Direct Assembly of 3,4‐Difunctionalized Benzofurans and Polycyclic Benzofurans by Phenol Dearomatization and Palladium‐Catalyzed Domino Reaction

A method to directly convert 2‐alkynylphenols to 3,4‐difunctionalized benzofurans and polycyclic benzofurans was developed. This protocol involves a hypervalent‐iodine‐mediated oxidative dearomatization to break the aromaticity of 2‐alkynylphenols, and a palladium‐catalyzed domino reaction to install two functional groups at the C3 and the C4 positions and restore the aromaticity of benzofurans.     

Palladium-catalyzed direct arylation of polysubstituted benzofurans

An efficient access to 2-substituted 3-arylbenzofurans through a palladium-catalyzed C3 direct arylation of 2-substituted benzofurans with aryl bromides is described. The scope and limitation of this reaction was studied. The method tolerates a variety of functional groups on the aryl halide and has been successfully extended to polysubstituted benzofurans to obtain the corresponding 3-arylbenzofurans with good to excellent yields.     

Allenylphosphonates/allenylphosphine oxides as intermediates/precursors for intramolecular cyclization leading to phosphorus-based indenes, indenones, benzofurans, and isochromenes

Utilizing internally available functional groups, a simple protocol for the efficient synthesis of phosphorus-based indenes, indenones, benzofurans, and isochromenes via intramolecular cyclization of allene intermediates/precursors is generated; the latter intermediates/precursors are conveniently obtained through aldehyde-, alkylidene-, and hydroxyl-functionalized propargyl alcohols and P(III)-Cl precursors. The structures of key products have been unequivocally confirmed by X-ray crystallography.     

CuBr-Catalyzed Coupling of N-Tosylhydrazones and Terminal Alkynes: Synthesis of Benzofurans and Indoles

A new method for the synthesis of benzofurans or indoles via ligand-free CuBr-catalyzed coupling/cyclization of terminal alkynes with N-tosylhydrazones derived from o-hydroxy- or o-aminobenzaldehydes has been developed. A wide range of functional groups were found that are able to tolerate the reaction conditions.     

Practical,Modular, and General Synthesis of Benzofurans through Extended Pummerer Annulation/Cross‐Coupling Strategy

Operationally simple, efficient, and widely applicable Pummerer annulations of simple phenols with ketene dithioacetal monoxides, with the aid of trifluoroacetic anhydride, have been shown to provide a variety of benzofurans having a methylthio group at the 2‐position. Subsequent and newly developed nickel‐catalyzed arylation at the methylthio group culminates in diversity‐oriented synthesis of multisubstituted benzofurans. Our extended Pummerer annulation/cross‐coupling sequence is powerful enough to synthesize biologically active natural products as well as highly fluorescent benzofuran derivatives.     

Practical,Modular, and General Synthesis of Benzofurans through Extended Pummerer Annulation/Cross‐Coupling Strategy

Operationally simple, efficient, and widely applicable Pummerer annulations of simple phenols with ketene dithioacetal monoxides, with the aid of trifluoroacetic anhydride, have been shown to provide a variety of benzofurans having a methylthio group at the 2‐position. Subsequent and newly developed nickel‐catalyzed arylation at the methylthio group culminates in diversity‐oriented synthesis of multisubstituted benzofurans. Our extended Pummerer annulation/cross‐coupling sequence is powerful enough to synthesize biologically active natural products as well as highly fluorescent benzofuran derivatives.     

Synthesis of substituted benzofurans via microwave-enhanced catch and release strategy

A microwave-enhanced procedure for the synthesis of substituted benzofurans starting from 2-(1-hydroxyalkyl)-phenols and using triphenylphosphine polystirene resin is reported. The benzofurans are isolated in good to high yields and purities by simple workup. The procedure can be applied to chiral alpha-alkyl-2-benzofuranmethanamines too.     

DABCO-Promoted Efficient and Convenient Synthesis of Benzofurans

An efficient and convenient synthesis of benzofurans has been described from phenacyl halides and o-hydroxy benzaldehyde in the presence of DABCO. The procedure is applicable for a variety of phenacyl halides and provide a variety of benzofurans. DABCO act as a base and as well as nucleophile.     

Palladium(0)‐Catalyzed Single and Double Isonitrile Insertion: A Facile Synthesis of Benzofurans,Indoles, and Isatins

A palladium(0)‐catalyzed cascade process consisting of isonitrile insertion and α‐Csp³?H cross‐coupling can be achieved for the synthesis of benzofurans and indoles. The construction of isatins by a Pd‐catalyzed cascade reaction incorporating double isonitrile insertion, amination, and hydrolysis has also been achieved. The key features of this work include diverse heterocycle synthesis, phosphine‐ligand‐free reaction conditions, a one‐pot procedure, simple and commercially available starting materials, broad functional‐group compatibility, and moderate to good reaction yields.     

Synthesis of cicerfuran, an antifungal benzofuran, and some related analogues

Routes were investigated for the synthesis of cicerfuran, a hydroxylated benzofuran from wild chickpea implicated in resistance to Fusarium wilt, and some of its analogues. A novel method is described for the synthesis of oxygenated benzofurans by epoxidation and cyclisation of 2′-hydroxystilbenes. The stilbene intermediates required could be synthesised by palladium-catalysed coupling of styrenes with mono-oxygenated aryl halides but not with di-oxygenated aryl halides. Stilbenes corresponding to the latter were synthesised by Wittig reactions.     

Titanium tetrachloride promoted cyclodehydration of aryloxyketones: Facile synthesis of benzofurans and naphthofurans with high regioselectivity

An efficient and facile method for the synthesis of a broad series of benzofurans and naphthofurans is described. The direct intramolecular cyclodehydration of aryloxyketones in the presence of titanium tetrachloride affords the corresponding benzofurans and naphthofurans with good regioselectivity and yields.     

Preparation of Highly Functionalised Benzofurans from ortho‐Hydroxyphenones and Dichloroethylene: Applications and Mechanistic Investigations

Highly functionalised benzofurans have been prepared from ortho‐hydroxyphenones and 1,1‐dichloroethylene. The key intermediate, a chloromethylene furan, smoothly rearranged into the corresponding benzofuran carbaldehyde under acidic conditions. Some mechanistic investigations have been performed and several biologically active benzofurans have been synthesised.     

Preparation and Cyclization of Aryloxyacetaldehyde Acetals; A General Synthesis of 2,3-Unsubstituted Benzofurans

An improved method for the preparation of 2,3-unsubstituted benzofurans is described. Specifically, the PPA catalysed cyclization of aryloxyacetaldehyde acetals to give (4–7)-substituted benzofurans has been achieved.     

Benzofuran derivatives. Part 4 , synthesis of benzofurans and 2,3,4,5-tetrahydro-1-benzoxepin-3,5-diones

By treatment of ethyl 4- or 5-substituted 2-acetylphenoxyacetates 1 with potassium hydroxide in dry dioxane, benzofurans 2–7 and 2,3,4,5-tetrahydro-1-benzoxepin-3,5-diones 8 were obtained. The relative yields of benzofurans 2–7 and 2,3,4,5-tetrahydro-1-benzoxepin-3,5-diones 8 varied with the types of 4- or 5-substituents. The electron-donating 4-methoxyl group favored the formation of benzoxepins. On the other hand, electron-withdrawing substituents such as the 4-nitro group favored the formation of benzofurans. When esters 1 were treated with sodium amide, 2,3-dihydrobenzofurans 2 were obtained exclusively regardless of 4- or 5-substituents.     

Copper‐Catalyzed Ring‐Opening Silylation of Benzofurans with Disilane

The catalytic ring‐opening silylation of benzofurans has been achieved by employing a copper catalyst and 1,2‐di‐tert‐butoxy‐1,1,2,2‐tetramethyldisilane, which could be easily prepared and handled without special care. The reaction afforded (E)‐o‐(β‐silylvinyl)phenols with complete stereoselectivity. The scope of benzofurans was well explored, and functional groups such as chloro, fluoro, and acetal were compatible with the reaction conditions. DFT calculations were used to determine the energy profile of the silylation and the origin of the stereoselectivity. The silylated product was proven to be useful as a synthetic intermediate and subsequently underwent transformations such as Pd‐catalyzed cross‐coupling with iodoarenes.     

Development of a General and Selective Nanostructured Cobalt Catalyst for the Hydrogenation of Benzofurans,Indoles and Benzothiophenes

The selective hydrogenation of benzofurans in the presence of a heterogeneous non-noble metal catalyst is reported. The developed optimal catalytic material consists of cobalt-cobalt oxide core–shell nanoparticles supported on silica, which has been prepared by the immobilization and pyrolysis of cobalt-DABCO-citric acid complex on silica under argon at 800 °C. This novel catalyst allows for the selective hydrogenation of simple and functionalized benzofurans to 2,3-dihydrobenzofurans as well as related heterocycles. The versatility of the reported protocol is showcased by the reduction of selected drugs and deuteration of heterocycles. Further, the stability, recycling, and reusability of the Co-nanocatalyst are demonstrated.     

Synthesis of benzo[b]furans via CuI-catalyzed ring closure

A wide variety of benzo[b]furans were synthesized efficiently via a CuI-catalyzed ring closure of 2-haloaromatic ketones. The methodology was tolerant to various functional groups, affording benzofurans in 72-99% yields.     

Facile synthesis of 2,3-disubstituted benzofurans via DBU-promoted intramolecular annulation of ortho oxyether aroylformates

A facile synthesis of 2,3-disubstituted benzofurans from ortho oxyether aroylformates has been developed. Under the mediation of DBU, the intramolecular annulation of ortho oxyether aroylformates proceeds smoothly to provide the corresponding 2,3-disubstituted benzofurans in moderate to good yields under mild conditions. Furthermore, a one-pot two-step synthesis of 2,3-disubstituted benzofurans has also been demonstrated from readily available ortho hydroxy aroylformates.     

Studies with enaminones: reactivity of 1,5‐disubstituted‐1,4‐pentadien‐3‐ones toward electrophilic reagents. a novel route to azolylazines,benzofuranals, pyranones

Several new enaminodienones prepared from substituted acetone and dimethylformamide dimethylacetal were used as precursors for synthesis of pyridines, pyranones and benzofurans.     

A Rhodium Nanoparticle–Lewis Acidic Ionic Liquid Catalyst for the Chemoselective Reduction of Heteroarenes

We describe a catalytic system composed of rhodium nanoparticles immobilized in a Lewis acidic ionic liquid. The combined system catalyzes the hydrogenation of quinolines, pyridines, benzofurans, and furan to access the corresponding heterocycles, important molecules present in fine chemicals, agrochemicals, and pharmaceuticals. The catalyst is highly selective, acting only on the heteroaromatic ring, and not interfering with other reducible functional groups.