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Communication

Quinoline Hydroxyalkylations from Iron-Catalyzed, Visible-Light-Driven Decarboxylations

by
Zita G. Ríos-Malváez
1,
Nelly González-Rivas
1,2 and
Erick Cuevas-Yañez
1,2,*
1
Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM, Carretera Toluca-Atlacomulco Km. 14.5, Toluca 50200, Estado de México, Mexico
2
Facultad de Química, Universidad Autónoma del Estado de México, Paseo Colón Esq, Paseo Tollocan, Toluca 50120, Estado de México, Mexico
*
Author to whom correspondence should be addressed.
Catalysts 2024, 14(12), 916; https://doi.org/10.3390/catal14120916
Submission received: 21 October 2024 / Revised: 20 November 2024 / Accepted: 28 November 2024 / Published: 12 December 2024
(This article belongs to the Special Issue Photocatalyzed and Electrochemical Processes for a Cleaner Environment)
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Abstract

:
One of the current challenges in organic synthesis is the direct alkylation of heterocyclic systems with a minimal impact on the environment. In this report, 4-substituted hydroxyalkyl quinolines were obtained by treating quinoline with different alkyl carboxylic acids in the presence of catalytic amounts of an iron (III) chloride–phenanthroline complex. The reaction was mediated by blue LED light under acidic conditions as a cleaner alternative to conventional heating, reducing the use of harmful substances.

1. Introduction

A significant trend that has come to the fore in recent years is visible-light photocatalysis applied to organic synthesis [1,2,3,4,5]. According to this concept, light energy drives pairs of chemical reactions that involve electron transfer, promoting both redox and radical reactions [6]. In these processes, the photocatalyst plays an essential role. A photocatalyst is defined as a material that induces a chemical reaction by providing the necessary energy from photo-irradiation. Typically, photocatalysts are based on ruthenium or iridium compounds. However, their relative scarcity has led to the use of earth-abundant metals in photocatalysis [7,8,9]. From this group, iron is emerging as an alternative source of photocatalysts, and some reports describe successful applications of these compounds in oxidations for the treatment of pollutants, among others [10,11,12].
In this regard, the use of catalytic iron compounds has been successfully applied in photoinduced oxidations [13,14,15,16], thiocarboxylations [17], polymerizations [18,19,20], hydrosilylations [21], decarboxylations [22,23], C-H activations [24], acyloxylations [25] and alkylations [26], showing a high potential in organic synthesis.
These features motivated us to re-examine a previous work by Sugimori and Yamada, who performed a selective methylation on the quinoline ring from acetic acid under acidic conditions using stoichiometric amounts of Fe2(SO4)3 as a decarboxylating agent at different wavelengths [27]. On the other hand, Jin and coworkers have described efficient iron-photocatalyzed couplings to pyridine and quinoline derivatives from decarboxylation reactions carried out under basic conditions [22,23]. These conditions allow a new approach to the Minisci reaction which enables the alkylation of heterocyclic compounds by nucleophilic radical substitution, in particular the cross-dehydrogenative C-C coupling of N-heterocycles with ethers under mild conditions [28].
Moreover, among the Minisci-type reactions, hydroxyalkylations on aromatic rings represent a kind of transformations that has been less studied, which represents an interesting synthetic approach compared to electrophilic acid-mediated hydroxyalkylations, considered the most important synthetic method to obtain hydroxyalkyl arenes [29,30,31,32].
With these elements, we initially assumed that similar quinoline alkylation products would be obtained from visible-light photo-induced, iron-catalyzed decarboxylation on quinoline rings in an acidic medium. This report is the first to provide insight into the formation of 4-hydroxyalkyl quinolines under these conditions.

2. Results and Discussion

In the search for optimal conditions, the reaction between quinoline 1 and propionic acid was chosen as a model reaction in such a way that the influence of 4 parameters (iron catalyst, acid, sacrificial oxidant and reaction time) on the yield could be observed. Thus, treatment of these reagents under visible light irradiation, provided by 37 W 410–456 nm LED, afforded 1-quinolin-4-yl-ethanol 2 (Scheme 1).
The results are summarized in Table 1 and show some interesting details. Initial experiments using FeCl3·6H2O were unsuccessful. However, the change to the iron (III) chloride—phenanthroline complex, Fe(phen)Cl3·H2O [33], as the catalyst yielded compound 2. In addition, we found that both acid and sacrificial oxidant play an important role in these transformations, as depicted in Table 1, entries 7–9. The use of H2SO4 and KIO3 provided the best yields, reaching up to 81% after 96 h.
The effect of solvent was also investigated. In this respect, the use of DMSO produced dimethyl sulfone as the only reaction product, indicating that solvent oxidation occurs first. On the other hand, the use of other solvents such as acetonitrile proved fruitless, as some reagents were insoluble in these systems.
The structure of quinoline 2 has been determined by NMR spectroscopic techniques and shows a signal pattern in the 1H NMR spectrum, as seen in Figure 1. A doublet signal at δ 1.66 ppm corresponding to methyl hydrogens is correlated with a quartet signal at δ 5.70 ppm associated with methyne hydrogen attached to the quinoline C4 position, similar to that described in earlier articles [34,35]. This signal arrangement allows to establish the presence of a hydroxyethyl moiety substituting the C4 position on quinoline ring. The remaining spectroscopic analysis corroborated the proposed structure for hydroxyethyl quinoline 2.
This protocol was extended to other carboxylic acids (see Scheme 2), providing the respective hydroxyalkyl quinolines 2–4 after 48 h in 30–50% yields, as shown in Table 2.
The formation of these kinds of compounds has led us to propose a reaction mechanism, illustrated in Scheme 3. The interaction between the iron complex and the carboxylic acid 5 produces an iron carboxylate 6, which undergoes a decarboxylation promoted by blue light (456 nm) to generate an alkyl radical 7, which reacts with protonated quinoline to afford nitrogen-centered alkyl quinolyl radical cation 8, which is oxidized by Fe(III) species to cation 9 [36,37]. Acidic conditions promote free radical hydrogen abstraction at the C4-benzylic position of the quinoline and the resulting radical 11 is also oxidized to the respective cation 12, which is finally hydrolyzed to hydroxyalkyl quinoline 13. During this reaction sequence, the Fe(II) cation formed in previous steps is oxidized to Fe(III) by the action of KIO3 completing the catalytic cycle.
An outstanding fact that is noticed in this process is the relatively high degree of regioselectivity. In this respect, only the 4-substituted product was isolated, while substitution at the 2-position of quinoline was not detected under any of the conditions studied. A plausible explanation may be related to the findings on the solvent effect on radical substitution made by Hadrys and Phipps, who found that regioselectivity of Minisci-type addition to quinolines can be modulated by the solvent polarity, as polar solvents drive to 4-substituted quinolines [38].
To the best of our knowledge, these are the first examples about direct quinoline hydroxyalkylations involving both C-C bond formation and subsequent oxidation in a single process under mild conditions. This unexpected hydroxyalkylation is observed instead of typical decarboxylative alkylation for Minisci-type reactions. Worthy of mention is the combined use of photocatalytic and acidic conditions to give the titled compounds in contrast to 2-alkyl quinolines obtained under photocatalytic basic conditions as informed in precedent reports [22,23,27,39]. Thus, the selectivity in the product formation can be modulated by a simple pH change. In addition, Fe(phen)Cl3·H2O was found to be effective in catalyzing carboxylic acid decarboxylations to induce alkyl radical formation under visible light irradiation through an easy procedure with promising future applications. The results presented here are in agreement with those detailed by our group [40] using iron-bpy complexes, which shows a trend that deserves to be studied in depth.
The process described in this communication has some features worthy of consideration that make it an alternative method to the existing ones for the preparation of 4-substituted hydroxyalkyl quinolines, since it does not require organometallic reagents, specific temperatures, inert atmospheres, solvents, and additional steps. On the other hand, the highly aromatic nature of the quinoline core makes hydroxyalkylation based on electrophilic substitution difficult. This report highlights the direct, selective generation of a C-C bond at an “inactivated” 4-position as an alternative synthetic protocol, which is also important due to the presence of 4-substituted quinolines as a wide group of drugs and natural products [41,42,43].

3. Experimental Method

The starting materials were purchased from Aldrich Chemical Co. (Milwaukee, WI, USA) and were used without further purification. Solvents were distilled before use. Silica plates of 0.20 mm thickness were used for thin-layer chromatography. Melting points were determined with a Krüss Optronic melting point apparatus, and they are uncorrected. 1H and 13C NMR spectra were recorded using a Bruker (Billerica, MA, USA) Avance 300-MHz; the chemical shifts (δ) are given in ppm relative to TMS as internal standard (0.00). For analytical purposes, the mass spectra were recorded on a Shimadzu (Kyoto, Japan) GCMS-QP2010 Plus in the EI mode, 70 eV, 200 °C via direct inlet probe. Only the molecular and parent ions (m/z) are reported. IR spectra were recorded on a Bruker Tensor 27 equipment. Fe(phen)Cl3·H2O was synthesized according to a previous report [28].
  • General procedure of synthesis of 4-hydroxyalkyl quinolines
The corresponding carboxylic acid (5 mL) was added to a solution of quinoline (0.129 g, 1 mmol) and H2SO4 (0.1 mL) in H2O (25 mL). The mixture was treated successively with Fe(phen)Cl3·H2O (0.036 g, 0.1 mmol) and a 0.1 M aqueous solution of KIO3 (10 mL). The reaction mixture was sparged with nitrogen and degassed. The reaction mixture was stirred and irradiated with commercial 36 W 410–456 nm LEDs under a mini fan at room temperature for 48 h. A 1 M aqueous solution of K2CO3 (10 mL) was added; the product was extracted with CH2Cl2 (3 × 40 mL), the organic phases were joined and dried over Na2SO4, the solvent was removed under reduced pressure, and the final product was purified by column chromatography (SiO2, CH2Cl2/AcOEt 8:2).
  • 1-Quinolin-4-yl-ethanol (2)
Quinoline 1 and propionic acid afforded 1-Quinolin-4-yl-ethanol 2 as a white solid (40%) m.p. 120 °C (lit. 119–121 °C) [17]. IR (ATR, cm−1) νmax: 3172, 2960, 2922, 2854, 1590, 1572, 1509, 1465 cm−1. 1H NMR (300 MHz, CDCl3) δ 8.83 (d, J = 4.5 Hz, 1H), 8.11 (dd, J = 8.4, 0.7 Hz, 0H), 8.02 (dd, 2H), 7.69 (dd, J = 8.4, 6.9, 1.4 Hz, 1H), 7.59 (d, J = 4.5 Hz, 1H), 7.55 (dd, J = 8.3, 6.8, 1.4 Hz, 1H), 5.66 (q, J = 6.5 Hz, 1H), 1.65 (d, J = 6.5 Hz, 3H). 13C NMR (75 MHz, CDCl3) δ 151.60 (C), 150.58 (CH), 148.19 (C), 130.31 (CH), 129.23 CH), 126.68 (CH), 125.51 (C), 123.10 (CH), 116.79 (CH), 66.22 (CH), 24.77 (CH3). MS [EI+] m/z (%): 173 [M]+ (5), 172 [M − H]+ (30), 158 [M-CH3]+ (100), 129 [M-C2H4O]+ (70).
  • 3-Quinolin-4-yl-heptan-3-ol (3)
Quinoline 1 and 2-ethylhexanoic acid afforded 3-Quinolin-4-yl-heptan-3-ol 3 as a pale-yellow oil (27%). IR (ATR, cm−1) νmax: 3172, 2960, 2922, 2854, 1590, 1572, 1509, 1465 cm−1. 1H NMR (300 MHz, CDCl3) δ 8.90 (d, J = 4.4 Hz, 1H), 8.20 (d, J = 8.5 Hz, 1H), 8.11 (d, J = 8.5 Hz, 1H), 7.76 (dd, J = 8.5, 1.5 Hz, 1H), 7.63 (dd, J = 8.5, 1.5 Hz, 1H), 7.22 (dd, J = 4.5, 1.1 Hz, 1H), 1.98 (q, 2H), 1.82 (q, 2H), 1.56 (m, 2H), 1.43 (m, 2H), 0.96 (t, 3H), 0.88 (t, 3H). 13C NMR (75 MHz, CDCl3) δ 149.82 (C), 148.15 (CH), 148.06 (C), 129.98 (CH), 129.83 (CH), 127.33 (CH), 126.66 (C), 123.38 (CH), 120.79 (CH), 47.04 (CH2), 44.94 (CH2), 31.60 (CH2), 25.29 (CH2), 13.94 (CH3), 11.82 (CH3). MS [EI+] m/z (%): 243 [M]+ (5), 241 [M-C2H7]+ (100), 186 [M-C4H9]+ (90). Anal. Calcd. for C16H21NO (%): C, 78.97; H, 8.70; N, 5.76; found: C, 79.02; H, 8.78; N, 5.74.
  • 1-Quinolin-4-yl-nonan-1-ol (4)
Quinoline 1 and decanoic acid afforded 1-Quinolin-4-yl-nonan-1-ol 4 as a pale-yellow oil (25%). IR (ATR, cm−1) νmax: 3172, 2960, 2922, 2854, 1590, 1572, 1509, 1465 cm−1. 1H NMR (300 MHz, CDCl3) δ 8.91 (d, J = 4.5 Hz, 1H), 8.21–8.14 (m, 1H), 7.92 (dd, J = 8.4, 1.0 Hz, 1H), 7.76–7.68 (m, 1H), 7.60–7.53 (m, 2H), 5.63 (t, J = 7.0 Hz, 1H), 1.87 (t, 2H), 1.27 (s, 12H), 0.93 (s, 3H). 13C NMR (75 MHz, CDCl3) δ 150.29 (C), 150.16 (CH), 147.76 (C), 129.31 (CH), 126.65 (CH), 125.72 (C), 123.39 (CH), 116.67 (CH), 67.50 (CH), 34.11 (CH2), 32.03 (CH2), 29.59 (CH2), 29.49 (CH2), 29.37 (CH2), 25.14 (CH2), 22.82 (CH2), 14.26 (CH3). MS [EI+] m/z (%): 271 [M]+ (5), 158 [M-C8H17]+ (100). Anal. Calcd. for C18H25NO (%): C, 79.66; H, 9.28; N, 5.16; found: C, 79.59; H, 9.35; N, 5.19.

4. Conclusions

In conclusion, these hopeful results reveal a considerable potential use which deserve further intensive investigations. The reactions herein described avoid the use of harmful heavy metal-based chemicals by using only catalytic amounts of more environmentally friendly iron(III) chloride under visible-light irradiation as an alternative energy source to replace conventional and polluting heating used in traditional organic synthetic procedures. These characteristics suggest that this route to hydroxyalkyl quinolines will enjoy widespread application.

Author Contributions

Conceptualization E.C.-Y.; methodology, Z.G.R.-M.; software, N.G.-R.; validation, Z.G.R.-M. and N.G.-R.; formal analysis, N.G.-R. and Z.G.R.-M.; investigation, Z.G.R.-M. and E.C.-Y.; resources, E.C.-Y.; data curation, N.G.-R. and Z.G.R.-M.; writing—original draft preparation, E.C.-Y.; writing—review and editing, E.C.-Y.; visualization, Z.G.R.-M. and E.C.-Y.; supervision, E.C.-Y.; project administration, E.C.-Y.; funding acquisition, E.C.-Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by CONAHCYT-Mexico, fellowship for Z.G.R.-M. (CVU: 860116).

Data Availability Statement

Data are contained within the article.

Acknowledgments

Financial support from CONAHCYT (fellowship for Z.G.R.-M., CVU: 860116) is gratefully acknowledged. The authors would like to thank N. Zavala, A. Nuñez, L. Triana and M. C. Martínez for the technical support.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 14 00916 sch001
Scheme 1. Synthesis of hydroxyethyl quinoline 2 under photocatalytic conditions.
Scheme 1. Synthesis of hydroxyethyl quinoline 2 under photocatalytic conditions.
Catalysts 14 00916 sch001
Catalysts 14 00916 g001
Figure 1. 1H NMR spectrum of quinoline 2.
Figure 1. 1H NMR spectrum of quinoline 2.
Catalysts 14 00916 g001
Catalysts 14 00916 sch002
Scheme 2. Synthesis of hydroxyethyl quinolines.
Scheme 2. Synthesis of hydroxyethyl quinolines.
Catalysts 14 00916 sch002
Catalysts 14 00916 sch003
Scheme 3. Mechanism of formation of hydroxyethyl quinolines.
Scheme 3. Mechanism of formation of hydroxyethyl quinolines.
Catalysts 14 00916 sch003
Table 1. Synthesis of hydroxyethyl quinoline 2 under photocatalytic conditions.
Table 1. Synthesis of hydroxyethyl quinoline 2 under photocatalytic conditions.
EntryIron CompoundAcid SourceSacrificial OxidantReaction Time, h% Yield
1FeCl3·6H2Ononenone120
2FeCl3·6H2OnoneKIO3120
3FeCl3·6H2OH2SO4none120
4FeCl3·6H2OH2SO4KIO3120
5Fe(phen)Cl3·H2Ononenone120
6Fe(phen)Cl3·H2OnoneKIO3120
7Fe(phen)Cl3·H2OTFAKIO3120
8Fe(phen)Cl3·H2OH2SO4NaIO4125
9Fe(phen)Cl3·H2OH2SO4KIO31227
10Fe(phen)Cl3·H2OH2SO4KIO32037
11Fe(phen)Cl3·H2OH2SO4KIO34850
12Fe(phen)Cl3·H2OH2SO4KIO37278
13Fe(phen)Cl3·H2OH2SO4KIO39681
Table 2. Synthesis of hydroxyethyl quinolines.
Table 2. Synthesis of hydroxyethyl quinolines.
CompoundR1R2% Yield
2CH3H50
3CH3(CH2)3CH3CH231
4CH3(CH2)7H30
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Ríos-Malváez, Z.G.; González-Rivas, N.; Cuevas-Yañez, E. Quinoline Hydroxyalkylations from Iron-Catalyzed, Visible-Light-Driven Decarboxylations. Catalysts 2024, 14, 916. https://doi.org/10.3390/catal14120916

AMA Style

Ríos-Malváez ZG, González-Rivas N, Cuevas-Yañez E. Quinoline Hydroxyalkylations from Iron-Catalyzed, Visible-Light-Driven Decarboxylations. Catalysts. 2024; 14(12):916. https://doi.org/10.3390/catal14120916

Chicago/Turabian Style

Ríos-Malváez, Zita G., Nelly González-Rivas, and Erick Cuevas-Yañez. 2024. "Quinoline Hydroxyalkylations from Iron-Catalyzed, Visible-Light-Driven Decarboxylations" Catalysts 14, no. 12: 916. https://doi.org/10.3390/catal14120916

APA Style

Ríos-Malváez, Z. G., González-Rivas, N., & Cuevas-Yañez, E. (2024). Quinoline Hydroxyalkylations from Iron-Catalyzed, Visible-Light-Driven Decarboxylations. Catalysts, 14(12), 916. https://doi.org/10.3390/catal14120916

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