Palladium-Catalyzed Intramolecular Amidation of C(sp2)−H Bonds: Synthesis of 4-Aryl-2-quinolinones

Iodine-Catalyzed [5 + 1] Carbonylation of 2-Alkenyl/Pyrrolylanilines with CS2 as the Carbonylating Reagent

Novel metal-free iodine (I2)-catalyzed [5 + 1] carbonylation of 2-alkenyl/pyrrolylanilines with carbon disulfide (CS2) as the carbonylating reagent has been developed. This innovative method allows for the synthesis of valuable derivatives such as 4-aryl-2-quinolinones and pyrrolyl-fused quinoxalinones. Notably, this work represents the first instance where CS2 has been utilized as a carbonylating reagent source. The protocol demonstrates the utilization of various substrates, leading to diverse reactions that afford excellent yields under mild conditions. The method also shows good compatibility with functional groups present in the substrates, further enhancing its synthetic utility. Importantly, the developed reaction exhibits scalability, enabling gram-scale synthesis, and shows promise for the synthesis of druglike molecules. In this catalytic system, CS2 serves as the carbonyl source, while dimethyl sulfoxide plays multiple roles, including acting as an oxidant and a solvent. Mechanistic studies have been conducted to elucidate the underlying processes, with the formation of quinolone-2-thiones identified as crucial intermediates, facilitating the carbonylation annulation process.

Copper-Catalyzed Intermolecular Cross-dehydrogenative C-N Coupling at Room Temperature via Remote Activating Group Enabled Radical Relay Strategy

Employing N-fluorobenzenesulfonimide (NFSI) as a nitrogen-centered radical (NCR) precursor, an intermolecular C(sp²)-N coupling on heteroarenes or substituted benzenes with remote activated aniline derivatives via copper catalyzed N-N radical relay strategy at room temperature is developed. Good to excellent yields are acquired, and no ligand or additive is required. Reaction scope investigation and preliminary mechanistic studies demonstrate that the remote activating strategy and delicate control on the reactivities of active NCR species are essential to guarantee satisfactory chemo- and site-selectivity.

Ring Expansion of Isatins via 1,2-Phospha-Brook Rearrangement: A Route to the Synthesis of 2-Quinolinone-Derived p-Quinone Methides

A Lewis acid-mediated one-carbon homologation approach to installing a 2-quinolinone core embedded with para-quinone methides, in a high yield of up to 92%, and with high regioselectivity has been developed. Also, post-synthetic modifications, including C-P, C-S, and C-C bond formations, have been demonstrated by the 1,6-addition of suitable nucleophiles. Further, cyclopropanation of 2-quinolinone-embedded p-QM is also demonstrated affording a contiguous quaternary spiro center.

μ-Oxo-Hypervalent-Iodine-Catalyzed Oxidative C-H Amination for Synthesis of Benzolactam Derivatives

Benzolactams have unique biological activity and high utility in the synthesis of valuable compounds with direct applicability to oxindole alkaloids and antibacterial agents. Despite recent advances in organic chemistry and the growing number of reported methods for synthesizing benzolactams, their preparation still requires a multistep process. C-H amination reactions can convert aromatic C(sp²)-H bonds directly to C(sp²)-N bonds, and this direct approach to C-N bond formation offers effective access to benzolactams. Hypervalent iodine reagents are promising tools for achieving oxidative C-H amination. Motivated by our ongoing research efforts toward the development of useful hypervalent-iodine-mediated oxidative transformations, we herein describe an effective intramolecular oxidative C-H amination reaction based on μ-oxo hypervalent iodine catalysis for the synthesis of benzolactams bearing various functional groups.

Synthetic Strategies in the Preparation of Phenanthridinones

Phenanthridinones are important heterocyclic frameworks present in a variety of complex natural products, pharmaceuticals and displaying wide range of pharmacological actions. Its structural importance has evoked a great deal of interest in the domains of organic synthesis and medicinal chemistry to develop new synthetic methodologies, as well as novel compounds of pharmaceutical interest. This review focuses on the synthesis of phenanthridinone scaffolds by employing aryl-aryl, N-aryl, and biaryl coupling reactions, decarboxylative amidations, and photocatalyzed reactions.

Ring expansion and ring opening of 3-halooxindoles with N-alkoxycarbonyl-O-tosylhydroxylamines for divergent access to 4-aminoquinolin-2-ones and N-Cbz-N’-arylureas

The reaction of N-alkoxycarbonyl-O-tosylhydroxylamines with indol-2-ones in situ generated from 3-halooxindoles has been developed for divergently accessing 4-aminoquinolin-2-ones and N-Cbz-N’-arylureas in good to excellent yields.

Palladium-catalysed Heck-type alkenylation reactions in the synthesis of quinolines. Mechanistic insights and recent applications

Recent developments in Pd(0)- and Pd(ii)-catalysed alkenylation reactions for the synthesis of quinolines focusing on mechanistic understanding.

Route to Air and Moisture Stable β-Difluoroboryl Acrylamides

A method for the preparation of air stable difluoroboryl acrylamides is reported. In contrast to the ubiquitous organotrifluoroborate salts, difluoroboryl acrylamides are relatively nonpolar and are readily purified by silica chromatography. Difluoroboryl acrylamides serve as efficient substrates in cross-coupling reactions to afford the corresponding trisubstituted acrylamides in good to excellent yields. The utility of the difluoroboryl group in various chemical transformations is presented.

Palladium-Catalysed Synthesis and Transformation of Quinolones

Palladium-catalysed reactions have had a large impact on synthetic organic chemistry and have found many applications in target-oriented synthesis. Their widespread use in organic synthesis is due to the mild conditions associated with the reactions together with their tolerance of a wide range of functional groups. Moreover, these types of reactions allow the rapid construction of complex molecules through multiple bond-forming reactions in a single step, the so-called tandem processes. Pd-catalysed reactions have been applied to the synthesis of a large number of natural products and bioactive compounds, some of them of complex molecular structures. This review article aims to present an overview of the most important Pd-catalysed reactions employed in the synthesis and transformations of quinolin-2(1H)-ones and quinolin-4(1H)-ones. These compounds are widely recognized by their diverse bioactivity, being privileged structures in medicinal chemistry and useful structural moieties for the development of new drug candidates. Furthermore, they hold significant interest due to their host⁻guest chemistry; applications in chemical, biochemical and environmental analyses and use in the development of new synthetic methods. In some cases, the quinolone formation step cannot be ascribed to a claimed Pd-catalysed reaction but this reaction is crucial to get the appropriate substrate for cyclization into the quinolone. Herein we present and discuss different economical, efficient and selective synthetic strategies to access quinolone-type compounds.

Recent advances in intramolecular C–O/C–N/C–S bond formationviaC–H functionalization

This review presents the construction of C–X bonds (X = O/N/S) by using intramolecular C–H functionalization for the synthesis of heterocyclic compounds.

Weak Base-Promoted Lactamization under Microwave Irradiation: Synthesis of Quinolin-2(1H)-ones and Phenanthridin-6(5H)-ones

Quinolin-2(1H)-ones and phenanthridin-6(5H)-ones are synthesized in high yields by K₂CO₃-promoted cyclization of N-aryl-β-bromo-α,β-unsaturated amides and N-aryl-2-bromobenzamides in dimethylformamide under microwave irradiation.

Transition Metal Free C-N Bond Forming Dearomatizations and Aryl C-H Aminations by in Situ Release of a Hydroxylamine-Based Aminating Agent

We outline a simple protocol that accesses directly unprotected secondary amines by intramolecular C-N bond forming dearomatization or aryl C-H amination. The method is dependent on the generation of a potent electrophilic aminating agent released by in situ deprotection of O-Ts activated N-Boc hydroxylamines.

Divergent Synthesis of Polymethoxylated 4-Aryl-2-quinolones

Polymethoxylated 4-aryl-2-quinolones were synthesized from the corresponding (o-aminophenyl)propiolates via Cu-catalyzed hydroarylation and subsequent deprotection/lactam formation. Selective iodination of the C3 position of the product followed by coupling reactions of the resulting 3-iodinated 4-aryl-2-quinolone afforded 3-substituted-4-aryl-2-quinolones. Moreover, the N-benzyl protecting group was successfully replaced with other polyoxygenated benzyl groups.

Dirhodium-catalyzed C-H arene amination using hydroxylamines

Primary and N-alkyl arylamine motifs are key functional groups in pharmaceuticals, agrochemicals, and functional materials, as well as in bioactive natural products. However, there is a dearth of generally applicable methods for the direct replacement of aryl hydrogens with NH2/NH(alkyl) moieties. Here, we present a mild dirhodium-catalyzed C-H amination for conversion of structurally diverse monocyclic and fused aromatics to the corresponding primary and N-alkyl arylamines using NH2/NH(alkyl)-O-(sulfonyl)hydroxylamines as aminating agents; the relatively weak RSO2O-N bond functions as an internal oxidant. The methodology is operationally simple, scalable, and fast at or below ambient temperature, furnishing arylamines in moderate-to-good yields and with good regioselectivity. It can be readily extended to the synthesis of fused N-heterocycles.

Copper(i) catalyzed C(sp2)–N bond formation: synthesis of pyrrolo[3,2-c]quinolinone derivatives

An intramolecular copper-catalyzed direct C(sp²)–H activation/C(sp²)–N bond formation reaction has been developed for the synthesis of pyrrolo[3,2-c]quinolinone derivatives under an oxygen atmosphere. This approach presents an alternative route to the tricyclic core of martinellic acid or martinelline.

A convenient approach to an advanced intermediate toward the naturally occurring, bioactive 6-substituted 5-hydroxy-4-aryl-1H-quinolin-2-ones

An advanced intermediate for the total synthesis of the 5-hydroxy-4-aryl-3,4-dihydro-1H-quinolin-2-one natural products and a 3,4-bisdesoxy analog of peniprequinolone were synthesized.

The emergence of sulfoxides as efficient ligands in transition metal catalysis

Sulfoxides are capable of forming stable complexes with transition metals and there have been many comprehensive studies into their binding properties. However, the use of sulfoxides, particularly chiral sulfoxides, as ligands in transition metal catalysis is rather less well developed. This review aims to describe these catalytic studies and covers new developments that are showing very promising results and that have led to a renewed interest in this field.

A Novel One-step Synthesis of Quinoline-2(1H)-thiones and Selones by Treating 3-Aryl-3-(2-aminophenyl)-1-propyn-3-ols with a Base and Elemental Sulfur or Selenium

A one-step conversion of 3-aryl-3-(2-aminophenyl)-1-propyn-3-ols into quinoline-2(1 H)-thiones and quinoline-2(1 H)-selones was achieved only by treating the substrates with n-butyllithium and either elemental sulfur or selenium, respectively. The reactions were assumed to proceed through an intramolecular nucleophilic attack of the neighboring amino group to the plausible in situ generated reactive species related to chalcogenoketenes. The subsequent mCPBA oxidation of quinoline-2(1 H)-selones afforded quinolin-2(1 H)-ones in high yields.

Synthesis of quinolinones with palladium-catalyzed oxidative annulation between acrylamides and arynes

An unprecedented palladium-catalyzed oxidative annulation of acrylamides with benzyne precursors has been successfully developed. By using this mild "N-H activation/Heck reaction" method, a wide variety of quinolinones were conveniently prepared in one step with high efficiency.