Polysubstituted Pyrroles Research Articles

Cover Feature: Efficient Synthesis of Polysubstituted Pyrroles Based on [3+2] Cycloaddition Strategy Utilizing [1,2]‐Phospha‐Brook Rearrangement under Brønsted Base Catalysis (Chem. Eur. J. 57/2018)

Cover Feature: Efficient Synthesis of Polysubstituted Pyrroles Based on [3+2] Cycloaddition Strategy Utilizing [1,2]‐Phospha‐Brook Rearrangement under Brønsted Base Catalysis (Chem. Eur. J. 57/2018)

Efficient Synthesis of Polysubstituted Pyrroles Based on [3+2] Cycloaddition Strategy Utilizing [1,2]-Phospha-Brook Rearrangement under Brønsted Base Catalysis.

An efficient method for the synthesis of polysubstituted pyrroles was established based on the [3+2] cycloaddition strategy utilizing the [1,2]-phospha-Brook rearrangement under Brønsted base catalysis. The less-explored approach of the [3+2] cycloaddition, that is, the reaction of a C3 subunit with imines, was successfully achieved by making use of newly designed C3 subunits containing the requisite umpolung. The two-step formal [3+2] cycloaddition involves the catalytic generation of an α-oxygenated propargyl anion through the [1,2]-phospha-Brook rearrangement followed by γ-addition to the imine under Brønsted base catalysis and the subsequent intramolecular cyclization mediated by Au catalyst or a halogenation reagent to afford polysubstituted pyrroles having a variety of substituents in a positional selective manner. The pyrroles thus synthesized were amenable to further transformations, such as palladium-catalyzed cross-coupling reactions. The operationally very simple method with readily available substrates provides new access to a diverse array of well-organized polysubstituted pyrroles.

Synthesis of polysubstituted pyrroles via a gold(I)-catalyzed tandem three-component reaction at room temperature

A gold(I)-catalyzed three-component reaction of β-nitrostyrenes with 1,3-dicarbonyl compounds and primary amines to form polysubstituted pyrroles has been developed at room temperature in ethanol. The key advantages of the three-component reaction are the mild reaction conditions and environmentally safer solvent.

Copper Schiff base complex immobilized on silica‐coated Fe3O4 nanoparticles: a recoverable and efficient catalyst for synthesis of polysubstituted pyrroles

In this work, a copper Schiff base complex immobilized on silica‐coated Fe3O4 nanoparticles is synthesized, and studied as a highly efficient, recyclable, green and heterogeneous catalyst for the preparation of polysubstituted pyrroles under solvent‐free and mild conditions. This new catalyst was characterized by different techniques, such as Fourier transform infrared (FT‐IR), X‐ray powder diffraction (XRD), field‐emission scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), inductively coupled plasma (ICP) and vibrating sample magnetometry (VSM). The simple and environmentally one‐pot multicomponent condensation of nitromethane, an aryl aldehyde, a 1,3‐dicarbonyl compound and an amine in the presence of above catalyst affords the title compounds at room temperature. At the end, we compared the results for the synthesis of polysubstituted pyrroles in the presence of our nanocatalyst with previously reported catalysts in the literature.

Visible-Light-Induced C (sp3)–H Functionalization of Tosylhydrazones: Synthesis of Polysubstituted Pyrroles under Metal-Free Conditions

Iodine catalyzed C (sp3)-H functionalization of tosylhydrazones with β-enamino esters under visible light irradiation for the synthesis of trisubstituted pyrroles has been described. The present method is also applicable to α- substituted tosylhydrazones to yield the tetra-substituted pyrroles.

Divergent, Enantioselective Synthesis of Pyrroles, 3H-Pyrroles and Bicyclic Imidazolines by Ag- or P-Catalyzed [3+2] Cycloaddition of Allenoates with Activated Isocyanides.

The divergent, stereoselective formal [3+2] cycloadditions of allenoates with activated isocyanides catalyzed by silver or phosphine-based catalysts were investigated. Silver catalysis is capable of delivering a range of 3H-pyrroles in high stereoselectivities. These enantioenriched heterocycles can either undergo sequential cyclisation with isocyanoacetates to deliver unprecedented bicyclic imidazolines with excellent yields and stereoselectivity or undergo unusual aromatization pathways leading to polysubstituted pyrroles. On the other hand, a simple mix-and-go procedure using an amino acid-derived phosphine as the catalyst produces pyrroles bearing a benzylic stereocenter with good enantioselectivity.

An efficient and facile access to highly functionalized pyrrole derivatives.

A straightforward and one-pot synthesis of pyrrolo[3,4-c]pyrrole-1,3-diones via Ag(I)-catalyzed 1,3-dipolar cycloaddition of azomethine ylides with N-alkyl maleimide, followed by readily complete oxidation with DDQ, has been successfully developed. Further transformation with alkylamine/sodium alkoxide alcohol solution conveniently afforded novel polysubstituted pyrroles in good to excellent yields. This methodology for highly functionalized pyrroles performed well over a broad scope of substrates. It is conceivable that this efficient construction method for privileged pyrrole scaffolds could deliver more active compounds for medicinal chemistry research.

Copper-Catalyzed Synthesis of Polysubstituted Pyrroles through [3+1+1] Cycloaddition Reaction of Nitrones and Isocyanides.

An efficient, copper-catalyzed [3+1+1] cycloaddition reaction was developed for the expedient synthesis of pharmacologically interesting polysubstituted pyrroles from easily available nitrones and α-acidic isocyanides. The given approach features a new mode of cycloaddition between nitrones and isocyanides with wide substrate scope, good functional group tolerance, and operational simplicity. The operando infrared spectroscopy was used for the characterization of reaction intermediates.

Facile synthesis of polysubstituted 2,3-dihydropyrroles and pyrroles from Mn(OAc)3-promoted oxidative cyclization of alkenes with amines/alkyne esters or enaminone esters

A novel oxidative cyclization of alkenes with amines/alkyne esters or enaminone esters can be efficiently promoted by Mn(OAc)3, furnishing a series of polysubstituted 2,3-dihydropyrroles in moderate to excellent isolated yields (75–91%). Afterward addition of a suitable oxidant such as K2S2O8 can furnish efficient synthesis of the corresponding polysubstituted pyrroles in a one-pot pathway.

A Simple and Direct Synthesis of Pentasubstituted Pyrroles via [3+4] Annulation and Their In Vitro Evaluation as Thrombolytic Agents and Cytotoxicity Studies on L929 Cells

AbstractWe have developed two different methods for synthesis of two distinct polysubstituted pyrroles. The first method proceeds by the reaction of N,S‐acetal, arylglyoxals and malononitrile in the presence of H2O / PEG400 to the synthesis of 2‐(2‐argio‐1‐methyl‐5‐(methylthio)‐4‐nitro‐1H‐pyrrol‐3‐yl)‐2‐cyanoacetamide (4a‐4p). The second method for the synthesis of other divergent pyrroles 2‐(2‐argio‐1‐methyl‐5‐(methylthio)‐4‐nitro‐1H‐pyrrol‐3‐yl)acetonitrile (6a‐6f) under solvent free at thermal condition using methylcyanoacetate instead of malononitrile by decarboxylative elimination. Among the pyrroles 2‐(4‐methoxyphenyl) (4c), 2‐(4‐fluorophenyl) (4d) 2‐(4‐chlorophenyl) (4e), 2‐(2,4‐dichlorophenyl) (4f), 2‐(3‐chloro‐4‐fluorophenyl) (4g), 2‐(2‐bromo‐4‐chlorophenyl) (4h), (2‐(3‐bromophenyl) (4i), 2‐(4‐bromophenyl) (4j), (2‐(4‐hydroxyphenyl) (4l), and 2‐(3‐nitrophenyl) (4m) displayed moderate to good clot lysis. The cytotoxicity studies were also carried out on L929 cells for selected compounds. The test derivatives 4 c, 4 d, 4 g and 4 h showed good cell viability at lower concentration. The compound 4 f showed mild to non‐toxicity at higher and lower concentration. The density functional theory calculations (DFT) were carried out for the possible configurations of 6a‐argio‐2‐imino‐6‐methyl‐5‐(methylthio)‐4‐nitro‐3,3a,6,6a‐tetrahydro‐2H‐furo[2,3‐b] pyrrole‐3‐carbonitrile (D), 2‐amino‐6a‐argio‐6‐methyl‐5‐(methylthio)‐4‐nitro‐3a,6a‐dihydro‐6H‐furo[2,3‐b]pyrrole‐3‐carbonitrile (E) and 4c.

Copper-Promoted Regioselective Synthesis of Polysubstituted Pyrroles from Aldehydes, Amines, and Nitroalkenes via 1,2-Phenyl/Alkyl Migration.

The facile copper-catalyzed synthesis of polysubstituted pyrroles from aldehydes, amines, and β-nitroalkenes is reported. Remarkably, the use of α-methyl-substituted aldehydes provides efficient access to a series of tetra- and pentasubstituted pyrroles via an overwhelming 1,2-phenyl/alkyl migration. The present methodology is also accessible to non α-substituted aldehydes, yielding the corresponding trisubstituted pyrroles. On the contrary, the use of ketones, in place of aldehydes, does not promote the organic transformation, signifying the necessity of α-substituted aldehydes. The reaction proceeds under mild catalytic conditions with low catalyst loading (0.3-1 mol %), a broad scope, very good functional-group tolerance, and high yields and can be easily scaled up to more than 3 mmol of product, thus highlighting a useful synthetic application of the present catalytic protocol. Based on formal kinetic studies, a possible radical pathway is proposed that involves the formation of an allylic nitrogen radical intermediate, which in turn reacts with the nitroalkene to yield the desired pyrrole framework via a radical 1,2-phenyl or alkyl migration.

Oxidative nitrene transfer from azides to alkynes via Ti(ii)/Ti(iv) redox catalysis: formal [2+2+1] synthesis of pyrroles.

Catalytic oxidative nitrene transfer from azides with the early transition metals is rare, and has not been observed without the support of redox noninnocent spectator ligands. Here, we report the formal [2+2+1] coupling of azides and alkynes via TiII/TiIV redox catalysis from simple Ti halide imido precatalysts. These reactions yield polysubstituted N-alkyl pyrroles, including N-benzyl protected pyrroles and rare examples of very electron rich pentaalkyl pyrroles. Mechanistic analysis reveals that [2+2+1] reactions with bulky azides have different mechanistic features from previously-reported reactions using azobenzene as a nitrene source.

Transition-metal-free synthesis of polysubstituted pyrrole derivatives via cyclization of methyl isocyanoacetate with aurone analogues.

Presented herein is an unprecedented transition-metal-free cyclization of methyl isocyanoacetate with aurone analogues catalyzed by NaOH. Various 2,3,4-trisubstituted pyrroles were obtained in excellent yields (up to 99%). The high efficiency of this synthetic procedure, coupled with the operational simplicity and atom economy, makes it an attractive method for the synthesis of polysubstituted pyrroles.

Effects of a novel microtubule-depolymerizer on pro-inflammatory signaling in RAW264.7 macrophages

The Nuclear Factor-kappa B (NF-κB) pathway is vital for immune system regulation and pro-inflammatory signaling. Many inflammatory disorders and diseases, including cancer, are linked to dysregulation of NF-κB signaling. When macrophages recognize the presence of a pathogen, the signaling pathway is activated, resulting in the nuclear translocation of the transcription factor, NF-κB, to turn on pro-inflammatory genes. Here, we demonstrate the effects of a novel microtubule depolymerizer, NT-07-16, a polysubstituted pyrrole compound, on this process. Treatment with NT-07-16 decreased the production of pro-inflammatory cytokines in RAW264.7 mouse macrophages. It appears that the reduction in pro-inflammatory mediators produced by the macrophages after exposure to NT-07-16 may be due to activities upstream of the translocation of NF-κB into the nucleus. NF-κB translocation occurs after its inhibitory protein, IκB-α is phosphorylated which signals for its degradation releasing NF-κB so it is free to move into the nucleus. Previous studies from other laboratories indicate that these processes are associated with the microtubule network. Our results show that exposure to the microtubule-depolymerizer, NT-07-16 reduces the phosphorylation of IκB-α and also decreases the association of NF-κB with tubulin which may affect the ability of NF-κB to translocate into the nucleus. Therefore, the anti-inflammatory activity of NT-07-16 may be explained, at least in part, by alterations in these steps in the NF-κB signaling pathway leading to less NF-κB entering the nucleus and reducing the production of pro-inflammatory mediators by the activated macrophages.

Synthesis of Polysubstituted Pyrroles through a Formal [4 + 1] Cycloaddition/E1cb Elimination/Aromatization Sequence of Sulfur Ylides and α,β-Unsaturated Imines.

A reaction sequence comprising a formal [4 + 1] cycloaddition, an E1cb elimination, and an aromatization process is described in this work. By doing so, polysubstituted pyrroles were achieved from easily available chemicals, sulfur ylides, and α,β-unsaturated imines. This protocol features mild conditions, high efficiency, and wide substrate scopes.

Nitroalkenes as Latent 1,2-Biselectrophiles - A Multicatalytic Approach for the Synthesis of 1,4-Diketones and Their Application in a Four-Step One-Pot Reaction to Polysubstituted Pyrroles.

An NHC-catalyzed nitro-Stetter/elimination/Stetter reaction sequence employs nitroalkenes as latent 1,2-dication synthons providing a novel access to highly useful symmetrical and unsymmetrical 2-aryl substituted 1,4-diketone building blocks from commercially available aldehyde precursors. For less activated (aliphatic) aldehydes, a cooperative catalytic strategy has been developed via the merger of NHC and H-bonding catalysis. To further showcase the versatility of our approach, a great variety of these unprecedented 1,4-diketones are used to efficiently synthesize polysubstituted pyrroles-including those with hetaryl substituents-in good to excellent yields in a multicatalytic metal-free, four-step one-pot cascade reaction under mild, yet robust, conditions.

Synthesis of 1,2,3,5-substituted pyrroles from α-bromoacetophenones and 2-nitroethene-1,1-diamines

Abstract The simple synthesis of 1,2,3,5-substituted pyrroles from α-bromoacetophenones and 2-nitroethene-1,1-diamines in the presence of K 2 CO 3 in DMF at 120 °C is described. A range of fused and non-fused polysubstituted pyrroles were prepared in high yields with short reaction times.

Synthesis of Polysubstituted 3-Amino Pyrroles via Palladium-Catalyzed Multicomponent Reaction.

A novel approach for the synthesis of polysubstituted 3-amino pyrroles via palladium-catalyzed three-component tandem reaction was developed. The procedure constructs various polysubstituted 3-amino pyrroles with moderate to excellent yields under mild reaction conditions with assembly efficiency, readily available starting materials, and good functional group tolerance. Furthermore, this process was successfully applied to the synthesis of different 3-phenyl-1,4-dihydropyrrolo[3,2-b]indole derivatives via an intramolecular Buchwald-Hartwig cross-coupling reaction in two steps.

Manganese (III) acetate mediated synthesis of polysubstituted pyrroles under solvent-free ball milling

Under solvent-free ball milling conditions, a simple and mild method was developed for efficient synthesis of 2,5-dimethyl-3,4-dicarboxylate-pyrroles and N-substituted 3,4-diphenylpyrroles via condensation-annulation of amines with acetoacetate and 2-phenylacetaldehyde, respectively. The use of cheap and safe Mn(OAc)3 as a mediator, no use of commonly employed acetic acid as solvent, short reaction time and readily available starting materials make this protocol a good alternative to traditional synthesis of polysubstituted pyrroles.

Metal-free synthesis of polysubstituted pyrroles using surfactants in aqueous medium

An efficient and metal-free method has been developed for the synthesis of polysubstituted pyrrole derivatives with combination of sodium dodecyl sulphate (SDS) and Triton X-100 surfactants using water as a solvent at room temperature in 2–6 h and under microwave conditions (10 min) with good to excellent yields.