Syntheses of 2-Aroyl Benzofurans through Cascade Annulation on Arynes

Easy Access to Phenanthridinones via Metal-Free Cascade Benzannulation and C-N Bond Formation

A concise route for the synthesis of dihydrobenzo[j]phenanthridinones has been disclosed through an aryne annulation strategy under metal-free reaction conditions. The reaction involves multiple C-C and C-N bond cleavages/formations via Diels-Alder reaction, aromatization-driven C-N bond cleavage, and amide formation.

Nickel-Catalyzed Domino Reaction of α-Aryloxyacetonitriles with Arylboronic Acids: Synthesis of 2-Aroylbenzo[b]furans

We disclose the first catalytic domino reaction of α-(2-formylaryloxy)acetonitriles with arylboronic acids, yielding a range of 2-aroylbenzo[b]furans with yields of up to 93%. Ni(acac)2 serves as an effective dual catalyst. The protocol is also applicable to α-(2-acetylphenoxy)acetonitrile, giving rise to 3-methyl-2-aroylbenzo[b]furans. This domino process is efficient, additive-free, and compatible with a variety of aryl boronic acids, including those with CF3, NO2, CN, and CO2Me groups. Mechanistic studies highlight the dual activation facilitated by the nickel catalyst.

Base-Controlled Synthesis of Fluorescent Acridone Derivatives via Formal (4 + 2) Cycloaddition

A transition-metal-free formal (4 + 2) cycloaddition for the direct assembly of acridone derivatives has been developed from simple and easily accessible o-aminobenzamides and 2-(trimethylsilyl)aryl triflates. The base played an important role in the selective controlled synthesis of N-H and N-aryl acridones. A preliminary study on the fluorescence properties of N-aryl acridones demonstrated that they could be used as fluorescent materials with a broad emission range.

Substitution controlled aryne insertion: synthesis of diarylmethane/chromones

Aryne insertion reaction with 2-aroyl malonates/cyanoesters lead to the formation of diarylmethane or chromones depending on the substitution on the aryne ring. The presence of an electronegative atom at the ortho position of arynes generates chromones, whereas other arynes lead to the formation of diarylmethanes, via a cascade double aryne insertion.

Nanocatalysts: applications for the synthesis of N-containing five-membered heterocycles

Using transition metals as nanocatalysts has opened up a vast new area in heterocyclic chemistry in the modern day. Heterocyclic moieties are significant scaffolds that have both pharmacological and industrial applications. Various scientific groups have focused their attention on the expansion of simple reaction protocols by introducing better functional group compatibilities under mild reaction conditions through the use of easily available starting materials. This review provides an outline of the applications of metallic nanoparticles as proficient, recyclable, low-cost and green heterogeneous catalysts for the preparation of a wide range of key therapeutic five-membered nitrogen-containing heterocyclic compounds as well as some other significant functionalizations over the rings. This review mainly covers the literature published through the period from 2004 to 2021.

Palladium-Catalyzed Synthesis of Aryl Ketones from Carboxylic Acids and Arylboronic Acids Using 2-Chloroimidazolium Chloride as a Coupling Reagent

Carboxylic acids are an abundant and structurally diverse class of commercially available materials, which are commonly used as stable reagents in organic synthesis. The Suzuki–Miyaura coupling reaction directly using carboxylic acid as a substrate has been rarely reported. Here, we report an efficient coupling reaction of carboxylic acids with arylboronic acids in toluene in the presence of IPrCl-Cl, Pd(OAc)2, PPh3, and K3PO4·7H2O at 90 °C to give the corresponding aryl ketones.

Recent Advances in Construction of C(sp2)–O Bonds via Aryne Participated Multicomponent Coupling Reactions

Aryne chemistry is a powerful synthetic technique that forms new bonds to aromatic rings. The recent resurgence of aryne-based multicomponent coupling strategies has led to an influx of methodologies for the mild synthesis of arene derivatives. In particular, these innovative discoveries broaden and streamline approaches toward phenol ether motifs, which are a prevalent structural component across a broad range of chemistry related research fields. Herein, this review aims to provide a comprehensive overview of the recent progress in the construction of C(sp2)–O bonds via aryne-induced multicomponent reactions. Special attention has been paid to reaction design and mechanistic pathways.

1 Introduction

2 Insertion-Based MCRs

3 Nucleophilic-Addition-Based MCRs

4 Cycloaddition-Based MCRs

5 Summary

A formal [4 + 1] cycloaddition reaction of Baylis–Hillman bromides with sulfur ylides: facile access to α-alkenyl lactones

A formal [4 + 1] cycloaddition reaction of Baylis–Hillman adducts with sulfur ylides has been developed for the first time.

Recent advances in the application of ylide-like species in [4+1]-annulation reactions: an update review

In this review, advances in [4+1]‐annulation reactions involving sulfonium, sulfoxonium and ammonium ylides, as well as diazo compounds and carbenes are summarized over the last 6 years. Newly emerged methods...

Facile synthesis of α-aminophosphine oxides from diarylphosphine oxides, arynes and formamides

The straightforward synthesis of α-amino phosphine oxides via three-component reactions involving arynes, formamides and diarylphosphine oxides is disclosed. This method employs the aryne to activate formamide, without an external activating reagent, which is operationally simple under mild conditions with high efficiency. Furthermore, mechanistic perception suggests a cascade sequence including formal [2 + 2] cycloaddition of the aryne with a CO bond, and a 1,4-addition of the H-P(O) compounds to the enamine intermediates.

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.

Aromaticity-Driven Access to Cycloalkyl-Fused Naphthalenes

We report the efficient synthesis of cycloalkyl-fused naphthalenes through the [4 + 2]-cycloaddtion/decarboxylative aromatization of alkyne-tethered aryne insertion adducts. These scaffolds were difficult to synthesize using conventional reactions. The reaction proceeds via the formation of a benzopyrylium intermediate followed by intramolecular [4 + 2] cycloaddition and a subsequent decarboxylation pathway. This method is also compatible with allene-tethered substrates to afford similar products. In addition, the one-pot synthesis of polysubstituted naphthalenes via aryne insertion/benzannulation has also been developed in good yield.

o-Quinone Methides and o-Quinone Sulfides via Arynes: Synthesis of Ortho-Disubstituted Arenes and Heterocycles

In recent decades, o-quinone methides and o-quinone sulfides have been extensively highlighted as reactive intermediates for the synthesis of diversely functionalized ortho-disubstituted arenes and heterocycles. Additionally, ortho-disubstituted arenes offer a constructive path for the synthesis of fused carbocycles, heterocycles, natural products, and drug candidates. In the lieu of that, this Synopsis highlights a comprehensive overview on the potential applications of in situ generated o-quinone methides and o-quinone sulfides for one-pot synthesis of ortho-disubstituted arenes and heterocycles via arynes.

Potent α-amylase inhibitors and radical (DPPH and ABTS) scavengers based on benzofuran-2-yl(phenyl)methanone derivatives: Syntheses, in vitro, kinetics, and in silico studies

Thirty benzofuran-2-yl(phenyl)methanones 1-30 were synthesized and characterized their structures by spectroscopic techniques. Substituted phenacyl bromide and different derivatives of 2-hydroxy-benzaldehyde treated in the presence of anhydrous K2CO3 in acetonitrile at room temperature to afford the desired benzofurans 1-30. All compounds were screened for their in vitro α-amylase inhibitory and radical scavenging (DPPH and ABTS) activities. Results revealed that para substituted compounds were found to be more active than the others with IC50 values ranges for α-amylase inhibition (IC50 = 18.04-48.33 µM), DPPH (IC50 = 16.04-32.33 µM) and ABTS (IC50 = 16.99-33.01 µM) radical scavenging activities. Activities results were compared with the standards acarbose (IC50 = 16.08 ± 0.07 µM) for α-amylase, ascorbic acid (IC50 = 15.08 ± 0.03 and 15.09 ± 0.17 µM) for DPPH and ABTS radical scavenging activities, respectively. Kinetic studies predicted that all compounds followed non-competitive mechanism of inhibition. Molecular docking results showed good protein-ligand interactions profile against the corresponding target. To the best of our knowledge, out of thirty molecules, ten compounds 18-20, 22, and 25-30 were structurally new.

Diastereoselective synthesis of CF3-dihydrobenzofurans by [4+1] annulation of in situ-generated CF3-o-quinone methides and sulfur ylides

An efficient and highly diastereoselective synthesis of CF₃-dihydrobenzofurans by the reaction of in situ-generated CF₃-oQMs in the presence of a base with sulphur ylides is put forward. The generality of the present developed method was well studied with diverse substrates to access the corresponding products in excellent yields. The highly reactive CF₃-oQM has been utilized first time for the annulation reaction.

The first [4 + 1] annulation reaction of in situ-generated highly electrophilic CF₃-ortho-quinone methides with sulphur ylides has been put forth under mild reaction conditions to access CF₃-dihydrobenzofurans.

ZnCl2 -Catalyzed [4+1] Annulation of Alkylthio-Substituted Enaminones and Enaminothiones with Sulfur Ylides

Concise construction of furan and thiophene units has played an important role in the synthesis of potentially bioactive compounds and functional materials. Herein, an efficient Lewis acid ZnCl₂ catalyzed [4+1] annulation of alkylthio-substituted enaminones is reported, that is, α-oxo ketene N,S-acetals with sulfur ylides to afford 2-acyl-3-aminofuran derivatives. In a similar fashion, [4+1] annulation of the corresponding enaminothiones, that is, α-thioxo ketene N,S-acetals, with sulfur ylides efficiently proceeded to give multisubstituted 3-aminothiophenes. This method features wide substrate scopes as well as broad functional group tolerance, offering a concise route to highly functionalized furans and thiophenes.

Efficiently diastereoselective synthesis of functionalized hydro-carbazoles by base-mediated tandem annulation of 1-(2-amino-aryl)prop-2-en-1-ones and sulfur ylide

The base-promoted [3 + 3]/[1 + 4] tandem reaction of tosyl-protected o-amino α,β-unsaturated ketones and crotonate-derived sulfur ylide is developed for efficiently diastereoselective synthesis of functionalized hydrocarbazoles.

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.

Efficient access to fluorescent benzofuro[3,2-b]carbazoles via TFA-promoted cascade annulations of sulfur ylides, 2-hydroxy-β-nitrostyrenes and indoles

An efficient, TFA-promoted cascade annulation of sulfur ylides, 2-hydroxy-β-nitrostyrenes and indoles was established.

Tandem addition/cyclization for synthesis of 2-aroyl benzofurans and 2-aroyl indoles by carbopalladation of nitriles

Pd-Catalyzed tandem reaction of 2-(2-acylphenoxy)acetonitriles or 2-((2-benzoylphenyl)amino)acetonitrile with arylboronic acids for the synthesis of 2-aroyl benzofurans and 2-aroyl indoles.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

Organosulfur compounds have long played a vital role in organic chemistry and in the development of novel chemical structures and architectures. Prominent among these organosulfur compounds are those involving a sulfur(IV) center, which have been the subject of countless investigations over more than a hundred years. In addition to a long list of textbook sulfur-based reactions, there has been a sustained interest in the chemistry of organosulfur(IV) compounds in recent years. Of particular interest within organosulfur chemistry is the ease with which the synthetic chemist can effect a wide range of transformations through either bond formation or bond cleavage at sulfur. This review aims to cover the developments of the past decade in the chemistry of organic sulfur(IV) molecules and provide insight into both the wide range of reactions which critically rely on this versatile element and the diverse scaffolds that can thereby be synthesized.

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.

A cascade oxidation/[4 + 1] annulation of sulfonium salts for synthesis of polyfunctional furans: DMSO as one carbon source

A novel DMSO-involved cascade reaction of stabilized sulfonium salts has been established for direct construction of polyfunctional furans.

Asymmetric Sulfur-Ylide-Mediated Formal [4+1]-Annulation Reaction: Scope and Mechanism

A formal [4+1]-annulation strategy between sulfur ylides and 1,3-dienes was developed to afford functionalized cyclopentanoids. The process consists of a stereoselective cyclopropanation reaction followed, in situ, by a stereospecific MgI₂ -catalyzed vinylcyclopropane-cyclopentene rearrangement. The use of chiral sulfur ylides provided cyclopentanoids with excellent enantiocontrol. A combined experimental and computational mechanistic study showed that the stereospecificity of the rearrangement could be accounted for by a double S_N 2 reaction mechanism involving iodide.

Sequential σ-Bond Insertion/Benzannulation Involving Arynes: Selective Synthesis of Polysubstituted Naphthalenes

An interesting σ-bond insertion/benzannulation reaction for the synthesis of polysubstituted naphthalene derivatives has been developed from readily accessible ketones, arynes, and alkynoates. This practical and transition-metal-free method provides a novel route to diverse naphthalenes through a substrate-controlled rearrangement reaction with the cleavage of C-C bonds.

2,3-Diaroyl benzofurans from arynes: sequential synthesis of 2-aroyl benzofurans followed by benzoylation

A cascade synthetic strategy for the direct synthesis of 2-aroyl benzofurans from aryne precursors has been described. The synthesized 2-aroyl benzofurans were further benzoylated for the synthesis of 2,3-diaroyl benzofurans.

Expanding the synthesizable multisubstituted benzo[b]thiophenes via 6,7-thienobenzynes generated from o-silylaryl triflate-type precursors

Various 2,3-disubstituted 6,7-thienobenzynes have been efficiently generated from the corresponding o-silylaryl triflate-type precursors by activation with fluoride ions. The method has expanded the scope of synthesizable multisubstituted benzothiophenes, including those with various heteroatom substituents, and can be applied to the synthesis of EP4 antagonist analogs.

Various multisubstituted benzothiophenes, including those with various heteroatom substituents and EP4 antagonist analogs, have been prepared easily via 6,7-thienobenzynes generated from o-silylaryl triflate-type precursors.