Highly Regio- and Chemoselective Oxidative C–H/C–H Cross-Couplings of Anilines and Phenols Enabled by a Co-Oxidant-Free Rh(I)/Zn(NTf2)2/Air Catalytic System

Unveiling the Centrosymmetric Effect in the Design of Narrowband Fluorescent Emitters: From Single to Double Difluoroboron Cores

Narrowband fluorescent emitters are receiving significant attention due to the great potential for creating ultrahigh-definition organic light-emitting diode displays (UHD-OLED). Unveiling innovative mechanisms to design new high-performance narrowband fluorescent emitters is a concerted endeavor in both academic and industrial circles. Theoretical calculations reveal that the centrosymmetric dianilido-bipyridine boron difluoride framework (cs-DAPBF2) exhibits significantly reduced structural relaxation compared to previously reported asymmetric structures with monofluoroboron cores, creating new opportunities for the development of narrowband fluorescent emitters. In this work, we present a dual chelation-assisted C-H/C-H homocoupling strategy to efficiently synthesize the 3,3'-amino-2,2'-bipyridine skeleton, enabling the straightforward construction of a series of symmetric cs-DAPBF2-based fluorescent emitters. Through molecular optimization, we have developed a high-performance narrowband green fluorescent emitter, cs-DMeAPBF2-MP, which demonstrates a narrow full width at half-maximum (fwhm) of 20 nm, a high photoluminescence quantum yield (ΦPL) of 98%, a large molar absorptivity (ε) of 2.10 × 104 M-1 cm-1, and a high horizontal dipole ratio (Θ//) of 77%. These properties make cs-DMeAPBF2-MP a promising candidate for fabricating high-efficiency, narrowband green organic light-emitting diodes (OLEDs) with minimal efficiency roll-off. This study represents the first successful application of the DAPBF2 architecture in the design of narrowband fluorescent emitters for high-performance OLEDs.

The Versatile and Strategic O-Carbamate Directed Metalation Group in the Synthesis of Aromatic Molecules: An Update

The aryl O-carbamate (ArOAm) group is among the strongest of the directed metalation groups (DMGs) in directed ortho metalation (DoM) chemistry, especially in the form Ar-OCONEt2. Since the last comprehensive review of metalation chemistry involving ArOAms (published more than 30 years ago), the field has expanded significantly. For example, it now encompasses new substrates, solvent systems, and metalating agents, while conditions have been developed enabling metalation of ArOAm to be conducted in a green and sustainable manner. The ArOAm group has also proven to be effective in the anionic ortho-Fries (AoF) rearrangement, Directed remote metalation (DreM), iterative DoM sequences, and DoM-halogen dance (HalD) synthetic strategies and has been transformed into a diverse range of functionalities and coupled with various groups through a range of cross-coupling (CC) strategies. Of ultimate value, the ArOAm group has demonstrated utility in the synthesis of a diverse range of bioactive and polycyclic aromatic compounds for various applications.

Discovery of Organic Optoelectronic Materials Powered by Oxidative Ar-H/Ar-H Coupling

Efficient and streamlined synthetic methods that facilitate the rapid build-up of structurally diverse π-conjugated systems are of paramount importance in the quest for organic optoelectronic materials. Among these methods, transition-metal-catalyzed oxidative Ar-H/Ar-H coupling reactions between two (hetero)arenes have emerged as a concise and effective approach for generating a wide array of bi(hetero)aryl and fused heteroaryl structures. This innovative approach bypasses challenges associated with substrate pre-activation processes, thereby allowing for the creation of frameworks that were previously beyond reach using conventional Ar-X/Ar-M coupling reactions. These inherent advantages have ushered in new design patterns for organic optoelectronic molecules that deviate from traditional methods. This ground-breaking approach enables the transcendence of the limitations of repetitive material structures, ultimately leading to the discovery of novel high-performance materials. In this Perspective, we provide an overview of recent advances in the development of organic optoelectronic materials through the utilization of transition-metal-catalyzed oxidative Ar-H/Ar-H coupling reactions. We introduce several notable synthetic strategies in this domain, covering both directed and non-directed oxidative Ar-H/Ar-H coupling strategies, dual chelation-assisted strategy and directed ortho-C-H arylation/cyclization strategy. Additionally, we shed light on the role of oxidative Ar-H/Ar-H coupling reactions in the advancement of high-performance organic optoelectronic materials. Finally, we discuss the current limitations of existing protocols and offer insights into the future prospects for this field.

Silver-catalyzed nitrosation and nitration of aromatic amides using NOBF4

Divergent aromatic ring nitrosation and nitration of aromatic amides are reported using NOBF4 as the electrophile under silver-catalyzed conditions. The reactions proceed efficiently with a wide range of compatible functionalities providing ortho-position nitrosation products, deacylation nitrosation products, and nitration products from different tertiary and secondary aromatic amides.

Recent Advances in Aerobic Oxidative of C-H Bond by Molecular Oxygen Focus on Heterocycles

Aerobic oxidative cross-coupling represents one of the most straightforward and atom-economic methods for construction of C-C and C-X (X=N, O, S, or P) bonds using air as a sustainable external oxidant. The oxidative coupling of C-H bonds in heterocyclic compounds can effectively increase their molecular complexity by introducing new functional groups through C-H bond activation, or by formation of new heterocyclic structures through cascade construction of two or more sequential chemical bonds. This is very useful as it can increase the potential applications of these structures in natural products, pharmaceuticals, agricultural chemicals, and functional materials. This is a representative overview of recent progress since 2010 on green oxidative coupling reactions of C-H bond using O2 or air as internal oxidant focus on Heterocycles. It aims to provide a platform for expanding the scope and utility of air as green oxidant, together with a brief discussion on research into the mechanisms behind it.

Palladium-catalyzed interannular C-H amination of biaryl amines

A palladium-catalyzed interannular C-H amination of biaryl amines with O-benzoylhydroxylamines is reported. This reaction undergoes smoothly with operational practicality and good tolerance of functional groups, thereby providing a concise synthesis of 2,2'-diaminobiaryls. Moreover, the readily accessible scale-up synthesis and the ability to transform the products into structurally diverse N-containing heterocycles demonstrate the synthetic potential of this catalytic protocol.

Divergent Regioselective Csp2-H Difluoromethylation of Aromatic Amines Enabled by Nickel Catalysis

Herein, the first catalytic protocol for nickel-catalyzed ortho or para position difluoromethylation of various aromatic amines has been developed with the assistance of a bidentate phosphine ligand, offering an invaluable synthesis means to construct extensive p-difluoromethylated products and difluorooxindole derivatives with significant functional fragments. Furthermore, the gram-scale reaction, broad substrate scope, excellent functional-group compatibility, late-stage difluoromethylation of pesticides, and even formal synthesis of HDAC6 inhibitors further demonstrate the usefulness of this method.

Recent advances in rhodium-catalysed cross-dehydrogenative-coupling between two C(sp2)-H bonds

Rhodium-catalysed cross-dehydrogenative coupling (CDC) has received considerable attention in recent years. This modern technology has been considered as an attractive synthetic tool for selective C−C bond formation due to (1)...

Ru(II)-Catalyzed Difunctional Pyridyloxy-Directed Regio- and Stereospecific Addition of Carboxylic Acids to Internal Alkynes

A highly efficient Ru(II)-catalyzed regio- and stereospecific hydro-oxycarbonylation of unsymmetrical internal alkynes bearing a difunctional 2-pyridyloxy directing group with carboxylic acids has been developed, which provides allylic (Z)-enol esters in good to excellent yields with a broad substrate scope under mild conditions. The difunctional directing group can be diversely derivatized, particularly undergoing allylic substitution with various nucleophiles to afford β-functionalized (Z)-enol esters without directing groups.

Recent advances in rhodium-catalyzed C(sp2)-H (hetero)arylation

Arylation is a common behaviour in organic synthesis for the construction of complex structures, especially the biaryls. Among those reported arylation procedures, transition-metal-catalyzed direct C(sp²)-H arylation has been rapidly developed in recent decades and has become a reliable alternative to traditional cross-coupling procedures using organometallic reagents. Great achievements in rhodium-catalyzed C(sp²)-H arylation have been witnessed during the last decade. Aryl halides, simple arenes, aryl boronic acids, arylsilanes, aryl aldehyde, aryl carboxylic acid, diazides, etc. were successfully utilized as arylating reagents under rhodium-catalyzed conditions. In this review, recent achievements in rhodium-catalyzed arylations through C(sp²)-H bond activation were summarized together with the mechanism discussions.

Decoding Directing Groups and Their Pivotal Role in C-H Activation

Synthetic organic chemistry has witnessed a plethora of functionalization and defunctionalization strategies. In this regard, C-H functionalization has been at the forefront due to the multifarious applications in the development of simple to complex molecular architectures and holds a brilliant prospect in drug development and discovery. Despite been explored tremendously by chemists, this functionalization strategy still enjoys the employment of novel metal catalysts as well metal-free organic ligands. Moreover, the switch to photo- and electrochemistry has widened our understanding of the alternative pathways via which a reaction can proceed and these strategies have garnered prominence when applied to C-H activation. Synthetic chemists have been foraging for new directing groups and templates for the selective activation of C-H bonds from a myriad of carbon-hydrogen bonds in aromatic as well as aliphatic systems. As a matter of fact, by varying the templates and directing groups, scientists found the answer to the challenge of distal C-H bond activation which remained an obstacle for a very long time. These templates have been frequently harnessed for selectively activating C-H bonds of natural products, drugs, and macromolecules decorated with multiple C-H bonds. This itself was a challenge before the commencement of this field as functionalization of a site other than the targeted site could modify and hamper the biological activity of the pharmacophore. Total synthesis and pharmacophore development often faces the difficulty of superfluous reaction steps towards selective functionalization. This obstacle has been solved by late-stage functionalization simply by harnessing C-H bond activation. Moreover, green chemistry and metal-free reaction conditions have seen light in the past few decades due to the rising concern about environmental issues. Therefore, metal-free catalysts or the usage of non-toxic metals have been recently showcased in a number of elegant works. Also, research groups across the world are developing rational strategies for directing group free or non-directed protocols that are just guided by ligands. This review encapsulates the research works pertinent to C-H bond activation and discusses the science devoted to it at the fundamental level. This review gives the readers a broad understanding of how these strategies work, the execution of various metal catalysts, and directing groups. This not only helps a budding scientist towards the commencement of his/her research but also helps a matured mind searching out for selective functionalization. A detailed picture of this field and its progress with time has been portrayed in lucid scientific language with a motive to inculcate and educate scientific minds about this beautiful strategy with an overview of the most relevant and significant works of this era. The unique trait of this review is the detailed description and classification of various directing groups and their utility over a wide substrate scope. This allows an experimental chemist to understand the applicability of this domain and employ it over any targeted substrate.

Mechanochemical Solvent-Free Catalytic C-H Methylation

The mechanochemical, solvent-free, highly regioselective, rhodium-catalyzed C-H methylation of (hetero)arenes is reported. The reaction shows excellent functional-group compatibility and is demonstrated to work for the late-stage C-H methylation of biologically active compounds. The method requires no external heating and benefits from considerably shorter reaction times than previous solution-based C-H methylation protocols. Additionally, the mechanochemical approach is shown to enable the efficient synthesis of organometallic complexes that are difficult to generate conventionally.

Equivalent Loading of Directed Arenes in Pd(II)-Catalyzed Oxidative Cross-Coupling of Aryl C-H Bonds at Room Temperature

The unsymmetrical biaryls (Ar¹-Ar²) produced by the catalytic cross-couplings of aryl halides (Ar¹-halo) with aryl metallics (Ar²-M) in the loading ratio of 1:1 are popular in chemical synthesis. In contrast, there has been less precedence on the same biaryls produced effectively from two normal aryl C-H bonds with equivalent loading. Here, we report that, in a palladium/oxidant/acid catalytic system at room temperature, one arene (Ar¹-H, 1 equiv) can highly selectively couple with the other one (Ar²-H, 1 equiv) to afford the target Ar¹-Ar² just by controlling the directing groups and the substituted groups on their phenyl rings. The utility of this one-one cross-coupling is also demonstrated by synthesis of a few bioactive molecules.

Ligand Promoted Olefination of Anilides for Indirectly Introducing Fluorinated Functional Groups via Palladium Catalyst

We report a palladium-catalyzed, ligand promoted, C-H fluorine-containing olefination of anilides with 4-bromo-3,3,4,4-tetrafluorobutene as the fluorinated reagent, which has a potential transformation into other compounds due to its -CF₂CF₂Br functional group. -CF₂CF₂H was obtained by using the mild reducing agent sodium borohydride. Bioactive compounds such as aminoglutethimide derivative and propham were well-tolerated in this reaction, both of which highlight the synthetic importance of this method.

Dual C–H activation: Rh(iii)-catalyzed cascade π-extended annulation of 2-arylindole with benzoquinone

A rhodium-catalyzed, N–H free indole directed cyclization reaction of benzoquinone via a dual C–H activation strategy is disclosed. This protocol has a good functional group tolerance and affords useful indole-fused heterocylces. Besides, it is insensitive to moisture, commercially available solvent can be directly used and work quite well for this transformation.

A Rh-catalyzed cascade annulation of N–H free 2-arylindole with benzoquinone via dual C–H activation strategy was reported.

Ru(II)-Catalyzed and acidity-controlled tunable [5+1]/[5+2] annulation for building ring-fused quinazolines and 1,3-benzodiazepines

The Ru(ii)-catalyzed tunable [5+1]/[5+2] annulation of N-benzo[d]imidazole indolines with propargyl carbonates has been realized for the divergent synthesis of ring-fused quinazolines and 1,3-benzodiazepines bearing various functional groups. These transformations represent an efficient and practical strategy in constructing complex heterocycles via diversified C-H functionalization. A distinctive acidity-controlled reaction manner has been clarified to account for the chemoselectivity.

Copper-catalyzed remote C-H arylation of polycyclic aromatic hydrocarbons (PAHs)

The regioselective C–H arylation of substituted polycyclic aromatic hydrocarbons (PAHs) is a desired but challenging task. A copper-catalyzed C7–H arylation of 1-naphthamides has been developed by using aryliodonium salts as arylating reagents. This protocol does not need to use precious metal catalysts and tolerates wide variety of functional groups. Under standard conditions, the remote C–H arylation of other PAHs including phenanthrene-9-carboxamide, pyrene-1-carboxamide and fluoranthene-3-carboxamide has also accomplished, which provides an opportunity for the development of diverse organic optoelectronic materials.

Modular bismacycles for the selective C-H arylation of phenols and naphthols

Given the important role played by 2-hydroxybiaryls in organic, medicinal and materials chemistry, concise methods for the synthesis of this common motif are extremely valuable. In seeking to extend the lexicon of synthetic chemists in this regard, we have developed an expedient and general strategy for the ortho-arylation of phenols and naphthols using readily available boronic acids. Our methodology relies on in situ generation of a uniquely reactive Bi(V) arylating agent from a bench-stable Bi(III) precursor via telescoped B-to-Bi transmetallation and oxidation. By exploiting reactivity that is orthogonal to conventional metal-catalysed manifolds, diverse aryl and heteroaryl partners can be rapidly coupled to phenols and naphthols under mild conditions. Following arylation, high-yielding recovery of the Bi(III) precursor allows for its efficient re-use in subsequent reactions. Mechanistic interrogation of each key step of the methodology informs its practical application and provides fundamental insight into the underexploited reactivity of organobismuth compounds.

Electrochemical dehydrogenative cross-coupling of two anilines: facile synthesis of unsymmetrical biaryls

New ortho/para-selective dehydrogenative cross-coupling of aryl amines for producing biaryls and incorporating pharmacophores is depicted.