Supported Palladium-Catalyzed Carbonylative Cyclization of 2-Bromonitrobenzenes and Alkynes to Access Quinolin-4(1H)-ones

Palladium-Catalyzed Carbonylative Sonogashira Transformations: Advancements and Insights

Palladium-catalyzed carbonylative reactions, used as a tool for the insertion of carbonyl group into organic moieties, is a synthetically useful transformation. Carbonylative Sonogashira coupling is a convenient approach for the synthesis of α,β-acetylenic ketones which are important class of molecules in pharmaceutical and industrial fields. Development of greener approaches and environmentally benign catalytic systems put forward enormous opportunities in this field and moreover, these researches indicate the formation of heterocycles via this carbonylation strategy, which is a major highlight. Herein, we discuss the progress achieved in palladium-catalyzed carbonylative Sonogashira coupling from 2013 to 2024 and its future prospects.

One-Step Synthesis of 2-Arylquinolin-4(1H)-Ones from 1-(2-Aminoaryl)-3-Arylpropan-1-Ones via Pd(II)-Catalyzed Dehydrogenative Cyclization

In this study, we developed palladium-catalyzed dehydrogenative cyclization to transform 1-(2-aminoaryl)-3-arylpropan-1-ones into 2-arylquinolin-4(1H)-ones, also known as aza-flavones which are the bioisosteres of flavones, in an atom-economic manner. This method exhibited excellent chemical compatibility with a broad substrate scope, accommodating up to 25 derivatives. Additionally, kinetic studies were performed to elucidate the reaction mechanism. Further, 2-phenylquinolin-4(1H)-one was used as a common intermediate for synthesizing privileged structures such as 4-methoxyquinoline, N-methylquinoline-4(1H)-one, and 4-(pseudo)halogenated quinoline moieties.

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.

Synthetic approach to 2-alkyl-4-quinolones and 2-alkyl-4-quinolone-3-carboxamides based on common β-keto amide precursors

β-Keto amides were used as convenient precursors to both 2-alkyl-4-quinolones and 2-alkyl-4-quinolone-3-carboxamides. The utility of this approach is demonstrated with the synthesis of fourteen novel and four known quinolone derivatives, including natural products of microbial origin such as HHQ and its C5-congener. Two compounds with high activity against S. aureus have been identified among the newly obtained quinolones, with MICs ≤ 3.12 and ≤ 6.25 µg/mL, respectively.

Selective Electrochemical Halogenation of Functionalized Quinolone

This work describes an effective C3-H halogenation of quinoline-4(1H)-ones under electrochemical conditions, in which potassium halides serve as both halogenating agents and electrolytes. The protocol provides expedient access to different halogenated quinoline-4(1H)-ones with unique regioselectivity, broad substrate scope, and gram-scale synthesis employing convenient, environmentally friendly electrolysis, in an undivided cell. Mechanism studies have shown that halogen radicals can promote the activation of N-H bonds in quinolones.

Effective Synthesis of 4-Quinolones by Reductive Cyclization of 2'-Nitrochalcones Using Formic Acid as a CO Surrogate

4-Quinolones are the structural elements of many pharmaceutically active compounds. Although several approaches are known for their synthesis, the introduction of an aryl ring in position 2 is problematic with most of them. The reductive cyclization of o-nitrochalcones by pressurized CO, catalyzed by ruthenium or palladium complexes, has been previously reported to be a viable synthetic strategy for this aim, but the need for pressurized CO lines and autoclaves has prevented its widespread use. In this paper, we describe the use of the formic acid/acetic anhydride mixture as a CO surrogate, which allows us to perform the reaction in a cheap and commercially available thick-walled glass tube without adding any gaseous reagent. The obtained yields are often high and compare favorably with those previously reported by the use of pressurized CO. The procedure was applied to a three-step synthesis from commercially available and cheap reagents of the alkaloid Graveoline.

Heterogenized Phenanthroline-Pd(2+)-Catalyzed Alkoxycarbonylation of Aryl Iodides in Base-Free Conditions

A phenanthroline-based porous organic polymer-supported heterogeneous Pd catalyst (Pd@Phen-POP) is facilely synthesized by the solvent knitting of a Phen scaffold via the Lewis-acid-catalyzed Friedel-Crafts reaction using dichloromethane as a source for linker in the presence of AlCl₃. The catalyst very effectively catalyzes the alkoxycarbonylation of various substituted aryl iodides with various alcohols to give corresponding products in good to excellent yields. Owing to the heterotic nature of the catalyst, it can be easily separated by simple filtration from the reaction mixture and recycled.

Ni-Catalysed intramolecular reductive aminocarbonylation of 2-haloaryl-tethered nitroarenes for the synthesis of dibenzazepine-based heterocycles

A nickel-catalysed intramolecular reductive aminocarbonylation of 2-haloaryl-tethered nitroarenes is developed for rapid access to a variety of dibenzoazepinones and their derivatives.

Cobalt-catalyzed carbonylative synthesis of free (NH)-tetrahydro-β-carbolinones from tryptamine derivatives

A new cobalt-catalyzed carbonylative synthesis of free (NH)-tetrahydro-β-carbolinones from tryptamine derivatives has been developed. A variety of free (NH)-tetrahydro-β-carbolinones were produced in good yields. The oxidant, silver salt, can be recycled and reused.

Palladium-catalyzed carbonylative synthesis of indole-3-carboxamides from 2-ethynylanilines and nitroarenes

A facile and straightforward approach for the expedite construction of indole-3-carboxamide skeletons via a palladium-catalyzed carbonylative cyclization of 2-ethynylanilines with nitroarenes has been developed.