Direct Synthesis of Quinolines via Co(III)-Catalyzed and DMSO-Involved C–H Activation/Cyclization of Anilines with Alkynes

Recent advancement in the synthesis of quinoline derivatives via multicomponent reactions

The synthesis of quinoline derivatives through multicomponent reactions (MCRs) has emerged as an efficient and versatile strategy in organic synthesis. MCRs offer the advantage of constructing complex molecular architectures in a single step, utilising multiple starting materials in a convergent manner. This review provides an overview of recent advancements in the field of quinoline synthesis via MCRs. Various MCRs, such as the Povarov reaction, the Gewald reaction, and the Ugi reaction have been successfully employed for the synthesis of diverse quinoline scaffolds. These methodologies not only showcase high atom economy but also allow the incorporation of structural diversity into the final products. The versatility of MCRs enables the introduction of functional groups and substitution patterns tailored to specific applications. This review highlights the significance of quinoline derivatives in medicinal chemistry, materials science, and other interdisciplinary areas. The continuous innovation and development of novel MCR-based approaches for quinoline synthesis hold great promise for the rapid and efficient generation of valuable compounds with a wide range of biological and physicochemical properties.

p-TSA·H2O catalyzed metal-free and environmentally benign synthesis of 4-aryl quinolines from arylamine, arylacetylene, and dimethyl sulfoxide

An environmentally benign and metal-free synthesis of 4-aryl quinolines is reported by employing readily available arylamine, arylacetylene, and DMSO in the presence of 20 mol% p-TSA·H2O. In the present protocol, the solvent DMSO serves as a reactant cum solvent for providing the C2 carbon atom of the quinoline skeleton. Notably, the reaction proceeds effectively and efficiently without the involvement of any metal catalyst, ligand, and co-catalyst as additives and inert atmospheric reaction conditions. This method provides high atom economy and good yields, and two C-C and one C-N bonds are formed in a single step through a three-component reaction.

Rongalite as C1 Synthon in the Synthesis of Divergent Pyridines and Quinolines

Rongalite has been used as a cheap and efficient carbon synthon for the synthesis of divergent N-heteroaromatics, including different pyridines and quinolines. The selective synthesis of different products can be achieved by employing enaminones or enaminones/anilines as reaction partners. In addition, compared with the reaction using conventional aldehyde synthons, rongalite displays an evident advantage in providing products with considerably higher product yields under milder conditions. The GC-MS analysis of the reaction process has been performed to probe the possible reaction mechanism.

A Pummerer Reaction-Enabled Modular Synthesis of Alkyl Quinoline-3-carboxylates and 3-Arylquinolines from Amino Acids

Concise synthesis of functionalized quinolines has received continuous research attention owing to the biological importance and synthetic potential of bicyclic N-heterocycles. However, synthetic routes to the 2,4-unsubstituted alkyl quinoline-3-carboxylate scaffold, which is an important motif in drug design, remain surprisingly limited, with modular protocols that proceed from readily available materials being even more so. We herein report an acidic I₂-DMSO system that converts readily available aspartates and anilines into alkyl quinoline-3-carboxylate. This method can be extended to a straightforward synthesis of 3-arylquinolines by simply replacing the aspartates with phenylalanines. Mechanistic studies revealed that DMSO was activated by HI via a Pummerer reaction to provide the C1 synthon, while the amino acid catabolized to the C2 synthon through I₂-mediated Strecker degradation. A formal [3 + 2 + 1] annulation of these two concurrently generated synthons with aniline was responsible for the selective formation of the quinoline core. The synthetic utility of this protocol was illustrated by the efficient synthesis of human 5-HT4 receptor ligand. Moreover, an unprecedented chemoselective synthesis of 2-deuterated, 3-substituted quinoline, featuring this reaction, has been established.

Recent Advances in DMSO-Based Direct Synthesis of Heterocycles

Besides serving as a low-toxicity, inexpensive and easily accessible solvent, dimethyl sulfoxide (DMSO) has also been extensively used as a versatile reagent for the synthesis of functionalized molecules. Dimethyl sulfoxide can not only be utilized as a carbon source, a sulfur source and an oxygen source, but also be employed as a crucial oxidant enabling various transformations. The past decade has witnessed a large number of impressive achievements on the direct synthesis of heterocycles as well as modifications of heterocyclic compounds by applying DMSO as a reagent. This review summarized the DMSO-based direct heterocycle constructions from 2012 to 2022.

Modification of Pyrrolo[2,1-a]isoquinolines and Pyrrolo[1,2-a]quinolines with Ammonium Acetate and Dimethyl Sulfoxide via Methylthiomethylation

An efficient methylthiomethylation of pyrroloisoquinolines and pyrroloquinolines has been reached by the use of ammonium acetate and dimethyl sulfoxide. Methylthiomethylated heterocycles can be obtained in moderate to good yields in most cases, while trace amounts to good yields of methylene-bridged products can be observed. Choice of DMSO activator and its amount have a great influence on the chemoselectivity of this process. It is worth noting that this process can also be scalable. Another feature of this process is that the product can be transformed to sulfone and sulfoxide easily.

Recent Advance on Dimethyl Sulfoxide (DMSO) Used as a Multipurpose Reactant

Abstract:

Dimethyl sulfoxide (DMSO) is not only a common and cheap aprotic polar solvent with low toxicity, but also serves as an efficient and multipurpose reactant and has widely been used in organic synthesis. DMSO as an important precursor can effectively introducea broad range of functional fragments into organic molecules, such as -Me, -CH, -CH2, -SMe2, -CH2SMe, -CH2SOMe, -SMe, -SO2Me, -SOMe or as O substituents, and serves as a mild oxidant in organic transformations. Many significant achievements based on DMSO as a synthon in synthetic chemistry have rapidly made over the past several years. To help researchers further understand the recent advances in the field, the review summarizes the applications of DMSO as carbon, sulfur, and oxygen sources and is used as the dual synthon in synthetic transformations.

Electrophilic amidomethylation of arenes with DMSO/MeCN reagents

An efficient electrophilic amidomethylation of aromatics was described with DMSO as the CH2 source and nitrile as the nitrogen source.

DMSO as a Dual Carbon Synthon in One-pot Tandem Synthesis of N-alkylated Quinazolinones from Anthranilamides and Acetophenones

A new, efficient, metal-free, and DMSO intervened approach for the synthesis of N-alkylated quinazolinones from readily available 2-aminobenzamide and aryl methyl ketones in the presence of an oxidizing agent has...

Iron-catalyzed [3+2+1] annulation of 2-aminobenzimidazoles/3-aminopyrazoles and aromatic alkynes using N,N-dimethylaminoethanol as one carbon synthon for the synthesis of pyrimido[1,2-a]benzimidazoles and pyrimido[1,2-b]indazoles

A simple and efficient method for the synthesis of pyrimido[1,2-a]benzimidazoles and pyrimido[1,2-b]indazoles from 2-aminobenzimidazoles/3-aminoindazoles, alkynes and N,N-dimethylaminoethanol in a three-component [3+2+1] annulation catalyzed by FeCl3 has been established, where N,N-dimethylaminoethanol...

Direct oxidation of N-ynylsulfonamides into N-sulfonyloxoacetamides with DMSO as a nucleophilic oxidant

N-Arylethynylsulfonamides are oxidized into N-sulfonyl-2-aryloxoacetamides directly and efficiently with dimethyl sulfoxide (DMSO) as both an oxidant and solvent with microwave assistance. DFT calculations indicate that DMSO nucleophilically attacks the ethylic triple bond and transfers its oxygen atom to the triple bond to form zwitterionic anionic N-sulfonyliminiums to trigger the reaction. Then it nucleophilically attacks the generated iminium intermediates to accomplish the oxidation via the second oxygen atom transfer. The current method provides a straightforward and efficient strategy to transform various N-arylethynylsulfonamides into N-sulfonyl-2-aryloxoacetamides, sulfonyl oxoacetimides, without any other electrophilic activators or oxidants.

Iodine-imine Synergistic Promoted Povarov-Type Multicomponent Reaction for the Synthesis of 2,2'-Biquinolines and Their Application to a Copper/Ligand Catalytic System

An efficient iodine-imine synergistic promoted Povarov-type multicomponent reaction was reported for the synthesis of a practical 2,2'-biquinoline scaffold. The tandem annulation has reconciled iodination, Kornblum oxidation, and Povarov aromatization, where the methyl group of the methyl azaarenes represents uniquely reactive input in the Povarov reaction. This method has broad substrate scope and mild conditions. Furthermore, these 2,2'-biquinoline derivatives had been directly used as bidentate ligands in metal-catalyzed reactions.

Cobalt-Catalyzed, Directed Intermolecular C-H Bond Functionalization for Multiheteroatom Heterocycle Synthesis: The Case of Benzotriazine

Transition-metal-catalyzed, directed intermolecular C-H bond functionalization is synthetically useful but heavily underexplored in multiheteroatom heterocycle synthesis. Herein we report a cobalt catalytic method for the formation of a three-nitrogen-bearing benzotriazine scaffold via the coupling of arylhydrazine and oxadiazolone. This synthetic protocol features a low-cost base metal catalyst, a maximum number of heteroatoms built into a heterocycle, a distinct synthetic logic for benzotriazines, a superior step economy, and a broad substrate scope.

Formylation and Bromination of Pyrrolo[2,1-a]isoquinoline Derivatives with Bromoisobutyrate and Dimethyl Sulfoxide

We have developed an efficient formylation of pyrroloisoquinolines using bromoisobutyrate and dimethyl sulfoxide as carbonyl reagent. Various formylated pyrroloisoquinolines could be prepared in good yields (up to 94%). This formylation process can be easily scaled up to gram scale with good yield. In most cases of pyrroloisoquinolines without methoxy groups, the combination of bromoisobutyrate and dimethyl sulfoxide could act as a bromination reagent, delivering brominated pyrroloisoquinolines in acceptable to good yields (up to 82%).

An expedient route to tricyanovinylindoles and indolylmaleimides from o-alkynylanilines utilising DMSO as a one-carbon synthon

A Pd(ii)/Cu(ii) catalysed domino synthesis of tricyanovinylindoles has been achieved using DMSO as a one-carbon synthon. The reaction proceeds via the construction of 2-aryl-3-formyl indole followed by sequential addition of malononitrile and a CN resulting in two C-C, one C[double bond, length as m-dash]C and one C-N bonds in the final product. Furthermore, post-synthetic modification results in the unprecedented formation of 4-cyano-3-indolylmaleimides. Photophysical studies of selected compounds show emission in the visible range.

Synthetic and medicinal perspective of quinolines as antiviral agents

In current scenario, various heterocycles have come up exhibiting crucial role in various medicinal agents which are valuable for mankind. Out of diverse range of heterocycle, quinoline scaffold have been proved to play an important role in broad range of biological activities. Several drug molecules bearing a quinoline molecule with useful anticancer, antibacterial activities etc have been marketed such as chloroquine, saquinavir etc. Owing to their broad spectrum biological role, various synthetic strategies such as Skraup reaction, Combes reaction etc. has been developed by the researchers all over the world. But still the synthetic methods are associated with various limitations as formation of side products, use of expensive metal catalysts. Thus, several efforts to develop an efficient and cost effective synthetic protocol are still carried out till date. Moreover, quinoline scaffold displays remarkable antiviral activity. Therefore, in this review we have made an attempt to describe recent synthetic protocols developed by various research groups along with giving a complete explanation about the role of quinoline derivatives as antiviral agent. Quinoline derivatives were found potent against various strains of viruses like zika virus, enterovirus, herpes virus, human immunodeficiency virus, ebola virus, hepatitis C virus, SARS virus and MERS virus etc.

Construction of isoxazolone-fused phenanthridines via Rh-catalyzed cascade C-H activation/cyclization of 3-arylisoxazolones with cyclic 2-diazo-1,3-diketones

A Rh(iii)-catalyzed cascade C-H activation/intramolecular cyclization of 3-aryl-5-isoxazolones with cyclic 2-diazo-1,3-diketones was described, leading to the formation of isoxazolo[2,3-f]phenanthridine skeletons. The protocol features the simultaneous one-pot formation of two new C-C/C-N bonds and one heterocycle in moderate-to-good yields with good functional group compatibility. It is amenable to large-scale synthesis and further transformation.

Cp*Co(III)-Catalyzed C-H Hydroarylation of Alkynes and Alkenes and Beyond: A Versatile Synthetic Tool

The use of earth-abundant first-row transition metals, such as cobalt, in C-H activation reactions for the construction and functionalization of a wide variety of structures has become a central topic in synthetic chemistry over the last few years. In this context, the emergence of cobalt catalysts bearing pentamethylcyclopentadienyl ligands (Cp*) has had a major impact on the development of synthetic methodologies. Cp*Co(III) complexes have been proven to possess unique reactivity compared, for example, to their Rh(III) counterparts, obtaining improved chemo- or regioselectivities, as well as yielding new reactivities. This perspective is focused on recent advances on the alkylation and alkenylation reactions of (hetero)arenes with alkenes and alkynes under Cp*Co(III) catalysis.

Cobalt-Catalyzed Oxidative C-H Activation: Strategies and Concepts

Inexpensive cobalt-catalyzed oxidative C-H functionalization has emerged as a powerful tool for the construction of C-C and C-Het bonds, which offers unique potential for transformative applications to modern organic synthesis. In the early stage, these transformations typically required stoichiometric and toxic transition metals as sacrificial oxidants; thus, the formation of metal-containing waste was inevitable. In contrast, naturally abundant molecular O₂ has more recently been successfully employed as a green oxidant in cobalt catalysis, thus considerably improving the sustainability of such transformations. Recently, a significant momentum was gained by the use of electricity as a sustainable and environmentally benign redox reagent in cobalt-catalyzed C-H functionalization, thereby preventing the consumption of cost-intensive chemicals while at the same time addressing the considerable safety hazards related to the use of molecular oxygen in combination with flammable organic solvents. Considering the unparalleled potential of the aforementioned approaches for sustainable green synthesis, this Review summarizes the recent progress in cobalt-catalyzed oxidative C-H activation until early 2020.

DMSO/t-BuONa/O2-Mediated Aerobic Dehydrogenation of Saturated N-Heterocycles

Aromatic N-heterocycles such as quinolines, isoquinolines, and indolines are synthesized via sodium tert-butoxide-promoted oxidative dehydrogenation of the saturated heterocycles in DMSO solution. This reaction proceeds under mild reaction conditions and has a good functional group tolerance. Mechanistic studies suggest a radical pathway involving hydrogen abstraction of dimsyl radicals from the N-H bond or α-C-H of the substrates and subsequent oxidation of the nitrogen or α-aminoalkyl radicals.

Rh-Catalyzed C-H Amination/Annulation of Acrylic Acids and Anthranils by Using -COOH as a Deciduous Directing Group: An Access to Diverse Quinolines

A method for the synthesis of diverse polysubstituted quinolines from readily available acrylic acids and anthranils has been developed. The weakly coordinating -COOH directing group, which can be tracelessly removed in the cascade cyclization, is essential for this reaction. Diverse polysubstituted quinolines were obtained under mild reaction conditions with simple H₂O and CO₂ as byproducts. More importantly, 1,2,3,4-tetrahydroacridine, which is the core skeleton of tacrine (an Alzheimer's disease drug), was conveniently synthesized.

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.

N-Iminopyridinium ylide-directed, cobalt-catalysed coupling of sp2 C-H bonds with alkynes

N-Iminopyridinium ylides are competent monodentate directing groups for cobalt-catalysed annulation of sp2 C-H bonds with internal alkynes. The pyridine moiety in the ylide serves as an internal oxidant and is cleaved during the reaction. The annulation reactions possess excellent compatibility with heterocyclic substrates, tolerating furan, thiophene, pyridine, pyrrole, pyrazole, and indole functionalities.

Substituent-controlled chemoselective synthesis of multi-substituted pyridones via a one-pot three-component cascade reaction

A substituent-controlled chemoselective cycloaddition reaction which afforded a variety of 2-pyridones and 4-pyridones in good to excellent yields, respectively, has been developed.

Cobalt-Catalyzed Allylation of Amides with Styrenes Using DMSO as Both the Solvent and the α-Methylene Source

An efficient synthesis of privileged allylic amines has been developed via cobalt-catalyzed allylation of amides with styrenes, in which DMSO was used as both the solvent and the α-methylene source. This transformation features high yields, and selectivity for the (E)-isomer of the linear product. Through the experimental and computational investigations, a sequential K₂S₂O₈-mediated oxidative coupling/cobalt-assisted regioselective alkene insertion/β-H elimination/alkene dissociation/hydride transfer process has also been deduced.