Polysubstituted Quinolines Research Articles

Base‐Catalyzed Domino Isomerization/Oxidant‐Free Dehydrogenative Annulation of Allylic Alcohols: Scope, Mechanism, and Application

AbstractA domino reaction comprising four consecutive steps based on the strategy of isomerization of allylic alcohols was developed. This base‐catalyzed protocol provided an approach for constructing polysubstituted quinolines without additional additives. A wide range of di‐ or trisubstituted γ‐aminoaryl allylic alcohols bearing alkyl or (hetero)aryl substituents were transformed to a range of structurally diverse quinolines. The utility of this transformation was demonstrated by the application in the concise synthesis of several polysubstituted quinoline derivatives, including natural products and pharmacological agents. Preliminary mechanistic experiments suggest that the isomerization of γ‐aminoaryl allylic alcohol proceeds via an intramolecular 1,3‐hydrogen shift whereas for the aromatization of the dihydroquinoline intermediate two possible pathways exist: acceptorless dehydrogenation and transfer hydrogenation.

Nickel–PNN catalysed sustainable synthesis of polysubstituted quinolines under microwave irradiation

This manuscript describes the synthesis of triazolyl-pyridine-based pincer cationic and neutral nickel complexes and their application in microwave-assisted synthesis of quinolines.

Divergent Synthesis of Quinolines: Exploiting the Duality of Free Radicals.

Herein, we present a green scheme for the divergent synthesis of two polysubstituted quinolines from a singular substrate via exploiting free-radical duality. Photocatalytically generated imine radicals produce 3,4-disubstituted quinolines via a novel rearrangement in the presence of an inorganic base. Alternatively, they react in the presence of an organic base to furnish 2,3-disubstituted quinolines. Mechanism studies support the hypothesis that the electrophilic/nucleophilic bias of free radicals can be adjusted by altering the reaction conditions.

Iron‐Catalyzed Transfer Hydrogenation: Divergent Synthesis of Quinolines and Quinolones from ortho‐Nitrobenzyl Alcohols

AbstractHerein, we report the divergent synthesis of quinolines and quinolones via a transfer hydrogenative condensation of ortho‐nitrobenzyl alcohols in one step. The reaction proceeded using the cyclopentadienone iron complex without any additional redox reagents. After transfer hydrogenation between ortho‐nitrobenzyl alcohols and secondary alcohols, the subsequent Friedländer annulation affords polysubstituted quinoline products in 22–90% (39 examples). The developed method was also applied to synthesize quinolones by using primary alcohols instead of secondary alcohols (12 examples). The obtained quinoline products were converted into several drug candidates to demonstrate its synthetic potential.

An Economical and Eco‐Efficient Ammonium Chloride Promoted Friedländer Condensation: A Study of Microwave‐Assisted Versus Conventional Heating.

AbstractA new approach to Friedländer hetero‐annulations reaction is presented here for the synthesis of polysubstituted quinolines and polycyclic quinolines by the use of an inexpensive, nontoxic and readily available NH4Cl promoter. As a promoter, it shows good compatibility with various substrates, its easy removal, no side product, enhances the atom economy and makes the reaction eco‐friendly. Both microwave irradiation and conventional heating accomplished the reaction. The present method provides a comparative study of microwave irradiation versus conventional heating.

Iron-Catalyzed Oxidative Cyclization of 2-Amino Styrenes with Alcohols and Methyl Arenes for the Synthesis of Polysubstituted Quinolines.

Herein, we present the iron-catalyzed oxidative cyclization of alcohol/methyl arene with 2-amino styrene to synthesize polysubstituted quinoline. Low-oxidation level substrates such as alcohols and methyl arenes are converted to aldehydes in the presence of an iron catalyst and di-t-butyl peroxide. Then, the quinoline scaffold is synthesized through imine condensation/radical cyclization/oxidative aromatization. Our protocol showed a broad substrate scope, and various functionalization and fluorescence applications of quinoline products demonstrated its synthetic ability.

Visible-light-driven radical Friedländer hetero-annulation of 2-aminoaryl ketone and α-methylene carbonyl compound via organic dye fluorescein through a single-electron transfer (SET) pathway

The discoveries recommend that the photoinduced conditions of fluorescein-determined go about as impetus for photochemically combining polysubstituted quinolines in ethanol at room temperature under air environment by means of revolutionary Friedländer hetero-annulation of 2-aminoaryl ketone and α-methylene carbonyl compound. This study lays out an original capability for photochemically orchestrating fluorescein. This non-metallic organic dye is economically accessible and modest, producing great outcomes, accelerating the cycle, and achieving a high compound economy. The turnover number (TON) and turnover recurrence (TOF) of polysubstituted quinolines have been determined. This cycle will likewise run on a gram scale, demonstrating the chance of modern applications.

Zinc‐Catalyzed [4+2] Annulation of 2‐Aminoarylnitriles with Ynamides: An Easy Access to Polysubstituted Quinolines

AbstractThe zinc‐catalyzed [4+2] annulation of 2‐aminoarylnitriles with ynamides offers an easy one‐step access to polysubstituted quinolines. In this new protocol, inexpensive ZnCl2 is used for the first time as an efficient alternative of noble‐metal catalysts. This zinc catalytic system offers the desired polysubstituted quinolines in yields up to 87% with a broad substrate scope and good functional group tolerance. The large‐scale experiment proves the practical utility of this method. Interestingly, the newly synthesized product decorated with an o‐fluorophenyl substituent is transformed to 11‐aminoindolo[2,3‐b]quinoline by deprotection of the benzenesulfonyl group and subsequent regioselective aromatic nucleophilic substitution in combined yield of 62%.

Choline based deep eutectic solvent mediated Friedlander annulation: A sustainable and regiospecific approach to polysubstituted quinoline

Polysubstituted quinolines have been synthesized by Friedlander annulation reaction of 2-aminobenzophenone with ketones mediated by choline-based deep eutectic solvents (DESs). We have investigated the condensation reaction in different choline-based DES and found choline chloride-zinc chloride DES to be the best catalyst with excellent yield of products. Moreover, regiospecificity was observed only under basic choline hydroxide medium in moderate yield. The deep eutectic solvent acts as dual role of solvent as well as catalyst and can be recycled. Mild reaction conditions, simple work-up procedure, excellent product yield, and use of recyclable catalyst are special features of this methodology, which makes the protocol a sustainable alternative to earlier reported methods of quinoline synthesis.

Synthesis and NMR Spectroscopic Characteristics of Novel Polysubstituted Quinolines Incorporating Furoxan Moiety

Synthesis and NMR Spectroscopic Characteristics of Novel Polysubstituted Quinolines Incorporating Furoxan Moiety

Phenanthrenequinone-Sensitized Photocatalytic Synthesis of Polysubstituted Quinolines from 2-Vinylarylimines.

Visible-light-excited 9,10-phenanthrenequinone (PQ*) was used as a photocatalyst for the synthesis of polysubstituted quinolines via the electrocyclization of 2-vinylarylimines. Up to quantitative yields of 2,4-disubstituted quinolines were received after 1 h of excitation with blue LEDs at room temperature when MgCO3 was used as an additive in DCM. On the basis of experimental and DFT studies, we propose that PQ* induces one-electron oxidation of the imine substrate that triggers the electrocyclization mechanism.

Enhanced catalytic performance of ZnO/carbon materials in the green synthesis of poly-substituted quinolines

A highly efficient methodology for the selective synthesis of nitrogen heterocycles via Friedländer reaction using carbon materials supported ZnO catalysts under the green chemistry domain is presented. The influence of the physicochemical properties of different carbon supports, in particular an activated carbon (AC), multi-walled carbon nanotubes (MWCNT) and a carbon aerogel (CA), on the catalytic performance is discussed. The developed catalysts are easily prepared by simple incipient wetness impregnation and a subsequent thermal treatment. These ZnO/carbon catalysts showed a great performance in the Friedländer condensation of 2-amino-5-chlorobenzaldehyde and carbonylic compounds with enolizable hydrogens, under solvent-free and mild conditions, affording in all cases selectively a total conversion to the corresponding quinoline. Both the Zn loading in combination with the developed microporosity of the selected carbon supports seem to be the key factors determining the catalytic performance. Yields obtained with ZnO/carbon composites catalysts are superior to those obtained by others widely used in fine chemistry such as, Zn-catalysts supported on mesoporous silica (SBA-15) and Zn-metal-organic-frameworks (MOF).

Yb(OTf)3-Mediated Annulation of Cyclopropane-1,1-dicarbonitriles with 2-Aminobenzaldehydes for Synthesis of Polysubstituted Quinolines.

A Yb(OTf)3-mediated annulation of cyclopropane-1,1-dicarbonitriles and 2-aminobenzaldehydes for the synthesis of polysubstituted quinolines in generally good yields was investigated. In the cascade reaction, the protocol includes ring opening, intermolecular nuclophilic addition, intramolecular nuclophilic addition, and demalononitrile aromatization, in which the malononitrile group serves as a deciduous directing group mediated by Yb(OTf)3.

Iron catalyzed metal-ligand cooperative approaches towards sustainable synthesis of quinolines and quinazolin-4(3H)-ones

Herein we report simple, efficient, and economically affordable metal-ligand cooperative strategies for synthesizing quinolines and quinazolin-4(3H)-ones via dehydrogenative functionalization of alcohols. Various polysubstituted quinolines and quinazolin-4(3H)-ones were prepared in good yields via dehydrogenative coupling of readily available alcohols with ketones and 2-aminobenzamides, respectively under air using a well-defined Fe(II)-catalyst, ([FeL1Cl2] (1)) bearing a redox-active azo-aromatic pincer 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline) (L1). Control experiments and mechanistic investigation disclose that the one-electron reduced mono-anionic species [1]⁻ bearing an iron-stabilized azo-anion radical ligand catalyzes these reactions. Both iron and the redox-active arylazo ligand participate synergistically during the different steps of these catalytic reactions.

Carbocatalytic Cascade Synthesis of Polysubstituted Quinolines from Aldehydes and 2‐Vinyl Anilines

AbstractOxidized active carbon (oAC) catalyses the formation of polysubstituted quinolines from o‐vinyl anilines and aldehydes. The reaction proceeds in a cascade manner through condensation, electrocyclization and dehydrogenation, and gives access to a wide range of quinolines with alkyl and/or aryl substituents as demonstrated with 40 examples. The metal‐free catalytic procedure allows a heterogeneous protocol for the synthesis of various polysubstituted quinolines. The mechanistic studies imply that both the acid and quinoidic groups in oAC are integral for the catalytic manifold.magnified image

Mild and efficient copper-catalyzed oxidative cyclization of oximes with 2-aminobenzyl alcohols at room temperature: synthesis of polysubstituted quinolines.

A simple and efficient ligand-free Cu-catalyzed protocol for the synthesis of polysubstituted quinolines via oxidative cyclization of oxime acetates with 2-aminobenzyl alcohols at room temperature has been developed. The presented approach provides a new synthetic pathway leading to polysubstituted quinolines with good functional group tolerance under mild conditions. Moreover, this transformation can be applied for the preparation of quinolines on a gram scale. Oxime acetates serve as the internal oxidants in the reactions, thus making this method very attractive.

Choline Based Deep Eutectic Solvent Mediated Friedlander Annulation: A Sustainable and Regiospecific Approach to Polysubstituted Quinolines

Choline Based Deep Eutectic Solvent Mediated Friedlander Annulation: A Sustainable and Regiospecific Approach to Polysubstituted Quinolines

Efficient Organoruthenium Catalysts for α‐Alkylation of Ketones and Amide with Alcohols: Synthesis of Quinolines via Hydrogen Borrowing Strategy and their Mechanistic Studies

AbstractA new family of phosphine free organometallic ruthenium(II) catalysts (Ru1–Ru4) supported by bidentate NN Schiff base ligands (L1–L4 where L1=N,N‐dimethyl‐4‐((2‐phenyl‐2‐(pyridin‐2‐ylmethyl)hydrazineylidene)methyl) aniline, L2=N,N‐diethyl‐4‐((2‐phenyl‐2‐(pyridin‐2‐ylmethyl)hydrazineylidene)methyl)aniline, L3=N,N‐dimethyl‐4‐((2‐phenyl‐2‐(pyridin‐2‐yl)hydrazineylidene)methyl)‐ aniline and L4=N,N‐diethyl‐4‐((2‐phenyl‐2‐(pyridin‐2‐yl)hydrazineylidene)methyl) aniline) was prepared and characterized. These half‐sandwich complexes acted as catalysts for C−C bond formation and exhibited excellent performance in the dehydrogenative coupling of ketones and amides. In the synthesis of C–C bonds, alcohols were utilized as the alkylating agent. A broad range of substrates, including sterically hindered ketones and alcohols, were well tolerated under the optimized conditions (TON up to 47000 and TOF up to 11750 h−1). This ruthenium (II) catalysts were also active towards the dehydrogenative cyclization of o‐amino benzyl alcohol for the formation of quinolines derivatives. Various polysubstituted quinolines were synthesized in moderate to excellent yields (TON up to 71000 and TOF up to 11830 h−1). Control experiments were carried out and the ruthenium hydride intermediate was characterized to support the reaction mechanism and a probable reaction pathway of dehydrogenative coupling for the C−C bond formation has been proposed.

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.

Environmentally Friendly Nafion-Mediated Friedländer Quinoline Synthesis under Microwave Irradiation: Application to One-Pot Synthesis of Substituted Quinolinyl Chalcones

An efficient and eco-friendly synthetic route for Friedländer quinoline synthesis of polysubstituted quinolines is described. This green chemical method starts from various 2-aminobenzophenones and mono- or dicarbonyl synthons and uses reusable Nafion NR50 material as a solid catalyst in ethanol under microwave irradiation. The protocol has a high generality of functional groups and provides the desired quinolines in good to excellent yields. Some structures were confirmed by single-crystal X-ray diffraction analysis.