Synthesis and antioxidant activity of new tetraarylpyrroles

Evaluation of Tungsten Catalysis among Early Transition Metals for N-Aryl-2,3,4,5-tetraarylpyrrole Synthesis: Modular Access to N-Doped π-Conjugated Material Precursors

Low-valent tungsten species generated from WCl6 and N,N'-bis(trimethylsilyl)-2,5-dimethyldihydropyrazine (Si-Me2-DHP) promotes the catalytic formation of N-phenyl-2,3,4,5-tetraarylpyrroles 3aa-ka from diarylacetylenes 1a-k and azobenzene (2a). An initial catalyst activation process is a three-electron reduction of WCl6 with Si-Me2-DHP to afford transient 'WCl3' species. Catalytically active bis(imido)tungsten(VI) species via successive one-electron reduction and N═N bond cleavage of 2a was revealed by isolating W(═NPh)2Cl2(PMe2Ph)2 from imidotungsten(V) trichloride and 2a in the presence of PMe2Ph. The superior catalytic activity of the tungsten catalyst was clarified by a density functional theory study: activation energies for the key three steps, [2 + 2]-cycloaddition of W═NPh and diarylacetylene to form (iminoalkylidene)tungsten species, enyne metathesis with second diarylacetylene, and C-N bond formation, are reasonable values for the catalytic reaction at 180 °C. In addition, this tungsten catalyst overcame two distinct deactivation processes: α-enediamido formation and aggregation of the low-valent species, both of which were observed for previously developed vanadium and titanium catalysts. We also demonstrated the synthetic utility of pentaarylpyrroles 3aa and 3ba as well as N-(2-bromophenyl)-2,3,4,5-tetraarylpyrrole 3ab by derivatizing their π-conjugated compounds 9aa, 10ba, and 11ab.

Catalyst-free synthesis of acenaphthoindolopyrimidine derivatives

A one pot three component reaction of acenaphthoquinone, barbituric acid/thiobarbituric acid/N,N-dimethyl barbituric acid and arylamines in ethanol for the synthesis of acenaphthoindolopyrimidine derivatives is reported. The reactions take place without a catalyst and gentle conditions. This method is facile and has some benefits such as, readily available starting materials, green solvent, catalyst-free, no column chromatographic purification and good to high yields.

Substituted pyrrolyl-cyanopyridines on the platform of acylethynylpyrroles via their 1 : 2 annulation with acetonitrile under the action of lithium metal

A facile one-pot synthesis of 2-(pyrrolyl)-4-aryl(hetaryl)-5-cyano-6-methylpyridines in 63–87% yield via the cyclization of available acylethynylpyrroles with two molecules of acetonitrile under the action of lithium metal at room temperature has been developed.

Two-pot synthesis and photophysical studies of 1,6-disubstituted 5-aza-indoles from succinaldehyde and N-aryl propargylic-imines

A two-pot synthesis of 5-aza-indoles has been developed from aqueous succinaldehyde and N-aryl propargylic-imines. This overall protocol involves: (i) the metal-free [3 + 2] annulation of aqueous succinaldehyde and N-aryl propargylic-imines to access 2-alkynyl-pyrrole-3-aldehydes and (ii) Ag-catalyzed 6-endo-dig-cyclization to obtain substituted 5-aza-indoles in the second pot. The 5-aza-indoles showed engaging photophysical activities, and the practicality of this pot-economic gram-scale synthesis has been demonstrated.

Revisit to the synthesis of 1,2,3,4-tetrasubstituted pyrrole derivatives in lactic acid media as a green solvent and catalyst

In this study, for the first time, lactic acid was used as a bio-based green catalyst and reaction medium for the synthesis of 1,2,3,4-tetrasubstituted pyrrole derivatives from one-pot three-component reaction of commercially available primary amines, 1,3-dicarbonyl compounds, and trans-β-nitrostyrene at room temperature. Thirty-three corresponding pyrroles, of which eight are novel and have been reported for the first time, were synthesized in high to excellent yields in lactic acid media and characterized by spectroscopic analysis. In all examined cases, lactic acid represented many advantages, including shorter reaction time, ease of product isolation, higher yields, no by-products, no chromatographic process, and lower volatility in the reaction. This bio-based green solvent can also be recycled and reused three times without loss of its efficiency as a catalyst and solvent.

Synthesis of Highly Functionalized 4-Amino-2-(trifluoromethyl)-1H-pyrroles

In this work, the reactivity of 5-bromo-1,1,1-trifluoro-4-methoxypent-3-en-2-one toward primary aliphatic amines was studied. The reaction was found to be extremely selective to synthesize a series of 1-alkyl-4-(aminoalkyl)-2-(trifluoromethyl)-1H-pyrroles (13 examples, up to 90% yield) and a series of highly functionalized β-enaminones (6 examples, up to 78% yield), with only the amount of amine and the reaction conditions needing to be controlled. The structure of the products was unambiguously determined by single crystal X-ray diffraction and 2D NMR experiments.

Highly Functionalized Pyrrolylpyridines from 2-(Acylethynyl)-pyrroles

A novel family of pharmaceutically prospective, densely functionalized (aryl-, hetaryl-, acyl-, and vinyl-substituted) pyrrolylpyridines has been assembled in up to 95% yields via the amination (NH4Cl/K2CO3/DMSO system, 90 °C, 16 h) of 2-(acylethynyl)pyrroles, followed by cyclization (MeOH, reflux, 6 h, up to 90% yield) of the formed intermediate 1-(pyrrol-2-yl)-1-aminoenones with acetylenic ketones (Bohlmann–Rahtz reaction). The intermediate pyrrolyl aminodienones, prospective building blocks for organic synthesis, can be separately synthesized (DMSO, 90 °C, 6 h) in 70–86% yields. A novel facet of this chemistry is stereoselective synthesis of C-vinylated pyridines, (E)-3-[5-acyl-2-aryl-6-(pyrrol-2-yl)pyridin-3-yl]-1-arylprop-2-en-1-ones, by involving the second molecule of acylacetylene into the reaction.

Nanocrystalline ZnO: A Competent and Reusable Catalyst for the Preparation of Pharmacology Relevant Heterocycles in the Aqueous Medium

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Nanoparticle catalyzed synthesis is a green and convenient method to achieve most of the chemical transformations in water or other green solvents. Nanoparticle ensures an easy isolation process of catalyst as well as products from the reaction mixture avoiding the hectic work up procedure. Zinc oxide is a biocompatible, environmentally benign and economically viable nanocatalyst with effectivity comparable to the other metal nanocatalyst employed in several reaction strategies. This review mainly focuses on the recent applications of zinc oxide in the synthesis of biologically important heterocyclic molecules under sustainable reaction conditions.

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Application of zinc oxide in organic synthesis: Considering the achievable advantages of this nanocatalyst, presently several research groups are paying attention in anchoring zincoxide or its modified structure in several types of organic conversions e.g. multicomponent reactions, ligand-free coupling reactions, cycloaddition reaction, etc. The advantages and limitations of this nanocatalyst are also demonstrated. The present study aims to highlight the recent multifaceted applications of ZnO towards the synthesis of diverse heterocyclic motifs. Being a promising biocompatible nanoparticle, this catalyst has an important contribution in the fields of synthetic chemistry and medicinal chemistry.

Regiodivergent Synthesis of Penta-Substituted Pyrroles through a Cascade [3 + 2] Cyclization of C-Acylimines with Activated Alkynes and Aromatic Nucleophiles

Highly robust one-pot, four-component cascade cyclization reaction of α-keto aldehydes, anilines, activated alkynes, and aromatic nucleophiles is developed to synthesize a diverse range of pharmaceutically important penta-substituted pyrroles. The reaction proceeds through the cascade cyclization of acylimines (in situ formed) with activated alkynes and aromatic nucleophiles such as indoles, pyrroles, and naphthols at room temperature under calcium(II) catalysis with high yields and broad substrate diversity.

One-pot synthesis of dihydro-8H acenaphtho[1',2':4,5]pyrrolo[1,2-a]imidazole-diol derivatives

A simple and efficient method for the synthesis of dihydro-8H-acenaphtho[1',2':4,5]pyrrolo[1,2-a]imidazole-diol derivatives via one-pot, four-component reaction of 1,1-bis(methylthio)-2-nitroethene, various amines, and acenaphthoquinone was developed. All the reactions were carried out in ethanol at reflux without any catalyst. The main advantages of this method are good to high yields, experimental simplicity, mild reaction conditions, simple workup, and easy purification.

Expeditious and eco-friendly synthesis of new multifunctionalized pyrrole derivatives and evaluation of their antioxidant property

Diminution of oxidative stress-mediated diseases is an essential pharmaceutical objective in modern biomedical research. The present work stresses upon the efficient and eco-friendly synthesis of an array of novel diversely functionalized pyrrole derivatives which are found to be antioxidants with reactive oxygen species (ROS) shielding competency against the deleterious consequence of oxidative stress. The results of the investigation displayed the effect of structural modification of the pyrrole derivatives on their respective antioxidant properties to various ROS. Noteworthy, the pyrrole moiety bearing 4-hydroxycoumarin or 2-hydroxy-1,4-naphthoquinone as substituent showed outstanding defensive potency towards OH and O₂^- while, nitrogen atom linked with aliphatic side-chain in the pyrrole scaffold made a strong affirmative impression in DPPH scavenging assay. More interestingly, an influencing reducing power was observed in pyrrole derivatives carrying cyclohexane 1,3-dione as one of the substituents. To have a comprehensive acuteness into the antioxidant capacity of the synthesized pyrrole derivatives against Trolox as a standard antioxidant, a crucial approach was taken into account by calculating TEAC (Trolox Equivalent Antioxidant Capacity) in case of OH and DPPH scavenging activity.

One-pot Multicomponent Synthesis of pyrrolo[1,2-d][1,4]benzoxazines and pyrrolo[1, 2-a]pyrazines in Water Catalyzed by Fe3O4@SiO2@L-Arginine-SA Magnetic Nanoparticles

AIMS

Synthesis of pyrrolo[1,2-d][1,4]benzoxazines and pyrrolo[1,2-a]pyrazines using magnetic nanoparticles.

BACKGROUND

One-pot, three component reaction for the synthesis of pyrrolo[1,2-d][1,4]benzoxazines and pyrrolo[1,2-a]pyrazines is reported. For the synthesis of pyrrolo[1,2-d][1,4]benzoxazines use of 2- aminophenols, dialkylacetylenedicarboxylates and β -nitrostyrene derivatives and Pyrrolo[1,2-a]pyrazines synthesized from reaction of ethylenediamine, dialkylacetylenedicarboxylates and β-nitrostyrene derivatives is discussed.

MATERIALS AND METHODS

2-aminophenol (0.5 mmol) and dimethylacetylenedicarboxylate (0.5 mmol) in water (3 ml) were stirred at room temperature for 10 min. Then, β-nitrostyrene (0.5 mmol) and Fe3O4@SiO2@LArginine- SA MNPs (0.07 g) were added and the mixture was refluxed for 5 h. After completion of the reaction, the mixture was cooled to room temperature and the catalyst was separated with external magnet and product extracted with dichloromethane. More purification of products was performed by column chromatography (nhexane/ ethyl acetate 4:1). Ethylenediamine (0.6 mmol) was added to dialkylacetylenedicarboxylate (0.6 mmol) in 3 ml water and was stirred for 10 min at room temperature. Later, β -nitrostyrene (0.5 mmol) and Fe3O4@SiO2@L-Arginine-SA MNPs (0.06 g) were added to mixture reaction and refluxed for 3 h. After completion, the mixture reaction was cooled to room temperature and the catalyst was separated by an external magnet. Then, the product was extracted with dichloromethane. For more purification column chromatography was used (n-hexane/ethylacetate 1:1).

RESULTS AND DISCUSSIONS

In this research, we have synthesized new derivatives of pyrrolo[1,2- d][1.4]benzoxazines and pyrrolo[1,2-a]pyrazines in green conditions consisting of use of water as a green solvent and magnetic nanoparticles.

CONCLUSION

In this research, we have synthesized new derivatives of pyrrolo[1,2-d][1.4]benzoxazines and pyrrolo[1,2-a]pyrazines in green conditions consisting of use of water as a green solvent and magnetic nanoparticles which were easily separated from mixture with an external magnet and had the capability to be recovered and reused. Also, in this work, the yield was good and the time of reactions was low compared with prior research.

Multicomponent Reaction of Aldehydes, Amines and Oxalacetate Analogues Leading to Biologically Attractive Pyrrole Derivatives

Pyrrole is a very important pharmacophoric moiety. It has been widely incorporated into the skeleton of antitumor, anti-inflammatory, antibacterial, antioxidant and antifungal active substances. Access to this key heterocycle by diverse routes is particularly attractive in terms of chemistry, and also from the environmental point of view. The present minireview summarizes the reported methods for the preparation of highly substituted pyrrole derivatives based on the one-pot multicomponent reaction of aldehydes, primary amines, and oxalacetate analogues as well as their biology.

Sequential multicomponent catalytic synthesis of pyrrole-3-carboxaldehydes: evaluation of antibacterial and antifungal activities along with docking studies

A sequential multicomponent method is developed to access highly substituted N-arylpyrrole-3-carbaldehydes and tested for antibacterial and antifungal activities against bacterial strains.

Synthesis of 2,3,4-trisubstituted pyrrole derivatives via [3 + 2] cyclization of activated methylene isocyanides with 4-(arylidene)-2-substituted oxazol-5(4H)-ones

An efficient base-catalyzed [3 + 2] cyclization between isocyanides and 4-(arylidene)-2-substituted oxazol-5(4H)-ones has been successfully developed to form 2,3,4-trisubstituted and 2,2,3,4-tetrasubstituted pyrrole derivatives.

Efficient and environmentally sustainable domino protocol for the synthesis of diversified spiroheterocycles with privileged heterocyclic substructures using bio-organic catalyst in aqueous medium

An efficient and environmentally sustainable synthetic protocol has been presented to synthesize structurally diverse spiroxindoles spiroannulated with indenopyrroloimidazoles, pyranopyrroloimidazoles, chromenopyrroloimidazoles, and imidazopyrrolopyrimidines involving three-component reaction of isatins, hydantoin, and β-diketones in the presence of green and sustainable bio-organic catalyst, β-amino acid, 2-aminoethanesulfonic acid (taurine), in aqueous media. The synthetic efficiency, operational simplicity, and reusability of catalyst make the present synthetic protocol cost effective, time efficient, and eco-friendly to synthesize molecules with structural diversity and molecular complexity and expected to contribute significantly not only to drug discovery research but also to pharmaceutical and medicinal chemistry.

Transition metal-free one-pot synthesis of substituted pyrroles by employing aza-Wittig reaction

A mild and metal-free one-pot synthetic strategy has been developed for the construction of substituted pyrroles by employing aza-Wittig reaction from a unique and unexplored combination of chromones and phenacyl azides. This method does not compromise the diverse substitutions on both the phenacyl azides and chromones. The merits of this method are wide substrate scope, easy functionalization, short reaction time, operationally simple, and higher yields. Moreover, this method is amenable for the generation of a library of key pyrrole building blocks.

A mild and metal-free one-pot synthetic strategy has been developed for the construction of substituted pyrroles by employing aza-Wittig reaction from a unique and unexplored combination of chromones and phenacyl azides.

Gas-phase UV absorption spectra and OH-oxidation kinetics of 1H-1,2,3-triazole and pyrazole

In this work, we report the gas phase UV absorption spectra and the kinetics of the OH-oxidation of 1H-1,2,3-triazole and pyrazole. UV spectra were determined between 200 and 250 nm, at 350 ± 2 K and at pressures between 0.09 and 0.3 Torr. The reported maximal UV absorption cross sections are (cm2 per molecule): σ 206 nm, 1H-1H-1,2,3-triazole = 2.04 × 10-18 and σ 203 nm, pyrazole = 5.44 × 10-18. The very low absorption capacity of these compounds beyond 240 nm indicates that their atmospheric photodissociation is negligible. The OH-oxidation of these species was performed in an atmospheric simulation chamber coupled to an FTIR spectrometer and to a GC/MS over the temperature range 298-357 K and at atmospheric pressure. Experiments were conducted in relative mode using benzaldehyde, trans-2-hexenal and heptane as references. The obtained rate constants at 298 K were (×10-11 cm3 per molecule per s): k(OH + 1H-1,2,3-triazole) = 2.16 ± 0.41; k(OH + pyrazole) = 2.94 ± 0.42. These results were compared to those available in the literature and discussed in terms of structure-reactivity and temperature dependency. Their tropospheric lifetimes with respect to reaction with OH radicals were then estimated.

Synthesis of N-Pyrrolyl(furanyl)-Substituted Piperazines, 1,4-Dizepanes, and 1,4-Diazocanes

The synthetic potential of 5-bromo-1,1,1-trifluoro-4-methoxypent-3-en-2-one toward the catalyst-free synthesis of N-pyrrolyl(furanyl)-piperazines, 1,4-diazepanes, and 1,4-diazocanes through a telescoped protocol is reported. This three-component one-pot method provided 23 examples with high chemo- and regioselectivity at yields up to 96%.

A Simple and Efficient Synthesis of Highly Substituted Indeno[1,2-b]pyrrole and Acenaphtho[1,2-b]pyrrole Derivatives by Tandem Three-Component Reactions

A green, convenient and tandem procedure for the efficient synthesis of highly substituted indeno[1,2-b]pyrrole and acenaphtho[1,2-b]pyrrole derivatives by domino three-component reaction of tryptamine/benzylamine, 1,3-dicarbonyl compounds and ninhydrin/ acenaphthenequinone is described. The significant features of this procedure were characterized by mild reaction conditions, high yields, operational simplicity and it being environmentally benign.

Ball Milling Promoted N-Heterocycles Synthesis

In the last years, numerous protocols have been published using ball milling for organic synthesis. Compared to other methods such as microwave or ultrasound irradiation and ionic liquids, ball mill chemistry is an economical, and ecofriendly method in organic synthesis that is rather underrepresented in the knowledge of organic chemists. The aim of this review is to explore the advantages of the application of ball milling in synthesis of N-heterocyclic compounds.

One-pot sequential multicomponent reaction between in situ generated aldimines and succinaldehyde: facile synthesis of substituted pyrrole-3-carbaldehydes and applications towards medicinally important fused heterocycles

An efficient sequential multi-component method for the synthesis of N-arylpyrrole-3-carbaldehydes has been developed. This reaction involved a proline-catalyzed direct Mannich reaction-cyclization sequence between succinaldehyde and in situ generated Ar/HetAr/indolyl-imines, followed by IBX-mediated oxidative aromatization in one-pot operation. The practical utility of this procedure is shown at gram-scale and the synthesis of diverse bioactive fused heterocyclic scaffolds such as pyrroloquinoline, pyrrolo-oxadiazole, dihydro pyrroloquinoline, and pyrrolo-phenanthridine.

Dihydroindeno[1,2-b]pyrroles: new Al3+selective off–on chemosensors for bio-imaging in living HepG2 cells

An approach for the expeditious synthesis of a new Al³⁺-selective turn-on dihydroindeno[1,2-b]pyrrole probe under environmentally benevolent conditions and its bio-imaging studies on HepG2 cell.

Preparation of chitosan nanoparticles from shrimp shells and investigation of its catalytic effect in diastereoselective synthesis of dihydropyrroles

Preparation of chitosan nanoparticles (CS-NPs) was examined from shrimp shells for their catalytic activity. The yield of crude chitosan was 87.8%. The structure of chitosan nanoparticles was determined by FT-IR, SEM and XRD analysis. Then, diastereoselective synthesis of dihydropyrroles was done using chitosan nanoparticles in water under ultrasonic irradiation. This polymeric nanocatalyst could be used instead of the old toxic commercial organic basic catalysts and could be readily isolated from the reaction mixture and recycled several times without significant loss of catalytic activity.