Cobalt(III)- and Rhodium(III)-Catalyzed C–H Amidation and Synthesis of 4-Quinolones: C–H Activation Assisted by Weakly Coordinating and Functionalizable Enaminone

Silver(i)/base-promoted propargyl alcohol-controlled regio- or stereoselective synthesis of furan-3-carboxamides and (Z)-enaminones

A novel and facile regioselective synthesis of furan-3-carboxamides by a silver(i)/base-promoted reaction of propargyl alcohol with 3-oxo amides has been demonstrated. This one-pot protocol provides a rapid synthetic approach to diverse trisubstituted furan-3-carboxamides via cascade nucleophilic addition, intramolecular cyclization, elimination, and isomerization reactions. Employing a substituted propargyl alcohol, (Z)-enaminones have been obtained with high stereoselectivities by a Ag2CO3-promoted reaction starting from 3-oxo amides via C-N bond cleavage.

Cobalt(iii)-catalyzed C–H amidation of weakly coordinating sulfoxonium ylides and α-benzoylketene dithioacetals

Cobalt(iii)-catalyzed mild C–H amidation of weakly coordinating sulfoxonium ylides and α-benzoylketene dithioacetals has been realized.

Cp*CoIII-catalyzed formal [4+2] cycloaddition of benzamides to afford quinazolinone derivatives

A Cp*Co^III-catalyzed arene C–H bond amidation/annulation of benzamides was developed to afford quinazolinone derivatives in one-pot with high yields and broad substrate scope.

Rhodium(iii)-catalyzed cascade reactions of benzoic acids with dioxazolones: discovery of 2,5-substituted benzoxazinones as AIE molecules

Rhodium-catalyzed cascade reactions of benzoic acids with 1,4,2-dioxazol-5-ones afford 2,5-substituted benzoxazinones, which exhibited AIE properties with an ESIPT phenomenon.

Recent Progress on Cyclic Nitrenoid Precursors in Transition-Metal-Catalyzed Nitrene-Transfer Reactions

Nitrene-transfer reactions are powerful synthetic tools for the direct incorporation of nitrogen atoms into organic molecules. The discovery of novel nitrene-transfer reactions has been dominantly supported not only by improvements in transition-metal catalysts but also by the employment of novel precursors of nitrenoids. Since pioneering work involving the use of organic azides and iminoiodinanes as practical synthetic tools for nitrogen-containing compounds was reported, a new approach using various N-heterocycles containing strain energy or a weak bond has emerged. In this review, we briefly summarize the history of nitrene-transfer chemistry from the viewpoint of its precursors. In particular, the use of N-heterocycles such as 2H-azirines, 1,4,2-dioxazol-5-ones, 1,2,4-oxadiazol-5-ones, isoxazol-5(4H)-ones, and isoxazoles is comprehensively described, showing the recent remarkable progress in this chemistry.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Rh(III)-Catalyzed One-Pot Synthesis of Benzimidazoquinazolines via C-H Amidation-Cyclization of N-LG-2-phenylbenzoimidazoles

An efficient protocol to synthesize substituted benzo[4,5]imidazo[1,2- c]quinazolines starting from N-LG-2-phenylbenzoimidazole and dioxazolones catalyzed by Rh(III) or Ir(III) has been developed. Various substituted benzo[4,5]imidazo[1,2- c]quinazolines could be easily provided in up to 99% yield. A large range of substrates and functional groups are compatible for this transformation. This method features low catalyst loading, acid-free conditions, and low solvent consumption.

[Cp*RhIII ]/Ionic Liquid as a Highly Efficient and Recyclable Catalytic Medium for C-H Amidation

A [Cp*Rh^III ]-catalyzed direct C-H amidation is carried out in ionic liquid. Both C(sp² )-H bonds of (hetero)arenes and alkenes and unactivated C(sp³ )-H bonds can be easily amidated with high functional-group tolerance and excellent yields under these conditions. Notably, using [Cp*Rh^III ]/[BMIM]BF₄ (BMIM=1-butyl-3-methylimidazolium) as the green and recyclable medium is environmentally benign, in light of characteristics such as the reusability of the expensive rhodium catalyst, avoidance of highly toxic organic solvents, and mild reaction conditions, as well as a short reaction time.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.

Weinreb Amide Directed Versatile C-H Bond Functionalization under (η5 -Pentamethylcyclopentadienyl)cobalt(III) Catalysis

The (η⁵ -pentamethylcyclopentadienyl)cobalt(III) (Cp*Co^III )-catalyzed C-H bond functionalization of aromatic, heteroaromatic, and α,β-unsaturated Weinreb amides was explored. C-H allylation reactions with the use of allyl carbonate and a perfluoroalkene, oxidative alkenylation reactions with the use of ethyl acrylate, iodination reactions with the use of N-iodosuccinimide, and amidation reactions with the use of dioxazolones were catalyzed by Cp*Co(CO)I₂ in the presence of a cationic Ag salt and AgOAc to afford various synthetically useful building blocks. Mechanistic studies of the C-H allylation disclosed that the C-H activation step was rate determining and virtually irreversible.

Cp*Co(iii)-catalyzed amidation of olefinic and aryl C-H bonds: highly selective synthesis of enamides and pyrimidones

A highly efficient and selective synthesis of enamides via C-H amidation of N-methoxy acrylamides with dioxazolones is realized under [Cp*CoIII] catalysis. The resulting enamide can further selectively cyclize to form pyrimidones, which can also act as a directing group for a second C-H amidation. All these three classes of products were selectively delivered under controlled conditions.

Discovery of Benzimidazole-Quinolone Hybrids as New Cleaving Agents toward Drug-Resistant Pseudomonas aeruginosa DNA

A series of benzimidazole-quinolone hybrids as new potential antimicrobial agents were designed and synthesized. Bioactive assays indicated that some of the prepared compounds exhibited potent antibacterial and antifungal activities. Notably, 2-fluorobenzyl derivative 5 b (ethyl 7-chloro-6-fluoro-1-[[1-[(2-fluorophenyl)methyl]benzimidazol-2-yl]methyl]-4-oxo-quinoline-3-carboxylate) showed remarkable antimicrobial activity against resistant Pseudomonas aeruginosa and Candida tropicalis isolated from infected patients. Active molecule 5 b could not only rapidly kill the tested strains, but also exhibit low toxicity toward Hep-2 cells. It was more difficult to trigger the development of bacterial resistance of P. aeruginosa against 5 b than that against norfloxacin. Molecular docking demonstrated that 5 b could effectively bind with topoisomerase IV-DNA complexes, and quantum chemical studies theoretically elucidated the good antimicrobial activity of compound 5 b. Preliminary experimental reaction mechanism exploration suggested that derivative 5 b could not intercalate into DNA isolated from drug-resistant P. aeruginosa, but was able to cleave DNA effectively, which might further block DNA replication to exert powerful bioactivities. In addition, compound 5 b is a promising antibacterial agent with membrane disruption abilities.

Ru(ii)-Catalyzed C6-selective C–H amidation of 2-pyridones

An efficient Ru-catalyzed C6 site-selective amidation of 2-pyridones has been accomplished with dioxazolone under mild conditions.

Copper(ii)-mediated, carbon degradation-based amidation of phenylacetic acids toward N-substituted benzamides

The carbon degradation-based amidation of phenylacetic acids with aryl amides has been realized in the presence of Cu(OAc)₂, which provides a practical route in the synthesis of N-aryl secondary benzamides.

A copper-catalyzed three component reaction of aryl acetylene, sulfonyl azide and enaminone to form iminolactone via 6π electrocyclization

We developed a copper-catalyzed three component reaction of aryl acetylene, enaminone and sulfonyl azide to construct iminolactone via copper-catalyzed alkyne–azide cycloaddition (CuAAC), Michael addition of metalated ketenimine followed by elimination and 6π electrocyclization.

Cp*Rh(iii)-catalyzed annulation of N-methoxybenzamide with 1,4,2-bisoxazol-5-one toward 2-aryl quinazolin-4(3H)-one derivatives

A [Cp*Rh^III]-catalyzed annulation of N-methoxybenzamide with 1,4,2-bisoxazol-5-one was developed, affording a series of 2-aryl quinazolin-4(3H)-one derivatives.

Preparation and reactivity of a square-planar PNP cobalt(ii)–hydrido complex: isolation of the first {Co–NO}8–hydride

The synthesis of a square-planar cobalt(ii) hydrido complex supported by a pyrrole-based PNP ligand has been reinvestigated and its reactivity with various small molecules examined.

Synthesis of 2-aminobenzaldehydes by rhodium(iii)-catalyzed C–H amidation of aldehydes with dioxazolones

Various aldehydes were directly amidated with dioxazolones to afford 2-aminobenzaldehydes through rhodium(iii)-catalyzed CHO-directed C–H activation.

Cobalt(iii)-catalyzed site-selective C–H amidation of pyridones and isoquinolones

In this study, Cp*Co(iii)-catalyzed site-selective amidation of pyridones and isoquinolones using oxazolones as the amidation reagent is reported.

Co(III)-Catalyzed C-H Activation: A Site-Selective Conjugate Addition of Maleimide to Indole at the C-2 Position

The cobalt(III)-catalyzed site-selective C-2 functionalization of indole has been developed using the pyrimidinyl group as a directing group. This reaction furnishes 3-arylated succinimide derivatives in excellent yields in a shorter duration using an inexpensive Co catalyst. Highly selective C-2 functionalization of indoles was achieved in the presence of the highly reactive C-3 position. This protocol is compatible with a variety of N-pyrimidinyl indole and maleimide derivatives, and it can be easily scaled-up. This method is also applicable for maleic ester and heteroarenes.

Antimicrobial activity of thiophene derivatives derived from ethyl (E)-5-(3-(dimethylamino)acryloyl)-4-methyl-2-(phenylamino)thiophene-3-carboxylate

Background

The thiophene nucleus has been recognized as an important entity in the synthesis of heterocyclic compounds with promising pharmacological characteristics.

Results

A number of new heterocyclic compounds incorporating thiophene species have been prepared from the titled enaminone via the reaction with different nucleophiles and electrophiles. The structure elucidation of the designed compounds was derived from their spectral information. The results of antimicrobial activity of the prepared compounds revealed that derivatives 7b and 8 exhibited activity comparable to the standard drugs ampicillin and gentamicin for all tested bacteria species. Additionally, compound 3 displayed potent activity against Aspergillus fumigates, whereas compounds 5, 6, and 7a showed good activity against Syncephalastrum racemosum.

Conclusions

We have synthesized a number of new thiophene-containing compounds. The results of antimicrobial activity of the prepared compounds revealed that changing the substituents at position-2 of thiophene ring significantly affect their biological activity. The pyridine side chain derivatives in compounds 7a, 7b and 8 showed excellent antimicrobial activity.

RhIII-Catalyzed site-selective amidation with nitrone as a traceless directing group: an approach to functionalized arylaldehydes

A unique Rh^III-catalyzed C–H amidation of nitrones with 1,4,2-dioxazol-5-ones has been developed, providing a new approach to functionalized arylaldehydes.

Recent advances using [Cp*Co(CO)I2] catalysts as a powerful tool for C–H functionalisation

This perspective highlights recent applications of Cp*Co^III catalysts in C–H functionalisation protocols, exemplifying both terminal couplings and heterocycle formation.

Regioselective three-component synthesis of 2,3-disubstituted quinolines via the enaminone modified Povarov reaction

The enaminone modified three-component Povarov reactions enable the regioselective synthesis of 2,3-disubstituted quinolines.

The one-pot synthesis of quinolines via Co(iii)-catalyzed C–H activation/carbonylation/cyclization of anilines

A new and versatile Co(iii)-catalyzed C–H activation/carbonylation/cyclization cascade reaction has been disclosed.