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The green synthesis of N-hydroxyethyl-substituted 1,2,3,4-tetrahydroquinolines with acidic ionic liquid as catalyst

  • Hui Guo EMAIL logo , Haonan Li , Xiaoyue Cao , Zuoyao Wang , Qian Zhang and Guobao Zhang
Published/Copyright: October 26, 2020
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Green Processing and Synthesis
From the journal Green Processing and Synthesis Volume 9 Issue 1

Abstract

N-Hydroxyethyl-substituted 1,2,3,4-tetrahydroquinolines were synthesized by the reaction of 2-(phenylamino)ethanol with unsaturated ketone catalyzed by acidic ionic liquid N-methyl-2-pyrrolidonium dihydrogen phosphate [NMPH]H2PO4, obviating the need for toxic and expensive catalysts. The acidic ionic liquid not only showed superior performance over H3PO4 but also was stable and could be reused at least five times with a slight loss of activity. It provided a straightforward and efficient protocol for the synthesis of 1,2,3,4-tetrahydroquinoline derivatives.

Keywords: N-hydroxyethyl substituted 1,2,3,4-tetrahydroquinoline; ionic liquid; 2-(phenylamino)ethanol; unsaturated ketone

1 Introduction

1,2,3,4-Tetrahydroquinoline derivatives have attracted continuous attention due to their important physiological and biological properties [1,2]. A great deal of protocols for the preparation of 1,2,3,4-tetrahydroquinoline derivatives have been developed. Diels–Alder reaction catalyzed by Lewis acids (e.g., Yb(OTf)3) is the most useful protocol for the synthesis of 1,2,3,4-tetrahydroquinoline derivatives [3,4,5]. In addition to the classical method, Khan et al. found that 1,2,3,4-tetrahydroquinoline derivatives could also be synthesized by the Povarov reaction using [Fe2(SO4)]3·xH2O as a catalyst [6]. Li et al. developed a domino reaction of aromatic amines, cyclic enol ethers and hemiacetals catalyzed by InCl3 for the synthesis of 1,2,3,4-tetrahydroquinoline derivatives [7]. However, these metal-based catalysts own their drawbacks such as toxicity, corrosiveness and expensive cost. Recently, Chen and Li reported that the 1,2,3,4-tetrahydroquinoline derivatives could be prepared using acidic cation-exchange resin as a catalyst [8], and Wang and coworkers found that 2-methyl-4-anilino-1,2,3,4-tetrahydroquinoline derivatives could be synthesized by the tandem cyclization between anilines and N-vinyl amides with radical cation salt as a catalyst [9]. However, all the products obtained by the methods were a mixture of cis- and trans-isomers. Therefore, it is very necessary to develop effective and economical methodology for the synthesis of 1,2,3,4-tetrahydroquinoline derivatives.

Ionic liquids have emerged as green catalysts and reaction media in recent years [10,11,12,13]. They have been applied in many reactions such as the synthesis of methyl caprylate [14], extraction of Luteolin from Peanut Shells [15] and three-component cyclic condensation of aromatic aldehydes, malononitrile and dimedone [16]. To the best of our knowledge, relevant reports about the synthesis of 1,2,3,4-tetrahydroquinoline derivatives with ionic liquids have been demonstrated by several examples. Zhou et al. reported the regioselective reduction of quinolines in ionic liquid [BMIM]PF6 with Ru/N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine as a catalyst [17]. Li et al. found that quinolines could also be regioselectively reduced in ionic liquid [Rmim][p-CH3C6H4SO3] using [RuCl2(TPPTS)2] as a catalyst [18]. However, the synthesis of 1,2,3,4-tetrahydroquinoline derivatives catalyzed by ionic liquid still is an intriguing challenge. Herein, we, for the first time, present a straightforward and efficient protocol for the synthesis of novel 1,2,3,4-tetrahydroquinoline derivatives using acidic ionic liquid as a catalyst.

2 Materials and methods

2.1 General

1H and 13C NMR spectra were recorded in CDCl3 with a Bruker AVANCE DMX 500 spectrometer at 100 and 400 MHz, respectively. Chemical shifts are reported in ppm (δ), relative to tetramethylsilane (TMS) as the internal standard. IR spectra were measured with a Nicolet Nexus FTIR 670 spectrophotometer. All reactions were carried out with efficient stirring in a round bottom flask at 37°C, unless otherwise stated, and monitored by TLC. MVK was distilled before use, and other chemicals were obtained from commercial suppliers and were used without further purification. The acidic ionic liquid [NMPH]H2PO4 was prepared using an earlier reported procedure [19].

2.2 Typical procedure for the synthesis of 2-(phenylamino)ethanol

To a mixture of aniline (0.1 mol, 9.3 g) and 2-chloroethanol (0.05 mol, 4 g), Et3N (15 mL) was added. Then, the mixture was heated to reflux and stirred for 8 h. After the completion of reaction, the mixture was neutralized with the saturated NaHCO3 solution, extracted with ethyl acetate and dried over anhydrous sodium sulfate. Then, the solvent was evaporated, and the product was isolated by column chromatography. A yellow oil; 1H NMR (400 MHz, CDCl3): δ = 3.27 (t, J = 4 Hz, 2H), 3.79 (t, J = 4 Hz, 2H), 6.63–6.76 (m, 3H), 7.16–7.20 (m, 2H); 13C NMR (100 MHz, CDCl3): δ = 46.1, 61.0, 113.3, 117.9, 129.3, 148.0.

2.3 Typical procedure for the synthesis of N-hydroxyethyl substituted 1,2,3,4-tetrahydroquinolines

To a mixture of 2-(phenylamino)ethanol (0.5 mmol, 68 mg) in [NMPH]H2PO4 (0.5 mmol), MVK (0.5 mmol, 35 mg) and CH2Cl2 (1 mL) were added. After addition, the mixture reacted for 12 h at 37°C. The reaction was monitored by TLC [solvent system–PE:EA (1:1)]. After the completion of reaction, the reaction mixture was extracted with CH2Cl2 for several times. The solvent was evaporated, and the product was isolated by column chromatography. Yellow oil; IR (neat): 3384, 2956, 2929, 2868, 1602, 1503, 1338, 1287, 1047 cm−1; 1H NMR (400 MHz, CDCl3): δ = 1.29 (d, J = 7.2 Hz, 3H), 1.69–1.72 (m, 1H), 2.00–2.02 (m, 1H), 2.87–2.94 (m, 1H), 3.36–3.45 (m, 2H), 3.46–3.48 (m, 2H), 3.83 (t, J = 5.6 Hz, 2H), 6.63–6.70 (m, 2H), 7.06 (t, J = 7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ = 22.5, 29.6, 30.8, 46.9, 54.1, 59.7, 111.3, 116.4, 126.9, 127.9, 128.2, 145.0; HRMS: calculated for C12H17NO (M+) 191.131, found 191.131.

3 Results and discussion

3.1 Effects of ionic liquids

Initial studies were carried out using the reaction of 2-(phenylamino)ethanol with methyl vinyl ketone (MVK) as a model reaction. Table 1 presents the effect of different ionic liquids on the reaction. In a first set of experiments, ionic liquids of the general [cation][BF4] and [BMIM]PF6 were tested as catalysts and a reaction medium (Table 1, entries 1–3). The results showed that the 1,2,3,4-tetrahydroquinoline derivative could not be obtained in these ionic liquids. To obtain 1,2,3,4-tetrahydroquinoline derivative, some acidic ionic liquids were used to catalyze the reaction (Table 1, entries 4–7). Although the acidic ionic liquids could promote the reaction and produce the corresponding 1,2,3,4-tetrahydroquinoline derivative, the best yield was only 30% when ionic liquid [NMPH]H2PO4 was used as a catalyst (Table 1, entry 7).

Table 1

The effect of solvent on the reaction

EntryIonic liquidYieldb (%)
1[BMIM]BF40a
2[BMIM]PF60a
3[OMIM]BF40a
4[HMIM]HSO412a
5[BMIM]HSO418a
6[NMPH]HSO419a
7[NMPH]H2PO430a
  1. a

    Reaction conditions: 0.5 mmol MVK, 0.5 mmol 2-(phenylamino)ethanol, 0.5 mmol ionic liquid, 37°C, 24 h.

  2. b

    Yield determined by HPLC.

Although better result could be obtained in ionic liquid [NMPH]H2PO4, the result still could not meet our needs. To obtain higher yield, the reaction of 2-(phenylamino)ethanol with MVK was carried out in the ionic liquid/solvent two phase system. It was found that the 1,2,3,4-tetrahydroquinoline derivative could not be produced in [NMPH]H2PO4/DMSO and [NMPH]H2PO4/DMF (Table 2, entries 1 and 2), and the reactions were less efficient in [NMPH]H2PO4/THF and other ionic liquid/solvent systems (Table 2, entries 3–8). To our delight, a promising result (89% yield) was achieved when the [NMPH]H2PO4/CH2Cl2 system was employed (Table 2, entry 10). The good result could be due to the extraction ability of CH2Cl2 for the product.

Table 2

The effect of ionic liquid/solvent two phase system on the reaction

EntryIonic liquid/solvent two-phase systemYieldb (%)
1[NMPH]H2PO4/DMSO0a
2[NMPH]H2PO4/DMF0a
3[NMPH]H2PO4/THF19a
4[NMPH]H2PO4/CH3CN27a
5[NMPH]H2PO4/Et2O25a
6[NMPH]H2PO4/acetone31a
7[NMPH]H2PO4/1,4-dioxane43a
8[NMPH]H2PO4/toluene35a
9[NMPH]H2PO4/CHCl372a
10[NMPH]H2PO4/CH2Cl289a
11CH2Cl20c
12H3PO4/CH2Cl240d
  1. a

    Reaction conditions: 0.5 mmol MVK, 0.5 mmol 2-(phenylamino)ethanol, 1 mL solvent, 0.5 mmol ionic liquid [NMPH]H2PO4, 37°C, 24 h.

  2. b

    Yield determined by HPLC.

  3. c

    Reaction conditions: 0.5 mmol MVK, 0.5 mmol 2-(phenylamino)ethanol, 1 mL solvent, 37°C, 24 h.

  4. d

    Reaction conditions: 0.5 mmol MVK, 0.5 mmol 2-(phenylamino)ethanol, 1 mL solvent, 0.5 mmol H3PO4, 37°C, 24 h.

A control experiment was designed to demonstrate that the reaction was an acidic ionic liquid-catalyzed process. In the absence of the acidic ionic liquid, the reaction of 2-(phenylamino)ethanol with MVK could not produce the 1,2,3,4-tetrahydroquinoline derivative even in CH2Cl2 (Table 2, entry 11). Moreover, the reaction with H3PO4 as a catalyst was also carried out, but the yield was significantly lower even under the same reaction conditions (Table 1, entry 12).

3.2 Effects of time

The effect of the reaction time was presented in Table 3. The yield increased as time prolonged, and the best result was obtained when the reaction was carried out for 12 h. Longer reaction time could not increase the yield.

Table 3

The effect of time on the reactionsa

EntryTime (h)Yieldb (%)
1115
2329
3551
4878
51289
62489
  1. a

    Reaction conditions: 0.5 mmol MVK, 0.5 mmol 2-(phenylamino)ethanol, 1 mL CH2Cl2, 1 mmol ionic liquid [NMPH]H2PO4, 37°C.

  2. b

    Yield determined by HPLC.

3.3 Effects of different substrates

With the optimal reaction conditions in hands, we then examined the scope and the limitation of this strategy for other structurally diverse substrates, and the results were summarized in Table 3. The reaction of 2-(phenylamino)ethanol with MVK produced 1-(2-hydroxyl-ethyl)-4-methyl-1,2,3,4-tetrahydroquinoline with high yield (Table 4, entry 1). A series of substituted 2-(phenylamino)ethanols could also react with MVK to produce the corresponding 1,2,3,4-tetrahydroquinoline derivatives (Table 4, entries 2 and 3), albeit in lower yield. 2-(3-Chlorophenylamino)ethanol reacted with sterically hindered unsaturated ketone, such as pent-1-en-3-one, and produced the 1-(2-hydroxyl-ethyl)-7-chloro-4-ethyl-1,2,3,4-tetrahydroquinoline with lower yield (Table 4, entry 4).

Table 4

The synthesis of 1,2,3,4-tetrahydroquinoline derivatives with acidic ionic liquid as catalysta

EntrySubstrate 1Substrate 2ProductYieldb (%)
1
3a89
2
3b85
3
3c80
4
3d65
5
3e78
6
3f73
7
3g85
8
3h78
  1. a

    Reaction conditions: 0.5 mmol substrate 1, 0.5 mmol substrate 2, 0.5 mmol acidic ionic liquid [NMPH]H2PO4, 1 mL CH2Cl2, 37°C, 12 h.

  2. b

    Yield determined by HPLC.

2-(2-Nitrophenylamino)ethanol was examined under the same reaction conditions, but the corresponding 1,2,3,4-tetrahydroquinoline derivatives could not be obtained (Table 4, entries 5 and 6), and it could be due to the steric effect of the substituent group. Aniline and N-ethylbenzenamine were also examined under the same reaction conditions, but the corresponding 1,2,3,4-tetrahydroquinoline derivatives could not be obtained (Table 4, entries 7 and 8). The results showed that the existence of hydroxyl in the 2-(phenylamino)ethanol moiety could have an important effect on the synthesis of 1,2,3,4-tetrahydroquinoline derivatives.

3.4 Reuse of the ionic liquid

In order to test the reuseability of [NMPH]H2PO4, the reaction of 2-(phenylamino) ethanol with MVK was repeated five times under the same reactions, and the results were presented in Table 5. The results showed that the acidic ionic liquid [NMPH]H2PO4 was stable and could be reused at least 5 times with a slight loss of activity. Graph: use this for the first paragraph in a section, or to continue after an extract.

Table 5

The recycling of [NMPH]H2PO4a

RunYieldb
189
289
389
487
587
  1. a

    Reaction conditions: 0.5 mmol MVK, 0.5 mmol 2-(phenylamino)ethanol, 1 mmol ionic liquid [NMPH]H2PO4, 1 mL CH2Cl2, 37°C, 12 h.

  2. b

    Yield determined by HPLC.

4 Conclusions

Novel N-hydroxyethyl-substituted 1,2,3,4-tetrahydroquinolines were synthesized with the acidic ionic liquid as a catalyst for the first time. The acidic ionic liquid showed superior performance over H3PO4 under the same condition, and the acidic ionic liquid could be reused for at least five times with the consistent activity. The developed protocol provided a simple and efficient alternative for the synthesis of tetrahydroquinoline derivatives.

Acknowledgements

This work was financially supported by the Excellent Youth Training Programme Foundation of Henan Academy of Sciences (200402002).

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Received: 2020-06-02
Revised: 2020-08-09
Accepted: 2020-08-23
Published Online: 2020-10-26

© 2020 Hui Guo et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/gps-2020-0056
Keywords for this article
N-hydroxyethyl substituted 1,2,3,4-tetrahydroquinoline; ionic liquid; 2-(phenylamino)ethanol; unsaturated ketone
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  23. Green synthesis and characterization of carboxymethyl guar gum: Application in textile printing technology
  24. Potential of adsorbents from agricultural wastes as alternative fillers in mixed matrix membrane for gas separation: A review
  25. Bactericidal and cytotoxic properties of green synthesized nanosilver using Rosmarinus officinalis leaves
  26. Synthesis of biomass-supported CuNi zero-valent nanoparticles through wetness co-impregnation method for the removal of carcinogenic dyes and nitroarene
  27. Synthesis of 2,2′-dibenzoylaminodiphenyl disulfide based on Aspen Plus simulation and the development of green synthesis processes
  28. Catalytic performance of the biosynthesized AgNps from Bistorta amplexicaule: antifungal, bactericidal, and reduction of carcinogenic 4-nitrophenol
  29. Optical and antimicrobial properties of silver nanoparticles synthesized via green route using honey
  30. Adsorption of l-α-glycerophosphocholine on ion-exchange resin: Equilibrium, kinetic, and thermodynamic studies
  31. Microwave-assisted green synthesis of silver nanoparticles using dried extracts of Chlorella vulgaris and antibacterial activity studies
  32. Preparation of graphene oxide/chitosan complex and its adsorption properties for heavy metal ions
  33. Green synthesis of metal and metal oxide nanoparticles from plant leaf extracts and their applications: A review
  34. Synthesis, characterization, and electrochemical properties of carbon nanotubes used as cathode materials for Al–air batteries from a renewable source of water hyacinth
  35. Optimization of medium–low-grade phosphorus rock carbothermal reduction process by response surface methodology
  36. The study of rod-shaped TiO2 composite material in the protection of stone cultural relics
  37. Eco-friendly synthesis of AuNPs for cutaneous wound-healing applications in nursing care after surgery
  38. Green approach in fabrication of photocatalytic, antimicrobial, and antioxidant zinc oxide nanoparticles – hydrothermal synthesis using clove hydroalcoholic extract and optimization of the process
  39. Green synthesis: Proposed mechanism and factors influencing the synthesis of platinum nanoparticles
  40. Green synthesis of 3-(1-naphthyl), 4-methyl-3-(1-naphthyl) coumarins and 3-phenylcoumarins using dual-frequency ultrasonication
  41. Optimization for removal efficiency of fluoride using La(iii)–Al(iii)-activated carbon modified by chemical route
  42. In vitro biological activity of Hydroclathrus clathratus and its use as an extracellular bioreductant for silver nanoparticle formation
  43. Evaluation of saponin-rich/poor leaf extract-mediated silver nanoparticles and their antifungal capacity
  44. Propylene carbonate synthesis from propylene oxide and CO2 over Ga-Silicate-1 catalyst
  45. Environmentally benevolent synthesis and characterization of silver nanoparticles using Olea ferruginea Royle for antibacterial and antioxidant activities
  46. Eco-synthesis and characterization of titanium nanoparticles: Testing its cytotoxicity and antibacterial effects
  47. A novel biofabrication of gold nanoparticles using Erythrina senegalensis leaf extract and their ameliorative effect on mycoplasmal pneumonia for treating lung infection in nursing care
  48. Phytosynthesis of selenium nanoparticles using the costus extract for bactericidal application against foodborne pathogens
  49. Temperature effects on electrospun chitosan nanofibers
  50. An electrochemical method to investigate the effects of compound composition on gold dissolution in thiosulfate solution
  51. Trillium govanianum Wall. Ex. Royle rhizomes extract-medicated silver nanoparticles and their antimicrobial activity
  52. In vitro bactericidal, antidiabetic, cytotoxic, anticoagulant, and hemolytic effect of green-synthesized silver nanoparticles using Allium sativum clove extract incubated at various temperatures
  53. The green synthesis of N-hydroxyethyl-substituted 1,2,3,4-tetrahydroquinolines with acidic ionic liquid as catalyst
  54. Effect of KMnO4 on catalytic combustion performance of semi-coke
  55. Removal of Congo red and malachite green from aqueous solution using heterogeneous Ag/ZnCo-ZIF catalyst in the presence of hydrogen peroxide
  56. Nucleotide-based green synthesis of lanthanide coordination polymers for tunable white-light emission
  57. Determination of life cycle GHG emission factor for paper products of Vietnam
  58. Parabolic trough solar collectors: A general overview of technology, industrial applications, energy market, modeling, and standards
  59. Structural characteristics of plant cell wall elucidated by solution-state 2D NMR spectroscopy with an optimized procedure
  60. Sustainable utilization of a converter slagging agent prepared by converter precipitator dust and oxide scale
  61. Efficacy of chitosan silver nanoparticles from shrimp-shell wastes against major mosquito vectors of public health importance
  62. Effectiveness of six different methods in green synthesis of selenium nanoparticles using propolis extract: Screening and characterization
  63. Characterizations and analysis of the antioxidant, antimicrobial, and dye reduction ability of green synthesized silver nanoparticles
  64. Foliar applications of bio-fabricated selenium nanoparticles to improve the growth of wheat plants under drought stress
  65. Green synthesis of silver nanoparticles from Valeriana jatamansi shoots extract and its antimicrobial activity
  66. Characterization and biological activities of synthesized zinc oxide nanoparticles using the extract of Acantholimon serotinum
  67. Effect of calcination temperature on rare earth tailing catalysts for catalytic methane combustion
  68. Enhanced diuretic action of furosemide by complexation with β-cyclodextrin in the presence of sodium lauryl sulfate
  69. Development of chitosan/agar-silver nanoparticles-coated paper for antibacterial application
  70. Preparation, characterization, and catalytic performance of Pd–Ni/AC bimetallic nano-catalysts
  71. Acid red G dye removal from aqueous solutions by porous ceramsite produced from solid wastes: Batch and fixed-bed studies
  72. Review Articles
  73. Recent advances in the catalytic applications of GO/rGO for green organic synthesis
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