was designed and fully characterized by ¹H NMR, ¹³C NMR, IR, mass, X-ray diffraction patterns (XRD) and transmission electron microscopy (TEM) analysis. Catalytic application of {[HMIM]C(NO₂)₃} was studied on the synthesis of polyhydroquinoline derivatives by the four-component reaction of various aromatic aldehydes, 1,3-dione, β-ketoester and ammonium acetate at room temperature under solvent-free and mild conditions. Additional investigations showed that the nano ionic liquids acidity plays a key role in the acid-catalyzed reactions. Some important advantages of this work are low cost, cleaner reaction profile, relatively short reaction time, high yield, ease of product isolation, recyclability of the catalyst and compliance with the green chemistry protocols.

Experimental

General procedure for the preparation of nano ionic liquid catalyst: 1-methylimidazolium trinitromethanide

To a round-bottomed flask (100 mL) containing 1-methylimidazole (3 mmol; 0.246 g) in CH₃CN (10 mL), was added trinitromethane (3.1 mmol; 0.468 g) drop wise and heated over a period of 120 min at 80 °C. Afterward the solvent was removed by distillation under reduced pressure, the product was dried under vacuum at 80 °C for 3 h. A yellow solid was formed (Scheme 1) quantitatively.

1-Methylimidazolium trinitromethanide {[HMIM]C(NO₂)₃}. M.p: 54–56 °C; yield: 97% (0.679 g); spectral data: IR (KBr): υ 3433, 3144, 1584, 1383 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 3.87 (s, 3H, –CH₃), 7.68 (d, 1H, J = 3.2 Hz, –CH); 7.71 (d, 1H, J = 3.2 Hz, –CH), 9.08 (s, 1H, –CH), 14.30 (brs, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 35.8, 46.5, 120.2, 123.6, 136.3; MS: m/z = 233 [M]⁺, 234 [M + H]⁺.

General procedure for the synthesis of polyhydroquinoline derivatives

To a mixture of 1,3-dione (1 mmol), aromatic aldehyde (1 mmol), β-ketoester (1 mmol) and ammonium acetate (1 mmol) in a test tube, was added 1-methylimidazolium trinitromethanide as a novel nano ionic liquid catalyst (0.5 mol%), and the resulting mixture was firstly stirred magnetically under solvent-free conditions at room temperature. After completion of the reaction, as monitored by TLC (n-hexane/ethyl acetate: 4/1) ethyl acetate (10 mL) was added to reaction mixture, stirred and refluxed for 3 min, and then was washed with water (10 mL) and decanted to separate catalyst from the other materials (the reaction mixture was soluble in hot ethyl acetate and nano ionic liquid catalyst was soluble in water). The aqueous layer was decanted and catalyst separated after removing of water. The remained catalyst was used for alternative reaction. The solvent of organic layer was evaporated and the crude product was purified by recrystallization from ethanol (95%). In this study, nano ionic liquid catalyst was recycled and reused for six times without significant loss of its catalytic activity.

Spectral data

Methyl 4-(2,5-dimethoxyphenyl)-2-methyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5a). Yellow solid; M.p: 238–240 °C; yield: 96% (0.343 g); IR (KBr): υ 3434, 3287, 3211, 3074, 2991, 1692 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 1.88–2.18 (m, 6H, –CH₂), 2.48 (s, 3H, –CH₃), 3.51 (s, 3H, –CH₃), 3.63 (s, 3H, –CH₃), 3.66 (s, 3H, –CH₃), 5.04 (s, 1H, –CH), 6.56 (d, 1H, J = 3.2 Hz, ArH), 6.65 (d, 1H, J = 3.2 Hz, ArH), 6.79 (s, 1H, ArH), 9.05 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 18.2, 21.4, 26.7, 32.6, 37.3, 50.9, 55.5, 56.8, 103.8, 110.0, 111.1, 113.1, 116.5, 137.0, 143.8, 152.0, 152.5, 153.3, 168.3, 194.7; MS: m/z = 357 [M]⁺.

Methyl 4-(4-hydroxy-3-methoxyphenyl)-2-methyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5b). White solid; M.p: 224–226 °C; yield: 94% (0.323 g); IR (KBr): υ 3394, 3313, 3228, 3076, 2951, 1682 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 2.08–2.16 (m, 1H, –CH₂), 2.20 (t, 2H, J = 8.0 Hz, –CH₂), 2.26 (s, 3H, –CH₃), 2.33–2.40 (m, 1H, –CH₂), 2.47 (t, 2H, J = 8.4 Hz, –CH₂), 3.55 (s, 3H, –CH₃), 3.68 (s, 3H, –CH₃), 4.81 (s, 1H, –CH), 6.48 (d, 1H, J = 2.0 Hz, ArH), 6.59 (s, 1H, ArH), 6.70 (d, 1H, J = 2.0 Hz, ArH), 8.63 (s, 1H, –OH), 9.10 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 18.7, 21.3, 26.6, 35.0, 37.2, 51.1, 55.9, 111.7, 112.2, 115.5, 119.6, 139.3, 144.5, 145.0, 145.1, 147.3, 151.6, 168.0, 195.2; MS: m/z = 343 [M]⁺.

Methyl 4-(4-(dimethylamino)phenyl)-2-methyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5c). Yellow solid; M.p: 253–255 °C; yield: 95% (0.322 g); IR (KBr): υ 3283, 3213, 3074, 2949, 1696 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 1.73–1.80 (m, 2H, –CH₂), 1.89 (t, 2H, J = 8.8 Hz, –CH₂), 2.20 (t, 2H, J = 5.0 Hz, –CH₂), 2.27 (s, 3H, –CH₃), 2.44 (s, 3H, –CH₃), 2.78 (s, 3H, –CH₃), 2.80 (s, 3H, –CH₃), 4.78 (s, 1H, –CH), 6.56 (d, 2H, J = 8.4 Hz, ArH), 6.95 (d, 2H, J = 8.8 Hz, ArH), 9.37 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 18.7, 21.3, 26.6, 26.8, 31.3, 34.6, 37.2, 37.3, 128.2, 128.4, 136.3, 136.5, 145.0, 149.0, 149.2, 151.2, 151.3, 168.1, 195.2, 195.3; MS: m/z = 340 [M]⁺.

Methyl 4-(biphenyl-4-yl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5d). White solid; M.p: 256–258 °C; yield: 98% (0.392 g); IR (KBr): υ 3289, 3219, 3077, 2958, 1703 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.87 (s, 3H, –CH₃), 1.01 (s, 3H, –CH₃), 2.03 (d, 1H, J = 8.2 Hz, –CH₂), 2.21 (d, 1H, J = 8.0 Hz, –CH₂), 2.30 (s, 3H, –CH₃), 2.33 (d, 1H, J = 5.0 Hz, –CH₂), 2.46 (d, 1H, J = 8.6 Hz, –CH₂), 3.55 (s, 3H, –CH₃), 4.91 (s, 1H, –CH), 7.23 (d, 2H, J = 8.0 Hz, ArH), 7.33 (t, 1H, J = 7.4 Hz, ArH), 7.42 (d, 2H, J = 7.6 Hz, ArH), 7.50 (d, 2H, J = 8.0 Hz, ArH), 7.60 (d, 2H, J = 7.6 Hz, ArH), 9.14 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 18.8, 27.1, 29.5, 32.7, 35.8, 50.7, 51.2, 103.5, 110.3, 126.7, 126.9, 127.5, 128.3, 129.3, 138.1, 140.6, 145.9, 147.2, 150.1, 167.8, 194.8; MS: m/z = 401 [M]⁺.

Dimethyl 4,4′-(1,4-phenylene)bis(2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate) (5e). Yellow solid; M.p: 343–345 °C; yield: 92% (0.526 g); IR (KBr): υ 3431, 3284, 3212, 3085, 2956, 1704 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.78 (s, 3H, –CH₃), 0.82 (s, 3H, –CH₃), 0.98 (s, 6H, –CH₃), 1.09 (d, 1H, J = 7.2 Hz, –CH₂), 1.91 (s, 1H, –CH₂), 2.02 (d, 1H, J = 5.6 Hz, –CH₂), 2.11 (d, 1H, J = 9.0 Hz, –CH₂), 2.17 (d, 1H, J = 8.8 Hz, –CH₂), 2.24 (d, 1H, J = 2.4 Hz, –CH₂), 2.26 (s, 6H, –CH₃), 2.29 (d, 1H, J = 4.0 Hz, –CH₂), 2.35 (d, 1H, J = 3.2 Hz, –CH₂), 3.50 (s, 3H, –CH₃), 3.53 (s, 3H, –CH₃), 4.78 (s, 1H, –CH), 4.82 (s, 1H, –CH), 6.93 (d, 4H, J = 0.4 Hz, ArH), 9.07 (s, 2H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 26.8, 27.2, 29.3, 29.5, 31.6, 32.7, 35.1, 35.3, 127.0, 127.1, 145.1, 145.2, 145.7, 148.8, 149.9, 150.1, 167.9, 194.8, 194.9; MS: m/z = 572 [M]⁺.

Methyl 4-(2,5-dimethoxyphenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5f). Yellow solid; M.p: 193–195 °C; yield: 97% (0.373 g); IR (KBr): υ 3278, 3241, 3208, 3077, 2946, 1701 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.87 (s, 3H, –CH₃), 1.00 (s, 3H, –CH₃), 1.94 (d, 1H, J = 8.0 Hz, –CH₂), 2.15 (d, 1H, J = 8.0 Hz, –CH₂), 2.17 (s, 3H, –CH₃), 2.30 (d, 1H, J = 8.4 Hz, –CH₂), 2.43 (d, 1H, J = 8.4 Hz, –CH₂), 3.50 (s, 3H, –CH₃), 3.62 (s, 3H, –CH₃), 3.65 (s, 3H, –CH₃), 5.01 (s, 1H, –CH), 6.62 (s, 1H, ArH), 6.64 (d, 2H, J = 3.2 Hz, ArH), 6.78 (d, 2H, J = 2.0 Hz, ArH), 8.99 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 18.5, 26.7, 29.8, 32.5, 33.1, 40.0, 50.8, 50.9, 55.5, 56.5, 103.4, 109.0, 111.3, 112.6, 116.9, 136.7, 144.4, 150.6, 151.9, 153.1, 168.2, 198.3; MS: m/z = 385 [M]⁺.

Methyl 2,7,7-trimethyl-5-oxo-4-(1-phenylprop-1-en-2-yl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5g). Yellow solid; M.p: 193–195 °C; yield: 91% (0.332 g); IR (KBr): υ 3424, 3284, 3213, 3081, 2956, 1704 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 1.00 (s, 6H, –CH₃), 1.03 (s, 3H, –CH₃), 1.76 (d, 4H, J = 1.2 Hz, –CH₂), 2.27 (s, 3H, –CH₃), 3.61 (s, 3H, –CH₃), 4.45 (s, 1H, –CH), 6.19 (s, 1H, –CH), 7.13 (d, 2H, J = 7.2 Hz, ArH), 7.17 (t, 1H, J = 7.2 Hz, ArH), 7.29 (d, 2H, J = 7.6 Hz, ArH), 9.00 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 16.3, 18.6, 26.8, 26.9, 29.7, 32.4, 32.5, 50.9, 51.1, 102.5, 108.7, 125.1, 126.3, 128.6, 128.9, 129.1, 138.4, 143.0, 145.9, 150.5, 168.1, 195.0; MS: m/z = 365 [M]⁺.

Methyl 4-(4-hydroxy-3-methoxyphenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5h). White solid; M.p: 273–275 °C; yield: 95% (0.352 g); IR (KBr): υ 3372, 3292, 3243, 3069, 2956, 1702 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.88 (s, 3H, –CH₃), 1.01 (s, 3H, –CH₃), 2.01 (d, 1H, J = 7.8 Hz, –CH₂), 2.20 (d, 1H, J = 8.0 Hz, –CH₂), 2.26 (s, 3H, –CH₃), 2.30 (d, 1H, J = 6.4 Hz, –CH₂), 2.44 (d, 1H, J = 8.4 Hz, –CH₂), 3.55 (s, 3H, –CH₃), 3.66 (s, 3H, –CH₃), 4.76 (s, 1H, –CH), 6.50 (d, 1H, J = 2.0 Hz, ArH), 6.58 (s, 1H, ArH), 6.70 (d, 1H, J = 1.6 Hz, ArH), 8.63 (s, 1H, –OH), 9.03 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 18.7, 26.8, 32.6, 35.2, 51.1, 55.9, 112.2, 115.4, 119.7, 127.3, 129.0, 139.3, 145.0, 145.2, 145.9, 147.3, 149.7, 168.0, 184.7, 194.9; MS: m/z = 371 [M]⁺.

Methyl 4-(4-(dimethylamino)phenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5i). Yellow solid; M.p: 228–230 °C; yield: 95% (0.349 g); IR (KBr): υ 3280, 3202, 3072, 2961, 1699 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.86 (s, 3H, –CH₃), 1.00 (s, 3H, –CH₃), 1.99 (d, 1H, J = 8.8 Hz, –CH₂), 2.18 (d, 1H, J = 8.0 Hz, –CH₂), 2.26 (s, 3H, –CH₃), 2.28 (d, 1H, J = 5.0 Hz, –CH₂), 2.42 (d, 1H, J = 8.4 Hz, –CH₂), 2.80 (s, 6H, –CH₃), 3.52 (s, 3H, –CH₃), 4.73 (s, 1H, –CH), 6.55 (d, 2H, J = 8.8 Hz, ArH), 6.95 (d, 2H, J = 8.8 Hz, ArH), 9.00 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 18.7, 27.0, 29.6, 32.6, 35.4, 50.8, 51.1, 110.7, 112.6, 121.4, 128.2, 137.0, 145.1, 149.6, 195.1; MS: m/z = 368 [M]⁺.

Ethyl 4-(2,5-dimethoxyphenyl)-2-methyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (6a). Yellow solid; M.p: 197–199 °C; yield: 95% (0.352 g); IR (KBr): υ 3285, 3203, 3073, 2941, 1689 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 1.14 (t, 3H, J = 7.0 Hz, –CH₃), 1.75 (t, 2H, J = 5.2 Hz, –CH₂), 1.91 (q, 2H, J = 6.6 Hz, –CH₂), 2.16 (s, 3H, –CH₃), 2.48 (t, 2H, J = 9.2 Hz, –CH₂), 3.63 (s, 3H, –CH₃), 3.65 (s, 3H, –CH₃), 3.98 (m, 2H, –CH₂), 5.02 (s, 1H, –CH), 6.62 (d, 1H, J = 3.2 Hz, ArH), 6.65 (d, 1H, J = 3.2 Hz, ArH), 6.76 (s, 1H, ArH), 9.03 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 14.6, 18.3, 21.4, 26.7, 33.1, 37.3, 55.5, 56.7, 59.3, 103.7, 110.1, 111.1, 113.1, 117.0, 137.0, 144.0, 152.1, 152.4, 153.2, 167.8, 194.7; MS: m/z = 371 [M]⁺.

Ethyl 4-(biphenyl-4-yl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (6b). White solid; M.p: 196–198 °C; yield: 98% (0.406 g); IR (KBr): υ 3306, 3080, 2956, 1690 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.87 (s, 3H, –CH₃), 1.02 (s, 3H, –CH₃), 1.17 (t, 3H, J = 7.0 Hz, –CH₃), 2.02 (d, 1H, J = 8.8 Hz, –CH₂), 2.20 (d, 1H, J = 8.2 Hz, –CH₂), 2.30 (s, 3H, –CH₃), 2.34 (d, 1H, J = 7.6 Hz, –CH₂), 2.46 (d, 1H, J = 8.6 Hz, –CH₂), 4.02 (q, 2H, J = 7.2 Hz, –CH₂), 4.90 (s, 1H, –CH), 7.25 (d, 2H, J = 8.4 Hz, ArH), 7.34 (t, 1H, J = 7.8 Hz, ArH), 7.42 (d, 2H, J = 8.0 Hz, ArH), 7.50 (d, 2H, J = 8.4 Hz, ArH), 7.61 (d, 2H, J = 9.2 Hz, ArH), 9.10 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 14.6, 18.8, 27.1, 29.5, 32.7, 36.0, 50.7, 59.6, 103.9, 110.3, 126.6, 126.9, 127.5, 128.5, 129.3, 138.1, 140.1, 145.5, 147.3, 150.1, 167.3, 194.8; MS: m/z = 415 [M]⁺.

Diethyl 4,4′-(1,4-phenylene)bis(2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate) (6c). White solid; M.p: 367–369 °C; yield: 92% (0.552 g); IR (KBr): υ 3453, 3283, 3221, 3087, 2960, 1702 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.98 (s, 6H, –CH₃), 1.02 (s, 6H, –CH₃), 1.04 (s, 6H, –CH₃), 1.11 (t, 6H, J = 7.0 Hz, –CH₃), 1.96 (d, 2H, J = 8.0 Hz, –CH₂), 2.15 (d, 2H, J = 8.2 Hz, –CH₂), 2.27 (d, 2H, J = 8.0 Hz, –CH₂), 2.41 (d, 2H, J = 8.4 Hz, –CH₂), 3.98 (q, 4H, J = 9.6 Hz, –CH₂), 4.73 (s, 2H, –CH), 6.76 (s, 2H, ArH), 6.94 (s, 2H, ArH), 9.00 (s, 2H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 14.8, 15.5, 16.4, 18.5, 21.3, 22.0, 26.8, 26.9, 28.4, 128.1, 128.2, 128.4, 128.5, 129.1, 138.4, 152.1, 152.6, 167.6, 195.3, 195.5; MS: m/z = 600 [M]⁺.

Ethyl 4-(2,5-dimethoxyphenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (6d). White solid; M.p: 191–193 °C; yield: 96% (0.383 g); IR (KBr): υ 3307, 3231, 3099, 2959, 1691 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.86 (s, 3H, –CH₃), 1.00 (s, 3H, –CH₃), 1.14 (t, 3H, J = 7.2 Hz, –CH₃), 1.93 (d, 1H, J = 8.0 Hz, –CH₂), 2.14 (d, 1H, J = 8.2 Hz, –CH₂), 2.18 (s, 3H, –CH₃), 2.26 (d, 1H, J = 8.6 Hz, –CH₂), 2.42 (d, 1H, J = 8.6 Hz, –CH₂), 3.63 (s, 3H, –CH₃), 3.64 (s, 3H, –CH₃), 3.94 (q, 2H, J = 5.4 Hz, –CH₂), 4.99 (s, 1H, –CH), 6.62 (d, 1H, J = 3.2 Hz, ArH), 6.65 (d, 1H, J = 2.4 Hz, ArH), 6.77 (s, 1H, ArH), 8.97 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 14.6, 18.5, 26.7, 29.8, 32.5, 33.5, 40.1, 50.8, 55.5, 56.3, 59.3, 103.3, 109.0, 111.3, 112.4, 117.3, 136.6, 144.5, 150.5, 152.0, 153.0, 167.7, 194.3; MS: m/z = 399 [M]⁺.

Ethyl 2,7,7-trimethyl-5-oxo-4-(1-phenylprop-1-en-2-yl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (6e). Yellow solid; M.p: 218–220 °C; yield: 90% (0.341 g); IR (KBr): υ 3281, 3211, 3080, 2956, 1699 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 1.00 (s, 3H, –CH₃), 1.03 (s, 3H, –CH₃), 1.22 (t, 3H, J = 7.2 Hz, –CH₃), 1.76 (s, 3H, –CH₃), 2.10 (d, 1H, J = 8.0 Hz, –CH₂), 2.22 (d, 1H, J = 8.2 Hz, –CH₂), 2.27 (s, 3H, –CH₃), 2.30 (d, 1H, J = 6.6 Hz, –CH₂), 2.42 (d, 1H, J = 8.4 Hz, –CH₂), 4.10 (q, 2H, J = 6.8 Hz, –CH₂), 4.46 (s, 1H, –CH), 6.21 (s, 1H, –CH), 7.13 (d, 2H, J = 7.4 Hz, ArH), 7.17 (t, 1H, J = 7.2 Hz, ArH), 7.29 (d, 2H, J = 7.6 Hz, ArH), 8.96 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 14.8, 16.2, 18.6, 26.9, 29.7, 32.4, 50.9, 59.4, 102.7, 108.6, 125.3, 126.3, 128.6, 129.0, 138.4, 142.8, 145.6, 150.6, 167.6, 194.9; MS: m/z = 379 [M]⁺.

Ethyl 2-amino-4-(2,4-dinitrophenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (7a). Brown solid; M.p: 247–249 °C; yield: 98% (0.394 g); IR (KBr): υ 3311, 3267, 3197, 3108, 3007, 1620 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 1.93 (t, 6H, J = 5.8 Hz, –CH₂), 2.17 (t, 3H, J = 6.2 Hz, –CH₃), 2.47 (q, 2H, J = 5.8 Hz, –CH₂), 4.96 (s, 1H, –CH), 7.24 (d, 1H, J = 9.6 Hz, ArH), 8.35 (d, 1H, J = 6.0 Hz, ArH), 8.86 (s, 1H, ArH), 9.36 (s, 1H, –NH), 10.19 (s, 2H, –NH₂); ¹³C NMR (100 MHz, DMSO-d₆): δ 26.9, 28.2, 29.7, 31.7, 32.6, 35.5, 104.5, 112.4, 115.4, 139.5, 144.8, 145.0, 147.2, 149.7, 162.0, 162.8, 167.6, 194.8; MS: m/z = 402 [M]⁺.

Ethyl 2-amino-4-(4-hydroxy-3-methoxyphenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (7b). White solid; M.p: 211–13 °C; yield: 93% (0.333 g); IR (KBr): υ 3423, 3279, 3201, 3069, 2946, 1696 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 2.13 (t, 3H, J = 5.2 Hz, –CH₃), 2.19 (d, 1H, J = 5.2 Hz, –CH₂), 2.37 (q, 2H, J = 7.4 Hz, –CH₂), 2.44 (t, 4H, J = 6.2 Hz, –CH₂), 2.96 (d, 1H, J = 5.4 Hz, –CH₂), 3.69 (s, 3H, –CH₃), 5.76 (s, 1H, –CH), 6.54 (s, 2H, –NH₂), 6.70 (d, 1H, J = 2.0 Hz, ArH), 6.74 (s, 1H, ArH), 6.74 (s, 1H, –OH), 6.79 (d, 1H, J = 1.6 Hz, ArH), 8.52 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 21.0, 29.1, 32.1, 35.4, 55.4, 55.9, 60.6, 100.5, 101.4, 113.1, 115.0, 116.5, 121.0, 136.4, 144.5, 147.0, 167.4, 174.8, 195.9; MS: m/z = 358 [M]⁺.

Ethyl 2-amino-4-(4-(dimethylamino)phenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (7c). Yellow solid; M.p: 259–261 °C; yield: 93% (0.330 g); IR (KBr): υ 3269, 3174, 3062, 2921, 1641 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 1.90 (m, 2H, –CH₂), 2.20 (t, 3H, J = 5.2 Hz, –CH₃), 2.35 (q, 2H, J = 6.6 Hz, –CH₂), 2.44 (t, 2H, J = 6.8 Hz, –CH₂), 2.48 (t, 2H, J = 8.0 Hz, –CH₂), 2.72 (s, 3H, –CH₃), 2.89 (s, 3H, –CH₃), 4.78 (s, 1H, –CH), 6.54 (d, 1H, J = 8.8 Hz, ArH), 6.60 (d, 1H, J = 8.8 Hz, ArH), 6.87 (d, 1H, J = 8.4 Hz, ArH), 6.95 (d, 1H, J = 8.8 Hz, ArH), 7.72 (s, 2H, –NH₂), 9.34 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 20.8, 21.3, 26.8, 29.8, 31.0, 31.3, 35.9, 37.3, 112.2, 112.7, 112.9, 113.4, 127.3, 128.4, 136.3, 148.6, 149.0, 151.2, 195.2; MS: m/z = 355 [M]⁺.

Ethyl 2-amino-4-(biphenyl-4-yl)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (7d). Orange solid; M.p: 191–193 °C; yield: 97% (0.404 g); IR (KBr): υ 3305, 3080, 3030 2955, 1690 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.88 (s, 3H, –CH₃), 1.02 (s, 3H, –CH₃), 1.17 (t, 3H, J = 7.0 Hz, –CH₃), 2.02 (d, 1H, J = 8.0 Hz, –CH₂), 2.20 (d, 1H, J = 8.0 Hz, –CH₂), 2.30 (s, 2H, –NH₂), 2.34 (d, 1H, J = 7.4 Hz, –CH₂), 2.46 (d, 1H, J = 8.4 Hz, –CH₂), 4.02 (q, 2H, J = 7.2 Hz, –CH₂), 4.90 (s, 1H, –CH), 7.25 (d, 2H, J = 8.4 Hz, ArH), 7.33 (t, 1H, J = 6.0 Hz, ArH), 7.42 (d, 2H, J = 8.0 Hz, ArH), 7.50 (d, 2H, J = 8.4 Hz, ArH), 7.61 (d, 2H, J = 8.4 Hz, ArH), 9.10 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 14.6, 18.8, 27.1, 29.5, 32.7, 36.1, 50.7, 59.6, 103.9, 110.3, 126.6, 127.0, 127.5, 128.5, 129.3, 138.1, 140.6, 145.5, 147.4, 150.1, 167.3, 194.8; MS: m/z = 416 [M]⁺.

Diethyl 4,4′-(1,4-phenylene)bis(2-amino-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate) (7e). White solid; M.p: 248–250 °C; yield: 91% (0.548 g); IR (KBr): υ 3491, 3427, 3310, 2960, 1691 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.82 (s, 6H, –CH₃), 1.01 (t, 6H, J = 7.2 Hz, –CH₃), 1.02 (s, 6H, –CH₃), 2.03 (d, 2H, J = 8.0 Hz, –CH₂), 2.27 (d, 2H, J = 8.0 Hz, –CH₂), 2.43 (d, 2H, J = 8.6 Hz, –CH₂), 2.57 (d, 2H, J = 8.6 Hz, –CH₂), 3.93 (q, 4H, J = 8.2 Hz, –CH₂), 4.40 (s, 2H, –CH), 6.94 (s, 4H, ArH), 7.51 (s, 4H, –NH₂), 9.14 (s, 2H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 14.5, 26.4, 29.3, 32.3 50.3, 59.1, 78.2, 97.4, 106.8, 115.9, 127.4, 132.8, 159.6, 162.4, 196.2; MS: m/z = 602 [M]⁺.

Ethyl 2-amino-4-(2,5-dimethoxyphenyl)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (7f). White solid; M.p: 182–184 °C; yield: 96% (0.384 g); IR (KBr): υ 3424, 3314, 2956, 1689 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.86 (s, 3H, –CH₃), 1.03 (s, 3H, –CH₃), 1.10 (t, 3H, J = 7.0 Hz, –CH₃), 2.00 (d, 1H, J = 8.0 Hz, –CH₂), 2.26 (d, 1H, J = 8.0 Hz, –CH₂), 2.36 (d, 1H, J = 8.8 Hz, –CH₂), 2.57 (d, 1H, J = 8.8 Hz, –CH₂), 3.62 (s, 3H, –CH₃), 3.67 (s, 3H, –CH₃), 3.91 (q, 2H, J = 5.2 Hz, –CH₂), 4.49 (s, 1H, –CH), 6.67 (d, 1H, J = 3.2 Hz, ArH), 6.71 (d, 1H, J = 3.2 Hz, ArH), 6.77 (s, 1H, ArH), 7.48 (s, 2H, –NH₂), 9.37 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 14.7, 26.3, 29.4, 32.1, 32.2, 50.5, 55.6, 56.2, 59.0, 76.2, 111.6, 112.3, 113.5, 118.2, 133.8, 152.3, 152.6, 160.1, 163.0168.8, 196.2; MS: m/z = 400 [M]⁺.

Ethyl 2-amino-7,7-dimethyl-5-oxo-4-(1-phenylprop-1-en-2-yl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (7g). Yellow solid; M.p: 127–129 °C; yield: 90% (0.342 g); IR (KBr): υ 3275, 3181, 3063, 2959, 1647 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 1.00 (s, 6H, –CH₃), 1.04 (s, 3H, –CH₃), 1.10 (t, 3H, J = 5.6 Hz, –CH₃), 2.11 (d, 2H, J = 7.8 Hz, –CH₂), 2.23 (d, 2H, J = 7.8 Hz, –CH₂), 2.33 (q, 2H, J = 8.6 Hz, –CH₂), 2.57 (s, 1H, –CH), 2.47 (s, 2H, –NH₂), 6.17 (s, 1H, –CH), 7.08 (d, 2H, J = 7.6 Hz, ArH), 7.16 (d, 2H, J = 7.2 Hz, ArH), 7.29 (d, 1H, J = 7.6 Hz, ArH), 9.19 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 18.1, 19.0, 26.8, 28.6, 29.7, 32.5, 36.8, 42.5, 50.9, 111.3, 119.6, 123.3, 125.5, 125.9, 126.3, 127.7, 128.1, 128.5, 128.9, 129.5, 138.5, 142.5, 144.9, 144.9, 195.2; MS: m/z = 380 [M]⁺.

Ethyl 2-amino-4-(4-hydroxy-3-methoxyphenyl)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (7h). Yellow solid; M.p: 281–283 °C; yield: 94% (0.363 g); IR (KBr): υ 3414, 3274, 3194, 3070, 2962, 1687 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆): δ 0.88 (s, 6H, –CH₃), 1.01 (t, 3H, J = 7.2 Hz, –CH₃), 2.02 (d, 2H, J = 8.0 Hz, –CH₂), 2.19 (q, 2H, J = 8.0 Hz, –CH₂), 2.33 (d, 2H, J = 8.4 Hz, –CH₂), 2.46 (s, 2H, –NH₂), 3.65 (s, 3H, –CH₃), 4.71 (s, 1H, –CH), 6.52 (d, 1H, J = 1.6 Hz, ArH), 6.53 (s, 1H, ArH), 6.70 (d, 1H, J = 2.0 Hz, ArH), 8.58 (s, 1H, –OH), 9.23 (s, 1H, –NH); ¹³C NMR (100 MHz, DMSO-d₆): δ 26.8, 29.6, 32.3, 32.6, 50.8, 55.9, 78.7, 112.2, 112.6, 115.2, 120.2, 139.0, 144.8, 147.1, 149.4, 159.5, 194.9, 196.4; MS: m/z = 386 [M]⁺.

Acknowledgements

The authors gratefully acknowledge the Bu-Ali Sina University Research Council and Center of Excellence in Development of Environmentally Friendly Methods for Chemical Synthesis (CEDEFMCS) for providing support to this work.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4ra09117e

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