Reagent-Free Intramolecular Hydroamination of Ynone-Tethered Aryl-sulfonamide: Synthesis of Polysubstituted 4-Quinolones

An efficient reagent-free method for the synthesis of polysubstituted 4-quinolone from 2-substituted alkynoyl aryl-sulfonamide was developed. This developed method tolerates various functional groups and gives the corresponding 4-quinolones. We have successfully extended this method to the synthesis of dihydro-4-quinolones from 2-alkenoyl aryl sulfonamide derivatives.

Enhanced Selectivity in 4-Quinolone Formation: A Dual-Base System for Palladium-Catalyzed Carbonylative Cyclization with Fe(CO)5

The use of gaseous CO in Pd-catalyzed carbonylative quinolone synthesis presents challenges related to safety and precise pressure control. In response, a streamlined non-gaseous synthesis of 4-quinolone compounds has been developed. This study introduces a tunable CO-releasing system utilizing Fe(CO)5 activated by a dual-base system of piperazine and triethylamine. This alternative liquid CO resource facilitates the palladium-catalyzed carbonylative C-C coupling and subsequent intramolecular cyclization. By tuning the tandem kinetics of carbonylation and cyclization, this non-gaseous method achieves the successful synthesis of 22 distinct 4-quinolones with excellent yields. This is achieved through the three-component condensation of sub-stoichiometric amounts of Fe(CO)5 with 2-iodoaniline and terminal alkynes. Operando mechanistic studies have revealed a novel CO transfer mechanism that facilitates homogeneous carbonylative cyclization, distinguishing this method from traditional techniques. In addition to addressing safety concerns, this approach also provides precise control over selectivity, with significant implications for pharmaceutical research and the efficient synthesis of pharmaceutical and bioactive compounds.

Cu-Catalyzed Tandem C-N and C-C Bond Formation Leading to 4(1H)-Quinolones: A Scaffold with Diverse Biological Properties from Totally New Raw Materials in a Single Step

A novel Cu-catalyzed tandem C-N and C-C bond-formation reaction has been developed to furnish 2-substituted-4-(1H)-quinolones. 4-(1H)-quinolones play an important role in medicinal chemistry. Many 2-aryl(alkyl)-4(1H)-quinolones are found to exhibit diverse biological properties. While traditional methods have inherent issues [like starting materials with incompatible functional groups (NH2 and keto groups)], many modern methods either require activated starting materials (like Ynones) or employ expensive metals (Pd, Rh, Au, etc.) involving carbonylation using CO or metal complexes. Our protocol presents an environmentally friendly one-step method for the construction of these useful 2-substituted-4-(1H)-quinolones from easily available aryl boronic acid (or pinacolate ester) and nitriles as new raw materials, using a cheap Cu-catalyst and O2 (air) as a green oxidant. We further extended its application to the synthesis of various natural products, including the first formal total synthesis of punarnavine. A plausible mechanism involving an aryl nitrilium ion (formed due to the intermolecular C-N bond-forming coupling between aryl boron species and the nitrile group) followed by tandem intramolecular C-C bond formation has been proposed.

Synthesis of 3-Functionalized 4-Quinolones from Readily Available Anthranilic Acids

We report herein an efficient synthesis of 3-functionalized 4-quinolones, a class of privileged pharmacophores found in numerous biologically and pharmaceutically active compounds. Our synthetic strategy features a telescoped two-step sequence starting from readily available anthranilic acids and functionalized methane derivatives bearing an electron-withdrawing group, such as methyl sulfones, methyl ketones, and acetonitrile. The method delivers good to excellent yields for a variety of structurally diverse substrates, showing good functional group tolerability. We believe that the disclosed method offers a highly efficient and practical entry to functionalized 4-quinolones under mild conditions that is amenable to preparative-scale synthesis.

Recent advances in the synthesis of pharmaceutically active 4-quinolone and its analogues: a review

4-Quinolone and its analogs are heterocyclic classes of organic compounds displaying biologically active and a broad spectrum of pharmaceutical drug scaffolds. 4-Quinolone is the first-line chemotherapeutic treatment for a wide spectrum of bacterial infections. Recently, 4-quinolone and its derivatives have been shown to have the potential to cure and regulate various acute and chronic diseases, including pain, ischemia, immunomodulation, inflammation, malarial, bacterial infection, fungal infection, HIV, and cancer, based on several reports. This review highlights and provides brief information to better understand the development of experimental progress made to date in the synthetic protocol towards 4-quinolone and its analogs. Thus, classical synthesis protocol, metal-free reaction protocol, and transition metal-catalyzed reaction procedures are briefly discussed along with the pharmaceutical activities of selected 4-quinolone derivatives.

Hydrogen Bond Assisted Three-Component Tandem Reactions to Access N-Alkyl-4-Quinolones

Hydrogen-bonding catalytic reactions have gained great interest. Herein, a hydrogen-bond-assisted three-component tandem reaction for the efficient synthesis of N-alkyl-4-quinolones is described. This novel strategy features the first proof of polyphosphate ester (PPE) as a dual hydrogen-bonding catalyst and the use of readily available starting materials for the preparation of N-alkyl-4-quinolones. The method provides a diversity of N-alkyl-4-quinolones in moderate to good yields. The compound 4h demonstrated good neuroprotective activity against N-methyl-ᴅ-aspartate (NMDA)-induced excitotoxicity in PC12 cells.

Cycloisomerization of π-Coupled Heteroatom Nucleophiles by Gold Catalysis: En Route to Regiochemically Defined Heterocycles

Since the dawn of millennium, catalytic gold chemistry is at the forefront to set off diverse organic reactions via unique activation of π-bonded molecules. Within this purview, cycloisomerization of heteroatom nucleophiles linked to a π-system is one of the well recognized chemistry for the construction of numerous heterocyclic cores. Though the rudimentary aspects of this transformation are reviewed by several groups in different timeline, a holistic view on regiochemistry of such reactions went largely overlooked. Hence, this account emphasizes the gold catalyzed regioselective cycloisomerization of structurally distinctive π-connected hetero-nucleophiles leading to different heterocycles documented in the last two decades. From an application perspective, this account also highlights those methodologies which find a role in the total synthesis of natural products. Wherever appropriate, mechanistic details and contributing factors for selectivity are also discussed.

One-Pot Synthesis of 4-Quinolone via Iron-Catalyzed Oxidative Coupling of Alcohol and Methyl Arene

Herein, we describe the iron(III)-catalyzed oxidative coupling of alcohol/methyl arene with 2-amino phenyl ketone to synthesize 4-quinolone. Alcohols and methyl arenes are oxidized to the aldehyde in the presence of an iron catalyst and di-tert-butyl peroxide, followed by a tandem process, condensation with amine/Mannich-type cyclization/oxidation, to complete the 4-quinolone ring. This method tolerates various kinds of functional groups and provides a direct approach to the synthesis of 4-quinolones from less functionalized substrates.

Gold(iii)-catalyzed azide-yne cyclization/O-H insertion cascade reaction for the expeditious construction of 3-alkoxy-4-quinolinone frameworks

A gold-catalyzed 6-endo-dig azide-yne cyclization/O-H insertion cascade reaction of azide-tethered alkynes with alcohols has been developed, and it provides an expeditious access to 3-alkoxy-4-quinoline derivatives in good to high yields under mild and neutral reaction conditions with broad substrate generality. The utility of this method is emphasized by a scalable experiment and concise total synthesis of a bioactive natural product Leiokinine A, and other bioactive quinoline analogs.

Oxidative Cyclization of o-(1-Hydroxy-2-alkynyl)-N-tosylanilides for the Synthesis of 4-Quinolones

The treatment of easily accessible o-(1-hydroxy-2-alkynyl)-N-tosylanilides 1 with excess manganese(IV) oxide in the presence of substoichiometric tetrabutylammonium iodide (TBAI) in chloroform (or in the absence of TBAI in dimethylformamide, DMF) promoted a sequential oxidation/intramolecular hydroamination to give 4-quinolones 3 and/or (Z)-2-alkylidene-3-oxindoles (Z)-4 in good yields. Possibly, MnO₂ played dual roles as an oxidant and as a Lewis acidic activator of intermediary ynones 2. The product distributions between 3 and (Z)-4 could be controlled by the choice of solvents.

Access to 2-Alkyl/Aryl-4-(1H)-Quinolones via Orthogonal "NH3" Insertion into o-Haloaryl Ynones: Total Synthesis of Bioactive Pseudanes, Graveoline, Graveolinine, and Waltherione F

An efficient one-pot synthesis of 4-(1H)-quinolones through an orthogonal engagement of diverse o-haloaryl ynones with ammonia in the presence of Cu(I), involving tandem Michael addition and ArCsp₂-N coupling, is presented. The substrate scope of this convenient protocol, wherein ammonium carbonate acts as both an in situ ammonia source and a base toward diverse 2-substituted 4-(1H)-quinolones, has been mapped and its efficacy validated through concise total synthesis of bioactive natural products pseudanes (IV, VII, VIII, and XII), graveoline, graveolinine, and waltherione F.

Gold-Catalyzed Hydroamination of Propargylic Alcohols: Controlling Divergent Catalytic Reaction Pathways To Access 1,3-Amino Alcohols, 3-Hydroxyketones, or 3-Aminoketones

A versatile approach to the valorization of propargylic alcohols is reported, enabling controlled access to three different products from the same starting materials. First, a general method for the hydroamination of propargylic alcohols with anilines is described using gold catalysis to give 3-hydroxyimines with complete regioselectivity. These 3-hydroxyimines can be reduced to give 1,3-amino alcohols with high syn selectivity. Alternatively, by using a catalytic quantity of aniline, 3-hydroxyketones can be obtained in high yield directly from propargylic alcohols. Further manipulation of the reaction conditions enables the selective formation of 3-aminoketones via a rearrangement/hydroamination pathway. The utility of the new chemistry was exemplified by the one-pot synthesis of a selection of N-arylpyrrolidines and N-arylpiperidines. A mechanism for the hydroamination has been proposed on the basis of experimental studies and density functional theory calculations.

Gold-catalyzed cyclization of 1-(2′-azidoaryl) propynols: synthesis of polysubstituted 4-quinolones

α-Imino gold carbene intermediate is produced from 1-(2′-azidoaryl) propynols, which triggers a 1,2-carbon migration and is converted to 2,3-disubstituted 4-quinolones. The reaction works under mild conditions and tolerates various functional groups.

Theoretical investigation on the mechanism of Cu(ii)-catalyzed synthesis of 4-quinolones: effects of additives HOTf vs. HOTs

Hydrogen-bond donor/proton-donor ability is revealed to be the primary factor that controls the catalytic capability of additives (HOTf vs. HOTs).

Rhodium(iii)-catalyzed [3 + 3] annulation reactions of N-nitrosoanilines and cyclopropenones: an approach to functionalized 4-quinolones

We report Rh(iii)-catalyzed [3 + 3] annulation reactions for the preparation of functionalized 4-quinolones from available N-nitrosoanilines and cyclopropenones.

Transition-metal-free oxidative intermolecular cyclization reaction: synthesis of 2-aryl-4-quinolones

Herein, a novel and efficient intermolecular cyclization of 2-aminoacetophenones with aldehydes was developed for the synthesis of 2-aryl-4-quinolones through C–C and C–N bond formation.

Direct synthesis of 2-aryl-4-quinolones via transition-metal-free intramolecular oxidative C(sp(3))-H/C(sp(3))-H coupling

A novel, metal-free oxidative intramolecular Mannich reaction was developed between secondary amines and unmodified ketones, affording a simple and direct access to a broad range of 2-arylquinolin-4(1H)-ones through C(sp(3))-H activation/C(sp(3))-C(sp(3)) bond formation from readily available N-arylmethyl-2-aminophenylketones, using TEMPO as the oxidant and KO(t)Bu as the base.

A microwave-assisted multicomponent synthesis of substituted 3,4-dihydroquinazolinones

A series of structurally diverse 3,4-dihydroquinazolinones was synthesized via a novel cascade imine/cyclization/aza-Henry reaction in moderate to excellent yields.