Ruthenium-catalysed cross-coupling reaction of ketones with transformable directing groups as alkenyl electrophiles

Herein, we report the development of ruthenium-catalysed cross-coupling reaction of β-ketoamides as alkenyl electrophiles with organoboronates. This reaction presumably proceeds via the cleavage of the alkenyl C-N bond of the β-enaminoamide, which is generated in situ from the β-ketoamide and pyrrolidine, and is promoted by a nearby amide directing group and a ruthenium catalyst.

Synthesis of Axially Chiral Biaryls through Cobalt(II)-Catalyzed Atroposelective C-H Arylation

Highly efficient synthesis of axially chiral biaryl amines through cobalt-catalyzed atroposelective C-H arylation using easily accessible cobalt(II) salt and salicyloxazoline ligand has been reported. This methodology provides a straightforward and sustainable access to a broad range of enantioenriched biaryl-2-amines in good yields (up to 99 %) with excellent enantioselectivities (up to 99 % ee). The synthetic utility of the unprecedented method is highlighted by its scalability and diverse transformations.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Ru-Catalyzed C-H Arylation of Acrylic Acids with Aryl Bromides

In the presence of a [Ru(p-cymene)Cl₂]₂/triethylphosphine/lithium carbonate catalyst system, aryl bromides undergo (Z)-selective couplings with unprotected 2-arylacrylic acids to form (Z)-diarylacrylic acids. This vinylic C-H functionalization proceeds in high yields of up to 94% and (Z/E)-ratios of up to 99:1, tolerating a wide range of functional groups. Mechanistic studies indicate that the vinylic C-H activation proceeds via base-assisted cyclometalation rather than via a Heck-type mechanism, which explains its orthogonal stereoselectivity.

RhIII-Catalyzed heteroarylation of N-2,6-difluorophenyl arylamides with heteroaryl boronate esters

An efficient strategy to aryl-heteroaryl formation via RhIII-catalyzed C–H heteroarylation of arenes with N-heterocyclic boronates has been disclosed.

C-H bond functionalization by high-valent cobalt catalysis: current progress, challenges and future perspectives

Over the last decade, high-valent cobalt catalysis has earned a place in the spotlight as a valuable tool for C-H activation and functionalization. Since the discovery of its unique reactivity, more and more attention has been directed towards the utilization of cobalt as an alternative to noble metal catalysts. In particular, Cp*Co(III) complexes, as well as simple Co(II) and Co(III) salts in combination with bidentate chelation assistance, have been extensively used for the development of novel transformations. In this review, we have demonstrated the existing trends in the C-H functionalization methodology using high-valent cobalt catalysis and highlighted the main challenges to overcome, as well as perspective directions, which need to be further developed in the future.

Palladium-Catalyzed Arylation of C(sp2)-H Bonds with 2-(1-Methylhydrazinyl)pyridine as the Bidentate Directing Group

Palladium-catalyzed C(sp²)-H arylation of ortho C-H bonds involving 2-(1-methylhydrazinyl)pyridine (MHP) as the directing group has been investigated. The reaction proceeds smoothly under an air atmosphere to generate biaryl derivatives in an environmentally friendly manner while tolerating a wide range of functional groups. Notably, the directing group present in the product could be easily removed under mild reductive conditions.

A Study of an 8-Aminoquinoline-Directed C(sp2)-H Arylation Reaction on the Route to Chiral Cyclobutane Keto Acids from Myrtenal

This work outlines a synthetic route that can be used to access chiral cyclobutane keto acids with two stereocenters in five steps from the inexpensive terpene myrtenal. Furthermore, the developed route includes an 8-aminoquinoline-directed C(sp2)-H arylation as one of its key steps, which allows a wide range of aryl and heteroaryl groups to be incorporated into the bicyclic myrtenal scaffold prior to the ozonolysis-based ring-opening step that furnishes the target cyclobutane keto acids. This synthetic route is expected to find many applications connected to the synthesis of natural product-like compounds and small molecule libraries.

RhIII-Catalyzed C-H (Het)arylation/Vinylation of N-2,6-Difluoroaryl Acrylamides

Rh^III-catalyzed sp² C-H cross-coupling of acrylamides with organoboron reactants has been accomplished using a commercially available N-2,6-difluoroaryl acrylamide auxiliary. A broad range of aryl and vinyl boronates as well as a variety of heterocyclic boronates with strong coordinating ability can serve as the coupling partners. This transformation proceeds under moderate reaction conditions with excellent functional group tolerance and high regioselectivity.

Recent advances in chelation-assisted site- and stereoselective alkenyl C–H functionalization

This review highlights recent advances in vicinal- and geminal-group-directed alkenyl C–H functionalizations which proceeded by endo- and exo-cyclometallation.

Cobalt-Catalyzed Oxidative C-H Activation: Strategies and Concepts

Inexpensive cobalt-catalyzed oxidative C-H functionalization has emerged as a powerful tool for the construction of C-C and C-Het bonds, which offers unique potential for transformative applications to modern organic synthesis. In the early stage, these transformations typically required stoichiometric and toxic transition metals as sacrificial oxidants; thus, the formation of metal-containing waste was inevitable. In contrast, naturally abundant molecular O₂ has more recently been successfully employed as a green oxidant in cobalt catalysis, thus considerably improving the sustainability of such transformations. Recently, a significant momentum was gained by the use of electricity as a sustainable and environmentally benign redox reagent in cobalt-catalyzed C-H functionalization, thereby preventing the consumption of cost-intensive chemicals while at the same time addressing the considerable safety hazards related to the use of molecular oxygen in combination with flammable organic solvents. Considering the unparalleled potential of the aforementioned approaches for sustainable green synthesis, this Review summarizes the recent progress in cobalt-catalyzed oxidative C-H activation until early 2020.

Direct Hiyama Cross-Coupling of (Hetero)arylsilanes with C(sp2)-H Bonds Enabled by Cobalt Catalysis

We report a chelation-assisted C-H arylation of various indoles with sterically and electronically diverse (hetero)arylsilanes enabled by cost-effective Cp*-free cobalt catalysis. Key to the success of this strategy is the judicious choice of copper(II) fluoride as a bifunctional sliane activator and catalyst reoxidant. This methodology features a broad substrate scope and good functional group compatibility. The synthetic versatility of this protocol has been highlighted by the gram-scale synthesis and late-stage diversification of biologically active molecules.

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.

Synthesis of Benzofulvenes via Cp*Co(III)-Catalyzed C-H Activation and Carbocyclization of Aromatic Ketones with Internal Alkynes

A highly efficient and practical synthesis of benzofulvenes was developed via ketone-directed Cp*Co(III)-catalyzed sequential C-H activation, addition, cyclization, and dehydration cascade processes between simple aromatic ketones and alkynes. The reaction tolerates a variety of functional groups, and various benzofulvenes were efficiently synthesized in 42-92% yields.

Synthesis of 1-naphthols via Cp*Co(iii)-catalyzed C–H activation and cyclization of sulfoxonium ylides with alkynes

A highly practical synthesis of 1-naphthols was developed via Cp*Co(iii)-catalyzed C–H activation and cyclization between sulfoxonium ylides and alkynes.

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.

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.

Selective Synthesis of Aryl Nitriles and 3-Imino-1-oxoisoindolines via Nickel-Promoted C(sp2)-H Cyanations

An efficient nickel-promoted selective monocyanation of benzamides with TMSCN via 8-aminoquinoline directed ortho C-H activation has been developed. Varieties of functionalized ortho-cyanated (hetero)aryl nitriles can be selectively synthesized in moderate to good yields. These cyanation products can be easily transformed into various 3-imino-1-oxoisoindolines in a one-pot procedure. The mild reaction conditions, use of cheap and commercially available reagents, wide functional group tolerance, and operational convenience make this protocol practical to the synthetic community.

Highly mono-selective ortho-methylthiolation of benzamides via cobalt-catalyzed sp2 C–H activation

A highly mono-selective ortho-methylthiolation of benzamides was achieved via Co-catalyzed coupling of benzamides with DMSO.

Synthesis of 4-benzylpyridines via Pd-catalyzed CH3-arylation of 4-picoline

A highly efficient synthesis of 4-benzylpyridines was developed via Pd-catalyzed C(sp³)–H arylation between 4-picoline and aryl halides. It was found that the best yields were achieved with a simple Pd(PPh₃)₄ catalyst and Cs₂CO₃ as the base.

Discovery of 2-(pyridin-2-yl)aniline as a directing group for the sp2 C–H bond amination mediated by cupric acetate

2-(Pyridin-2-yl) aniline was designed as a new, removable directing group in promoting C–H amination mediated by cupric acetate.

Efficient syntheses of 3-hydroxyimino-1-isoindolinones and 3-methylene-1-isoindolinones via Cu-promoted C–H activation–nitroalkylation–intramolecular cyclization tandem processes

Efficient and selective syntheses of 3-hydroxyimino-1-isoindolinones and 3-methylene-1-isoindolinones were achieved via 8-aminoquinoline assisted Cu-promoted coupling of benzamides with nitroalkanes.