A Domino Copper-Catalyzed CN and CO Cross-Coupling for the Conversion of Primary Amides into Benzoxazoles

Synthesis and characterisation of copper(I) complexes with relevance to intramolecular Ullmann O,S-arylation

Copper-catalysed intramolecular Ullman arylation has been frequently used to synthesise benzoxazoles and benzothiazoles. Despite widespread use, investigations into the mechanism and speciation of copper-containing complexes relevant to the catalytic pathway have remained relatively limited. Accordingly, this study aims to elucidate the structural details of potential copper(I) intermediates through the analysis of their solid-state structures using X-ray crystallography, while also investigating the reactivities of these complexes. Five novel copper complexes are reported which are formed prior to the aryl halide activation step and feature distinct aggregation modes based on either Cu4N4O4C4 or Cu4N4S4C4 clusters.

CuI-Amidobis(phosphine)-Catalyzed Direct Amidation of Unactivated Alkanes via C(sp3)-H Activation

Herein, we describe an acid-base-free, sustainable, and efficient method for direct amidation of unactivated alkanes and toluene derivatives, using the dimeric CuI complex [CuI{o-Ph2PC6H4CONC6H4PPh2-o}2] (here onward referred to as [PNP-Cu]2). Using this method, C(sp3)-N bond formation was achieved through the activation of very challenging C(sp3)-H bonds in cycloalkanes, alkenes, allyl groups, and benzyl groups, with tolerance toward ketonic groups, heterocycles, and halide functionalities. One of the precatalysts, (PNHP-Cu-Npht) was isolated and structurally characterized. Isomerization in allyl-functionalized alkanes and selective benzylic alkylation in ketones were observed. This is a novel method for C(sp3)-N bond formation via direct N-alkylation of phthalimide, sulfonamide, benzamide, and phosphamidate.

Design and Synthesis of Artificial Nucleobases for Sequence-Selective DNA Recognition within the Major Groove

We present the design and synthesis of artificial specific nucleobases, each one recognizing a single base pair within the major groove of duplex DNA. Computational calculations indicate that PNAs modified with these nucleobases enable the formation of highly stable triple helices with no sequence restrictions through multiple hydrogen bonding and π⋅⋅⋅π stacking interactions, without significantly widening the DNA double helix. New synthetic routes were developed to the structures of these fused heterocycles which have rarely been described in the literature. NMR titration experiments indicate specific hydrogen bonding at the Hoogsteen sites. The new building blocks allow the construction of four PNA monomers for each canonic base pair and their covalent connection to PNA oligomers. These can be designed complementary to any given DNA sequence. With high efficiency and relative simplicity of operation, the described methodologies and strategies hence form the basis for a new supramolecular ligand system targeting double-stranded DNA without strand invasion.

Metal-Free Oxidative Annulation of Phenols and Amines: A General Synthesis of Benzoxazoles

The ubiquity of benzoxazoles in natural products, drugs, and functional materials has stimulated numerous efforts toward their synthesis; however, the developed methods rely on prefunctionalized substrates and lack generality. Under metal-free conditions, a highly general synthesis of benzoxazoles direct from abundant and easily available phenols and amines is developed via a modular phenol functionalization controlled by TEMPO. In the reaction, various phenols and primary amines with a broad range of functional groups are compatible, producing structurally and functionally diverse benzoxazoles (64 examples) without or with trace observation of the byproducts of phenol transformation with amines. The practical synthesis, especially for drug tafamidis, demonstrates decisive advantages in generality, selectivity, efficiency, and atom- and step-economies over traditional methods, even in the cases of low yields. Mechanistically, the radical adducts of TEMPO with ortho-cyclohexa-2,4-dien-1-one radicals rather than the well-recognized cyclohexa-3,5-diene-1,2-diones may serve as intermediates.

DMF-Assisted Radical Cyclization of o-Isocyanodiaryl Ethers via 1,5-Aryl Migration: Construction of 2-Arylbenzoxazoles

A novel DMF-assisted radical cyclization of o-isocyanodiaryl ethers via 1,5-aryl migration has been developed for the synthesis of a series of 2-arylbenzoxazoles by the FeCl₃/TBHP/Et₃N catalytic system in DMF. However, N,N-dimethylbenzo[d]thiazole-2-carboxamide and N,N-dimethylbenzo[d]selenazole-2-carboxamide were obtained from the corresponding substrate 2-isocyanophenyl p-methoxyphenyl thioether and 2-isocyanodiphenyl selenoether under the same conditions. A possible mechanism may involve aryl 1,5-migration and DMF-assisted radical cyclization of o-isocyanodiaryl ethers.

Copper(i)-catalyzed regioselective Ullmann-type coupling of primary carbamates and 5-substituted-1,2,3-triiodobenzenes: facile synthesis of 2,3-diiodinated N-aryl carbamates

Mild, efficient, and unprecedented synthesis of 2,3-diiodinated N-aryl carbamates via highly regioselective Ullmann-type cross-coupling of 5-substituted-1,2,3-triiodobenzene and carbamate.

One-Pot Multicomponent Reaction of Catechols, Ammonium Acetate, and Aldehydes for the Synthesis of Benzoxazole Derivatives Using the Fe(III)-Salen Complex

The Fe(III)-salen complex has been applied successfully as a catalyst for the novel, simple, efficient, and one-pot multicomponent synthesis of benzoxazole derivatives from catechols, ammonium acetate as the nitrogen source, and aldehydes (nontoxic and cheap alternatives of amines) for the first time. Using this procedure, a wide range of benzoxazoles was successfully synthesized in the presence of a catalyst in EtOH under mild conditions, and all products were obtained in excellent yields. To the best of our knowledge, this method is the first example of the multicomponent synthesis of benzoxazole derivatives using these starting materials. The notable features such as the use of air that is considered as a benign oxidant and EtOH as a green solvent, ease of product separation, readily available and inexpensive aldehydes, and mild conditions make our procedure more efficient and practical for organic synthesis. Moreover, the current protocol is successfully applied to synthesize desirable products on a large scale.

Efficient Cu-catalyzed intramolecular O-arylation for synthesis of benzoxazoles in water

An efficient method was developed for synthesis of benzoxazoles by Cu-catalyzed intramolecular O-arylation of o-halobenzanilides in water. This strategy provides several advantages, such as high yields, water as a green solvent and functional groups tolerance.

An efficient method was developed for synthesis of benzoxazoles by Cu-catalyzed intramolecular O-arylation of o-halobenzanilides in water.

Access to C4-arylated benzoxazoles from 2-amidophenol through C-H activation

A Pd-catalyzed aerobic approach to access C4-aryl benzoxazoles by tandem C-H ortho-arylation and acid-mediated annulation of 2-amidophenol has been presented. The directing potential of the -NHCOR group over the -OH group was exploited for selective arylation adjacent to the amide group. Deuterium labeling experiments suggest that palladation predominantly occurs adjacent to the -NHCOR group and is the key step during benzoxazole formation. One-pot hydrolysis of the resulting C4-arylated benzoxazole was also accomplished to access structurally challenging 3-aryl aminophenols for further applications.

Synthesis of Benz-Fused Azoles via C-Heteroatom Coupling Reactions Catalyzed by Cu(I) in the Presence of Glycosyltriazole Ligands

Glycosyl triazoles are conveniently accessible and contain multiple metal-binding units that may assist in metal-mediated catalysis. Azide derivatives of d-glucose have been converted to their respective aryltriazoles and screened as ligands for the synthesis of 2-substituted benz-fused azoles and benzimidazoquinazolinones by Cu-catalyzed intramolecular Ullmann type C-heteroatom coupling. Good to excellent yields for a variety of benz-fused heterocyles were obtained for this readily accessible catalytic system.

Synthesis of benzoxazoles via the copper-catalyzed hydroamination of alkynones with 2-aminophenols

We describe herein the synthetic method to benzoxazole derivatives via the copper-catalyzed hydroamination of alkynones with 2-aminophenols.

A facile approach for the synthesis of nido-carborane fused oxazoles via one pot deboronation/cyclization of 9-amide-o-carboranes

One pot deboronation/cyclization of 9-amide-o-carboranes for construction of nido-7,8-carborane fused oxazoles.

Synthesis of benzoxazoles via an iron-catalyzed domino C-N/C-O cross-coupling reaction

An eco-friendly and efficient method has been developed for the synthesis of 2-arylbenzoxazoles via a domino iron-catalyzed C–N/C–O cross-coupling reaction. Some of the issues typically encountered during the synthesis of 2-arylbenzoxazoles in the presence of palladium and copper catalysts, including poor substrate scope and long reaction times have been addressed using this newly developed iron-catalyzed method.

The synthesis of benzoxazoles via an iron-catalyzed cascade C–N and C–O coupling is described.

Synthesis and characterization of a novel oxo-bridged binuclear iron(iii) complex: its catalytic application in the synthesis of benzoxazoles using benzyl alcohol in water

A novel oxo-bridged binuclear iron(iii) complex was found to be an efficient catalyst in the synthesis of benzoxazoles from benzyl alcohols.

Synthesis of 2-methylbenzoxazoles directly from N-phenylacetamides catalyzed by palladium acetate

A method to synthesize 2-methylbenzoxazoles directly from N-phenylacetamides catalyzed by Pd(OAc)₂ in moderate to excellent yields has been achieved.

Electrochemical synthesis of benzoxazoles from anilides – a new approach to employ amidyl radical intermediates

The electroorganic synthesis of a variety of benzoxazoles starting from easy accessible anilides is reported.

N-Heterocyclic carbene copper(i) complex-catalyzed synthesis of 2-aryl benzoxazoles and benzothiazoles

A new an efficient synthesis of 2-aryl benzoxazoles and benzothiazoles by intramolecular cyclization of 2-haloanilides/2-halothioanilides using a copper(i)-NHC complex is described.

A comparative study of the catalytic activity of Co- and CoFe2O4-NPs in C–N and C–O bond formation: synthesis of benzimidazoles and benzoxazoles from o-haloanilides

Herein, new methods and a comparison of the results for dehalogenative intramolecular C–X bond formation using two inexpensive and efficient catalysts are reported.

Diacetoxyiodobenzene assisted C–O bond formation via sequential acylation and deacylation process: synthesis of benzoxazole amides and their mechanistic study by DFT

An efficient method for the transformation of N-substituted-N′-benzoylthioureas to substituted N-benzoxazol-2-yl-amides due to oxidative dehydrogenation by diacetoxyiodobenzene.

Copper-catalyzed synthesis of benzoxazoles via tandem cyclization of 2-halophenols with amidines

This work reports a simple, efficient and alternative synthetic route for the preparation of benzoxazoles via tandem cyclization of 2-halophenols with amidines.

Intramolecular oxidative deselenization of acylselenoureas: a facile synthesis of benzoxazole amides and carbonic anhydrase inhibitors

A mild, efficient and one pot procedure to access benzoxazoles using easily accessible acylselenoureas as starting materials has been discovered.

Access to 2-(Het)aryl and 2-Styryl Benzoxazoles via Palladium-Catalyzed Aminocarbonylation of Aryl and Vinyl Bromides

A sequential one-pot procedure for the synthesis of either 2-(hetero)aryl or 2-styryl benzoxazoles is reported, starting from aryl and vinyl bromides, respectively, involving an initial aminocarbonylation with 2-aminophenols as nucleophiles followed by an acid mediated ring closure to generate the heterocycle. The methodology displays a broad substrate scope in moderate to excellent yields and can be exploited for (13)C-isotope labeling. Finally, this carbonylative protocol was applied to the synthesis of a potential Alzheimer's plaque binder and a selective PPAR antagonist including site-specific labeling with (13)C-carbon monoxide.