Design, synthesis, In-vitro, In-silico and DFT studies of novel functionalized isoxazoles as antibacterial and antioxidant agents

A series of new isoxazolederivatives incorporating the sulfonate ester function has been synthesized from 2-benzylidenebenzofuran-3(2 H)-one, known as aurone. The synthesis of the target compounds was carried out following an efficient methodology that allows access to the desired products in a reproducible way and with good yield. The structures of the synthesized compounds were established using NMR (1H and 13C) spectroscopy and mass spectrometry. A theoretical study was performed to optimize the geometrical structures and to calculate the structural and electronic parameters of the synthesized compounds. The calculations were also carried out to understand the influence and the effect of substitutions on the chemical reactivity of the studied compounds. The synthesized isoxazoles were screened for their antioxidant and antibacterial activities. The findings demonstrate that the studied compounds exhibit good to moderate antibacterial activity against the tested bacteria (Staphylococcus aureus, Bacillus subtilis, and Escherichia coli). Moreover, a number of the tested isoxazole derivatives exhibit high effectiveness against DPPH free radicals. Besides that, molecular docking studies were carried out to predict binding affinity and identify the most likely binding interactions between the active molecules and the target microorganisms' proteins. A 100 ns molecular dynamics study was then conducted to examine the dynamic behavior and stability of the highly potent isoxazole 4e in complex with the target bacterial proteins. Finally, the ADMET analyses suggest that all the synthesized isoxazoles have good pharmacokinetic profiles and non-toxicity and non-carcinogenicity in biological systems.

Preparation of pyridopyrazines through tandem Pd-catalyzed C-N/C-C coupling reactions of Ugi adducts

A Pd-catalyzed selective tandem cyclization of the Ugi adduct via Buchwald-Hartwig/C-H bond functionalization reactions has been reported. This sequence offers an interesting approach for synthesizing a wide range of pyrido[1,2-a]pyrazine-3,6-dione scaffolds under mild reaction conditions in moderate to excellent yields. The scope and limitations of the protocol are discussed.

Efficient approach to 1,1'-bisindoles via copper(I)-catalyzed double domino reaction

A highly efficient copper(I)-catalyzed approach for the synthesis of 1,1'-bisindoles that is based on the formation of four bonds in one step has been developed. The unprecedented three component reaction between one molecule of a 1,2-bis(2-bromoaryl)hydrazine and two molecules of a 1,3-diketone employing 10 mol% CuI as a catalyst and Cs2CO3 as a base in DMSO at 100 °C for 24 h delivers substituted 1,1'-bisindoles with yields up to 92%. The new method proceeds as a double domino condensation/Ullmann type C-C coupling. It allows an efficient and practical access to substituted 1,1'-bisindoles in one step from easily available starting materials.

Cu-Catalyzed tandem cyclization and coupling of enynones with enaminones for multisubstituted furans & furano-pyrroles

A synthetic strategy that efficiently constructs complex molecular diversity in a few steps will always be embraced by organic chemists. Here, we report a cascade reaction of enynones with enaminones via carbene insertion and aryl migration to engineer distinctive multisubstituted furans with an all-carbon quaternary center, and could extend the protocol in the same pot towards furano-pyrrole bis-heterocycles. Heterogeneity of this protocol was proved with the upshot of divergent chemical space under a relatively mild reaction environment.

Flexible Approach for the Synthesis of Annulated 4H-Pyrans Based on a Cu(I)-Catalyzed C-Allylation/O-Vinylation Reaction of Cyclic 1-Bromoallyl Tosylates with Cyclic and Acyclic 1,3-Dicarbonyls

The Cu(I)-catalyzed reaction between five-, six-, seven-, and eight-membered cyclic 1-bromoallyl tosylates and five- and six-membered cyclic 1,3-dicarbonyls in DMF at 80 °C using Cs₂CO₃ as a base and 2-picolinic acid as an additive selectively delivers a wide array of bisannulated 4H-pyrans in a single step with yields up to 92%. The transformations are considered to proceed as intermolecular C-allylations/intramolecular O-vinylations. With six-membered cyclic 1-bromoallyl tosylates and acyclic β-ketoesters as substrates, the corresponding 5,6,7,8-tetrahydro-4H-chromene-3-carboxylates are obtained with yields up to 59%.

Cu-Catalysed tandem reactions for building poly hetero atom heterocycles-green chemistry tool

Of late, regio-selective tandem reactions are given much attention due to the formation of several multiple bonds in a single synthetic operation, avoids altering the reaction conditions, isolation of the intermediates during the reaction, reduces the production of toxic waste to the environment and can produce highly complex organic molecules with desired selectivity. Though, it requires the well-built knowledge for optimization of the process, it permits to make the complex organic molecules with least number of steps, and it has eventually made great interest and inspiration to the upcoming organic chemists. Presentation of current book chapter presents the Cu-Catalysed tandem reactions for building poly hetero atom heterocyclic compounds via green approach.

Tandem aza-Michael addition-vinylogous aldol condensation: synthesis of N-bridged pyridine fused quinolones

Herein, we present a tandem aza-Michael addition-vinylogous aldol condensation strategy for the synthesis of N-bridged pyridine fused quinolone derivatives from quinolones and ynones. The presented tandem transformation features the construction of C-N and CC bonds in a single operation, under transition metal-free conditions. The wide substrate scope and gram scale synthesis of pyridine fused quinolone derivatives expand the synthetic value of the presented protocol.

Recent Advances in the Tandem Copper-Catalyzed Ullmann-Goldberg N-Arylation–Cyclization Strategies

N‒Aryl bond formation under copper catalysis has been playing a pivotal role and has been extensively used as a key step in the total syntheses of several therapeutic molecules. The...

Copper-catalyzed synthesis of 1-(2-benzofuryl)-N-heteroarenes from o-hydroxy-gem-(dibromovinyl)benzenes and N-heteroarenes

An efficient method for the synthesis of 1-(2-benzofuryl)-N-heteroarenes is developed from o-hydroxy-gem-(dibromovinyl)benzenes and N-heteroarenes under copper-catalyzed tandem reaction conditions. This methodology displayed a broad substrate scope and high yields in the preparation of a variety of 1-(2-benzofuryl)-N-heteroarenes. Further, 1-(2-benzofuryl)-N-heteroarenes were also applied in the synthesis of polycyclic benzofuro-indolo-pyridine scaffolds under palladium-catalyzed dehydrogenative coupling conditions. Overall, the present tandem approach is general, synthetically advantageous and avoids air-sensitive reagents.

Tandem copper catalyzed regioselective N-arylation-amidation: synthesis of angularly fused dihydroimidazoquinazolinones and the anticancer agent TIC10/ONC201

Herein, we present a copper-catalyzed tandem reaction of 2-aminoimidazolines and ortho-halo(hetero)aryl carboxylic acids that causes the regioselective formation of angularly fused tricyclic 1,2-dihydroimidazo[1,2-a]quinazolin-5(4H)-one derivatives. The reaction involved in the construction of the core six-membered pyrimidone moiety proceeded via regioselective N-arylation-condensation. The presented protocol been successfully applied to accomplish the total synthesis of TIC10/ONC201, which is an active angular isomer acting as a tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL): a sought after anticancer clinical agent.

Relieving the stress together: annulation of two different strained rings towards the formation of biologically significant heterocyclic scaffolds

Small carbo- and heterocycles have become versatile building blocks owing to their intrinsic ring strain and ease of synthesis. However, the traditional approaches of heterocycle synthesis involved the combination of one strained-carbocycle or heterocycle with one unsaturated molecule. On the contrary, there is an exciting possibility of combining two different strained rings to furnish varieties of heterocycles, where one of the strained rings can act as a valuable alternative to the unsaturated molecule. These strategies are also useful to access multi-functionalized rings. Despite these distinctive synthetic benefits, this chemistry has not drawn considerable attention of the community. In this minireview, we explicitly choose this topic to reveal the unexplored possibilities with these different strained rings. This minireview provides comprehensive details with the mechanistic rationale about the reactivity of these pairs of small rings when they are allowed to react together in the presence of different Lewis acids. Subsequently, it will also open a new avenue for heterocycle synthesis.

Lewis-acid-promoted cyclization reaction: synthesis of N3-chloroethyl and N3-thiocyanatoethyl quinazolinones

A Lewis-acid-promoted cyclization reaction of benzoyl chlorides with 2-(4,5-dihydrooxazol-2-yl)anilines, which can offer a series of N3-chloroethyl quinazolinones, is disclosed.

Copper-catalysed N-arylation of 5-aminopyrazoles: a simple route to pyrazolo[3,4-b]indoles

A copper-catalysed intramolecular N-arylation of 5-aminopyrazoles is demonstrated for the first time. Highly substituted pyrazolo[3,4-b]indoles are synthesized. In particular, the indole core is decorated with halogens and alkyl and methoxy groups. Furthermore, a selective N-arylation of unsymmetrical diaryl bromide containing pyrazoles is exemplified, resulting in valuable pyrazolo[1,5-a]benzimidazoles.

Tandem Copper-Catalyzed Regioselective N-Arylation-Aza-Michael Addition: Synthesis of Tetracyclic 5H-Benzothiazolo[3,2-a]quinazoline Derivatives

A copper-catalyzed tandem process integrating regioselective N-arylation, followed by aza-Michael addition, is disclosed using 2-aminobenzothiazoles and ortho-halo cinnamic acid congeners. This process generated diverse tetracyclic 5H-benzothiazolo[3,2-a]quinazoline derivatives in moderate to good yields. The present tandem reaction appears to proceed through concomitant ring opening of 2-aminobenzothiazole and S-arylation to give the ortho-cyanamide-substituted diaryl thioether intermediate. The thus generated intermediate likely undergoes an unprecedented Truce-Smiles-type rearrangement involving S- to N-aryl migration, followed by reformation of the thiazole ring and intramolecular aza-Michael addition to furnish the title products.

Copper-catalyzed [2+3]-annulation of N-H imines with vinyl azides: access to polyaryl 2H-imidazoles

A practical method for the synthesis of 2H-imidazoles via a [2+3] annulation of N-H imines with vinyl azides using a copper catalyst is developed. In this conversion, environmentally friendly oxygen is used as the sole oxidant and N2 and H2O are the only by-products. The catalytic transformation, operating under mild conditions, is operationally simple and is considered as a readily available catalytic system having good substrate and functional compatibility with high atom-efficiency without the need for additional ligands or additives.

Cu(I)-Catalyzed Ligand-Free Tandem One-Pot or Sequential Annulation via Knoevenagel Intermediates: An Entry into Multifunctional Naphthalenes, Phenanthrenes, Quinolines, and Benzo[b]carbazoles

A simple but efficient one-pot or sequential copper-catalyzed protocol using 2-bromoaldehydes and active methylene group containing substrates that affords multifunctional naphthalenes, phenanthrenes, quinolines, and benzo[b]carbazoles via Knoevenagel condensation, C-arylation, and decarboxylation, followed by aromatization, is developed. The reaction utilizes the potential of Knoevenagel intermediates and does not require any ancillary ligand. The phenanthrene products thus obtained show moderate fluorescence activity. Structural elaboration of the products to obtain dihydrobenzoquinazolines is also highlighted.

Copper-catalyzed synthesis of 2-aminopyridylbenzoxazoles via domino reactions of intermolecular N-arylation and intramolecular O-arylation

A simple and general approach to nitrogen-containing heterocycles via copper-catalyzed domino reaction has been developed, and the corresponding 2-aminopyridylbenzoxazole derivatives were obtained in good to excellent yields using the readily available starting materials. This method possesses unique step economy features, and is of high tolerance towards various functional groups in the substrates.

Synthesis of C2-tetrasubstituted indolin-3-ones via Cu-catalyzed oxidative dimerization of 2-aryl indoles and cross-addition with indoles

An efficient protocol for the synthesis of 2,2-disubstituted indolin-3-ones under mild conditions has been developed. This reaction involves the copper-catalyzed in situ oxidative de-aromatization of 2-arylindoles to indol-3-one, followed by self-dimerization as well as cross-addition with indoles under mild conditions. The result generates a wide variety of C2-tetrasubstituted indolin-3-ones with good to high yields (62–82%).

A general protocol for the synthesis of 2,2-disubstituted indolin-3-ones has been developed through self-dimerization of 2-aryl indoles and cross-addition with indoles under mild Cu-catalyzed oxidative conditions with good to high yields.

Heterocyclic iodoniums as versatile synthons to approach diversified polycyclic heteroarenes

Polycyclic heteroarenes are important scaffolds in the construction of pharmaceuticals. We have previously developed a series of novel heterocyclic iodoniums. In our current work, these unique iodoniums were employed to construct various complex polycyclic heteroarenes with structural diversity via tandem dual arylations. As a result, indole, thiophene and triphenylene motifs were fused into these heterocycles with high molecular quality, which might provide promising fragments in drug discovery. Moreover, these heterocycles could be diversified at a late stage.

The transformation of heterocyclic iodoniums led to the construction of heterocycles with a high structural diversity.

Synthesis of N-Fused Benzimidazole-4,7-diones via Sequential Copper-Catalyzed C-N Coupling/Cyclization and Oxidation

2-(2-Bromovinyl)- and 2-(2-bromoaryl)-benzimidazoles, including their 4,7-dimethoxy analogs, react with primary amides by microwave irradiation (or usual heating) in dimethylformamide in the presence of a catalytic amount of CuI along with a base to give the corresponding benzo[4,5]imidazo[1,2-c]-pyrimidines and -quinazolines in good yields. Treatment of benzo[4,5]imidazo[1,2-c]-pyrimidines and -quinazolines having methoxy group on benzimidazole moiety with aqueous ceric ammonium nitrate affords unprecedented N-fused hybrid scaffolds, benzo[4,5]imidazo[1,2-c]-pyrimidin-6,9-diones and -quinazoline-8,11-diones, respectively, in high yields.