Intermolecular C-O addition of carboxylic acids to arynes

Fluorinated 2-arylchroman-4-ones and their derivatives: synthesis, structure and antiviral activity

A number of new biologically interesting fluorinated 2-arylchroman-4-ones and their 3-arylidene derivatives were synthesized based on the p-toluenesulfonic acid-catalyzed one-pot reaction of 2-hydroxyacetophenones with benzaldehydes. It was found that obtained (E)-3-arylidene-2-aryl-chroman-4-ones reacted with malononitrile under base conditions to form 4,5-diaryl-4H,5H-pyrano[3,2-c]chromenes. The structures of the synthesized fluorinated compounds were confirmed by 1H, 19F, and 13C NMR spectral data, and for some representatives of heterocycles also using NOESY spectra and X-ray diffraction analysis. A large series of obtained flavanone derivatives as well as products of their modification (35 examples) containing from 1 to 12 fluorine atoms in the structure was tested in vitro for cytotoxicity in MDCK cell line and for antiviral activity against influenza A virus. Among the studied heterocycles 6,8-difluoro-2-(4-(trifluoromethyl)phenyl)chroman-4-one (IC50 = 6 μM, SI = 150) exhibited the greatest activity against influenza A/Puerto Rico/8/34 (H1N1) virus. Moreover, this compound appeared active against phylogenetically distinct influenza viruses, A(H5N2) and influenza B (SI's of 53 and 42, correspondingly). The data obtained suggest that the fluorinated derivatives of 2-arylchroman-4-ones are prospective scaffolds for further development of potent anti-influenza antivirals.

Polyphosphoric acid-promoted one-pot synthesis and neuroprotective effects of flavanones against NMDA-induced injury in PC12 cells

We report herein an efficient polyphosphoric acid (PPA) promoted one-pot protocol for the synthesis of flavanone derivatives from 2-hydroxyacetophenones and benzaldehydes. A variety of flavanones were produced in moderate to excellent yields and evaluated for their neuroprotective effects against N-methyl-d-aspartate (NMDA)-induced excitotoxicity in PC12 cells. Derivatives bearing electron-donating groups exhibited better neuroprotective activity. Compound 3m demonstrated the best protective potency and reversed the intracellular calcium (Ca²⁺) influx caused by NMDA, suggesting that flavanones protected the PC12 cells against NMDA-induced neurotoxicity via inhibition of Ca²⁺ overload.

Nitrogen-Rich Porous Organic Polymers with Supported Ag Nanoparticles for Efficient CO2 Conversion

As CO₂ emissions increase and the global climate deteriorates, converting CO₂ into valuable chemicals has become a topic of wide concern. The development of multifunctional catalysts for efficient CO₂ conversion remains a major challenge. Herein, two porous organic polymers (NPOPs) functionalized with covalent triazine and triazole N-heterocycles are synthesized through the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The NPOPs have an abundant microporous content and high specific surface area, which confer them excellent CO₂ affinities with a CO₂ adsorption capacity of 84.0 mg g^-1 and 63.7 mg g^-1, respectively, at 273 K and 0.1 MPa. After wet impregnation and in situ reductions, Ag nanoparticles were supported in the NPOPs to obtain Ag@NPOPs with high dispersion and small particle size. The Ag@NPOPs were applied to high-value conversion reactions of CO₂ with propargylic amines and terminal alkynes under mild reaction conditions. The carboxylative cyclization transformation of propargylic amine into 2-oxazolidinone and the carboxylation transformation of terminal alkynes into phenylpropiolic acid had the highest TOF values of 1125.1 and 90.9 h^-1, respectively. The Ag@NPOP-1 was recycled and used five times without any significant decrease in catalytic activity, showing excellent catalytic stability and durability.

Visible-Light-Induced Dual Acylation of Alkenes for the Construction of 3-Substituted Chroman-4-ones

Heterocyclic compounds, especially oxygen-containing heterocyclic compounds, are crucial moieties in bioactive compounds and drug leads. Substituted chroman-4-ones are a kind of the most significant structural skeletons. Herein, we report a visible-light-induced dual acylation of alkenes for constructing 3-substituted chroman-4-ones, which undergoes a radical tandem cyclization reaction through carbon-carbon bond cleavage of oxime esters by a nitrogen-centered radical strategy. A series of 3-substituted chroman-4-ones were prepared with up to 86% yield.

Oxidant-Free Selective Synthesis of Functionalized Chroman-4-ones from ortho-Hydroxyacetophenones under HOAc/DMSO Conditions

A metal-free and oxidant-free acid-promoted DMSO activation and subsequent reaction is reported. In this protocol, two molecules of DMSO are activated by HOAc and serve as dual synthons which react with ortho-hydroxyacetophenones, affording 3-(methylthiomethyl)chroman-4-ones in moderate to good yields with high selectivity.

De novo Assembly of the Benzenoid Ring as a Core Strategy for Synthesis of the Isoindolinone Natural Products Isohericerin, Erinacerin A, and Sterenin A

Here we describe the use of the hexadehydro-Diels-Alder (HDDA) reaction for the de novo construction of the isoindolinone scaffold and its application to the synthesis of the title natural products. The key isoindolinone-forming HDDA reaction involved an unprecedented substrate motif in which an amide carbonyl group was conjugated to the 4π 1,3-diyne component. In addition, a dimethylsilyl (-SiMe₂H) substituent was exploited to trigger a Fleming-Tamao-Kumada oxidation for the installation of an essential phenolic hydroxyl group.

Benzyne-Mediated Esterification Reaction

A benzyne-mediated esterification of carboxylic acids and alcohols under mild conditions has been realized, which is made possible via a selective nucleophilic addition of carboxylic acid to benzyne in the presence of alcohol. After a subsequent transesterification with alcohol, the corresponding esters can be produced efficiently. This benzyne-mediated protocol can be used on the modification of Ibuprofen, cholesterol, estradiol, and synthesis of nandrolone phenylpropionate. In addition, benzyne can also be used to promote lactonization and amidation reaction.

Direct synthesis of ortho-methylthio allyl and vinyl ethers via three component reaction of aryne, activated alkene and DMSO

A transition-metal free synthetic strategy for the direct synthesis of ortho-methylthio allyl and vinyl ethers via cascade three-component coupling of aryne, activated alkene and DMSO.

Transition-metal-free synthesis of CMe2CF3-containing chroman-4-ones via decarboxylative trifluoroalkylation

(NH₄)₂S₂O₈-mediated decarboxylative trifluoroalkylation of alkenes with 3,3,3-trifluoro-2,2-dimethylpropanoic acid under metal-free conditions has been described.

Synthesis and Antimicrobial Activity of Methoxy- Substituted γ-Oxa-ε-lactones Derived from Flavanones

Six γ-oxa-ε-lactones, 4-phenyl-3,4-dihydro-2H-1,5-benzodioxepin-2-one (5a) and its five derivatives with methoxy groups in different positions of A and B rings (5b–f), were synthesized from corresponding flavanones. Three of the obtained lactones (5b,c,f) have not been previously described in the literature. Structures of all synthesized compounds were confirmed by complete spectroscopic analysis with the assignments of signals on ¹H and ¹³C-NMR spectra to the corresponding atoms. In most cases, lactones 5a–f exerted an inhibitory effect on the growth of selected pathogenic bacteria (Escherichia coli, Bacillus subtilis, and Staphylococcus aureus), filamentous fungi (Fusarium graminearum, Aspergillus niger, and Alternaria sp.), and yeast (Candida albicans). The broadest spectrum of activity was observed for unsubstituted lactone 5a, which was particularly active against filamentous fungi and yeast. Lactones with methoxy groups in the 3′ (5c) and 4′ (5d) position of B ring were more active towards bacteria whereas lactone substituted in the 7 position of the A ring (5e) exhibited higher antifungal activity. In most cases, the introduction of lactone function increased the activity of the compound compared to its flavonoid precursors, chalcones 3a–e, and flavanones 4a–f.

Aryne insertion into the PO bond: one-pot synthesis of quaternary phosphonium triflates

A novel transition-metal free synthetic strategy for the direct synthesis of quaternary phosphonium triflates via insertion of aryne into phosphine oxide.

A cascade process for the synthesis of ortho-formyl allyl aryl ethers and 2H-chromen-2-ol derivatives from arynes via trapping of o-quinone methide with an activated alkene

A transition-metal free synthetic strategy for the direct synthesis of ortho-formyl substituted allyl aryl ethers and 2H-chromen-2-ol derivatives via a cascade three-component coupling of arynes, activated alkene and N,N-dimethylformamide.

Synthesis of (2-hydroxyphenyl)(fusedphenyl)methanones via the photo-induced rearrangement of 2′-arylisoflavones

The photo-induced rearrangement of 2′-arylisoflavones (aryl = phenyl, 1-naphenyl, and 2-naphenyl) for the synthesis of (2-hydroxyphenyl)(fusedphenyl)methanones in EtOH under Ar at room temperature has been developed.

K2S2O8-Mediated Selective Trifluoromethylacylation and Trifluoromethylarylation of Alkenes under Transition-Metal-Free Conditions: Synthetic Scope and Mechanistic Studies

A practical and efficient method for selective intramolecular radical trifluoromethylacylation and -arylation of alkenes with inexpensive CF₃SO₂Na and K₂S₂O₈ in aqueous media has been developed, respectively, affording the highly chemoselective synthesis of CF₃-functionalized chroman-4-ones and chromanes in satisfactory yields. Control experiments and DFT calculations indicate that the CF₃SO₂Na/K₂S₂O₈ system is capable of trifluoromethylating the substrate of alkenes without a transition metal catalyst and the oxidation of CF₃SO₂Na to ·CF₃ by K₂S₂O₈ is involved in the rate-determining step.

Novel Covalent Triazine Framework for High-Performance CO2 Capture and Alkyne Carboxylation Reaction

Carbon dioxide capture and conversion have attracted extreme enthusiasm from the scientific community owing to global warming and environmental problems. However, conversion of CO₂ under atmospheric pressure is of great challenge because of the inertness of CO₂. Herein, we present a novel covalent triazine framework (CTF-DCE) prepared via ZnCl₂-catalyzed ionothermal trimerization reaction of di(4-cyanophenyl)ethyne, which displays a high Brunauer-Emmett-Teller surface area of 1355 m² g^-1 and an excellent CO₂ capture capacity of 191 mg/g at 273 K/1 bar. More importantly, silver species can be successfully fixed on the CTF matrix to produce a stable CTF-DCE-Ag heterogeneous catalyst for outstanding catalysis in the terminal alkyne carboxylation reactions under atmospheric pressure. CTF-DCE-Ag exhibited over sixfold higher turnover numbers than Ag@MIL-101. The recyclability test of the CTF-DCE-Ag catalyst demonstrated a great potential application in various environmental and energy-related applications.

Transition-Metal-Free Cyclization of Propargylic Alcohols with Aryne: Synthesis of 3-Benzofuranyl-2-oxindole and 3-Spirooxindole Benzofuran Derivatives ⊥

An unprecedented base-mediated cyclization of propargylic alcohols with aryne is reported, providing a novel method for the synthesis of 3-benzofuranyl-2-oxindole and 3-spirooxindole benzofuran scaffolds via a propargyl Claisen rearrangement/cycloaddition pathway. The nature of the substituent on acetylene group of propargylic alcohol influences the outcome of the reaction. The protocol offers a transition-metal-free and operationally simple methodology with broad substrate scope as a ready access to complex oxindole-linked heterocyclic compounds.

Mild synthesis of triarylsulfonium salts with arynes

Reactions between arynes and alkyl sulfides have been extensively studied over the past few decades. These reactions commonly end with a dealkylation process and thus deliver thioethers as final products. In contrast, the transformation described furnishes valuable triarylsulfonium salts, in lieu of thioethers, from arynes and diarylsulfides. The reaction features mild conditions and a broad substrate scope. A suite of functional groups such as ketones, esters, nitriles, aryl ethers and aryl halides is tolerated, which can be issues faced by traditional synthetic methods. The practicality of the reaction and its extension to the synthesis of triphenyl selenonium salt are also exhibited herein.

Reactivity of arynes toward functionalized alkenes: intermolecular Alder-ene vs. addition reactions

The selectivity between two different manifolds of reactions of arynes reacting with functionalized alkenes is described.

A domino reaction of 2-isocyanophenyloxyacrylate and aryne to synthesize arenes with vicinal olefin and benzoxazole

An unusual domino reaction of 2-isocyanophenyloxyacrylate and aryne has been disclosed. The present strategy experiences nucleophilic addition, Michael addition, carbon–oxygen cleavage, and cyclization, thus enabling the quick aryne vicinal difunctionalization by the installation of a benzoxazole and an olefin.

Diversity-Oriented Synthesis of Spiroannulated Benzofuran-3-one Scaffold of Leptosphaerin C and Congeners via Aryne Insertion

A concise synthesis of functionalized cyclohexenone-fused spirobenzofuran-3-ones under mild reaction conditions was developed. The reaction proceeds via insertion of aryne into the C-O bond followed by a regioselective intramolecular conjugate addition. The use of silyl-protected acid was crucial for the transformation. This protocol was successfully applied for the synthesis of leptosphaerin C core and its novel analogues.

Fused Multifunctionalized Chromenes from Tetraynes and α,β-Unsaturated Aldehydes

The synthesis of fused, highly substituted chromenes in a one-pot-three-step cascade hexadehydro-Diels-Alder reaction of tetraynes followed by an intermolecular α,β-unsaturated aldehyde rearrangement is reported. The target compounds were prepared by the condensation of malonates with 3-bromo-1-propyne, and the resulting 2,2-di(1-propyn-3-yl)malonates underwent cross-coupling with phenylethynyl bromides to afford 2,2-di(5-phenyl-2,4-pentadiynyl)malonates, which underwent intramolecular cyclization to produce tricyclic chromenes. The overall transformation involves the formation of four new C-C bonds and one new C-aryl-O-C-aryl bond by both intramolecular cyclization and intermolecular rearrangement reactions. These constitute a key strategy for the construction of a highly substituted natural chromene core and a robust method for producing other chromenes.