Nickel(II)-Catalyzed Site-Selective C-H Bond Trifluoromethylation of Arylamine in Water through a Coordinating Activation Strategy

Construction of Biaryl Sulfonamides via Pd(II)-Catalyzed Cross-Coupling of C(sp2)-H Bonds with Iodobenzenesulfonamides

This study describes the utility of Pd(II)-catalyzed C-H arylation of benzamides for constructing biaryl sulfonamides. Sulfonamides are known for their promising applications in pharmaceuticals and agrochemicals. A literature review revealed that biaryl sulfonamides were generally constructed via the traditional cross-coupling reactions. We report a progressive method for obtaining biaryl sulfonamides via the Pd(II)-catalyzed bidentate directing group (8-aminoquinoline or picolinamide)-assisted cross-coupling of sp2 C-H bonds of aromatic carboxamides with iodobenzenesulfonamides. After the C-H arylation reactions, we attempted the removal of the 8-aminoquinoline from the synthesized biaryl scaffolds possessing the carboxamide and sulfonamide moieties using triflic acid. In some cases, we observed the occurrence of decarboxylation and Friedel-Crafts acylation, affording interesting aromatic scaffolds possessing the sulfonamide moiety. The current work contributes toward developing alternative ways for assembling various biaryl sulfonamides.

Synthesis of biaryl-based carbazoles via C-H functionalization and exploration of their anticancer activities

The synthesis of a library of new biaryl-based carbazoles via bidentate directing group-assisted C-H functionalization and preliminary screening of the anticancer properties of biaryl-based carbazoles is reported. While various classes of modified carbazoles are known for their applications in materials and medicinal chemistry, to our knowledge, the biological activities of designed biaryl-based carbazoles have been rarely known. Given the prominence of carbazoles in research in medicinal chemistry, we envisioned the scope for new scaffolds of carbazole-based biaryl structures. We screened the synthesized biaryl-based carbazoles for their anticancer properties against various cancer cell lines such as HeLa (cervical cancer), HCT116 (colon cancer), MDA-MB-231 and MDA-MB-468 (breast cancer). In addition, the hits were also tested in the human embryonic kidney cell line HEK293T to assess their impact on the viability of normal human cells in the presence of these compounds. In this preliminary study, we identified some of the biaryl-based carbazoles as lead compounds with anticancer activities.

Polar-Effect-Directed Control in Site-Selectivity of Radical Substitution Enables C-H Perfluoroalkylation of Coumarins

A novel Ru-catalyzed protocol for C-7 selective C-H trifluoromethylation of coumarins in the presence of light is presented. This reaction undergoes a radical type nucleophilic substitution instead of a radical type electrophilic substitution owing to the benzocore activation as a result of lowering the lowest unoccupied molecular orbital (LUMO).

Photo-induced difluoroalkylation/cyclization of alkyne ketones: a novel strategy to access difluoroalkyl thiofavones

A photo-induced electron donor-acceptor (EDA) complex enabled tandem reaction of alkyne ketones via a radical difluoroalkylation/cyclization cascade sequence is reported. The EDA complex plays a key role, and the C-Br bond homolysis process may also be involved for this transformation. Varieties of difluoroalkyl-substituted thiofavones can be smoothly assembled in moderate to good yields under photocatalyst-, metal- and oxidant-free conditions, thus offering potential applications for pharmaceutical research.

Picolinamide-assisted ortho-C-H functionalization of pyrenylglycine derivatives using aryl iodides

Chemical transformations involving the pyrenylglycine motif (an unnatural amino acid) and practical methods toward it are seldom known. This work aimed at developing a method for synthesizing novel pyrenylglycine (pyrene-based glycine) unnatural amino acid derivatives. To realize this, initially, a new pyrenylglycine substrate possessing the picolinamide moiety was assembled via the Ugi multicomponent reaction. The picolinamide moiety linked to amine substrates is a well-known bidentate directing group for accomplishing the site-selective γ-C-H functionalization of amines. Subsequently, it was aimed at using a Pd(II)-catalyzed bidentate directing group-aided γ-C-H arylation strategy for generating a wide range of unprecedented examples of C(2)-H arylated pyrenylglycines. Accordingly, pyrenylglycine possessing the picolinamide moiety was subjected to Pd(II)-catalyzed C(2)-H arylation in the non-K-region to afford a library of C(2)-arylated pyrenylglycines (π-extended pyrenes). Additionally, pyrenylglycine-based small peptides were assembled using C(2)-arylated pyrenylglycines. The X-ray structure of a representative compound was obtained, which corroborated the structure of pyrenylglycine and the regioselectivity of C(2)-H arylation of the pyrene in the non-K-region.

Transition-Metal-Catalyzed Directed C-H Functionalization in/on Water

Directing group assisted C-H bond functionalization using transition-metal-catalysis has emerged as a reliable synthetic tool for the construction of regioselective carbon-carbon/heteroatom bonds. Off late, "in/on water directed transition-metal-catalysis", though still underdeveloped, has appeared as one of the prominent themes in sustainable organic chemistry. This article covers the advancements, mechanistic insights and application of the sustainable directed C-H bond functionalization of (hetero)arenes in/on water in the presence of transition-metal-catalysis.

Regioselective C-H Trifluoromethylation and Its Related Reactions of (Hetero)aromatic Compounds

Fluorinated functional groups, including trifluoromethyl group, play important roles in the development of drugs, agrochemicals, and organic functional materials. Therefore, the development of highly effective and practical reactions to introduce fluorinated functional groups into (hetero)aromatic compounds is highly desirable. We have achieved several regioselective C-H trifluoromethylation and related reactions by electrophilic and nucleophilic activation of six-membered heteroaromatic compounds and steric protection of aromatic compounds. These reactions proceed in good to excellent yields, even on a gram scale, with high functional group tolerance, and are applicable to the regioselective trifluoromethylation of drug molecules. In this personal account, the background of the introduction reactions of fluorinated functional groups, our reaction designs to achieve regioselective C-H trifluoromethylation and the related reactions of (hetero)aromatic compounds are explained.

A Redox Transmetalation Step in Nickel-Catalyzed C-C Coupling Reactions

Ni-catalyzed C-H functionalization reactions are becoming efficient routes to access a variety of functionalized arenes, yet the mechanisms of these catalytic C-C coupling reactions are not well understood. Here, we report the catalytic and stoichiometric arylation reactions of a nickel(II) metallacycle. Treatment of this species with silver(I)-aryl complexes results in facile arylation, consistent with a redox transmetalation step. Additionally, treatment with electrophilic coupling partners generates C-C and C-S bonds. We anticipate that this redox transmetalation step may be relevant to other coupling reactions that employ silver salts as additives.

Recent advances in the application of Langlois' reagent in olefin difunctionalization

In this review, we summarise the recent applications of Langlois' reagent in the radical-mediated difunctionalization of alkenes. Among the various trifluoromethylation reagents, Langlois' reagent is an exceptional compound, and many important organic transformations have been realized by employing such reagents. Various organic transformations of Langlois' reagent, especially in radical chemistry, have been developed in recent years. This review describes several key activation methods for Langlois' reagent in the difunctionalization of alkenes by showcasing selected cornerstone research areas and related mechanisms to stimulate the interest of readers in promoting the wider development and application of Langlois' reagent.

Recent Advances in Transition-Metal Mediated Trifluoromethylation Reactions

Fluorine compounds are known for their abundance in more than 20% of pharmaceutical and agrochemical products mainly due to the enhanced lipophilicity, metabolic stability and pharmacokinetic properties of organofluorides. Consequently,...

Oxidative C–C/C–X coupling in organometallic nickel complexes: insights from DFT

NiIII and NiIV-center complexes prefer direct reductive elimination than reacting through five-coordinate intermediates. 32+ complex in the presence of Cl− undergoes Cl–Csp2 elimination preferably over Cl–Csp3 and Csp3–Csp2 elimination.

Photoinduced Trifluoromethylation of Arenes and Heteroarenes Catalyzed by High-Valent Nickel Complexes

We describe a series of air-stable Ni^III complexes supported by a simple, robust naphthyridine-based ligand. Access to the high-valent oxidation state is enabled by the CF₃ ligands on the nickel, while the naphthyridine exhibits either a monodentate or bidentate coordination mode that depends on the oxidation state and sterics, and enables facile aerobic oxidation of Ni^II to Ni^III . These Ni^III complexes act as efficient catalysts for photoinduced C(sp² )-H bond trifluoromethylation reactions of (hetero)arenes using versatile synthetic protocols. This blue LED light-mediated catalytic protocol proceeds via a radical pathway and demonstrates potential in the late-stage functionalization of drug analogs.

Applications of Nickel(II) Compounds in Organic Synthesis

This review article summarizes the applications of nickel(II) compounds in organic synthesis since 2016. In recent years, the field of nickel(II) catalysis is gaining considerable interest due to readily available, low-cost nickel(II)-compounds and several key properties of nickel. This review article is organized by the reaction type, although some reactions can be placed in multiple sections.

Photoredox-Catalyst-Enabled para-Selective Trifluoromethylation of tert-Butyl Arylcarbamates

The direct incorporation of a trifluoromethyl group on an aromatic ring using a radical pathway has been extensively investigated. However, the direct highly para-selective C-H trifluoromethylation of a class of arenes has not been achieved. In this study, we report a light-promoted 4,5-dichlorofluorescein (DCFS)-enabled para-selective C-H trifluoromethylation of arylcarbamates using Langlois reagent. The preliminary mechanistic study revealed that the activated organic photocatalyst coordinated with the arylcarbamate led to para-selective C-H trifluoromethylation. Ten-gram scale reaction performs well highlighting the synthetic importance of this new protocol.

Regio- and Stereoselective Functionalization Enabled by Bidentate Directing Groups

Chelation-assisted C-H bond and alkene functionalization using bidentate directing groups offers an elegant and versatile approach to overcome regiocontrol issues by allowing the catalyst to come into close proximity with the targeted sites. In this personal account, we highlight our recent works in developing regio- and stereocontrolled functionalizations through transition-metal catalysis enabled by bidentate directing groups. We classify our results into two categories: (1) regioselective alkene functionalization using bidentate directing groups, and (2) asymmetric C-H functionalization using chiral bidentate directing groups. Furthermore, density functional theory studies to elucidate the origin of the regio- and stereoselectivity exerted by bidentate directing groups are discussed.

Copper(II)-catalysed direct C3-H esterification of indoles assisted by an N,N-bidentate auxiliary moiety

The regioselective direct C3-esterification of indoles with OXA is developed in an efficient reaction with carboxylic acids using the catalyst CuBr2 and oxidants Ag2CO3 and K2S2O8. The simple experimental procedure is proved to be broadly applicable to a range of substrates, including aromatic and aliphatic acids, and the corresponding products were obtained in good yields up to 87%. At the same time, it provides a valuable approach to produce C3-benzyl derivatives of indoles through reaction with benzyl carboxylic acid under the same reaction conditions.

Self-Catalyzed Phototandem Perfluoroalkylation/Cyclization of Unactivated Alkenes: Synthesis of Perfluoroalkyl-Substituted Quinazolinones

A novel visible-light-induced radical tandem trifluoromethylation/cyclization of unactivated alkenes with sodium perfluoroalkanesulfinates (R_f = CF₃, C₃F₇, C₄F₉, C₆F₁₃, C₈F₁₇) under air atmosphere has been developed. A range of quinazolinones containing unactivated alkene moiety and sodium perfluoroalkanesulfinates were compatible with this transformation, leading to a variety of perfluoroalkyl-substituted quinazoline alkaloids. Remarkably, the experiment can be carried out without any metal catalyst, strong oxidant, or external photosensitizer.

Palladium-Catalyzed C2-Regioselective Perfluoroalkylation of the Free (NH)-Heteroarenes

A highly regioselective and atom-efficient strategy for the construction of fused free (NH) heteroarenes through a palladium-catalyzed perfluoroalkyl insertion reaction has been accomplished. This protocol employed multiple iodofluoroalkanes as practical and available perfluoroalkyl sources to provide an operationally simple and versatile route for the synthesis of perfluoroalkylated indoles. Moreover, indoles without the assistance of guide groups were utilized as substrates, achieving C(sp²)-H site-selective functionalization of indoles in yields up to 95%. Furthermore, this protocol was also used for late-stage C2 perfluoroalkylation of bioactive compounds such as auxin, tryptophan, and melatonin analogues.

Green strategies for transition metal-catalyzed C–H activation in molecular syntheses

Sustainable strategies for the activation of inert C–H bonds towards improved resource-economy.

Nickel-catalysed fluoromethylation reactions

This review highlights important developments in nickel-catalysed mono-, di- and tri-fluoromethylation, trifluoromethylthiolation and trifluoromethylselenolation.

Directing Group-Promoted Inert C-O Bond Activation Using Versatile Boronic Acid as a Coupling Agent

A simple Ni(cod)₂ and carbene mediated strategy facilitates the efficient catalytic cross-coupling of methoxyarenes with a variety of organoboron reagents. Directing groups facilitate the activation of inert C-O bonds in under-utilized aryl methyl ethers enabling their adaptation for C-C cross-coupling reactions as less toxic surrogates to the ubiquitous haloarenes. The method reported enables C-C cross-coupling with readily available and economical arylboronic acid reagents, which is unprecedented, and compares well with other organoboron reagents with similarly high reactivity. Extension to directing group assisted chemo-selective C-O bond cleavage, and further application towards the synthesis of novel bifunctionalized biaryls is reported. Key to the success of this protocol is the use of directing groups proximal to the reaction center to facilitate the activation of the inert C-OMe bond.

Copper(II)-Catalyzed Direct Amination of 1-Naphthylamines at the C8 Site

A new and simple protocol for C8-H amination of 1-naphthylamine derivatives was developed using copper salt and di-tert-butyl peroxide (DTBP) as the catalyst and oxidant, respectively. This reaction proceeded smoothly under the additive and solvent-free conditions. In addition, this amination showed excellent regioselectivity and could tolerate various functional groups.

Synthesis of quinazoin-4-ones through an acid ion exchange resin mediated cascade reaction

An interesting cascade reaction of N-(2-(4,5-dihydrooxazol-2-yl)phenyl)benzamide in the presence of an acid ion exchange resin is described. In this reaction, a range of substrates bearing various substituent groups are well compatible. This work provides a green and atom-economical alternative approach for the synthesis of quinazolin-4-ones in good yields.

High-Valent NiIII and NiIV Species Relevant to C-C and C-Heteroatom Cross-Coupling Reactions: State of the Art

Ni catalysis constitutes an active research arena with notable applications in diverse fields. By analogy with its parent element palladium, Ni catalysts provide an appealing entry to build molecular complexity via cross-coupling reactions. While Pd catalysts typically involve a M⁰/M^II redox scenario, in the case of Ni congeners the mechanistic elucidation becomes more challenging due to their innate properties (like enhanced reactivity, propensity to undergo single electron transformations vs. 2e⁻ redox sequences or weaker M–Ligand interaction). In recent years, mechanistic studies have demonstrated the participation of high-valent Ni^III and Ni^IV species in a plethora of cross-coupling events, thus accessing novel synthetic schemes and unprecedented transformations. This comprehensive review collects the main contributions effected within this topic, and focuses on the key role of isolated and/or spectroscopically identified Ni^III and Ni^IV complexes. Amongst other transformations, the resulting Ni^III and Ni^IV compounds have efficiently accomplished: i) C–C and C–heteroatom bond formation; ii) C–H bond functionalization; and iii) N–N and C–N cyclizative couplings to forge heterocycles.

Facile Fabrication of Glycosylpyridyl-Triazole@Nickel Nanoparticles as Recyclable Nanocatalyst for Acylation of Amines in Water

In this report, novel glycosylpyridyl-triazole@nickel nanoparticles (GPT-Ni) were successfully prepared via click chemistry and were fully characterized by various spectroscopy measurements. The as-prepared catalysts could be used as a recyclable catalyst for the catalytic acylation of amines by employing N,N-dimethylacetamide (DMA), N,N-dimethylpropionamide (DMP), and N,N-dimethylformamide (DMF) as acylation reagents in water, providing the corresponding amides in good yields. The practicability of this methodology is highlighted by the good recyclability of the catalyst. A unique mechanism was proposed for the catalytic process.

Bidentate Directing Groups: An Efficient Tool in C-H Bond Functionalization Chemistry for the Expedient Construction of C-C Bonds

During the past decades, synthetic organic chemistry discovered that directing group assisted C-H activation is a key tool for the expedient and siteselective construction of C-C bonds. Among the various directing group strategies, bidentate directing groups are now recognized as one of the most efficient devices for the selective functionalization of certain positions due to fact that its metal center permits fine, tunable, and reversible coordination. The family of bidentate directing groups permit various types of assistance to be achieved, such as N,N-dentate, N,O-dentate, and N,S-dentate auxiliaries, which are categorized based on the coordination site. In this review, we broadly discuss various C-H bond functionalization reactions for the formation of C-C bonds with the aid of bidentate directing groups.

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

Fluorine chemistry plays an increasingly important role in pharmaceutical, agricultural, and materials industries. The incorporation of fluorine-containing groups into organic molecules can improve their chemical and physical properties, which attracts continuous interest in organic synthesis. Among various reported methods, transition-metal-catalyzed fluorination/fluoroalkylation has emerged as a powerful method for the construction of these compounds. This review attempts to describe the major advances in the transition-metal-catalyzed incorporation of fluorine, trifluoromethyl, difluoromethyl, trifluoromethylthio, and trifluoromethoxy groups reported between 2011 and 2019.