N-Heterocyclic Carbene-Catalyzed Intramolecular Aldehyde−Nitrile Cross Coupling: An Easy Access to 3- Aminochromones

Photoredox-Catalyzed Tandem Cyclization of Enaminones with N-Sulfonylaminopyridinium Salts toward the Synthesis of 3-Sulfonaminated Chromones

A photoredox-catalyzed intermolecular tandem sulfonamination/cyclization of enaminones was realized by using N-aminopyridinium salts as the sulfonaminated reagents without transition-metal catalysts or bases. The reaction exhibits a broad scope and good functional group tolerance, good yields, and regioselectivity. Preliminary mechanistic studies support the radical property of the reaction and the involvement of N-centered radical intermediates.

Copper-Catalyzed Intramolecular Aldehyde-Ketone Nucleophilic Additions for the Synthesis of Chromans Bearing a Tertiary Alcohol Motif

The synthesis of chroman-3-ol derivatives via intramolecular nucleophilic additions has been established. Aldehydes can be used as alkyl carbanion equivalents via reductive polarity reversal which is facilitated by a copper catalyst and N-heterocyclic carbene ligand under mild conditions. The key to success is the difference in reaction activity between aldehydes and ketones. Finally, this methodology also can be used to construct other cyclic structures containing tertiary alcohols including tetraline, cyclohexane, indan, and 9,10-dihydrophenanthrene.

Transition-Metal-Free Synthesis of 3-Acyl Chromones by the Tandem Reaction of Ynones and Methyl Salicylates

A facile and effective tandem reaction of ynones and methyl salicylates was developed to obtain a broad range of 3-acyl chromones in moderate-to-excellent yields. This protocol underwent a Michael addition and cyclization process, which exhibited easily accessible substrates, broad substrate scope, and high regioselectivity under mild and transition-metal-free conditions. Moreover, gram-scale reaction and further chemical transformation of the products were also further studied.

Investigation of Direct and Retro Chromone-2-Carboxamides Based Analogs of Pseudomonas aeruginosa Quorum Sensing Signal as New Anti-Biofilm Agents

Biofilm formation is considered a major cause of therapeutic failure because bacteria in biofilms have higher protection against antimicrobials. Thus, biofilm-related infections are extremely challenging to treat and pose major concerns for public health, along with huge economic impacts. Pseudomonas aeruginosa, in particular, is a “critical priority” pathogen, responsible for severe infections, especially in cystic fibrosis patients because of its capacity to form resistant biofilms. Therefore, new therapeutic approaches are needed to complete the pipeline of molecules offering new targets and modes of action. Biofilm formation is mainly controlled by Quorum Sensing (QS), a communication system based on signaling molecules. In the present study, we employed a molecular docking approach (Autodock Vina) to assess two series of chromones-based compounds as possible ligands for PqsR, a LuxR-type receptor. Most compounds showed good predicted affinities for PqsR, higher than the PQS native ligand. Encouraged by these docking results, we synthesized a library of 34 direct and 25 retro chromone carboxamides using two optimized routes from 2-chromone carboxylic acid as starting material for both series. We evaluated the synthesized carboxamides for their ability to inhibit the biofilm formation of P. aeruginosa in vitro. Overall, results showed several chromone 2-carboxamides of the retro series are potent inhibitors of the formation of P. aeruginosa biofilms (16/25 compound with % inhibition ≥ 50% at 50 μM), without cytotoxicity on Vero cells (IC50 > 1.0 mM). The 2,4-dinitro-N-(4-oxo-4H-chromen-2-yl) benzamide (6n) was the most promising antibiofilm compound, with potential for hit to lead optimization.

Photoredox-Catalyzed Cascade of o-Hydroxyarylenaminones to Access 3-Aminated Chromones

Reported herein is a photoredox-catalyzed amination of o-hydroxyarylenaminones with tert-butyl ((perfluoropyridin-4-yl)oxy)carbamate, a versatile amidyl-radical precursor developed in our laboratory. This work establishes a new cascade pathway for the assembly of a range of 3-aminochromones under mild conditions. Downstream transformations of the obtained 3-aminochromones to construct diverse amino pyrimidines greatly broaden the applications of this photocatalyzed protocol.

Chromone a Privileged Scaffold in Drug Discovery: Developments on the Synthesis and Bioactivity

Chromones are the class of secondary metabolites broadly occurred in the plant kingdom in a noticeable quantity. This rigid bicyclic system has been categorized "as privileged scaffolds in compounds" in medicinal chemistry. The wide biological responses made them an important moiety in a drug discovery program. This review provides updates on the various methods of synthesis of chromones and biological applications in medicinal chemistry. Various synthetic strategies for the construction of chromones include readily available phenols, salicylic acid and its derivatives, ynones, chalcones, enaminones, chalcones and 2-hydroxyarylalkylketones as starting materials. Synthesis of chromones by using metal, metal free, nanomaterials and different catalysts are included. Details of diverse biological activities such as anti-cancer agents, antimicrobial agents, anti-viral property, anti-inflammatory agents, antioxidants, Monoamine Oxidase-B (MAO-B) Inhibitors, anti-Alzheimer's agents, anti-diabetic agent, antihistaminic potential, antiplatelet agents of chromone derivatives are diecussed.

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).

The base-induced regioselective radical arylation of 3-aminochromone with aryl hydrazine

A simple and efficient direct radical C-2 arylation of 3-aminochromone derivatives with aryl hydrazine under basic conditions is described.

NHC-catalyzed green synthesis of functionalized chromones: DFT mechanistic insights and in vitro activities in cancer cells

A simple green protocol for the synthesis of 3-aminochromone derivatives using a NHC catalyzed intramolecular hydroacylation reaction was developed. Further functional 3-aminochromes were evaluated for their anticancer activity.

An efficient tandem synthesis of chromones from o-bromoaryl ynones and benzaldehyde oxime

A transition-metal-free approach was developed to synthesize chromones from o-bromoaryl ynones and benzaldehyde oxime by sequential C–O bond formation.

Copper-Catalyzed Diversity-Oriented Synthesis (DOS) of 4-Amino-2H-chromen-2-imines: Application of Kemp Elimination toward O-Heterocycles

We report herein a copper-catalyzed sequential multicomponent reaction of benzo[d]isoxazoles with terminal alkynes and sulfonyl azides, which produced divergent 4-amino-2H-chromen-2-imines with excellent chemical selectivity. The reaction tolerated a broad range of functional groups, and released only N₂ as the sole byproduct. The sulfonyl imino group could be removed to give biologically active free 4-amino-2H-chromenone in good yield.

NHC catalyzed enantioselective Coates-Claisen rearrangement: a rapid access to the dihydropyran core for oleuropein based secoiridoids

A simple protocol for the synthesis of the dihydropyran core structure of secoiridoids using NHC catalyzed Coates-Claisen rearrangement is described.

Recent advances in N-heterocyclic carbene catalyzed achiral synthesis

N-Heterocyclic carbenes (NHCs) have emerged as powerful and elegant organocatalysts in a variety of newly developed and unprecedented enantioselective transformations due to their unique umpolung capacity. As a supplement to conventional enantioselective organocatalysis, NHC-induced non-asymmetric catalysis has gradually attracted much interest in recent years. Herein, this review aims to reveal the recent developments in NHC-promoted non-asymmetric umpolung transformations resulting in the expeditious construction of versatile achiral natural heterocycles, carbocycles and acylated products.

Discovery of New Chemical Entities for Old Targets: Insights on the Lead Optimization of Chromone-Based Monoamine Oxidase B (MAO-B) Inhibitors

The discovery of new chemical entities endowed with potent, selective, and reversible monoamine oxidase B inhibitory activity is a clinically relevant subject. Therefore, a small library of chromone derivatives was synthesized and screened toward human monoamine oxidase isoforms (hMAO-A and hMAO-B). The structure-activity relationships studies strengthen the importance of the amide spacer and the direct linkage of carbonyl group to the γ-pyrone ring, along with the presence of meta and para substituents in the exocyclic ring. The most potent MAO-B inhibitors were N-(3'-chlorophenyl)-4-oxo-4H-chromene-3-carboxamide (20) (IC50 = 403 pM) and N-(3',4'-dimethylphenyl)-4-oxo-4H-chromene-3-carboxamide (27) (IC50 = 669 pM), acting as competitive and noncompetitive reversible inhibitors, respectively. Computational docking studies provided insights into enzyme-inhibitor interactions and a rationale for the observed selectivity and potency. Compound 27 stands out due to its favorable toxicological profile and physicochemical properties, which pointed toward blood-brain barrier permeability, thus being a valid candidate for subsequent animal studies.

A facile strategy for accessing 3-alkynylchromones through gold-catalyzed alkynylation/cyclization of o-hydroxyarylenaminones

A strategy based on tandem alkynylation ofo-hydroxyarylenaminones followed by intramolecular cyclization has been developed to generate a diverse array of 3-alkynyl chromones.

Metal-free catalytic cascade to chromones: direct coupling of salicylaldehydes and activated alkynes triggered by aryloxyl radicals

The first intermolecular addition reaction of aryloxyl radicals to CC bonds was disclosed, which can afford biologically important chromonsviaa PhNMe₃I-catalyzed direct coupling of salicylaldehydes and activated internal alkynes in only one step.

A model β-sheet interaction and thermodynamic analysis of β-strand mimetics

Two novel β-strand mimetics are synthesized and their binding to a model peptide is studied in detail by ¹H NMR.

Non-asymmetric organocatalysis

Asymmetric organocatalysis is now an established methodology for the preparation of chiral compounds. However, these are not the only valuable molecules which can be conveniently obtained. Organocatalytic reactions affording achiral compounds are gaining momentum, opening unexplored pathways in the synthesis of densely functionalized aromatic moieties, olefins and useful molecules such as natural substances.

Access to quinolines through gold-catalyzed intermolecular cycloaddition of 2-aminoaryl carbonyls and internal alkynes

A facile and general method leading to polyfunctionalized quinolines was developed. In the presence of a highly efficient combination encompassing (PPh)(3)AuCl and AgOTf, the reactions between 2-aminocarbonyls and an array of internal alkynes proceeded smoothly to afford quinoline derivatives in good to excellent yields (up to 93%).

Efficient synthesis of benzofuranones: N-heterocyclic carbene (NHC)/base-catalyzed hydroacylation-Stetter-rearrangement cascade

A N-heterocyclic carbene/base-catalyzed cascade reaction leading to the formation of functionalized benzofuranones is reported. The reaction proceeds via an intramolecular hydroacylation of unactivated alkynes followed by an intermolecular Stetter reaction and a base-catalyzed chromanone to benzofuranone rearrangement.