Copper-Catalyzed Annulative Amination of ortho-Alkynylphenols with Hydroxylamines: Synthesis of 3-Aminobenzofurans by Umpolung Amination Strategy

Copper-Catalyzed Tandem Cyclization/Chalcogenation with Elemental S8/Se: Concise Synthesis of 3-(β-Hydroxychalcogen)benzofurans

A novel copper-catalyzed cyclization/chalcogenation of o-alkynylphenols with epoxides and elemental S8/Se was developed for the synthesis of a 3-chalcogen-benzofuran architecture in a domino process with no intermediate isolation or purification. Various sensitive functional groups were compatible at room temperature and furnished chalcogenation derivatives in moderate to good yields.

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.

Chemo- and regio-selective amidation of indoles with isocyanates using borane Lewis acids

A metal-free synthetic route using boranes has been developed for the amidation of indoles. A detailed mechanistic study was carried out to understand the reaction mechanism.

Benzofuran: A Key Heterocycle - Ring Closure And Beyond

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The benzofuranyl motif present in compounds exhibits various medicinal properties and non-drug applications. These derivatives are naturally occurring compounds or synthetic materials, which cover a broad spectrum of pharmacological activities like anti-inflammatory, anti-diabetic, anti- depressant, anti-HIV, anti-microbial, anti-proliferative, anti-convulsant, cytotoxic, analgesic, etc. Few of the commercially interesting compounds from this class are, ailanthoidol (anti-inflammatory), amiodarone, dronedarone, celivarone (anti-arrhythmic), bufuralol (muscular airways relaxant), morphine, 5-(2-aminopropyl)benzofuran; 5-APB, 6-(2-aminopropyl)benzofuran; 6-APB (CNS), rifampicin (antibiotic), etc., whereas, some of the non-drug applications are in perfumery industry (bergapten) and as tannin activators in sunscreen preparations (psoralen, 8-methoxypsoralen, and angelicin). Considering these interesting biological activities and commercial utilities, a review on the synthetic aspects of this privileged scaffold was attempted. For the benefit of natural product-based drug discovery, available sources of these derivatives, extraction process and reported biological activities have also been outlined in this review.

Metal and Oxidant-Free Brønsted Acid-Mediated Cascade Reaction to Substituted Benzofurans

Substituted hydroxy-benzofurans are easily accessible by treatment of resorcinols and 1,2-diaza-1,3-dienes (DDs) under acidic conditions. The reaction happens through an uncommon Michael reaction between aromatic derivatives as aromatic C(sp²)-H nucleophiles and DDs as acceptors. Also, the behavior of different phenols and 2-naphthol was investigated.

Electrochemical synthesis of some 2-aminobenzofuran-3-carbonitrile and 2-aminobenzofuran-3-carboxylate derivatives: product diversity by changing the applied current density

Green syntheses of two different series of new benzofuran derivatives were carried out by anodic oxidation of 4,4′-biphenol (4BP) in the presence of some CH-acid compounds (malononitrile, methyl cyanoacetate and ethyl cyanoacetate) as nucleophiles by controlling the potential during electrolysis.

Transition-Metal-Catalyzed Electrophilic Amination: Application of O-Benzoylhydroxylamines in the Construction of the C-N Bond

Transition-metal-catalyzed electrophilic amination has been developed into a powerful tool for C-N bond construction. So far, O-benzoylhydroxylamines are the most widely used electrophilic aminating reagents. Herein, we summarize the recent advances of O-benzoylhydroxylamines involved in electrophilic amination catalyzed by transition metals. Several pioneering studies and some of the relevant mechanisms are discussed in this review.

Chasing the Elusive Benzofuran Impurity of the THR Antagonist NH-3: Synthesis, Isotope Labeling, and Biological Activity

We have synthesized and established the structure of a long-suspected, but hitherto unknown, benzofuran side product (EBI) formed during the synthesis of NH-3. Understanding the mechanism of its formation has enabled isotope (D) labeling. We further developed a highly efficient method for separating EBI from NH-3. Interestingly, EBI was found to be a very potent thyroid hormone receptor (THR) agonist, while NH-3 is an antagonist. In this process, we have also achieved a significantly improved synthesis of NH-3.

Copper-catalyzed oxyamination of electron-deficient alkenes with N-acyloxyamines

An intermolecular version of copper-catalyzed oxyamination of electron-deficient alkenes by making use of N-acyloxyamines as both amino and oxygen donors was developed.

Copper-catalyzed diamination of unactivated alkenes with hydroxylamines

A copper-catalyzed regio- and stereoselective diamination of unactivated alkenes has been developed with O-acylhydroxylamines as electrophilic nitrogen sources and oxidants. This method provides the first example of metal-catalyzed alkene diamination for directly installing an electron-rich amino group and extends the diamination scope for the synthesis of diverse 1,2-diamines. It offers a rapid and efficient approach to construct a wide range of 1,2-diamines that are an important structural motif in organic synthesis, medicines, catalysts and ligands.

Radical cascade reaction of alkynes with N-fluoroarylsulfonimides and alcohols

Cascade reactions initiated by radical addition to alkynes are synthetically very attractive because they enable access to highly complex molecular skeletons in only few synthetic steps under usually mild conditions. Here we report a general radical cascade reaction of alkynes, N-fluoroarylsulfonimides and alcohols, enabling the efficient synthesis of important α-amino-α-aryl ketones from readily available starting materials via a single operation. During this process, the highly regioselective nitrogen-centred radical addition to internal and terminal alkynes generating vinyl radicals and the next explicit migration of aryl group from the nitrogen source lead the following efficient desulfonylation, oxygenation, and semi-pinacol rearrangement. In addition, the semi-pinacol rearrangement precursors, α-alkyloxyl-α,α-diaryl imines, could also be efficiently obtained under milder conditions. This methodology might open a new entry for designing intermolecular radical cascade reaction of alkynes.

Rhodium(iii)-catalyzed oxidative bicyclization of 4-arylbut-3-yn-1-amines with internal alkynes through C–H functionalization

A new Rh(iii)-catalyzed oxidative bicyclization through C–H functionalization is presented for the synthesis of benzo[g]indoles.

Direct Arylation of Benzo[b]furan and Other Benzo-Fused Heterocycles

The direct arylation of benzo[b]furan, benzo[b]thiophene, and indole has been studied by using aromatic bromides as the aryl source. The protocol employing common reagents and a Pd catalyst has led to the regioselective arylation of these heterocycles at the 2-position. A range of functional groups were tolerated, providing quick access to a variety of arylated benzo-fused heterocycles that would be accessible more elaborately using classical synthetic strategies. This is the first systematic study of the direct arylation of benzo[b]furan.

Iron-catalyzed intermolecular hydroamination of styrenes

An iron-catalyzed formal hydroamination of alkenes has been developed. It features O-benzoyl-N,N-dialkylhydroxylamines as the electrophilic nitrogen source and cyclopentylmagnesium bromide as the reducing agent for intermolecular hydroamination of styrene and derivatives with good yield and excellent Markovnikov regioselectivity. The reaction presumably proceeds through the iron-catalyzed hydrometalation of styrene followed by electrophilic amination with the electrophilic O-benzoylhydroxylamine.

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.

Copper-catalyzed enantioselective formal hydroamination of oxa- and azabicyclic alkenes with hydrosilanes and hydroxylamines

A CuCl/(R,R)-Ph-BPE-catalyzed enantioselective formal hydroamination of oxa- and azabicyclic alkenes with polymethylhydrosiloxane (PMHS) and O-benzoylhydroxylamines has been developed. The efficient and stereoselective net addition of hydrogen and nitrogen atoms provides the corresponding optically active oxa- and azanorbornenyl- and -norbornanylamines in good yields and good enantiomeric ratios.

Recent progress in copper-catalyzed electrophilic amination

This perspective encompasses the recent trends and developments in copper-catalyzed electrophilic amination for the construction of various amines and their derivatives.