Transition-metal-free base catalyzed intramolecular cyclization of 2-ynylphenols for efficient and facile synthesis of 2-substituted benzo[b]furans

Fused diethynylbenzenes and phenanthrenes via arynes with alkynylsilanes

A method for the hydroalkynylation and catalytic cyclization reactions of hexadehydro-Diels-Alder-derived benzynes is described. Diethynylbenzene derivatives are generated in a one-step reaction via trimethylsilyl-alkyne groups with benzyne formed by heating the appropriate tetrayne substrate. Trimethyl(phenylethynyl)silane loses TMS and binds to the electron-deficient site on HDDA-derived benzynes, and then phenanthrene was synthesized under mild reaction conditions by transition-metal-free, base promoted intramolecular cyclization.

Organic redox cascade cyclization of 2-alkynylquinones by ascorbic acid in combination with a copper catalyst and its application to formal synthesis of liphagal

The combination of a quinone-ascorbic acid organic redox reaction and a concomitant copper catalysis in situ enables new approach to hydroxybenzofurans with structural variations.

Gold(I)-Catalyzed Tandem Cyclization/Hydroarylation of o-Alkynylphenols with Haloalkynes

A convenient and mild protocol for the gold-catalyzed intermolecular coupling of o-alkynylphenols with haloalkynes to give vinyl benzofurans is reported. In this work, the gold catalyst SIPrAuCl and the co-catalyst NaBARF would corporately promote the intramolecular cyclization of the o-alkynylphenol to benzofuran, and then a selective hydroarylation of benzofuran to haloalkyne was catalyzed by the same catalysts. Computational studies suggest that the hydroarylation process takes place via a concerted nucleophilic attack pathway of the benzofuran to the C2 carbon of the activated haloalkyne, and reveal the original driving force of this hydroarylation process.

Palladium-Catalyzed Stagewise Strain-Release-Driven C-C Activation of Bicyclo[1.1.1]pentanyl Alcohols

A palladium-catalyzed chemoselective coupling of readily available bicyclo[1.1.1]pentanyl alcohols (BCP-OH) with various halides is reported, which offers expedient approaches to a wide range of cyclobutanone and β,γ-enone skeletons via single or double C-C activation. The chemistry shows a broad substrate scope in terms of both the range of BCP-OH and halides including a series of natural product derivatives. Moreover, dependency of reaction chemodivergence on base additive has been investigated through experimental and density functional theory (DFT) studies, which is expected to significantly enrich the reaction modes and increase the synthetic potential of BCP-OH in preparing more complex molecules.

Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates and vinylidene ortho-quinone methides

Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates with vinylidene ortho-quinone methides generated in situ via a formal (3 + 4) pathway.

A Pyridine-Acetylene-Aniline Oligomer: Saccharide Recognition and Influence of this Recognition Array on the Activity as Acylation Catalyst

In order to create new functions of foldamer-type hosts, various kinds of recognition arrays are expected to be developed. Here, a pyridine-acetylene-aniline unit is presented as a new class of a saccharide recognition array. The conformational stabilities of this array were analyzed by DFT calculation, and suggested that a pyridine-acetylene-aniline oligomer tends to form a helical structure. An oligomer of this array was synthesized, and its association for octyl β-D-glucopyranoside was confirmed by ¹ H NMR measurements. UV/Vis, circular dichroism, and fluorescence titration experiments revealed its high affinity for octyl glycosides in apolar solvents (K_a =10⁴ to 10⁵  M^-1 ). This oligomer was relatively stable under basic conditions, and therefore this array was expected to be applied to the derivatization of saccharides. A 4-(dialkylamino)pyridine attached pyridine-acetylene-aniline oligomer proved to catalyze the acylation of the octyl glucoside.

Synthesis of cyclopentaquinolinone and cyclopentapyridinone from ortho-alkynyl-N-arylaldehyde via superbase-promoted C-N, C-O and C-C bond formation

An environmentally benign, transition metal-free, superbase-mediated intramolecular annulation of o-alkynylaldehydes with primary amines forms highly functionalized amino-substituted cyclopentaquinolinones and cyclopentapyridinones via C-N, C-C, and C[double bond, length as m-dash]O bond formation. Contrary to the traditional approaches of ring closures, a different mode of annulation is disclosed. The protocol involves the in situ generations of imine intermediate followed by potassium hydroxide-promoted intramolecular cyclization and subsequent dimethyl sulfoxide induced dehydrogenation leads to the formation of N-heterocycles. X-ray crystallographic studies support the assigned structures of the amino-fused N-heterocycles.

Recent Achievement in the Synthesis of Benzo[b]furans

BACKGROUND

Benzo[b]furan derivatives are oxygen-containing heterocyclic compounds consisting of fused benzene and furan rings and are present in a large number of natural and non-natural compounds. This class of compounds has a wide spectrum of biological activities, such as antiarrhythmic, anticancer, inflammatory, antioxidant, antimicrobial, and antiviral. Furthermore, benzo[b]furan derivatives have also been applied in various areas, such as organic electroluminescence device materials and organic dyes, photosensitizing material, organic synthesis as building blocks or intermediates. Because of a broad range of applicability, the synthesis of benzo[b]furan derivative has drawn great attention of chemists and many studies on the synthesis of this class of compounds have been reported recently. This review will give an overview of benzo[b]furan preparation based on studies dating back to the year 2012.

OBJECTIVE

In this review, recent development in the synthesis of benzo[b]furans are discussed. There has been increasingly new methodologies for the construction of benzo[b]furans skeleton to improve efficiency or develop environmentally friendly procedures. In some studies, reaction mechanisms were also outlined.

CONCLUSION

Many methods for the synthesis of benzo[b]furans have been reported recently. Most of them involve cyclization or cycloisomerization processes. Unquestionably, more imaginative strategies for the construction of benzo[b]furan skeleton will be established in the near future. Application of known methods to natural products or drug synthesis, on industrial scale for the synthesis of economically or medicinally important benzo[ b]furans will probably be paid attention to.

Metal-free annulative hydrosulfonation of propiolate esters: synthesis of 4-sulfonates of coumarins and butenolides

An efficient metal-free and cost-effective method for the synthesis of coumarin and butenolide 4-sulfonates has been developed involving addition of sulfonic acids to ethyl propiolates followed by lactonization.

Palladium complexes with an annellated mesoionic carbene (MIC) ligand: catalytic sequential Sonogashira coupling/cyclization reaction for one-pot synthesis of benzofuran, indole, isocoumarin and isoquinolone derivatives

A Pd(ii) complex containing a mesoionic carbene and phosphine ligands is an efficient catalyst for tandem coupling/cyclization reaction.

Facile synthesis of 2-substituted benzo[b]furans and indoles by copper-catalyzed intramolecular cyclization of 2-alkynyl phenols and tosylanilines

A catalytic amount of CuCl and Cs₂CO₃ was employed to synthesize a variety of 2-substituted benzo[b]furans and indoles by an intramolecular cyclization of 2-alkynyl phenols and tosylanilines. This protocol features mild conditions, high yields and broad substrate scope, which makes it a practical method for the synthesis of 2-substituted benzo[b]furans and indoles.

A facile and inexpensive copper-catalyzed method was developed for the synthesis of 2-substituted benzo[b]furans and indoles.