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Advances in Heterocyclic Synthesis

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (31 August 2024) | Viewed by 14104

Special Issue Editor


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Guest Editor
Department of Pharmaceutical Sciences, University of Perugia Via del Liceo 1, 06100 Perugia, Italy
Interests: heterocycles; stereoselective synthesis; one-pot reactions; multicomponent reactions; organocatalytic methods; organoselenium chemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Heterocycles have a great impact in several areas of chemical research such as organic, bioorganic, medicinal and material chemistry. Such compounds are valuable ligands, auxiliaries or catalysts as well as key synthetic intermediates in organic synthesis. Moreover, heterocycles represent structural cores of bioactive natural products, pharmaceuticals, agrochemicals, polymers and materials. Given the widespread interest, a number of new methodologies for the assembling and the functionalization of heterocycles continues to appear every year in the literature. This Special Issue aims to present new developments in the field of heterocyclic chemistry. Potential topics include (but are not limited to) sustainable synthesis of heterocyclic compounds, one-pot or multicomponent reactions, synthesis of biologically relevant heterocycles.

Prof. Dr. Francesca Marini
Guest Editor

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Keywords

  • heterocycles
  • stereoselective synthesis
  • sustainable synthesis
  • one-pot reactions
  • multicomponent reactions
  • catalysis

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Published Papers (13 papers)

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14 pages, 609 KiB  
Article
Pd-Catalyzed Aromatic Dual C-H Acylations and Intramolecular Cyclization: Access to Quinoline-Substituted Hydroxyl Isoindolones
by Hongke Xu, Yuchen Yang, Fei Li and Yuzhu Yang
Molecules 2024, 29(22), 5397; https://doi.org/10.3390/molecules29225397 (registering DOI) - 15 Nov 2024
Abstract
A palladium-catalyzed aromatic dual C-H acylations followed with intramolecular cyclizations have been developed by the assistance of bidentate N-(quinolin-8-yl)benzamide. This tandem process involves the formation of three new chemical bonds, providing access to novel quinoline-substituted hydroxyl isoindolones skeleton under simple reaction conditions. [...] Read more.
A palladium-catalyzed aromatic dual C-H acylations followed with intramolecular cyclizations have been developed by the assistance of bidentate N-(quinolin-8-yl)benzamide. This tandem process involves the formation of three new chemical bonds, providing access to novel quinoline-substituted hydroxyl isoindolones skeleton under simple reaction conditions. The deuterium-labeled competition reaction has revealed that C-H bond cleavage is the turnover limiting step. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
13 pages, 1146 KiB  
Article
2-Bromopyridines as Versatile Synthons for Heteroarylated 2-Pyridones via Ru(II)-Mediated Domino C–O/C–N/C–C Bond Formation Reactions
by Miha Drev, Helena Brodnik, Uroš Grošelj, Franc Perdih, Jurij Svete, Bogdan Štefane and Franc Požgan
Molecules 2024, 29(18), 4418; https://doi.org/10.3390/molecules29184418 - 17 Sep 2024
Viewed by 637
Abstract
A novel methodology for the synthesis of 2-pyridones bearing a 2-pyridyl group on nitrogen and carbon atoms, starting from 2-bromopyridines, was developed employing a simple Ru(II)–KOPiv–Na2CO3 catalytic system. Unsubstituted 2-bromopyridine was successfully converted to the penta-heteroarylated 2-pyridone product using this [...] Read more.
A novel methodology for the synthesis of 2-pyridones bearing a 2-pyridyl group on nitrogen and carbon atoms, starting from 2-bromopyridines, was developed employing a simple Ru(II)–KOPiv–Na2CO3 catalytic system. Unsubstituted 2-bromopyridine was successfully converted to the penta-heteroarylated 2-pyridone product using this method. Preliminary mechanistic studies revealed a possible synthetic pathway leading to the multi-heteroarylated 2-pyridone products, involving consecutive oxygen incorporation, a Buchwald–Hartwig-type reaction, and C–H bond activation. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
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Graphical abstract

Graphical abstract
Full article ">Scheme 1
<p>Content status: selected syntheses of 2-pyridones (<b>a</b>–<b>e</b>) and C–C bond-forming reactions through C6–H functionalization of a 2-pyridone ring (<b>f</b>) [<a href="#B34-molecules-29-04418" class="html-bibr">34</a>,<a href="#B37-molecules-29-04418" class="html-bibr">37</a>,<a href="#B38-molecules-29-04418" class="html-bibr">38</a>,<a href="#B39-molecules-29-04418" class="html-bibr">39</a>,<a href="#B40-molecules-29-04418" class="html-bibr">40</a>,<a href="#B41-molecules-29-04418" class="html-bibr">41</a>,<a href="#B42-molecules-29-04418" class="html-bibr">42</a>,<a href="#B45-molecules-29-04418" class="html-bibr">45</a>].</p>
Full article ">Scheme 2
<p>The formation of pyridone by-products <b>2a</b> + <b>3a</b> in C–H-heteroarylation of 2-pyridylbenzene (our previous work [<a href="#B46-molecules-29-04418" class="html-bibr">46</a>]).</p>
Full article ">Scheme 3
<p>The scope of the <span class="html-italic">N</span>-pyridyl-pyridin-2-ones formation.</p>
Full article ">Scheme 4
<p>The synthesis of polypyridyl-2-pyridone <b>5</b>.</p>
Full article ">Scheme 5
<p>Control experiments.</p>
Full article ">Scheme 6
<p>Synthesis of and catalysis with cyclometallated complex <b>8</b>.</p>
Full article ">Scheme 7
<p>Plausible mechanism for 2-pyridone formation.</p>
Full article ">
17 pages, 3152 KiB  
Article
Synthesis of Benzofuran Derivatives via a DMAP-Mediated Tandem Cyclization Reaction Involving ortho-Hydroxy α-Aminosulfones
by Rong-Rong Zhu, Xi-Qiang Hou and Da-Ming Du
Molecules 2024, 29(16), 3725; https://doi.org/10.3390/molecules29163725 - 6 Aug 2024
Viewed by 718
Abstract
An efficient cascade cyclization strategy was developed to synthesize aminobenzofuran spiroindanone and spirobarbituric acid derivatives utilizing 2-bromo-1,3-indandione, 5-bromo-1,3-dimethylbarbituric acid, and ortho-hydroxy α-aminosulfones as substrates. Under the optimized reaction conditions, the corresponding products were obtained with high efficiency, exceeding 95% and 85% yields [...] Read more.
An efficient cascade cyclization strategy was developed to synthesize aminobenzofuran spiroindanone and spirobarbituric acid derivatives utilizing 2-bromo-1,3-indandione, 5-bromo-1,3-dimethylbarbituric acid, and ortho-hydroxy α-aminosulfones as substrates. Under the optimized reaction conditions, the corresponding products were obtained with high efficiency, exceeding 95% and 85% yields for the respective derivatives. This protocol demonstrates exceptional substrate versatility and robust scalability up to the Gram scale, establishing a stable platform for the synthesis of 3-aminobenzofuran derivative. The successful synthesis paves the way for further biological evaluations with potential implications in scientific research. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
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Graphical abstract
Full article ">Figure 1
<p>Compounds with benzofuran and 3-aminobenzofuran as core scaffolds.</p>
Full article ">Scheme 1
<p>Synthesis of 3-aminobenzofuran derivatives and our contributions.</p>
Full article ">Scheme 2
<p>Substrate expansion for the tandem cyclization reaction of <span class="html-italic">ortho</span>-hydroxy α-aminosulfone and 2-bromo-1,3-indandione. The reaction was conducted under the following conditions: <span class="html-italic">ortho</span>-hydroxy α-aminosulfone <b>1</b> (0.15 mmol), 2-bromo-1,3-indandione <b>2</b> (0.1 mmol), and DMAP (1 equiv.) in DCE (1.0 mL) was stirred for 20 h at room temperature, followed by silica gel column chromatography for the separation of the products.</p>
Full article ">Scheme 3
<p>Substrate scope for benzofuranobarbituric acid. <span class="html-italic">ortho</span>-hydroxy α-aminosulfone <b>1</b> (0.15 mmol) and 5-bromo-1,3-dimethylbarbituric acid <b>4</b> (0.1 mmol) in DCE (1.0 mL) were stirred for 10 h at room temperature. The product yield was isolated.</p>
Full article ">Scheme 4
<p>Gram-scale synthesis of <b>3aa</b> and <b>5aa</b>.</p>
Full article ">Scheme 5
<p>Further valuation of substrate scope.</p>
Full article ">Scheme 6
<p>Preliminary evaluation for asymmetric catalytic reaction. * The chiral carbon, absolute configuration not determined.</p>
Full article ">
18 pages, 2492 KiB  
Article
Product Selectivity Control in the Brønsted Acid-Mediated Reactions with 2-Alkynylanilines
by Valerio Morlacci, Massimiliano Aschi, Marco Chiarini, Caterina Momoli, Laura Palombi and Antonio Arcadi
Molecules 2024, 29(15), 3693; https://doi.org/10.3390/molecules29153693 - 4 Aug 2024
Viewed by 790
Abstract
Brønsted acid-catalysed/mediated reactions of the 2-alkynylanilines are reported. While metal-catalysed reactions of these valuable building blocks have led to the establishment of robust protocols for the selective, diverse-oriented syntheses of significant heterocyclic derivatives, we here demonstrate the practical advantages of an alternative methodology [...] Read more.
Brønsted acid-catalysed/mediated reactions of the 2-alkynylanilines are reported. While metal-catalysed reactions of these valuable building blocks have led to the establishment of robust protocols for the selective, diverse-oriented syntheses of significant heterocyclic derivatives, we here demonstrate the practical advantages of an alternative methodology under metal-free conditions. Our investigation into the key factors influencing the product selectivity in Brønsted acid-catalysed/mediated reactions of 2-alkynylanilines reveals that different reaction pathways can be directed towards the formation of diverse valuable products by simply choosing appropriate reaction conditions. The origins of chemo- and regioselectivity switching have been explored through Density Functional Theory (DFT) calculations. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
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Graphical abstract
Full article ">Figure 1
<p>Protonation site distribution and relative free-energies of <b>Ia</b>, <b>IIa</b>, and <b>IIIa</b> in DCE and EtOH.</p>
Full article ">Figure 2
<p>(<b>A</b>) Reaction scheme for <b>1a</b> dimerization under acid conditions and relative free energies in kJ/mol at 110 °C in DCE (black lines) and EtOH (red lines). (<b>B</b>) Possible reaction pathways for the formation of <b>8a</b> and (<b>C</b>) <b>7a</b>.</p>
Full article ">Figure 3
<p>Possible reaction pathways and relative free energies in kJ/mol in EtOH (110 °C) and DCE (40 °C).</p>
Full article ">Figure 4
<p>Reaction pathways to <b>5a</b> (Reaction conditions: <a href="#molecules-29-03693-t001" class="html-table">Table 1</a>, entry 7) and <b>VIIIa</b> (Reaction conditions: <a href="#molecules-29-03693-t001" class="html-table">Table 1</a>, entry 14) with relative free energies (kJ/mol) at 40 °C in DCE.</p>
Full article ">Scheme 1
<p>Brønsted acid-catalysed/mediated reaction of 2-alkynylanilines <b>1</b>.</p>
Full article ">Scheme 2
<p>Product selectivity control in the sequential reaction of 2-alkynylanilines <b>1</b> with ketones.</p>
Full article ">Scheme 3
<p>Hydration vs dimerization reaction of <b>1a</b>. Other products are given in <a href="#molecules-29-03693-t001" class="html-table">Table 1</a>.</p>
Full article ">Scheme 4
<p>Control experiment ruling out the formation of <b>7a</b> from <b>6a</b> (Reaction conditions: <a href="#molecules-29-03693-t001" class="html-table">Table 1</a>, entry 1).</p>
Full article ">Scheme 5
<p>Control experiment to suppress the dimerization of <b>1a</b> (Reaction conditions: <a href="#molecules-29-03693-t001" class="html-table">Table 1</a>, entry 1).</p>
Full article ">Scheme 6
<p>Synthesis of 2-(2-aminophenyl)quinoline derivatives <b>7</b>.</p>
Full article ">Scheme 7
<p>Hydration vs. dimerization of 2-alkynyl and 2-ethynyltrimethylsilyl anilines in EtOH at 110 °C.</p>
Full article ">Scheme 8
<p>Synthesis of 2-(2-aminophenyl)quinoline derivatives <b>8</b> in DCE at 110 °C and influence of the amount of <span class="html-italic">p</span>-TsOH on the regioselectivity.</p>
Full article ">
12 pages, 1476 KiB  
Article
Synthesis of Substituted 1,2-Dihydroisoquinolines by Palladium-Catalyzed Cascade Cyclization–Coupling of Trisubstituted Allenamides with Arylboronic Acids
by Masahiro Yoshida, Ryunosuke Imaji and Shinya Shiomi
Molecules 2024, 29(12), 2917; https://doi.org/10.3390/molecules29122917 - 19 Jun 2024
Viewed by 797
Abstract
1,2-Dihydroisoquinolines are important compounds due to their biological and medicinal activities, and numerous approaches to their synthesis have been reported. Recently, we reported a facile synthesis of trisubstituted allenamides via N-acetylation followed by DBU-promoted isomerization, where various substituted allenamides were conveniently synthesized [...] Read more.
1,2-Dihydroisoquinolines are important compounds due to their biological and medicinal activities, and numerous approaches to their synthesis have been reported. Recently, we reported a facile synthesis of trisubstituted allenamides via N-acetylation followed by DBU-promoted isomerization, where various substituted allenamides were conveniently synthesized from readily available propargylamines with high efficiency. In light of this research background, we focused on the utility of this methodology for the synthesis of substituted 1,2-dihydroisoquinolines. In this study, a palladium-catalyzed cascade cyclization–coupling of trisubstituted allenamides containing a bromoaryl moiety with arylboronic acids is described. When N-acetyl diphenyl-substituted trisubstituted allenamide and phenylboronic acid were treated with 10 mol% of Pd(OAc)2, 20 mol% of P(o-tolyl)3, and 5 equivalents of NaOH in dioxane/H2O (4/1) at 80 °C, the reaction proceeded to afford a substituted 1,2-dihydroisoquinoline. The reaction proceeded via intramolecular cyclization, followed by transmetallation with the arylboronic acid of the resulting allylpalladium intermediate. A variety of highly substituted 1,2-dihydroisoquinolines were concisely obtained using this methodology because the allenamides, as reaction substrates, were prepared from readily available propargylamines in one step. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
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Graphical abstract
Full article ">Figure 1
<p>Structure of biologically active molecules containing 1,2-dihydroisoquinoline moiety.</p>
Full article ">Figure 2
<p>Reactions using allenamide <b>2a</b> with various arylboronic acids <b>3</b>.</p>
Full article ">Figure 3
<p>Reactions using various allenamides <b>2</b> with phenylboronic acid (<b>3a</b>).</p>
Full article ">Scheme 1
<p>Palladium-catalyzed cyclization of allenamides and synthesis of allenamides.</p>
Full article ">Scheme 2
<p>Synthesis of trisubstituted allenamides.</p>
Full article ">Scheme 3
<p>Proposed mechanism for the production of 1,2-dihydroisoquinoline <b>4</b>.</p>
Full article ">
17 pages, 2498 KiB  
Article
Using Quinolin-4-Ones as Convenient Common Precursors for a Metal-Free Total Synthesis of Both Dubamine and Graveoline Alkaloids and Diverse Structural Analogues
by Rodrigo Abonia, Lorena Cabrera, Diana Arteaga, Daniel Insuasty, Jairo Quiroga, Paola Cuervo and Henry Insuasty
Molecules 2024, 29(9), 1959; https://doi.org/10.3390/molecules29091959 - 25 Apr 2024
Cited by 1 | Viewed by 1104
Abstract
The Rutaceae family is one of the most studied plant families due to the large number of alkaloids isolated from them with outstanding biological properties, among them the quinoline-based alkaloids Graveoline 1 and Dubamine 2. The most common methods for the synthesis [...] Read more.
The Rutaceae family is one of the most studied plant families due to the large number of alkaloids isolated from them with outstanding biological properties, among them the quinoline-based alkaloids Graveoline 1 and Dubamine 2. The most common methods for the synthesis of alkaloids 1 and 2 and their derivatives involves cycloaddition reactions or metal-catalyzed coupling processes but with some limitations in scope and functionalization of the quinoline moiety. As a continuation of our current studies on the synthesis and chemical transformation of 2-aminochalcones, we are reporting here an efficient metal-free approach for the total synthesis of alkaloids 1 and 2 along with their analogues with structural diversity, through a two-step sequence involving intramolecular cyclization, oxidation/aromatization, N-methylation and oxidative C-C bond processes, starting from dihydroquinolin-4-ones as common precursors for the construction of the structures of both classes of alkaloids. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
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Figure 1

Figure 1
<p>Structures of alkaloids Graveoline <b>1</b> and Dubamine <b>2</b> and the antibacterial compounds <b>3</b> and <b>4</b>.</p>
Full article ">Scheme 1
<p>Some representative synthetic approaches for obtaining Graveoline <b>1</b>.</p>
Full article ">Scheme 2
<p>Some representative synthetic approaches for obtaining Dubamine <b>2</b> and its derivatives.</p>
Full article ">Scheme 3
<p>Proposed synthetic sketch of the synthesis of alkaloids Graveoline <b>1</b> and Dubamine <b>2</b> and their structural analogues <b>23</b> and <b>24</b>, respectively.</p>
Full article ">Scheme 4
<p>Total synthesis of Graveoline <b>1</b>, Dubamine <b>2</b> and their corresponding quinolinic-analogues (<b>23</b>,<b>24</b>)<b>h</b> from dihydroquinolin-4-ones <b>22h</b>,<b>i</b> through the two-step synthetic approaches developed in this research work.</p>
Full article ">
15 pages, 3371 KiB  
Article
Electrochemical Radical Tandem Difluoroethylation/Cyclization of Unsaturated Amides to Access MeCF2-Featured Indolo/Benzoimidazo [2,1-a]Isoquinolin-6(5H)-ones
by Yunfei Tian, Dongyu Guo, Luping Zheng, Shaolu Yang, Ningning Zhang, Weijun Fu and Zejiang Li
Molecules 2024, 29(5), 973; https://doi.org/10.3390/molecules29050973 - 22 Feb 2024
Viewed by 881
Abstract
A metal-free electrochemical oxidative difluoroethylation of 2-arylbenzimidazoles was accomplished, which provided an efficient strategy for the synthesis of MeCF2-containing benzo[4,5]imidazo[2,1-a]-isoquinolin-6(5H)-ones. In addition, the method also enabled the efficient construction of various difluoroethylated indolo[2,1-a]isoquinolin-6(5H)-ones. [...] Read more.
A metal-free electrochemical oxidative difluoroethylation of 2-arylbenzimidazoles was accomplished, which provided an efficient strategy for the synthesis of MeCF2-containing benzo[4,5]imidazo[2,1-a]-isoquinolin-6(5H)-ones. In addition, the method also enabled the efficient construction of various difluoroethylated indolo[2,1-a]isoquinolin-6(5H)-ones. Notably, this electrochemical synthesis protocol proceeded well under mild conditions without metal catalysts or exogenous additives/oxidants added. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
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Figure 1

Figure 1
<p>Strategies for radical difluoroethylated heterocycles.</p>
Full article ">Figure 2
<p>Cyclic voltammograms of substrates in 0.1 M LiClO<sub>4</sub>/(CH<sub>3</sub>CN/H<sub>2</sub>O), using glassy carbon working electrode, platinum wire counter electrode, and Ag/AgNO<sub>3</sub> reference electrode at 50 mVs<sup>−1</sup> scan rates: a—background, b—<b>1a</b> (5 mM), c—<b>2a</b> (5 mM), d—<b>1a</b> (5 mM) and <b>2a</b> (5 mM).</p>
Full article ">Scheme 1
<p>Scope of the substrates 2-arylbenzimidazoles. Reaction conditions: carbon plate (10 mm × 10 mm × 3 mm) as the anode, platinum plate (10 mm × 10 mm × 0.20 mm) as the cathode, undivided cell, 2.1 V, <b>1</b> (0.2 mmol), <b>2a</b> (0.6 mmol), LiClO<sub>4</sub> (0.3 M), CH<sub>3</sub>CN (4.5 mL), H<sub>2</sub>O (1.5 mL), rt, 3h, isolated yields.</p>
Full article ">Scheme 2
<p>Scope of the substrates 2-arylindoles. Reaction conditions: carbon plate (10 mm × 10 mm × 3 mm) as the anode, platinum plate (10 mm × 10 mm × 0.20 mm) as the cathode, undivided cell, 2.1 V, <b>4</b> (0.2 mmol), <b>2</b> (0.6 mmol), LiClO<sub>4</sub> (0.3 M), CH<sub>3</sub>CN (4.5 mL), H<sub>2</sub>O (1.5 mL), rt, 3h, isolated yields.</p>
Full article ">Scheme 3
<p>Reactions for mechanistic determination: (<b>a</b>) a radical trapping experiment involved BHT; (<b>b</b>) a radical trapping experiment involved 1,1-diphenylethylene.</p>
Full article ">Scheme 4
<p>Proposed reaction mechanism.</p>
Full article ">
19 pages, 26194 KiB  
Article
Reactivity and Stability of (Hetero)Benzylic Alkenes via the Wittig Olefination Reaction
by Ajmir Khan, Mohammed G. Sarwar and Sher Ali
Molecules 2024, 29(2), 501; https://doi.org/10.3390/molecules29020501 - 19 Jan 2024
Cited by 3 | Viewed by 1465
Abstract
Wittig olefination at hetero-benzylic positions for electron-deficient and electron-rich heterocycles has been studied. The electronic effects of some commonly used protective groups associated with the N-heterocycles were also investigated for alkenes obtained in the context of the widely employed Wittig olefination reaction. [...] Read more.
Wittig olefination at hetero-benzylic positions for electron-deficient and electron-rich heterocycles has been studied. The electronic effects of some commonly used protective groups associated with the N-heterocycles were also investigated for alkenes obtained in the context of the widely employed Wittig olefination reaction. It was observed that hetero-benzylic positions of the pyridine, thiophene and furan derivatives were stable after Wittig olefination. Similarly, electron-withdrawing groups (EWGs) attached to N-heterocycles (indole and pyrrole derivatives) directly enhanced the stability of the benzylic position during and after Wittig olefination, resulting in the formation of stable alkenes. Conversely, electron-donating group (EDG)-associated N-heterocycles boosted the reactivity of benzylic alkene, leading to lower yields or decomposition of the olefination products. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
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Graphical abstract
Full article ">Figure 1
<p>EWGs and EDGs decrease or enhance the reactivity of the corresponding alkene.</p>
Full article ">Figure 2
<p>The reactivity trend of pyrrole, furan, thiophene and pyridine.</p>
Full article ">Scheme 1
<p>Synthesis of fused furans <b>4b</b> and <b>4c</b>.</p>
Full article ">Scheme 2
<p>Feist–Benary furan synthesis of <b>4s</b>.</p>
Full article ">Scheme 3
<p>Synthesis of fused indoles <b>3d</b>–<b>3f</b>.</p>
Full article ">Scheme 4
<p>Synthesis of tetrahydroisoqunoline derivatives <b>4k</b> and <b>4j</b>.</p>
Full article ">Scheme 5
<p>Wittig olefination of <b>4n</b>, followed by an HTIB-mediated ring expansion reaction.</p>
Full article ">Scheme 6
<p>Proposed mechanism for ring expansion reactions.</p>
Full article ">
15 pages, 3362 KiB  
Article
(3+2)-Cycloadditions of Levoglucosenone (LGO) with Fluorinated Nitrile Imines Derived from Trifluoroacetonitrile: An Experimental and Computational Study
by Grzegorz Mlostoń, Katarzyna Urbaniak, Marcin Palusiak, Zbigniew J. Witczak and Ernst-Ulrich Würthwein
Molecules 2023, 28(21), 7348; https://doi.org/10.3390/molecules28217348 - 30 Oct 2023
Cited by 1 | Viewed by 1298
Abstract
The in situ-generated N-aryl nitrile imines derived from trifluoroacetonitrile smoothly undergo (3+2)-cycloadditions onto the enone fragment of the levoglucosenone molecule, yielding the corresponding, five-membered cycloadducts. In contrast to the ‘classic’ C(Ph),N(Ph) nitrile imine, reactions with fluorinated C(CF3 [...] Read more.
The in situ-generated N-aryl nitrile imines derived from trifluoroacetonitrile smoothly undergo (3+2)-cycloadditions onto the enone fragment of the levoglucosenone molecule, yielding the corresponding, five-membered cycloadducts. In contrast to the ‘classic’ C(Ph),N(Ph) nitrile imine, reactions with fluorinated C(CF3),N(Ar) analogues lead to stable pyrazolines in a chemo- and stereoselective manner. Based on the result of X-ray single crystal diffraction analysis, their structures were established as exo-cycloadducts with the location of the N-Ar terminus of the 1,3-dipole at the α-position of the enone moiety. The DFT computation demonstrated that the observed reaction pathway results from the strong dominance of kinetic control over thermodynamic control. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
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Figure 1

Figure 1
<p>Levoglucosenone (<b>6</b>), its stereochemical structure, and selected products of cycloaddition reactions with a <span class="html-italic">C</span>(Ph),<span class="html-italic">N</span>(Ph) nitrile imine (<b>9</b>) and tropothione lead to polycylic, isomeric pyrazoles <b>7</b>/<b>7′</b> [<a href="#B30-molecules-28-07348" class="html-bibr">30</a>] and polycylic thiophene derivative <b>8</b> [<a href="#B39-molecules-28-07348" class="html-bibr">39</a>], respectively. In structures <b>7</b>/<b>7′</b>, the skeleton of <span class="html-italic">C</span>(Ph),<span class="html-italic">N</span>(PH) nitrile imine <b>9</b> is presented in red.</p>
Full article ">Figure 2
<p>The molecular structure of polycylic pyrazole <b>7</b> was estimated by means of a single crystal X-ray experiment. Atoms are represented by thermal elipsoids (50%) for clarity.</p>
Full article ">Figure 3
<p>Molecular structure of polycylic pyrazoline <span class="html-italic">exo</span>-<b>11a</b>, estimated by means of a single crystal X-ray experiment. Atoms are represented by thermal elipsoids (50%) for clarity.</p>
Full article ">Figure 4
<p>Competitive <span class="html-italic">exo</span>- and <span class="html-italic">endo</span>-approaches of nitrile imines <b>1</b> onto the enone fragment of levoglucosenone <b>6</b> in the transition state of the (3+2)-cycloaddition reaction.</p>
Full article ">Figure 5
<p>DFT calculations of the (3+2)-cycloadditions of trifluoromethyl-substituted nitrile imine <b>1b</b> with levoglucosenone <b>6</b> (PBE1PBE/def2tzvp + GD3BJ +PCM-dichloromethane) [kcal/mol] led to the regioisomeric pyrazolines <span class="html-italic">exo</span>-<b>11b</b>/<span class="html-italic">endo</span>-<b>11b</b> and <span class="html-italic">exo</span>-<b>11′b</b>/<span class="html-italic">endo</span>-<b>11′b</b>. Symbol<math display="inline"><semantics> <mrow> <msup> <mo> </mo> <mo>‡</mo> </msup> </mrow> </semantics></math>: transition state.</p>
Full article ">Figure 6
<p>Calculated atomic distances of the forming bonds of the transition states <b>TS-</b><span class="html-italic">exo</span><b>-11b</b> and <b>TS-</b><span class="html-italic">exo</span><b>-11′b</b> (PBE1PBE/def2tzvp + GD3BJ +PCM-dichloromethane). (<b>a</b>): <b>TS-</b><span class="html-italic">exo</span><b>-11b</b> atomic distances C–N 2.569 Å, C–C 2.253 Å; (<b>b</b>): <b>TS-</b><span class="html-italic">exo</span><b>-11′b</b> atomic distances C–N 2.323 Å C–C 2.353 Å.</p>
Full article ">Figure 7
<p>DFT calculations of the cycloadditions of diphenyl-substituted nitrile imine <b>9</b> with levoglucosenone <b>6</b> (PBE1PBE/def2tzvp + GD3BJ +PCM-dichloromethane, room temperature) [kcal/mol] led to diastereomeric and regioisomeric pyrazolines <span class="html-italic">exo</span>/<span class="html-italic">endo</span>-<b>10</b> and <span class="html-italic">exo</span>/<span class="html-italic">endo</span>-<b>10′</b>. Symbol<math display="inline"><semantics> <mrow> <msup> <mo> </mo> <mo>‡</mo> </msup> </mrow> </semantics></math>: transition state.</p>
Full article ">Scheme 1
<p>Generation of fluorinated nitrile imines <b>1</b> and two literature examples of their (3+2)-cycloadditions with chalcone <b>2</b> and thiochalcone <b>4</b>, leading to pyrazoline <b>3</b> and 1,3,4-thiadiazoline derivative <b>5</b>, respectively [<a href="#B7-molecules-28-07348" class="html-bibr">7</a>,<a href="#B14-molecules-28-07348" class="html-bibr">14</a>].</p>
Full article ">Scheme 2
<p>Selectivity was observed in the (3+2)-cycloaddition of <span class="html-italic">C</span>(Ph),<span class="html-italic">N</span>(Ph) nitrile imine (<b>9</b>) [<a href="#B7-molecules-28-07348" class="html-bibr">7</a>,<a href="#B30-molecules-28-07348" class="html-bibr">30</a>] with levoglucosenone (<b>6</b>) in THF solution at room temperature, providing pyrazolines <span class="html-italic">exo</span>-<b>10</b> and <span class="html-italic">exo</span>-<b>10′</b> as primary products, followed by oxidation to isolated pyrazole derivatives <b>7</b> and <b>7′</b>.</p>
Full article ">Scheme 3
<p>Highly selective (3+2)-cycloadditions of fluorinated nitrile imines <b>1a</b>–<b>1i</b>, derived from trifluoroacetonitrile, with levoglucosenone (<b>6</b>) leading to trifluoromethyl substituted, fused pyrazolines <b>11a</b>–<b>11i</b>.</p>
Full article ">Scheme 4
<p>Equation above: spontaneous oxidation of pyrazoline <span class="html-italic">exo</span>-<b>11i</b> with air oxygen during chromatographic purification, leading to the fused pyrazole <b>12a</b>. Equation below: dehydrogenation of pyrazoline <span class="html-italic">exo</span>-<b>11g</b> using MnO<sub>2</sub> as an oxidizing reagent, leading to the fused pyrazole <b>12b</b>.</p>
Full article ">Scheme 5
<p>Attempted oxidation of pyrazoline <span class="html-italic">exo</span>-<b>11g</b> with TCCA, leading to a mixture of fused pyrazole <b>12b</b> and its chlorinated derivative <b>12c</b>.</p>
Full article ">
24 pages, 3811 KiB  
Article
Novel Strigolactone Mimics That Modulate Photosynthesis and Biomass Accumulation in Chlorella sorokiniana
by Daria Gabriela Popa, Florentina Georgescu, Florea Dumitrascu, Sergiu Shova, Diana Constantinescu-Aruxandei, Constantin Draghici, Lucian Vladulescu and Florin Oancea
Molecules 2023, 28(20), 7059; https://doi.org/10.3390/molecules28207059 - 12 Oct 2023
Cited by 2 | Viewed by 1431
Abstract
In terrestrial plants, strigolactones act as multifunctional endo- and exo-signals. On microalgae, the strigolactones determine akin effects: induce symbiosis formation with fungi and bacteria and enhance photosynthesis efficiency and accumulation of biomass. This work aims to synthesize and identify strigolactone mimics that promote [...] Read more.
In terrestrial plants, strigolactones act as multifunctional endo- and exo-signals. On microalgae, the strigolactones determine akin effects: induce symbiosis formation with fungi and bacteria and enhance photosynthesis efficiency and accumulation of biomass. This work aims to synthesize and identify strigolactone mimics that promote photosynthesis and biomass accumulation in microalgae with biotechnological potential. Novel strigolactone mimics easily accessible in significant amounts were prepared and fully characterized. The first two novel compounds contain 3,5-disubstituted aryloxy moieties connected to the bioactive furan-2-one ring. In the second group of compounds, a benzothiazole ring is connected directly through the cyclic nitrogen atom to the bioactive furan-2-one ring. The novel strigolactone mimics were tested on Chlorella sorokiniana NIVA-CHL 176. All tested strigolactones increased the accumulation of chlorophyll b in microalgae biomass. The SL-F3 mimic, 3-(4-methyl-5-oxo-2,5-dihydrofuran-2-yl)-3H-benzothiazol-2-one (7), proved the most efficient. This compound, applied at a concentration of 10−7 M, determined a significant biomass accumulation, higher by more than 15% compared to untreated control, and improved the quantum yield efficiency of photosystem II. SL-F2 mimic, 5-(3,5-dibromophenoxy)-3-methyl-5H-furan-2-one (4), applied at a concentration of 10−9 M, improved protein production and slightly stimulated biomass accumulation. Potential utilization of the new strigolactone mimics as microalgae biostimulants is discussed. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
Show Figures

Figure 1

Figure 1
<p>The two major groups of naturally occurring canonical strigolactones. Chemical structures drawn by the authors, based on the stereochemical structures published by Xie et al. [<a href="#B39-molecules-28-07059" class="html-bibr">39</a>].</p>
Full article ">Figure 2
<p>(<b>a</b>) The X-ray molecular structure of compound <b>8</b> with atom labeling and thermal ellipsoids at 50% level. H-bond parameters: N1-H···O1 [N1-H 0.86 Å, H···O1 1.97 Å, N1···O1(1 − <span class="html-italic">x</span>, 2 − <span class="html-italic">y</span>, 1 − <span class="html-italic">z</span>) 2.820(5) Å, ∠N1HO1 169.1°]. (<b>b</b>) The role of π-π stacking in the formation of 1D supramolecular architecture in the crystal structure of compound <b>8</b>. Centroid-to-centroid contacts are drawn in orange-dashed lines.</p>
Full article ">Figure 3
<p>(<b>a</b>) The X-ray molecular structure of compound <b>7</b> (SL-F3) with atom labeling and thermal ellipsoids at 50% level. (<b>b</b>) Intermolecular H-bonds in the crystal structure of compound <b>7</b> (SL-F3). Non-relevant H-atoms are omitted. H-bond parameters: C2-H···O3 [C2-H 0.93 Å, H···O32.56 Å, C2···O3(<span class="html-italic">x</span>, 0.5 − <span class="html-italic">y</span>, −0.5 − <span class="html-italic">z</span>) 3.344(3) Å, ∠C2HO3 142.7°]; C8-H···O2 [C8-H 0.98 Å, H···O22.53 Å, C8···O2(<span class="html-italic">x</span>, 1 + <span class="html-italic">y</span>, <span class="html-italic">z</span>) 3.458(3) Å, ∠C8HO2 158.6°]; C9-H···O1 [C9-H 0.93 Å, H···O12.56 Å, C9···O1(0.5 − <span class="html-italic">x</span>, 1.5 − <span class="html-italic">y</span>, 1.5 − <span class="html-italic">z</span>) 3.360(3) Å, ∠C9HO13 144.7°]. (<b>c</b>) The 2D supramolecular layer of compound <b>7</b> (SL-F3) viewed along the <span class="html-italic">b</span> axis.</p>
Full article ">Figure 4
<p>Optical densities of the microalgae cultures. C1—control, without treatment. SC (solvent control)—treatment with dimethyl sulfoxide (DMSO), 10<sup>−7</sup> M. CGR24c1—reference control with GR24 at 10<sup>−7</sup> M. CGR24c2—reference control with GR24 at 10<sup>−9</sup> M. V1c1—SL-F1 at 10<sup>−7</sup> M, V1c2 SL-F1 at 10<sup>−9</sup> M; V2c1—SL-F2 at 10<sup>−7</sup> M, V2c2 SL-F2 at 10<sup>−9</sup> M; V3c1—SL-F3 at 10<sup>−7</sup> M, V3c2 SL-F3 at 10<sup>−9</sup> M; V4c1—SL-F5 at 10<sup>−7</sup> M, V4c2 SL-F5 at 10<sup>−9</sup> M; V5c1—SL-F6 at 10<sup>−7</sup> M, V5c2 SL-F6 at 10<sup>−9</sup> M. The values represent means  ±  standard errors. The values followed by the same letter do not differ significantly at <span class="html-italic">p</span> &lt; 0.05.</p>
Full article ">Figure 5
<p>The effect of strigolactone mimics and analog on the quantum yield (Y) of the photosynthetic system II after 14 days of growth. C1—control, without treatment. SC (solvent control)—treatment with dimethyl sulfoxide (DMSO), 10<sup>−7</sup> M. CGR24c1—reference control with GR24 at 10<sup>−7</sup> M. CGR24c2—reference control with GR24 at 10<sup>−9</sup> M. V1c1—SL-F1 at 10<sup>−7</sup> M, V1c2 SL-F2 at 10<sup>−9</sup> M; V2c1—SL-F2 at 10<sup>−7</sup> M, V2c2 SL-F2 at 10<sup>−9</sup> M; V3c1—SL-F3 at 10<sup>−7</sup> M, V3c2 SL-F3 at 10<sup>−9</sup> M; V4c1—SL-F5 at 10<sup>−7</sup> M, V4c2 SL-F5 at 10<sup>−9</sup> M; V5c1—SL-F6 at 10<sup>−7</sup> M, V5c2 SL-F6 at 10<sup>−9</sup> M. The values represent means  ±  standard errors. The values followed by the same letter do not differ significantly at <span class="html-italic">p</span> &lt; 0.05.</p>
Full article ">Figure 6
<p>Pigment concentration extracted from the biomass of microalgae after 14 days of growth: (<b>a</b>) chlorophyll <span class="html-italic">a</span>; (<b>b</b>) chlorophyll <span class="html-italic">b</span>; (<b>c</b>) total carotenoid; (<b>d</b>) total photosynthetic pigments. C1—control, without treatment. SC (solvent control)—treatment with the dimethyl sulfoxide (DMSO), 10<sup>−7</sup> M. CGR24c1—reference control with GR24 at 10<sup>−7</sup> M. CGR24c2—reference control with GR24 at 10<sup>−9</sup> M. V1c1—SL-F1 at 10<sup>−7</sup> M, V1c2 SL-F2 at 10<sup>−9</sup> M; V2c1—SL-F2 at 10<sup>−7</sup> M, V2c2 SL-F2 at 10<sup>−9</sup> M; V3c1—SL-F3 at 10<sup>−7</sup> M, V3c2 SL-F3 at 10<sup>−9</sup> M; V4c1—SL-F5 at 10<sup>−7</sup> M, V4c2 SL-F5 at 10<sup>−9</sup> M; V5c1—SL-F6 at 10<sup>−7</sup> M, V5c2 SL-F6 at 10<sup>−9</sup> M. The values represent means  ±  standard errors. The values followed by the same letter do not differ significantly at <span class="html-italic">p</span> &lt; 0.05.</p>
Full article ">Figure 7
<p>Biomass production of <span class="html-italic">Chlorella sorokiniana</span> microalgae after 14 days of growth. C1—control, without treatment. SC (solvent control)—treatment with the dimethyl sulfoxide (DMSO), 10<sup>−7</sup> M. CGR24c1—reference control with GR24 at 10<sup>−7</sup> M. CGR24c2—reference control with GR24 at 10<sup>−9</sup> M. V1c1—SL-F1 at 10<sup>−7</sup> M, V1c2 SL-F2 at 10<sup>−9</sup> M; V2c1—SL-F2 at 10<sup>−7</sup> M, V2c2 SL-F2 at 10<sup>−9</sup> M; V3c1—SL-F3 at 10<sup>−7</sup> M, V3c2 SL-F3 at 10<sup>−9</sup> M; V4c1—SL-F5 at 10<sup>−7</sup> M, V4c2 SL-F5 at 10<sup>−9</sup> M; V5c1—SL-F6 at 10<sup>−7</sup> M, V5c2 SL-F6 at 10<sup>−9</sup> M. The values represent means  ±  standard errors. The values followed by the same letter do not differ significantly at <span class="html-italic">p</span> &lt; 0.05.</p>
Full article ">Figure 8
<p><span class="html-italic">Chlorella sorokiniana</span> protein content after 14 days of growth—Bradford method. C1—control, without treatment. SC (solvent control)—treatment with the dimethyl sulfoxide (DMSO), 10<sup>−7</sup> M. CGR24c1—reference control with GR24 at 10<sup>−7</sup> M. CGR24c2—reference control with GR24 at 10<sup>−9</sup> M. V1c1—SL-F1 at 10<sup>−7</sup> M, V1c2 SL-F2 at 10<sup>−9</sup> M; V2c1—SL-F2 at 10<sup>−7</sup> M, V2c2 SL-F2 at 10<sup>−9</sup> M; V3c1—SL-F3 at 10<sup>−7</sup> M, V3c2 SL-F3 at 10<sup>−9</sup> M; V4c1—SL-F5 at 10<sup>−7</sup> M, V4c2 SL-F5 at 10<sup>−9</sup> M; V5c1—SL-F6 at 10<sup>−7</sup> M, V5c2 SL-F6 at 10<sup>−9</sup> M. The values represent means  ±  standard errors. The values followed by the same letter do not differ significantly at <span class="html-italic">p</span> &lt; 0.05.</p>
Full article ">Figure 9
<p><span class="html-italic">Chlorella sorokiniana</span> protein content after 14 days of growth—Biuret method. C1—control, without treatment. SC (solvent control)—treatment with the dimethyl sulfoxide (DMSO), 10<sup>−7</sup> M. CGR24c1—reference control with GR24 at 10<sup>−7</sup> M. CGR24c2—reference control with GR24 at 10<sup>−9</sup> M. V1c1—SL-F1 at 10<sup>−7</sup> M, V1c2 SL-F2 at 10<sup>−9</sup> M; V2c1—SL-F2 at 10<sup>−7</sup> M, V2c2 SL-F2 at 10<sup>−9</sup> M; V3c1—SL-F3 at 10<sup>−7</sup> M, V3c2 SL-F3 at 10<sup>−9</sup> M; V4c1—SL-F5 at 10<sup>−7</sup> M, V4c2 SL-F5 at 10<sup>−9</sup> M; V5c1—SL-F6 at 10<sup>−7</sup> M, V5c2 SL-F6 at 10<sup>−9</sup> M. The values represent means  ±  standard errors. The values followed by the same letter do not differ significantly at <span class="html-italic">p</span> &lt; 0.05.</p>
Full article ">Scheme 1
<p>Synthesis of SL mimics <b>3</b> (SL-F1) and <b>4</b> (SL-F2), derived from 3,5-disubstituted phenols.</p>
Full article ">Scheme 2
<p>The two possible reaction products starting from 3<span class="html-italic">H</span>-benzothiazol-2-one. Compound <b>7</b> is SL-F3.</p>
Full article ">Scheme 3
<p>Synthesis of SL mimics <b>9</b> (SL-F5) and <b>11</b> (SL-F6).</p>
Full article ">
11 pages, 1512 KiB  
Article
Synthesis of 4-(Phenylchalcogenyl)tetrazolo[1,5-a]quinolines by Bicyclization of 2-Azidobenzaldehydes with Phenylchalcogenylacetonitrile
by Loana I. Monzon, Nicole C. M. Rocha, Gabriela T. Quadros, Pâmela P. P. Nunes, Roberta Cargnelutti, Raquel G. Jacob, Eder J. Lenardão, Gelson Perin and Daniela Hartwig
Molecules 2023, 28(13), 5036; https://doi.org/10.3390/molecules28135036 - 27 Jun 2023
Cited by 1 | Viewed by 1350
Abstract
A general methodology to access valuable 4-(phenylchalcogenyl)tetrazolo[1,5-a]quinolines was developed by the reaction of 2-azidobenzaldehyde with phenylchalcogenylacetonitriles (sulfur and selenium) in the presence of potassium carbonate (20 mol%) as a catalyst. The reactions were conducted using a mixture of dimethylsulfoxide and water [...] Read more.
A general methodology to access valuable 4-(phenylchalcogenyl)tetrazolo[1,5-a]quinolines was developed by the reaction of 2-azidobenzaldehyde with phenylchalcogenylacetonitriles (sulfur and selenium) in the presence of potassium carbonate (20 mol%) as a catalyst. The reactions were conducted using a mixture of dimethylsulfoxide and water (7:3) as solvent at 80 °C for 4 h. This new methodology presents a good functional group tolerance to electron-deficient and electron-rich substituents, affording a total of twelve different 4-(phenylchalcogenyl)tetrazolo[1,5-a]quinolines selectively in moderate to excellent yields. The structure of the synthesized 4-(phenylselanyl)tetrazolo[1,5-a]quinoline was confirmed by X-ray analysis. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Commercially available drugs containing the tetrazole or quinoline moiety.</p>
Full article ">Figure 2
<p>Projection of the molecular structure of 4-(phenylselanyl)tetrazolo[1,5-<span class="html-italic">a</span>]quinoline (<b>3a</b>) obtained by X-ray crystallography.</p>
Full article ">Scheme 1
<p>Previous methods to prepare tetrazolo[1,5-<span class="html-italic">a</span>]quinolines. Method A: from 2-chloroquinoline and NaN<sub>3</sub> [<a href="#B32-molecules-28-05036" class="html-bibr">32</a>]; Method B: from 2-hydrazinylquinoline [<a href="#B29-molecules-28-05036" class="html-bibr">29</a>]; Method C: from 2-azidoarylidenes [<a href="#B31-molecules-28-05036" class="html-bibr">31</a>,<a href="#B34-molecules-28-05036" class="html-bibr">34</a>]; Method D: this work.</p>
Full article ">Scheme 2
<p>Reaction pathways of the cyclization starting from 2-azidobenzaldehyde <b>1a</b>. Path A: the first step is a Knoevenagel condensation to form <b>II</b>, followed by the cyclization to tetrazole <b>IV</b>. Path B: the first step is the formation of the triazole <b>III</b>, followed by the cyclization to quinazoline <b>V</b>.</p>
Full article ">Scheme 3
<p>4-(Arylselanyl)tetrazolo[1,5-<span class="html-italic">a</span>]quinolines <b>3a–h</b>: scope of 2-(arylselanyl)acetonitriles <b>2</b>.</p>
Full article ">Scheme 4
<p>4-(Arylthio)tetrazolo[1,5-<span class="html-italic">a</span>]quinolines <b>3i–l</b>: scope of 2-(arylthio)acetonitriles <b>2</b>.</p>
Full article ">Scheme 5
<p>Plausible mechanism.</p>
Full article ">

Review

Jump to: Research

33 pages, 11477 KiB  
Review
Synthesis and Biological Activity of Chromeno[3,2-c]Pyridines
by Anna V. Listratova, Roman S. Borisov, Nikolay Yu. Polovkov and Larisa N. Kulikova
Molecules 2024, 29(21), 4997; https://doi.org/10.3390/molecules29214997 - 22 Oct 2024
Viewed by 661
Abstract
The review summarizes all synthetic methodologies for the preparation of chromeno[3,2-c]pyridines and chromeno[3,2-c]quinolines. The proposed approaches are systemized based on ways for the construction of the heterocyclic system. The presence of these compounds in nature and their bioactivity are [...] Read more.
The review summarizes all synthetic methodologies for the preparation of chromeno[3,2-c]pyridines and chromeno[3,2-c]quinolines. The proposed approaches are systemized based on ways for the construction of the heterocyclic system. The presence of these compounds in nature and their bioactivity are also discussed. Natural products with an annelated chromeno[3,2-c]pyridine fragment are well-known and a number of alkaloids derived from this system as a key core have been recently isolated. These compounds demonstrate antimicrobial, antivirus, and cytotoxic activities, making chromeno[3,2-c]pyridine structural motifs promising for medicinal chemistry. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
Show Figures

Figure 1

Figure 1
<p>Natural chromeno[3,2-<span class="html-italic">c</span>]pyridines.</p>
Full article ">Figure 2
<p>Natural chromeno[3,2-<span class="html-italic">c</span>]pyridine.</p>
Full article ">Figure 3
<p>Natural chromeno[3,2-<span class="html-italic">c</span>]pyridines.</p>
Full article ">Scheme 1
<p>A proposed the biosynthetic pathway towards chromeno[3,2-<span class="html-italic">c</span>]pyridine moiety.</p>
Full article ">Scheme 2
<p>The first suggested synthetic ways towards chromeno[3,2-<span class="html-italic">c</span>]pyridines.</p>
Full article ">Scheme 3
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]quinolines <b>17</b>.</p>
Full article ">Scheme 4
<p>Cyclisation of 4-phenoxynicotinic acid <b>20</b> towards chromeno[3,2-<span class="html-italic">c</span>]pyridine <b>14</b>.</p>
Full article ">Scheme 5
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]quinolines <b>24</b>.</p>
Full article ">Scheme 6
<p>Cyclisation of 3-trifluoroacetyl-4-quinolyl ethers <b>26</b>.</p>
Full article ">Scheme 7
<p>An efficient method to chromeno[3,2-<span class="html-italic">c</span>]quinolines <b>31</b>.</p>
Full article ">Scheme 8
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]quinolines <b>33</b> and <b>34</b>.</p>
Full article ">Scheme 9
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]pyridine <b>39</b>.</p>
Full article ">Scheme 10
<p>A construction of chromeno[3,2-<span class="html-italic">c</span>]pyridine core based on condensation of morpholine enamine and salicylaldehyde.</p>
Full article ">Scheme 11
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]pyridine <b>14</b> starting form <span class="html-italic">β</span>-ketoester <b>45</b>.</p>
Full article ">Scheme 12
<p>Synthesis of a series of chromeno[3,2-<span class="html-italic">c</span>]pyridines via condensation of enamines <b>48</b> and salisylaldehydes <b>49</b>.</p>
Full article ">Scheme 13
<p>Synthesis of dye <b>57</b>.</p>
Full article ">Scheme 14
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]pyridine <b>14</b> via nucleophilic substitution.</p>
Full article ">Scheme 15
<p>Intramolecular cyclization of (2-chlorophenyl)(2-methoxypyridin-3-yl)methanone <b>60</b>.</p>
Full article ">Scheme 16
<p>Synthesis of a series of chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>62</b> from chromene-3-thiocarboxamides <b>61</b>.</p>
Full article ">Scheme 17
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]pyridine <b>67</b>.</p>
Full article ">Scheme 18
<p>Michael addition/intramolecular <span class="html-italic">O</span>-cyclization/elimination cascade.</p>
Full article ">Scheme 19
<p>An efficient method for the synthesis of chromeno[3,2-<span class="html-italic">c</span>]quinolones <b>77</b>.</p>
Full article ">Scheme 20
<p>One-pot three-component synthesis towards chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>81</b>.</p>
Full article ">Scheme 21
<p>The synthesis of benzo[5,6]chromeno[3,2-<span class="html-italic">c</span>]quinolones <b>83</b>.</p>
Full article ">Scheme 22
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]quinolones <b>87</b> and <b>88</b>.</p>
Full article ">Scheme 23
<p>Synthesis of a series of chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>92</b>.</p>
Full article ">Scheme 24
<p>Synthesis of chromenopyridines from 2-(2-dimethylaminoethenyl)chromones <b>95</b>.</p>
Full article ">Scheme 25
<p>Use of chromones <b>101</b> in construction of chromeno[3,2-<span class="html-italic">c</span>]pyridine core.</p>
Full article ">Scheme 26
<p>Synthesis of fluorescent chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>107</b> and <b>108</b>.</p>
Full article ">Scheme 27
<p>A TMSCl-promoted cyclization of 3-formylchromone with various anilines <b>110</b>.</p>
Full article ">Scheme 28
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>114</b> via 5+3] cycloaddition.</p>
Full article ">Scheme 29
<p>Intramolecular <span class="html-italic">C</span>-arylation in Ugi adduct chromones <b>119</b>.</p>
Full article ">Scheme 30
<p>Synthesis of a series of chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>124</b>.</p>
Full article ">Scheme 31
<p>[4+2]-cycloaddition in the construction of the chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>129</b> (<b>A</b>) and <b>131</b> (<b>B</b>).</p>
Full article ">Scheme 32
<p>Synthesis of thiophene-fused chromeno[3,2-<span class="html-italic">c</span>]pyridine <b>134</b>.</p>
Full article ">Scheme 33
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>138</b> via a domino three-component reaction.</p>
Full article ">Scheme 34
<p>An acid-promoted cascade cyclization of aryl group-substituted propargyl alcohol derivatives <b>139</b>.</p>
Full article ">Scheme 35
<p>Pd(II)-catalyzed tandem C–H alkenylation/C–O cyclization in the synthesis of chromeno[3,2-<span class="html-italic">c</span>]quinoline <b>142</b>.</p>
Full article ">Scheme 36
<p>Synthesis of chromenopyridodiazepinone <b>144</b> with chromeno[3,2-<span class="html-italic">c</span>]pyridine moiety.</p>
Full article ">Scheme 37
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]quinolones <b>147</b> via a Fe<sup>III</sup>-catalyzed imine formation/C-C coupling/oxidation cascade.</p>
Full article ">Scheme 38
<p>Stereochemistry in the synthesis of hexahydrochromenopyridines <b>150</b> and <b>151</b>.</p>
Full article ">Scheme 39
<p>Synthesis of chromeno[3,2-<span class="html-italic">c</span>]pyridines <b>154</b>.</p>
Full article ">
42 pages, 11760 KiB  
Review
Synthesis of Nitrogen-Containing Heterocyclic Scaffolds through Sequential Reactions of Aminoalkynes with Carbonyls
by Antonio Arcadi, Valerio Morlacci and Laura Palombi
Molecules 2023, 28(12), 4725; https://doi.org/10.3390/molecules28124725 - 12 Jun 2023
Cited by 4 | Viewed by 1859
Abstract
Sequential reactions of aminoalkynes represent a powerful tool to easily assembly biologically important polyfunctionalized nitrogen heterocyclic scaffolds. Metal catalysis often plays a key role in terms of selectivity, efficiency, atom economy, and green chemistry of these sequential approaches. This review examines the existing [...] Read more.
Sequential reactions of aminoalkynes represent a powerful tool to easily assembly biologically important polyfunctionalized nitrogen heterocyclic scaffolds. Metal catalysis often plays a key role in terms of selectivity, efficiency, atom economy, and green chemistry of these sequential approaches. This review examines the existing literature on the applications of reactions of aminoalkynes with carbonyls, which are emerging for their synthetic potential. Aspects concerning the features of the starting reagents, the catalytic systems, alternative reaction conditions, pathways and possible intermediates are provided. Full article
(This article belongs to the Special Issue Advances in Heterocyclic Synthesis)
Show Figures

Scheme 1

Scheme 1
<p>Gold-catalyzed synthesis of pyridines from propargylamine and carbonyls.</p>
Full article ">Scheme 2
<p>Transition metal-catalyzed sequential amination–cyclization–aromatization reaction.</p>
Full article ">Scheme 3
<p>Sequential reactions of carbonyl compounds and propargylamine catalyzed by Au-complex <b>8</b>.</p>
Full article ">Scheme 4
<p>Cu-catalyzed pyridine synthesis from cyclic ketones and propargylamine.</p>
Full article ">Scheme 5
<p>Linear vs. angular steroidal pyridines.</p>
Full article ">Scheme 6
<p>Copper-catalyzed synthesis of A-ring fused pyridine D-modified androstane derivatives.</p>
Full article ">Scheme 7
<p>Copper-catalyzed synthesis of betulin derivatives.</p>
Full article ">Scheme 8
<p>Optimization of the synthesis of relevant steroidal pyridines.</p>
Full article ">Scheme 9
<p>Gold-catalyzed synthesis of the carbacycloamine analogue <b>11</b>.</p>
Full article ">Scheme 10
<p>Gold-catalyzed synthesis of the potassium channel modulator <b>12</b>.</p>
Full article ">Scheme 11
<p>Synthesis of Wnt signal path inhibitors.</p>
Full article ">Scheme 12
<p>Gold-catalyzed synthesis of BAY-298.</p>
Full article ">Scheme 13
<p>Synthesis of BMS-846372.</p>
Full article ">Scheme 14
<p>Gold-catalyzed synthesis of the benzomorphane derivative <b>13</b>.</p>
Full article ">Scheme 15
<p>Gold-catalyzed synthesis of the tropane-related scaffold <b>14</b>.</p>
Full article ">Scheme 16
<p>Synthesis of 11β-hydroxysteroid dehydrogenase inhibitors.</p>
Full article ">Scheme 17
<p>Gold-catalyzed synthesis of the ligand <b>17</b>.</p>
Full article ">Scheme 18
<p>Gold-catalyzed synthesis of 2,5-dihydropyridines <b>18</b>.</p>
Full article ">Scheme 19
<p>Synthesis of pyridinium salts.</p>
Full article ">Scheme 20
<p>Metal-free synthesis of the hetero-anthracene derivative <b>20</b>.</p>
Full article ">Scheme 21
<p>Synthesis of the dihydrophenanthroline <b>21</b>.</p>
Full article ">Scheme 22
<p>Synthesis of natural products.</p>
Full article ">Scheme 23
<p>Construction of pyridines starting from (<span class="html-italic">S</span>)-(−)-perillaldehyde and (1<span class="html-italic">R</span>)-myrtenal.</p>
Full article ">Scheme 24
<p>Retrosynthetic pathway of suaveoline alkaloids.</p>
Full article ">Scheme 25
<p>Pyridine synthesis by a 6π-3-azatriene electrocyclization.</p>
Full article ">Scheme 26
<p>Synthesis of β- and γ-carbolines from indole aldehydes and substituted propargylic amines.</p>
Full article ">Scheme 27
<p>Synthesis of 4-benzylated carbolines <b>22</b>.</p>
Full article ">Scheme 28
<p>Alternative synthesis of polysubstituted pyridine derivatives from α,β-unsaturated carbonyl compounds and propargylamine hydrochloride.</p>
Full article ">Scheme 29
<p>Total synthesis of onychine <b>23</b>.</p>
Full article ">Scheme 30
<p>Mechanism for the formation of chromenopyridines <b>25</b>.</p>
Full article ">Scheme 31
<p>Sequential reaction of 2-(bis(prop-2-yn-1-ylamino)methyl benzaldehyde <b>26</b> with propargylamine.</p>
Full article ">Scheme 32
<p>Synthesis of naphthyridines <b>32</b>.</p>
Full article ">Scheme 33
<p>Synthesis of the chromenopyrazinone <b>33</b>.</p>
Full article ">Scheme 34
<p>Gold-catalyzed synthesis of pyrazines <b>34</b> from the reaction of propargylamine with aldehydes.</p>
Full article ">Scheme 35
<p>Proposed mechanism for the Au-catalyzed formation of pyrazines <b>34</b>.</p>
Full article ">Scheme 36
<p>Sequential reaction of propargylamine with aldehydes catalyzed by MCM-41-immobilized phosphine gold(I) complex [MCM-41-PPh<sub>3</sub>-AuNTf<sub>2</sub>].</p>
Full article ">Scheme 37
<p>Synthesis of 1,2,3-triazolo-1,4-benzodiazepines <b>35</b>.</p>
Full article ">Scheme 38
<p>Diversely substituted 1,2,3-triazolo-1,4-benzodiazepine <b>36</b>.</p>
Full article ">Scheme 39
<p>Indium-catalyzed multicomponent synthesis of 9<span class="html-italic">H</span>-benzo[<span class="html-italic">f</span>]imidazo [1,2-<span class="html-italic">d</span>][1,2,3]triazolo [1,5-<span class="html-italic">a</span>][1,4]diazepines <b>37</b>.</p>
Full article ">Scheme 40
<p>Indium-catalyzed synthesis of β-<span class="html-italic">(N</span>-indolyl)-α,β-unsaturated esters <b>40</b>.</p>
Full article ">Scheme 41
<p>Divergent sequential gold-catalyzed cyclization/alkenylation reaction of 2-alkynylanilines with 1,3-dicarbonyl compounds.</p>
Full article ">Scheme 42
<p><span class="html-italic">p</span>-TsOH promoted synthesis of 4-alkyl-2,3-disubstituted quinolines <b>42</b>.</p>
Full article ">Scheme 43
<p>Synthesis of dimeric quinolines <b>43</b>.</p>
Full article ">Scheme 44
<p>Iron(III)-catalyzed sequential condensation, cyclization and aromatization of 1,3-diketones with 2-ethynylaniline to afford 4-methyl-2,3-disubstituted quinolines <b>44</b>.</p>
Full article ">Scheme 45
<p>Sequential reaction of levulinic acid with 2-ethynylaniline under solventless conditions.</p>
Full article ">Scheme 46
<p>Copper(I)-catalyzed synthesis of 2-acylquinolines.</p>
Full article ">Scheme 47
<p>Copper-catalyzed synthesis of quinolines <b>45</b> from ethynylaniline and <span class="html-italic">N</span>, <span class="html-italic">O</span>-acetals.</p>
Full article ">Scheme 48
<p>Synthesis of 4-alkoxy-2-arylquinolines <b>46</b>.</p>
Full article ">Scheme 49
<p>Condensative cyclization of 6-amino-5-[(trimethylsilyl)ethynyl]-2<span class="html-italic">H</span>-chromen-2-one <b>47</b>.</p>
Full article ">Scheme 50
<p>Synergistic effect of Pd(II) and acid catalysts on the synthesis of ring-fused quinolines.</p>
Full article ">Scheme 51
<p>Sc(OTf)<sub>3</sub>-catalyzed bicyclization of 2-alkynylanilines with aldehydes.</p>
Full article ">Scheme 52
<p>Gold-catalyzed synthesis of polycyclic frameworks <b>54</b>.</p>
Full article ">Scheme 53
<p>Iodonium-induced tandem cyclization of <span class="html-italic">N</span>-(2<span class="html-italic">-</span>alkynylphenyl) imines <b>53</b>.</p>
Full article ">Scheme 54
<p>One-pot synthesis of 2,2′-disubstituted diindolylmethanes <b>57</b>.</p>
Full article ">Scheme 55
<p>Gold-catalyzed synthesis of 1-substituted 2-tosyl-2,3,4,5-tetrahydropyrido [4,3-<span class="html-italic">b</span>]indoles <b>62</b>.</p>
Full article ">Scheme 56
<p>Palladium-catalyzed synthesis of <span class="html-italic">N</span>-tosyl-3-hyroxymethyl indoles.</p>
Full article ">Scheme 57
<p>Cu(OTf)<sub>2</sub>-catalyzed synthesis of quinoline-annulated polyheterocyclic frameworks <b>64</b>.</p>
Full article ">Scheme 58
<p>Plausible reaction mechanism.</p>
Full article ">Scheme 59
<p>Palladium-catalyzed synthesis of 1-benzoazepine carbonitriles <b>71</b>.</p>
Full article ">Scheme 60
<p>Product-selectivity control of the sequential reaction of 2-alkynylaniline with ketones.</p>
Full article ">Scheme 61
<p>Proposed mechanism for the synthesis of quinolinones <b>72</b>.</p>
Full article ">Scheme 62
<p>Proposed mechanism for the synthesis of quinolines <b>73</b> and <span class="html-italic">N</span>-alkenylindoles <b>74</b>.</p>
Full article ">Scheme 63
<p>Alternative mechanism for the synthesis of quinolines <b>73</b>.</p>
Full article ">Scheme 64
<p>Synthesis of acridine derivatives.</p>
Full article ">Scheme 65
<p>Mn(OAc)<sub>3</sub>-mediated synthesis of 2-substituted quinolines from 2-alkynylanilines and β-ketoesters.</p>
Full article ">Scheme 66
<p>Sequential amination–annulation–aromatization reactions of β-(2-aminophenyl)-α,β-ynones <b>75</b> with enolizable ketones.</p>
Full article ">Scheme 67
<p>Product-selectivity control in the synthesis of polycyclic steroidal quinolines <b>76</b>.</p>
Full article ">Scheme 68
<p>Domino reactions of β-(2-aminophenyl)-α,β-ynones with 1,3-dicarbonyls.</p>
Full article ">Scheme 69
<p>Sequential aminopalladation of β-amino alkynes <b>79</b>.</p>
Full article ">Scheme 70
<p>Retrosynthetic assembly of <span class="html-italic">11H</span>-indolo [3,2-<span class="html-italic">c</span>]quinolines.</p>
Full article ">Scheme 71
<p>Gold-catalyzed synthesis of <span class="html-italic">11H</span>-indolo [3,2-<span class="html-italic">c</span>]quinoline <b>82</b>.</p>
Full article ">Scheme 72
<p>Brønsted acid-catalyzed synthesis of 2,2′-disubstituted <span class="html-italic">1H</span>,<span class="html-italic">1′H</span>-3,3′-biindoles <b>83</b>.</p>
Full article ">Scheme 73
<p>Proposed mechanism.</p>
Full article ">Scheme 74
<p>Gold-catalyzed reaction of 2-[(2-aminophenyl)ethynyl]phenylamines <b>81</b> with isatins and ketones.</p>
Full article ">Scheme 75
<p>Indium(III)-catalyzed sequential reaction of 2-alkynylanilines with 2-alkynylbenzaldehydes.</p>
Full article ">Scheme 76
<p>Synthesis of 2-alkoxyfuro [2,3-<span class="html-italic">c</span>]quinolones <b>87</b>.</p>
Full article ">Scheme 77
<p>Proposed mechanism.</p>
Full article ">Scheme 78
<p>Sequential multicomponent approach to 2,2-disubstituted 3-methyleneindolines <b>93</b>.</p>
Full article ">Scheme 79
<p>Synthesis of 1-tosyl-2,3,4,5-tetrahydro-<span class="html-italic">1H</span>-indeno [1,2-<span class="html-italic">b</span>]-pyridines <b>95</b>.</p>
Full article ">Scheme 80
<p>Synthesis of pyrrolo[1,2-<span class="html-italic">a</span>]quinolines <b>98</b>.</p>
Full article ">Scheme 81
<p>Platinum(II)-catalyzed synthesis of indolines <b>100</b>.</p>
Full article ">Scheme 82
<p>Platinum(II)-catalyzed synthesis of tetrahydroquinolines <b>102</b>.</p>
Full article ">
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