One-Step Catalytic Synthesis of Alkyl-Substituted Quinolines

Three-Component Synthesis of Quinoline-4-carboxylic Acids Based on Doebner Hydrogen-Transfer Reaction

The Doebner hydrogen-transfer reaction has been developed for the synthesis of substituted quinolines from anilines possessing electron-withdrawing groups, which are known to give products in low yields when used in the conventional Doebner reaction. This reaction can be applied to not only anilines having electron-withdrawing groups but also those having electron-donating groups and can be used in the large-scale synthesis of bioactive molecules.

FeCl3-Catalyzed Decyanative [4 + 2] Annulation of α-Aminonitriles with Alkynes: Access to 2,4-Diaryl Quinolines in Batch and Continuous-Flow Processes

FeCl₃-catalyzed decyanation of α-aminonitriles followed by a [4 + 2] annulation with terminal alkynes has been developed to synthesize 2,4-diaryl quinolines. A broad range of aniline, aldehyde, and arylacetylene derivatives were well tolerated to access 2,4-diaryl quinolines in moderate to good yields. The control experiment studies suggested that the reaction proceeds through a nonradical pathway involving Povarov-type [4 + 2] annulation from the in situ generated iminium species. The synthetic application of this strategy (i) includes gram-scale synthesis and (ii) a continuous-flow process for a few representative compounds in a shorter reaction time (22 min) and (iii) worked well with styrene as a proof of concept.

Deaminative Cyclization of Tertiary Amines for the Synthesis of 2-Arylquinoline Derivatives with a Nonsubstituted Vinylene Fragment

With triethylamine as a vinylene source, a convenient protocol for the regioselective synthesis of β,γ-nonsubstituted 2-arylquinolines from aldehydes and arylamines has been accomplished. The deaminative cyclization is also extended to long-chain tertiary alkylamines, enabling diverse alkyl groups to be concurrently installed into the pyridine rings. This process demonstrates a new conversion pathway for the simultaneous dual C(sp³)-H bond functionalization of tertiary amines, wherein the transient acyclic enamines generated in situ undergo the Povarov reaction.

One-Pot Synthesis of Novel Functionalized Fused Pyridine Derivatives via Consecutive Pyrrolidine Ring-Closure/Ring-Opening/Formal Aza-Diels-Alder Reactions

In this article, we report a highly regioselective method for the synthesis of new fused pyridine derivatives─2,3-disubstituted quinolines and 1,2-dihydro-3H-pyrazolo[3,4-b]pyridin-3-one derivatives. The method is based on the reaction of 1,1-diethoxybutane derivatives with aromatic and heterocyclic nucleophiles. The isolated compounds are similar to the products formed as a result of the Debner-Miller reaction. However, we have shown that the interaction of 1,1-diethoxybutane derivatives with (hetero)aromatic amines proceeds according to a mechanism different from that of the Doebner-Miller reaction. The proposed method is distinguished by the possibility of obtaining a wide range of substituted quinolines and 1,2-dihydro-3H-pyrazolo[3,4-b]pyridin-3-one derivatives in one step, the absence of the need to use expensive metal-containing catalysts, and a high product yield.

The Povarov Reaction: A Versatile Method to Synthesize Tetrahydroquinolines, Quinolines and Julolidines

The multicomponent Povarov reaction represents a powerful approach for the construction of substances containing N-heterocyclic frameworks. By using the Povarov reaction, in addition to accessing tetrahydroquinolines, quinolines and julolidines in a single step, it is possible to form the following new bonds: two Csp 3–Csp 3 and one Csp 3–Nsp 3, two Csp 2–Csp 2 and one Csp 2–Nsp 2, and four Csp 3–Csp 3 and two Csp 3–Nsp 1, respectively. This short review discusses the main features of the Povarov reaction, including its mechanism, the reaction scope by employing different catalysts and substrates, as well as stereoselective versions.

1 Introduction

2 Mechanism of the Povarov Reaction

3 Tetrahydroquinolines

4 Quinolines

5 Julolidines

6 Concluding Remarks

Synthesis and Applications of Asymmetric Catalysis Using Chiral Ligands Containing Quinoline Motifs

In the past decade, asymmetric synthesis of chiral ligands containing quinoline motifs, a family of natural products displaying a broad range of structural diversity and their metal complexes have become the most significant methodology for the generation of enantiomerically pure compounds of biological and pharmaceutical interest. This review provides comprehensive insight on the plethora of nitrogen-based chiral ligands containing quinoline motifs and organocatalysts used in asymmetric synthesis. However, it is circumscribed to the synthesis of quinoline-based chiral ligands and metal complexes, and their applications in asymmetric synthesis as a homogeneous and heterogeneous catalyst.

Navigating chemical reaction space – application to DNA-encoded chemistry

Databases contain millions of reactions for compound synthesis, rendering selection of reactions for forward synthetic design of small molecule screening libraries, such as DNA-encoded libraries (DELs), a big data challenge. To support reaction space navigation, we developed the computational workflow Reaction Navigator. Reaction files from a large chemistry database were processed using the open-source KNIME Analytics Platform. Initial processing steps included a customizable filtering cascade that removed reactions with a high probability to be incompatible with DEL, as they would e.g. damage the genetic barcode, to arrive at a comprehensive list of transformations for DEL design with applicability potential. These reactions were displayed and clustered by user-defined molecular reaction descriptors which are independent of reaction core substitution patterns. Thanks to clustering, these can be searched manually to identify reactions for DEL synthesis according to desired reaction criteria, such as ring formation or sp³ content. The workflow was initially applied for mapping chemical reaction space for aromatic aldehydes as an exemplary functional group often used in DEL synthesis. Exemplary reactions have been successfully translated to DNA-tagged substrates and can be applied to library synthesis. The versatility of the Reaction Navigator was then shown by mapping reaction space for different reaction conditions, for amines as a second set of starting materials, and for data from a second database.

The computational tool Reaction Navigator supports chemical reaction space navigation by filtering and clustering reactions from chemistry databases. The utility of the tool was demonstrated by identification of reactions for DNA-encoded libraries.

One-pot synthesis of 3-aminofurans using a simple and efficient recyclable CuI/[bmim]PF6 system

A one-pot three-component reaction of several 2-ketoaldehydes, secondary amines and terminal alkynes to access 3-aminofurans proceeded well in [bmim][PF₆] using a simple and cheap CuI catalyst. The resultant 3-aminofuran products were easily isolated using diethyl ether and the CuI/[bmim][PF₆] system was reused six times with a slight decrease in the activity.

High-Voltage-Tolerant Covalent Organic Framework Electrolyte with Holistically Oriented Channels for Solid-State Lithium Metal Batteries with Nickel-Rich Cathodes

By introducing lithiophilic groups and electrochemically stable quinolyl aromatic ring linkages, we prepared covalent organic frameworks (COFs) exhibiting a large band gap with an ultralow HOMO value (-6.2 eV under vacuum) and oxidative stability up to 5.6 V (versus Li⁺ /Li) as solid-state electrolytes (SSEs). The obtained flexible COF SSE thin films showed a holistically oriented arrangement along the (001) facet with remarkable ionic conductivity up to 1.5×10^-4  S cm^-1 at 60 °C and excellent mechanical strength with a high Young's modulus of 10.5 GPa. Molecular dynamic simulations showed that lithium ions are transmitted in this COF SSE by directional hopping paths with fast drift velocity. The COF SSE film was used to assemble all-solid-state lithium metal batteries with nickel-rich cathodes (NMC811). The batteries demonstrated stable cycling performance over 400 cycles, high coulombic efficiency (>99 %), and could also withstand abuse tests, such as folding.

One-Pot Synthesis of Triazatriphenylene Using the Povarov Reaction

The Povarov reaction combines aromatic amines, aldehydes, and alkynes in a single step and is regarded as an annulative π-extension reaction of aromatic amines. In this study, the Povarov reaction was investigated as an efficient tool for the synthesis of aza-polycyclic aromatic hydrocarbons via multiple π-extensions. The double Povarov reaction of 1,4-diaminobenzene yielded the 4,7-phenanthroline derivative as the major product, regardless of the steric repulsion in the product. The site selectivity mainly depended on the HOMO distribution of the intermediate rather than the steric factor. Based on these insights, a 1,5,9-triazatriphenylene derivative was synthesized via a triple Povarov reaction. The structures of the synthesized compounds were unambiguously determined by single-crystal X-ray diffraction analysis. The triazatriphenylene derivative formed a smooth and stable thin film upon vacuum vapor deposition and served as a hole-blocking material in organic light-emitting diodes.

Biradical o-iminobenzosemiquinonato(1-) complexes of nickel(ii): catalytic activity in three-component coupling of aldehydes, amines and alkynes

The six-coordinated bis-o-iminosemiquinone complex, NiL2 BIS, in which LBIS is the o-iminosemiquinone 1-electron oxidized form of the tridentate o-aminophenol benzoxazole-based ligand H2LBAP, was synthesized and characterized. The crystal structure of the complex reveals octahedral geometry with a NiN4O2 coordination sphere in which Ni(ii) has been surrounded by two tridentate LBIS ligands. This compound exhibits (S Ni = 1) with both spin and orbital contribution to the magnetic moment and antiferromagnetic coupling between two electrons on two LBIS ligands which results in a triplet spin ground state (S = 1). The electronic transitions and the electrochemical behavior of this open-shell molecule are presented here, based on experimental observations and theoretical calculations. The electrochemical behavior of NiL2 BIS was investigated by cyclic voltammetry and indicates ligand-centered redox processes. Three-component coupling of aldehydes, amines and alkynes (A3-coupling) was studied in the presence of the NiL2 BIS complex, and the previously reported four-coordinated bis-o-iminosemiquinone NiL2 NIS. Furthermore, among these two o-iminobenzosemiquinonato(1-) complexes of Ni(ii) (NiL2 NIS and NiL2 BIS), NiL2 NIS was found to be an efficient catalyst in A3-coupling at 85 °C under solvent-free conditions and can be recovered and reused for several cycles with a small decrease in activity.

Synthesis of Green/Blue Light Emitting Quinolines by Aza-D-A Reaction Using InCl3 Catalyst

An efficient InCl3-catalyzed sequential reaction of aromatic amines, aromatic aldehydes and functionalized alkynes leading to the formation of new quinoline derivatives exhibiting significant fluorescence activities is described. The photophysical investigations of quinolines were carried out by absorption and photoluminescence measurements. One particular compound 4 h having maximum intensity, emitting green colour (Φ = 0.78) with average life time of 6.20 ns was the best amongst the tested compounds. The presence of the amino group at the 4-aryl substituent of the quinoline backbone played an important role in executing the Povarov cyclization successfully and enhancing the flourescence properties of the newly synthesized quinolines.

Visible-light-induced and copper-catalyzed oxidative cyclization of substituted o-aminophenylacetylene for the synthesis of quinoline and indole derivatives

A visible-light-induced and copper-catalyzed oxidative cyclization of substituted o-aminophenylacetylene for the synthesis of quinoline and indole derivatives was developed.

Synthesis of Robust MOFs@COFs Porous Hybrid Materials via an Aza-Diels-Alder Reaction: Towards High-Performance Supercapacitor Materials

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have attracted enormous attention in recent years. Recently, MOF@COF are emerging as hybrid architectures combining the unique features of the individual components to enable the generation of materials displaying novel physicochemical properties. Herein we report an unprecedented use of aza-Diels-Alder cycloaddition reaction as post-synthetic modification of MOF@COF-LZU1, to generate aza-MOFs@COFs hybrid porous materials with extended π-delocalization. A a proof-of-concept, the obtained aza-MOFs@COFs is used as electrode in supercapacitors displaying specific capacitance of 20.35 μF cm^-2 and high volumetric energy density of 1.16 F cm^-3 . Our approach of post-synthetic modification of MOFs@COFs hybrids implement rational design for the synthesis of functional porous materials and expands the plethora of promising application of MOFs@COFs hybrid porous materials in energy storage applications.

Mechanochemical Synthesis of Functionalized Quinolines by Iodine Mediated Oxidative Annulation

An iodine-mediated environmentally benign synthesis of multi-substituted quinoline derivatives is developed using a solvent-free mechanochemical process. Appropriately designed and easily accessible protecting group-free aniline derivatives were used for the oxidative annulation reaction, and a series of quinoline derivatives with variable functionalities were synthesized up to 89 % isolated yield. Importantly, the activator iodine remains in the quinoline molecule and promotes further functionalizations. The present methodology is beneficial with regard to operational simplicity and mild reaction conditions.

Recent Progress in the Synthesis of Quinolines

BACKGROUND

Quinoline-containing compounds present in both natural and synthetic products are an important class of heterocyclic compounds. Many of the substituted quinolines have been used in various areas including medicine as drugs. Compounds with quinoline skeleton possess a wide range of bioactivities such as antimalarial, anti-bacterial, anthelmintic, anticonvulsant, antiviral, anti-inflammatory, and analgesic activity. Due to such a wide range of applicability, the synthesis of quinoline derivatives has attracted a lot of attention of chemists to develop effective methods. Many known methods have been expanded and improved. Furthermore, various new methods for quinoline synthesis have been established. This review will focus on considerable studies on the synthesis of quinolines date which back to 2014.

OBJECTIVE

In this review, we discussed recent achievements on the synthesis of quinoline compounds. Some classical methods have been modified and improved, while other new methods have been developed. A vast variety of catalysts were used for these transformations. In some studies, quinoline synthesis reaction mechanisms were also displayed.

CONCLUSION

Many methods for the synthesis of substituted quinoline rings have been developed recently. Over the past five years, the majority of those reported have been based on cycloisomerization and cyclization processes. Undoubtedly, more imaginative approaches to quinoline synthesis will appear in the literature in the near future. The application of known methods to natural product synthesis is probably the next challenge in the field.

Copper-based catalysts derived from salen-type ligands: synthesis of 5-substituted-1H-tetrazoles via [3+2] cycloaddition and propargylamines via A3-coupling reactions

Base-metal copper(ii) complexes derived from unsymmetrical salen-type ligands were designed and synthesized using ligands L¹H to L⁴H. These complexes were employed as catalysts for [3+2] cycloaddition and A³-coupling reactions.

Recent synthetic efforts in the preparation of 2-(3,4)-alkenyl (aryl) quinoline molecules towards anti-kinetoplastid agents

Leishmaniasis, Chagas disease and African sleeping sickness have been considered some of the most important tropical protozoan afflictions. As the number of drugs currently available to treat these human illnesses is severely limited and the majority has poor safety profiles and complicated administration schedules, actually there is an urgent need to develop new effective, safe and cost-effective drugs. Because quinoline alkaloids with antiprotozoal activity (quinine, chimanine, cryptolepine or huperzine groups) were historically and are still essential models for drug research to combat these parasitic infections, synthetic or semi-synthetic quinoline-based molecules are important for anti-kinetoplastid drug design approaches and synthetic methods of their preparation become a key task that is the central subject of this review. Its goal is to highlight the advances in the conventional and current syntheses of new 2-(3,4)-alkenyl (aryl) quinoline derivatives, which kill the most important kinetoplastid protozoa, – Leishmania and Trypanosoma and could be useful models for antileishmanial and antitrypanosomal research. An attempt has been made to present and discuss the more recent contributions in this field over the period 2015–2019, paying special attention to molecular design, synthetic efforts to new green reaction conditions for classical methods such as Skraup synthesis, Friedländer synthesis, Conrad–Limpach, Doebner–Miller, as well as contemporary methods like Gould–Jacobs, Meth–Cohn and Povarov reactions. This review includes brief general information on these neglected tropical diseases, their current chemotherapies, and primary natural models (quinoline alkaloids), suitable for development of anti-kinetoplastid quinoline-based agents. The main part of the review comprises critical discussion on the synthesis and chemistry of new quinolines diversely substituted by alkyl (alkenyl, aryl) fragments on the pyridine part of the quinoline skeleton, which could be considered interesting analogues of chimanine alkaloids. The methods described in this review were developed with the aim of overcoming the drawbacks of the traditional protocols using revolutionary precursors and strategies.

Leishmaniasis, Chagas disease and African sleeping sickness have been considered some of the most important tropical protozoan afflictions.

Oxidative [4+2] Cycloaddition of α-(N-Arylamino) Carbonyls with Aryl Alkenes by Multiple C-H Functionalizations and [1,2]-Aryl Shifts

A new, general copper-catalyzed oxidative tandem [4+2] cycloaddition of α-(N-arylamino) carbonyl compounds with aryl alkenes to produce highly substituted quinolines has been developed, which allows the formation of three new C-C bonds through a sequence of multiple C-H functionalizations, annulation, and [1,2]-aryl shifts.

Reaching Green: Heterocycle Synthesis by Transition Metal-Catalyzed C-H Functionalization in Sustainable Medium

Catalytic C-H functionalization has emerged as an efficient alternative to traditional coupling reactions. However, some of these reactions depend on environmentally harmful solvents, weakening the overall green nature of these methods. As organic processes consume large amount of solvents, the use of less harmful solvents enhance the sustainability of these reactions. Herein, we present an overview of transition metal-catalyzed C-H functionalization reactions for the synthesis of heterocycles in sustainable solvents based on CHEM21 solvent selection guide.

A visible-light-induced oxidative cyclization of N-propargylanilines with sulfinic acids to 3-sulfonated quinoline derivatives without external photocatalysts

A visible-light-induced oxidative cyclization of N-propargyl anilines with sulfinic acids to 3-sulfonated quinoline derivatives was developed under external photocatalyst-free conditions.

Photoredox-catalyzed cascade addition/cyclization of N-propargyl aromatic amines: access to 3-difluoroacetylated or 3-fluoroacetylated quinolines

3-Difluoroacetylated quinolines and 3-fluoroacetylated quinolines were synthesized via a visible-light-induced cascade addition/cyclization of N-propargyl aromatic amines catalyzed by fac-Ir(ppy)₃ under mild conditions.

Synthesis of substituted 4-hydroxyalkyl-quinoline derivatives by a three-component reaction using CuCl/AuCl as sequential catalysts

A new method to construct 4-hydroxyalkyl-quinoline derivatives is described via Cu(i) and Au(i) sequential catalyzed cyclization of anilines with aldehyde derivatives and aliphatic alkynes, respectively.

Synthesis and Reactivity of Propargylamines in Organic Chemistry

Propargylamines are a versatile class of compounds which find broad application in many fields of chemistry. This review aims to describe the different strategies developed so far for the synthesis of propargylamines and their derivatives as well as to highlight their reactivity and use as building blocks in the synthesis of chemically relevant organic compounds. In the first part of the review, the different synthetic approaches to synthesize propargylamines, such as A³ couplings and C-H functionalization of alkynes, have been described and organized on the basis of the catalysts employed in the syntheses. Both racemic and enantioselective approaches have been reported. In the second part, an overview of the transformations of propargylamines into heterocyclic compounds such as pyrroles, pyridines, thiazoles, and oxazoles, as well as other relevant organic derivatives, is presented.

An Efficient One-Pot Synthesis of Densely Functionalized Fused-Quinolines via Sequential Ugi4CC and Acid-Mediated Povarov-Type Reaction

A divergent synthesis of fused-quinolines has been explored by performing Ugi four-component condensation and sulfuric acid promoted deprotection/Povarov-type reaction in one-pot. The process involves Ugi condensation of propiolic acids, aldehydes/ketones, aminoaldehyde acetals and isocyanides followed by sulfuric acid promoted deprotection and Povarov-type reaction with anilines in ethanol. This method enables straightforward access to the structurally diverse 2,3-dihydro-1H-pyrrolo[3,4-b]quinolin-1-ones (DHPQ), 3,4-dihydrobenzo[b][1,6]naphthyridin-1(2H)-ones (DHBN), and 2,3,4,5-tetrahydro-1H-azepino[4,3-b]quinolin-1-ones (THAQ), starting from readily available starting materials.

Amine-Triggered Highly Facile Oxidative Benzannulation Reaction for the Synthesis of Anthranilates under Solvent-Free Calcium(II) Catalysis

An amine-triggered facile synthetic approach of anthranilates has been described through benzannulation of readily available chemicals under one-pot solvent-free conditions using Ca(OTf)₂ as the sustainable catalyst. In this regioselective approach, we described a reasonably longer cascade, which proceeds through β-enamino ester formation/Michael addition/intramolecular aldol reaction/elimination/aromatization/oxidative debenzylation/lactonization with a broad substrate scope and high yields. The isolation of intermediates authenticated the mechanism, and the synthetic utility of the products was also demonstrated.

Study of the Hetero-[4+2]-Cycloaddition Reaction of Aldimines and Alkynes. Synthesis of 1,5-Naphthyridine and Isoindolone Derivatives

Both experimental and computational studies for the cycloaddition reaction between N-(3-pyridyl)aldimines and acetylenes where 1,5-naphthyridines are obtained are reported. The reaction of benzaldimine with a methoxycarbonyl group in position 2 with phenyl acetylene, styrene, and indene afforded polycyclic isoindolone derivatives. The mechanism of reaction of N-(3-pyridyl)aldimines with olefins can be explained by an asynchronous [4+2] cycloaddition; in the case of acetylenes, the obtained results suggest a stepwise mechanism through a 3-azatriene.

A novel environmentally sustainable synthesis of Au–Ag@AgCl nanocomposites and their application as an efficient and recyclable catalyst for quinoline synthesis

An eco-friendly synthesis of Au–Ag@AgCl NCs was described using the tuber extract of Nephrolepis cordifolia. The synthetic utility of the NCs was demonstrated by the synthesis of pharmaceutically important quinoline derivatives.