Last Decade of Unconventional Methodologies for the Synthesis of Substituted Benzofurans

Palladium(ii) complexes bearing mesoionic carbene ligands: catalytic application in domino Sonogashira coupling/cyclization reactions for one-pot synthesis of benzofuran and indole derivatives

Bioactive heterocycles such as benzofuran and indole derivatives were synthesized from commercially available 2-iodoarenes and alkynes via domino Sonogashira coupling followed by cyclization reaction using well-defined palladium PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) complexes (2a and 2b). These reactions tolerate a variety of 2-iodoarenes and diversely substituted terminal alkynes, resulting in the corresponding product in moderate to good yields in an open-air atmosphere. In particular, two palladium(ii) PEPPSI complexes 2a and 2b were synthesized in good yields from the reaction of corresponding 1,2,3-triazol-5-ylidene (MIC: mesoionic carbene), PdCl2, KI, and K2CO3 in pyridine at 110 °C and structurally characterized by various spectroscopic techniques including NMR spectroscopy, IR spectroscopy, HRMS and elemental analysis studies. Complex 2b is also characterized by X-ray crystallography.

Synthesis of indol-3-yl-benzofurans and carbazoles via Cu(OTf)2-catalyzed [3 + 2] and [4 + 2] cycloaddition

An efficient Cu(OTf)2-catalyzed [3 + 2] cycloaddition of indole-3-acrylate with p-benzoquinone has been developed to construct two distinct indole-tethered benzofuran scaffolds, offering the first-ever selective access to these scaffolds. Moreover, the [4 + 2] cycloaddition reaction of indole-3-acrylate with vinyl ketone derivatives was used to synthesize carbazoles in a one-pot manner. The disclosed strategies provided a series of selective transformations under low-catalyst loading, with a broad substrate scope featuring diverse applicability and practical simplicity of the developed protocol with easily available substrates.

Diastereoselective Synthesis of Dihydrobenzofuran Spirooxindoles and Their Transformation into Benzofuroquinolinones by Ring Expansion of Oxindole Core

A mild and efficient approach for the diastereoselective synthesis of dihydrobenzofuran spirooxindoles using 3-chlorooxindoles and imines is presented. This process involves a formal [4 + 1] annulation, yielding the product with excellent diastereoselectivity. Furthermore, a novel method for constructing benzofuroquinolinone scaffolds through the ring expansion of oxindoles has been established. This method involves a lactam ring expansion to the quinolinone skeleton. Besides, a one-pot procedure for creating benzofuroquinolinone scaffolds from 3-chlorooxindoles and imines is also provided.

Development of on-DNA Formation of Benzofuran for DNA-Encoded Library Synthesis

Using a novel homologation-heterocyclization cascade, the on-DNA synthesis of benzofurans from aldehydes has been developed. The methodology, based on an innovative use of the Seyferth-Gilbert homologation, followed by a high yielding Sonogashira coupling in situ intramolecular cyclization one-pot, two-step reaction, provides a powerful and unique pathway for DNA-encoded library (DEL) synthesis of a wide array of pharmaceutically relevant benzofuran-based scaffolds.

Small molecule inhibitors of intestinal epithelial anion exchanger SLC26A3 (DRA) with a luminal, extracellular site of action

The anion exchanger protein SLC26A3 (down-regulated in adenoma, DRA) is expressed in the luminal membrane of intestinal epithelial cells in colon, where it facilitates the absorption of Cl^- and oxalate. We previously identified a 4,8-dimethylcoumarin class of SLC26A3 inhibitors that act from the SLC26A3 cytoplasmic surface, and demonstrated their efficacy in mouse models of constipation and hyperoxaluria. Here, screening of 50,000 new compounds and 1740 chemical analogs of active compounds from the primary screen produced five novel classes of SLC26A3-selective inhibitors (1,3-dioxoisoindoline-amides; N-(5-sulfamoyl-1,3,4-thiadiazol-2-yl)acetamides; thiazolo-pyrimidin-5-ones; 3-carboxy-2-phenylbenzofurans and benzoxazin-4-ones) with IC₅₀ down to 100 nM. Kinetic washout and onset of action studies revealed an extracellular site of action for the thiazolo-pyrimidin-5-one and 3-carboxy-2-phenylbenzofuran inhibitors. Molecular docking computations revealed putative binding sites for these inhibitors. In a loperamide model of constipation in mice, orally administered 7-(2-chloro-phenoxymethyl)-3-phenyl-thiazolo [3,2-a]pyrimidin-5-one (3a) significantly increased stool weight, pellet number and water content. SLC26A3 inhibitors with an extracellular site of action offer the possibility of creating non-absorbable, luminally acting inhibitors with minimal systemic exposure following oral administration. Our findings also suggest that inhibitors of related SLC26 anion transporters with an extracellular site of action might be identified for pharmacological modulation of selected epithelial ion transport processes.

Cu(ii) immobilized on poly(guanidine-sulfonamide)-functionalized Bentonite@MgFe2O4: a novel magnetic nanocatalyst for the synthesis of 1,4-dihydropyrano[2,3-c]pyrazole†

In this paper, we aim at synthesizing a new nanocomposite material in which bentonite acts as a nucleation site for MgFe₂O₄ nanoparticles precipitation in the attendance of an external magnetic field (MgFe₂O₄@Bentonite). Moreover, poly(guanidine-sulfonamide), as a novel kind of polysulfonamide, was immobilized on the surface of the prepared support (MgFe₂O₄@Bentonite@PGSA). Finally, an efficient and environment-friendly catalyst (containing nontoxic polysulfonamide, copper, and MgFe₂O₄@Bentonite) was prepared by anchoring a copper ion on the surface of MgFe₂O₄@Bentonite@PGSAMNPs. The synergic effect of MgFe₂O₄ magnetic nanoparticles (MNPs), bentonite, PGSA, and copper species was observed while conducting the control reactions. The synthesized Bentonite@MgFe₂O₄@PGSA/Cu, which was characterized using energy-dispersive X-ray spectroscopy (EDAX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy, was applied as a highly efficient heterogeneous catalyst to synthesize 1,4-dihydropyrano[2,3-c] pyrazole yielding up to 98% at 10 minutes. Excessive yield, quick reaction time, using water solvent, turning waste to wealth, and recyclability are the important advantages of the present work.

In this paper, we aim at synthesizing a new nanocomposite material in which bentonite acts as a nucleation site for MgFe₂O₄ nanoparticles precipitation in the attendance of an external magnetic field (MgFe₂O₄@Bentonite).

Selective synthesis of 3-formylbenzofuran and 3-acylbenzofuran using a chalcone rearrangement strategy

We developed a method for highly selective synthesis of two benzofuran isomers, by rearranging and subsequently transforming 2-hydroxychalcones. Depending on the reaction conditions, synthesis of 3-formylbenzofurans, unconventional products, and 3-acylbenzofurans was achieved through cyclized 2,3-dihydrobenzofurans obtained from the rearranged products. The facile synthesis of 3-formylbenzofurans facilitated synthesis of the natural product, puerariafuran, from the corresponding chalcone.

Study of the Pauson-Khand reaction in flow over alkynylphenyl vinyl ethers: towards the synthesis of tricyclic multisubstituted benzofurans

The use of flow methodology allows the use of alkynylphenyl vinyl ethers (benzo-fused 1,7 enynes) as substrates for the intramolecular Pauson-Khand reaction (PKr). Forced temperature and pressure conditions during a short reaction time minimize the substrate decomposition allowing the formation of the PK adduct. Substrates substituted at the internal position of the double bond and with internal triple bonds give better yields. The resulting products are cyclopentabenzofuranones present in diverse natural products and drugs that can be further functionalised.

Pd/Cu-catalyzed access to novel 3-(benzofuran-2-ylmethyl) substituted (pyrazolo/benzo)triazinone derivatives: their in silico/in vitro evaluation as inhibitors of chorismate mutase (CM)

In view of the reported chorismate mutase (CM or MtbCM) inhibitory activities of 3-indolylmethyl substituted (pyrazolo/benzo)triazinone derivatives the structurally similar 3-(benzofuran-2-ylmethyl) substituted (pyrazolo/benzo)triazinones were designed and evaluated in silico against CM. The docking of target molecules was performed at the interface site of MtbCM (PDB: 2FP2). All the best ranked molecules participated in a strong H-bonding with the ILE67 of the B chain at the backbone position in addition to several hydrophobic/van der Waals interactions with the hydrophobic residues. Based on encouraging docking results, the one-pot synthesis of newly designed benzofuran derivatives was carried out using tandem Pd/Cu-catalyzed Sonogashira cross-coupling followed by intramolecular cyclization of 2-iodophenols with appropriate terminal alkynes. A range of novel 3-(benzofuran-2-ylmethyl) substituted (pyrazolo/benzo)triazinone derivatives were prepared in high (>80%) yields. Three molecules i.e.3h, 3i and 3m that participated in good interaction with CM in silico showed encouraging (64–65%) inhibition at 30 μM in vitro. An SAR within this class of molecules suggested that the benzotriazinone series in general was better than the pyrazolotriazinone series. Based on molecular docking in silico, CM inhibition in vitro and computational ADME prediction the benzofuran derivatives 3i and 3m seemed to be of further medicinal interest in the context of discovery and development of new anti-tubercular agents.

We report the Pd/Cu-catalyzed synthesis, in silico molecular docking, in vitro CM inhibition and computational ADME prediction of novel 3-(benzofuran-2-ylmethyl) substituted (pyrazolo/benzo)triazinone derivatives.

Clarification on the Reactivity of Diaryl Diselenides toward Hexacyclohexyldilead under Light

In this study, the reactivity of organochalcogen compounds toward a representative alkyl-lead bond compound under light was investigated in detail. Under light irradiation, the Cy-Pb bond of Cy6Pb2 (Cy = cyclohexyl) undergoes homolytic cleavage to generate a cyclohexyl radical (Cy•). This radical can be successfully captured by diphenyl diselenide, which exhibits excellent carbon-radical-capturing ability. In the case of (PhS)2 and (PhTe)2, the yields of the corresponding cyclohexyl sulfides and tellurides were lower than that of (PhSe)2. This probably occurred due to the low carbon-radical-capturing ability of (PhS)2 and the high photosensitivity of the cyclohexyl-tellurium bond.

Synthesis of new methoxy derivatives of trans 2,3-diaryl-2,3-dihydrobenzofurans and evaluation of their anti-inflammatory activity

In the present study we synthesized new methoxy derivatives of trans 2,3-diaryl-2,3-dihydrobenzofurans, starting from suitable trans 2,3-diaryloxiranes, using regio- and stereoselective nucleophilic oxiranyl ring-opening reactions. The compounds were tested as anti-inflammatories in U937 cells. All compounds showed a significant role in inhibiting the NF-κB pathway and were able to restore normal ROS and NO level upon LPS activation. Moreover, regarding inhibition of ACLY, enantioenriched (50% ee) 7a₅₀ showed more potency than the racemic counterpart 7arac, together with a higher reduction of prostaglandin E₂ production, thus suggesting a stereoselective interaction in this pathway.

Skeleton Reorganization of Substituted Benzocyclobutenols through Rh-Catalyzed C-C Bond Cleavage Manipulated by Hydrogen Transfer

Although transition-metal-catalyzed C-C bond activation has been investigated extensively, C-C bond cleavage manipulated by hydrogen transfer has been unexplored. In this work, we disclose a skeleton reorganization of alkene-tethered benzocyclobutenols through Rh-catalyzed C-C bond cleavage coupled with intra- and intermolecular hydrogen transfer. The reaction pathway was well-tuned by the catalytic systems. As a result, divergent benzofurans bearing 4-β-hydroxy or 4-β-keto moieties were synthesized under pH- and redox-neutral conditions.

2,2-Bis(phenylselanyl)-1-(p-tolyl)vinyl 2-Oxo-2-(p-tolyl)acetate

2,2-Bis(phenylselanyl)-1-(p-tolyl)vinyl 2-oxo-2-(p-tolyl)acetate was synthesized via the reaction of p-tolylacetylene with diphenyl diselenide and benzoyl peroxide in benzene under atmospheric conditions. The molecular structure of the synthesized compound was evaluated using single-crystal X-ray analysis and spectral analyses. The process reported here provides a rare example of the direct and selective transformation of a terminal alkyne to the corresponding geminal diseleno-substituted alkene.

Stitching Ynones with Nitromethanes: Domino Synthesis of Functionally Enriched Benzofurans and Benzothiophenes

A convenient one-pot benzannulation of regioisomeric 2- or 3-substituted furan and thiophene ynones with a range of nitromethanes has been discovered to directly access densely and diversely functionalized benzofurans and benzothiophenes. In this protocol, the nitro group in nitromethanes functions as recursive carbanion activator to setup tandem Michael addition-6π-electrocyclization, and its eventual sacrificial elimination facilitates aromatization and overall benzannulation. This benzannulation was also explored with furan/thiophene based o-halo ynones wherein a Michael addition-S_NAr process operates and nitromethanes leave their imprint to deliver nitro substituted benzo-furans and -thiophenes.

Synthesis of functionalized diarylbenzofurans via Ru-catalyzed C–H activation and cyclization under air: rapid access to the polycyclic scaffold of diptoindonesin G

A method was developed for rapid assembly of 2,3-diarylbenzofuran-4-carboxylic acids from m-hydroxybenzoic acids and alkynes via Ru-catalyzed C–H alkenylation and cyclization, which was successfully applied for total synthesis of diptoindonesin G.

One-pot access to 2-amino-3-arylbenzofurans: direct entry to polyheterocyclic chemical space

As a means to make new benzofuran-embedded polycyclic structures, we established two efficient one-pot sequential coupling routes to 2-amino-3-arylbenzofurans and 2-amino-3-arylnaphtho[2,1-b]furans. Further ring formation (six- and seven-membered rings) with the resulting amine moiety at the C2 position of benzofurans was realized, leading to further expansion of benzofuran-based chemical space.

Structural Features Defining NF-κB Inhibition by Lignan-Inspired Benzofurans and Benzothiophenes

A series of 2-arylbenzofurans and 2-arylbenzothiophenes was synthesized carrying three different side chains in position five. The synthesized compounds were tested for NF-κB inhibition to establish a structure activity relationship. It was found that both, the side chain in position five and the substitution pattern of the aryl moiety in position two have a significant influence on the inhibitory activity.