Construction of the flavones and aurones through regioselective carbonylative annulation of 2-bromophenols and terminal alkynes

A comprehensive review on carbonylation reactions: catalysis by magnetic nanoparticle-supported transition metals

Magnetic catalysts have become a crucial innovation in carbonylation reactions, providing a sustainable and highly efficient means of synthesizing compounds that contain carbonyl groups. This review article explores the diverse and significant role of magnetic catalysts in various carbonylation processes, emphasizing their essential contributions to improving reaction rates, selectivity, and recyclability of catalysts. The distinctive magnetic properties of these catalysts enable straightforward separation and recovery, a feature that significantly mitigates waste and reduces environmental impact. As a result, magnetic catalysts' environmental and economic advantages position them as key players in contemporary synthetic chemistry, driving the evolution of green chemistry practices. Particularly noteworthy is the combination of magnetic nanoparticles with transition metals, resulting in the development of robust catalytic systems that exploit the complementary effects of magnetism and catalysis. Recent advances have showcased the adaptability of magnetic nanoparticles supported by transition metal catalysts in various carbonylation reactions, including carbonylative coupling, alkoxy carbonylation, thio carbonylation, and amino carbonylation. This review meticulously examines the mechanistic aspects of how magnetic fields influenced catalytic performance between 2014 and the end of 2024.

Copper-Catalyzed Carbonylative Cyclization of CO2: A Promising Approach for Synthesis of Flavone

Flavones are an important class of building blocks for numerous biologically active molecules, pharmaceuticals, and natural products. Reductive carbonylation of CO2 is a powerful method to provide high-value heterocycles quickly. However, examples of transition metal-catalyzed carbonylation to produce flavones using CO2 are quite scarce, and the related copper-catalyzed carbonylative cyclization of CO2 is not reported. Here, a general procedure is developed for the copper-catalyzed carbonylative C(sp3)-H bond synthesis of flavone using CO2 as the C1 source. Additionally, 13C-labeled flavones are successfully synthesized using [13C]-CO2, demonstrating significant inhibitor activity against MCF-7 cells in antitumor assays. Mechanistic investigations suggest that the phenolic group accelerates CO2 mass transfer by promoting nucleophilic addition to DBU-CO2 complexes, followed by selective intramolecular carbonylative cyclization.

Palladium-Catalyzed Carbonylation for General Synthesis of Aurones Using CO2

The carbonylation of alkynes using CO₂ to generate aurones is to date unknown. In this study, a palladium-catalyzed carbonylation of terminal aromatic alkynes and the waste hydrosilane, poly(methylhydrosiloxane) (PMHS), is carried out with 2-iodophenol using CO₂ to produce aurones. A variety of terminal alkynes and substituted 2-iodophenols are transformed into aurones in good yields. Preliminary mechanistic studies indicate that silyl formate, generated from CO₂ and PMHS, plays a crucial role in the carbonylation reaction.

Parallel Synthesis of Aurones Using a Homogeneous Scavenger

The ability to synthesize arrays of related compounds quickly and with good purity has become critical for a rapid exploration of their properties for biological or material applications. While a number of methods have been developed to enable this combinatorial synthesis, the existing options were not readily appliable to the synthesis of aurones using the simple Knoevenagel condensation approach. In order to avoid the time, expense, and lowered yields associated with flash column chromatography, we developed a scavenging approach for their synthesis. This method uses an excess of aldehyde to ensure complete conversion to aurones, followed by selective removal of the remaining aldehyde using a simple, inexpensive scavenger – isoniazid – and subsequent extraction with dilute acid, to produce the desired compounds with good purity under operationally simple conditions. This approach is expected to be applicable to many other reactions involving aldehydes as one of the reactants.

Direct Carbonylative Difunctional of Terminal Alkynes with Sodium Sulfinates to Access Olefin Sulfonyl Methyl Esters under Metal-Free Conditions

A metal-free difunctional carbonylation procedure toward the synthesis of olefin sulfonyl methyl esters has been developed. By employing easily available terminal alkynes and sodium sulfinates as the starting materials, a...

Aurones: A Golden Resource for Active Compounds

Deemed as poorly represented in nature, aurones have been often overlooked by researchers compared to other members of the flavonoid superfamily. However, over the past two decades, they have been reassessed by the scientific community, who are increasingly appreciating their ability to modulate several biological pathways. This review summarizes the recent literature on this class of compounds, which has been analyzed from both a chemical and a functional point of view. Original articles, reviews and editorials featured in Pubmed and Scifinder over the last twenty years have been taken into account to provide the readers with a view of the chemical strategies to obtain them, their functional properties, and their potential of technological use. The resulting comprehensive picture aims at raising the awareness of these natural derivatives as effective drug candidates, fostering the development of novel synthetic analogues.

Access to Chiral Chromenones through Organocatalyzed Mannich/Annulation Sequence

Herein we report an efficient and practical method to access chiral chromenones bearing one α-amino stereogenic center in the β position of the carbonyl group. The quinine-derived squaramide could efficiently promote Mannich/cycloketalization/dehydration tandem reactions between 1-(2-hydroxyaryl)-1,3-diketones and functionalized imines generated in situ, providing a wide range of chiral chromenones with propargylamine or α-amino ester moieties with good results (54 examples, up to 98% ee).

Regioselective Synthesis of Chromones via Cyclocarbonylative Sonogashira Coupling Catalyzed by Highly Active Bridged-Bis(N-Heterocyclic Carbene)Palladium(II) Complexes

The one-pot regioselective and catalytic synthesis of bioactive chromones and flavones was achieved via phosphine-free cyclocarbonylative Sonogashira coupling reactions of 2-iodophenols with aryl alkynes, alkyl alkynes, and dialkynes. The reactions are catalyzed by new dibromidobis(NHC)palladium(II) complexes. The new bridged N,N'-substituted benzimidazolium salts (L1, L2, and L3) and their palladium complexes C1, C2, and C3 were designed, prepared, and fully characterized using different physical and spectroscopic techniques. The molecular structures of complexes C1 and C3 were determined by single-crystal X-ray diffraction analysis. They showed a distorted square planar geometry, where the Pd(II) ion is bonded to the carbon atoms of two cis NHC carbene ligands and two cis bromido anions. These complexes displayed a high catalytic activity in cyclocarbonylative Sonogashira coupling reactions with low catalyst loadings. The regioselectivity of these reactions was controlled by using diethylamine as the base and DMF as the solvent.

Recent advances on synthesis and biological activities of aurones

Aurones are naturally occurring structural isomerides of flavones that have diverse bioactivities including antiviral, antibacterial, antifungal, anti-inflammatory, antitumor, antimalarial, antioxidant, neuropharmacological activities and so on. They constitute an important class of pharmacologically active scaffolds that exhibit multiple biological activities via diverse mechanisms. This review article provides an update on the recent advances (2013-2020.4) in the synthesis and biological activities of these derivatives. In the cases where sufficient information is available, some important structure-activity relationships (SAR) of their biological activities were presented, and on the strength of our expertise in medicinal chemistry and careful analysis of the recent literature, for the potential of aurones as medicinal drugs is proposed.

Carbonylative synthesis of heterocycles involving diverse CO surrogates

Recent advances in the carbonylative synthesis of heterocycles by using diverse CO surrogates as sources of CO are summarized and discussed.

Synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via tandem reactions under transition metal- and additive-free conditions

The synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via a sequential [3+2] cycloaddition/ring-opening/O-arylation reaction under transition metal- and additive-free conditions is reported.

Iridium-Catalyzed and Ligand-Controlled Carbonylative Synthesis of Flavones from Simple Phenols and Internal Alkynes

Flavones are important natural products with diverse biological activities. In this study, a novel procedure for the carbonylative synthesis of flavones has been developed by using simple phenols and internal alkynes as the substrates. Various flavones were isolated in moderate to good yields with excellent regioselectivity and functional group tolerance by using an iridium catalyst system. Notably, this is the first example of direct carbonylative annulation of non-preactivated phenols and alkynes to produce flavones, with the choice of ligand proving to be critical for the success of this transformation.

Selective palladium-catalyzed carbonylative synthesis of aurones with formic acid as the CO source

A general and practical strategy has been developed to prepare aurone derivatives.

Pd(OAc)2/SPPh3 accelerated activation of gem-dichloroalkenes for the construction of 3-arylchromones

The Pd-catalyzed regioselective intramolecular nucleophilic substitution of gem-dichloroalkene derivatives with salicylaldehydes leading to the synthesis of 3-arylchromones has been developed.