An intramolecular dinuclear zinc complex was used in asymmetric Friedel-Crafts alkylation of pyrrole with a wide range of chalcone derivatives. This dinuclear zinc complex was prepared in situ by reacting the chiral ligand (S,S)-1 with 2 equiv. of ZnEt₂. A series of β-pyrrole-substituted dihydrochalcones were formed mostly in excellent yields (up to 99%) and excellent enantioselectivities (up to >99% ee) by using 15 mol% catalyst loading under mild conditions. A possible mechanism was proposed to explain the origin of the asymmetric induction.

Ferrocenes bearing planar chirality have been demonstrated to be highly efficient ligands or catalysts in asymmetric catalysis. In view of their atom and step economies, direct asymmetric C—H bond functionalization is the most concise and powerful method for the construction of planar chiral ferrocenes compared with traditional approaches. This review summarizes recent progress on the development of novel methods to synthesize planar chiral compounds via transition- metal (Cu-, Pd-, Ir-, Rh-, Au-, Pt-) catalyzed asymmetric C—H bond functionalization. Preparation of a variety of new planar chiral ferrocene-based catalysts and ligands by utilizing these methods and their application in catalytic asymmetric reactions are also discussed.

A gold(I)-catalyzed 1,2-silyl migration on 1,8-di-substituted naphthalene rings was realized by synergistic effect of Lewis acid and water. High yields were achieved under relatively mild conditions.

The indoles motifs are widely found in the nature. One of the efficient strategy to access the indole derivatives is through the direct C-H functionalization of indole framework itself under transition-metal catalysis. Herein, the research advances on the transition-metal-catalyzed C-H arylation of indoles are reviewed.

A series of bis(alkoxo)palladium complexes (2 mol%) based on pyridine-containing alcohol ligand were tested for Fujiwara-Moritani reaction of thiophenes/furans with various olefins. The desired products were isolated in moderate to excellent yields under mild conditions. A possible concerted metalation-deprotonation (CMD) pathway for this transformation was proved by control experiments and ESI(+)-MS analysis.

Progress in the synthesis and application of the cyclopalladated derivatives of ferrocene with a donor nitrogen atom in the directing group is surveyed including the planar chirality and enantioselective catalysis of organic reactions and rearrangements. Transannular palladation has been found giving achiral 1,1'-disubstituted ferrocenes of ansa-structure. Cyclopalladated ferrocenes have been widely used as catalysts in the cross-coupling reactions (Suzuki, Heck, aza-Claisen, etc. )

The C (sp³)-H adjacent to heteroatoms can be readily functionalized to C-C, C-N, C-O bonds etc. via cascade[1, n]-hydride transfer/cyclization, which shows high potency to construct 5-membered, 6-membered and all carbon rings. This intriguing cascade process can be employed to synthesize common skeletons of significant natural products and pharmaceutical molecules. Chiral amines, Lewis acids and Brønsted acids have been successfully utilized to catalyze the asymmetric cascade reaction.

A metal-free, operationally simple synthetic protocol for the buildup of unsymmetric 1, 1'-biaryl-2, 2'-diamine compounds was reported. This reaction was performed by the treatment of 2-naphthols with aryl hydrazines under no transition metal catalyst and no ligand conditions, which has the advantages of simple operation and one-step synthesis.

In 1967, Fujiwara and Moritani reported a type of cross coupling reaction where an aromatic C-H bond is directly coupled to an olefinic C-H bond, generating a new C-C bond in the first time. This reaction is performed in the presence of a transition metal, and typically palladium. In the next few decades, palladium-catalyzed oxidative coupling reactions have become an important method in organic synthesis, and a lot of achievements in scientific research have emerged in the relevant areas. The progress in oxidative coupling reaction of olefins, alkynes and aromatic hydrocarbons catalyzed by palladium is reviewed.

C-H bonds are widely existed in almost all the organic compounds. Transition-metal-catalyzed C-H functionalizations usually have high reaction efficiency and high atom-economy. However, traditional strategies based on such transition-metal catalyzed C-H activations generally result in poor selectivities, because C-H bonds in one molecule facilely display similar reactivity. It is difficult to be utilized in preparation of natural products, pharmaceuticals and biomolecules. However, directing group can induce the metal to activate proximal C-H bonds via cyclometallated intermediates, improve the regioselectivity of the transformations. Therefore, it is extremely significant to deveplop auxiliary-induced C-H bonds activations. The research progress of directing group-induced C-H activation reactions and mechanisms for recent ten years are sumarized.

Chiral urea derivatives as organocatalysts were applied in the asymmetric aza-Friedel-Crafts reaction of α-naphthol with 14 N-tosyl aldimines. The desired chiral aminoarylnaphthols were obtained in 70%~86% yields with up to 78% enantiomeric excess (ee) under the screened optimal condition. The catalyst type and the substrate scope were broadened in this methodology.

3-Substituted imidazo[1,2-a] pyridines are important N-fused heterocycles with extensive application value in medicine, materials and other fields. C(3)-H bond functionalization strategy was a simple and effective way to build 3-substituted imidazo[1,2-a] pyridines. The recent advances of the access to 3-substituted imidazo[1,2-a] pyridines according to the type of bonding (C-C, C-S/Se, C-N/P) on C-3 position are briefly summarized, and a prospect for the future development is made.

An efficient and practical protocol for palladium-catalyzed direct C—H bond arylation of imidazo[1,2-a]pyridines with cheap aryl/heteroaryl chlorides has been developed. Various imidazo[1,2-a]pyridines with electron-neutral, electron-poor, electron-rich, even sterically hindered aryl chlorides and heteroaryl chlorides were successfully applied to the reaction in aqueous medium to achieve the 3-arylimidazo[1,2-a]pyridines in mostly good to excellent yields, thus representing a signi?- cant advancement in the implementation of the direct C—H bond arylation of imidazo[1,2-a]pyridines with aryl chlorides.

MIL-101 was synthesized by hydrothermal method, and Pd/MIL-101 catalyst was prepared by supporting palladium nanoparticles on metal-organic frameworks MIL-101. The microstructure and features of the catalyst were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), inductive coupled plasma (ICP), high resolution transmission electron microscopy (HRTEM) and N₂ adsorption, respectively. The experimental results reveal that the Pd nanoparticles on Pd/MIL-101 range from 1.5 nm to 2.5 nm, and the content of Pd nanoparticles is 1.5%. The catalytic experiments show that Pd/MIL-101 has a high catalytic activity for the C₂ arylation of benzofuran. For less active aryl bromides, the reaction gave moderate yields. Moreover, the catalyst could be recycled many times. After 5 runs of catalysis, the catalyst can still maintain high reactivity. This strategy provides a simple, effective method for the synthesis of benzofuran derivatives.

The chiral triarylmethane frameworks are featured in many biologically important molecules. As a result, the synthesis of chiral triarylmethanes has received tremendous attention from the chemists. Herein, we reported the chiral phosphoric acid catalyzed dehydrative arylation of 3-indolylmethanols with tryptophols, leading to the efficient synthesis of a series of structurally diversified chiral bisindolyl-substituted triarylmethanes in moderate to good yields (up to 80% yield) with acceptable enantioselectivities (up to 88% ee). The chiral phosphoric acid played an important role not only in the dehydration of 3-indolylmethanols, but also in the control of enantioselectivity via hydrogen-bonding and ion-pairing interactions. The only byproduct was water, indicating that this catalytic asymmetric dehydrative arylation reaction was environment-friendly and in accordance with the requirements of green chemistry. In addition, the mild reaction condition and wide substrate scope of the reaction have successfully demonstrated the great potential of organocatalysis in the chiral triarylmethanes.

A high efficient method for the synthesis of 1,3-diynes derivatives which employed terminal alkynes as the substrates and copper(I) oxide as the catalyst was developed. This method possessed the character of base-free and mild reaction conditions. The reaction mechanism was also studied. Furthermore, this reaction could be magnified to gram scale and the catalyst of copper(I) oxide could be recycled.

An efficient protocol for conversion of azobenzenes into their ortho-nitro derivatives via palladium-catalyzed C-H bond activation has been developed. Commercially available and less expensive Co(NO₃)₂·6H₂O was used as the nitrification reagent. Various o-nitroazobenzenes were obtained in excellent yields.

Palladium-catalyzed cross-dehydrogenative coupling of uracil or caffeine with unactivated arenes has been developed. The approach was characterized by using atmospheric pressure of molecular oxygen as the sole oxidant. Functional groups such as halo, ester, nitro, nitrile and ether are well-tolerated under the reaction conditions. This novel strategy provides a straightforward, facile and economical route to C6-aryl uracil derivatives or C8-aryl caffeine derivatives.

The catalyst-free addition of 2-methylazaarenes benzylic C(sp³)-H to electron-deficient olefins in neutral ionic liquid aqueous solution was reported, and a series of azaarene derivatives were obtained in good yields. This method is easy to operate and the reaction conditions are mild, which not only expands the application of ionic liquid in C(sp³)-H functionalization reaction, but also has positive significance for promoting the development of the green chemistry.

An efficient synthesis of α-substituted 1, 2-dihydroquinoline compounds through the oxidative C—H functionalization of N-acyl-dihydroquinoline with diverse organoboron reagents mediated by triphenylcarbium perchlorate (Ph₃CClO₄) is reported. The reaction exhibits good functional group tolerance, allowing for C—H alkynylation and alkenylation proceeding smoothly in good yields.

Phenols are important central motifs that are abundant in many natural products, pharmaceuticals and agrochemicals. Moreover, the high reactivity of phenol derivatives makes them versatile building blocks for organic synthesis. Over the past decade, the synthesis of phenol derivatives via C-H hydroxylation of aromatics has received much attention due to its potential as an atom efficient methodology. Herein, the research advances on the C-H hydroxylation of aromatics are reviewed categorized by the types of hydroxylation source used. Detailed substrate scopes and reaction mechanisms will be discussed, as well as the limitations of current procedures and the prospects for the future.

Primary anilines are widely used in pharmaceutical, agrochemicals and material chemistry. In recent years, the green and efficient methods for constructing carbon-nitrogen (C-N) bonds to introduce primary amines has been one of the hottest topics in chemical synthesis. The direct C-H primary amination of aromatic compounds have received considerable attention due to its high efficiency and practicality. The recent progress in the C-H primary amination of aromatic compounds reactions is reviewed. Furthermore, the synthetic challenge and prospect in the future development for the synthesis of primary anilines through direct C-H amination are summarized.

Alkaline-earth-metal compounds have been widely concerned due to its abundant reserve and the low-cost. In recent years, alkaline-earth-metal catalysis has achieved great progress in dehydrocoupling, hydroboration, hydrophosphination, hydroamination, hydrosilylation reactions experimentally and therotically. These types of reaction and catalytic mechanism, leading to indentify the role of alkaline-earth-metal in hydrogenation and dehydrogenation reaction are summarized. These reactions, in which the metal-hydride act as active species, generally undergo the reaction pathway involving the cleavage and formation of the metal-hydride covalent bond. The reaction features and mechanisms are generally recognized accrossing to the classification and discussion of these reactions, which would provide guidance for further development of alkaline-earth-metal catalysis.

Transition metal-catalyzed direct C-H bond functionalization strategy has aroused wide concerns due to its high atom-economy and step-economy. Imine synthons exhibit diverse reactivities and are commonly employed to assemble nitrogen-containing complex molecules through direct C-H functionalization strategies, their reaction types and mechanisms are summarized in this paper.

The functional switch of a C—H activation directing group to a pharmacophore is introduced and analyzed, and the value of the pharmacophore and the application of C—H activation are exemplified. It is concluded that many pharmacophores, such as N-containing heteroaromatic, nitrile, carboxylic acid, amide and sulfonamide groups, are ideal directing groups for C—H activation enabling the subsequent stages of drug synthesis, and showing that there is a correlation between a directing group and a pharmacophore. The late-stage functionalization will greatly simplify and effectively improve the possibility of discovering new drugs and potentially shortening the overall synthesis. The latest breakthroughs of C—H activation and application in the drug discovery process are reviewed as case studies, providing several industrial examples of using a pharmacophore as directing group for drug synthesis. It is believed that this development will promote a more rapid and green drug synthesis.

Carbon-hydrogen bonds are the most extensive and basic chemical bonds existed in organic compounds. Electrochemical functionalization and direct conversion of aromatic C—H bonds is a green, sustainable, and atomically economical transformation pathway, which avoids the pre-functionalization of reactants. The anodic electrooxidation of aromatics allows the formation of C—X (X=C, N, O, S) bonds and the preparation of fused aromatic rings without the use of oxidants. Certain C—H activation reactions with chemoselectivity and regioselectivity can also be achieved by the optimization of electrode materials, electrolytes, and solvents. Vourious reactions focusing on the electrochemical functionalizations of C—H bonds in aromatic compounds are mainly reviewed.

In recent years, low-valence iodine-catalyzed oxidative coupling reaction has made rapid progress, providing an effective method for the construction of C—C, C—O, C—N, C—S, C—P and other chemical bonds. Compared with the transition metal-catalyzed oxidation coupling reaction, this protocol is metal-free under mild conditions. It avoids the high cost and toxicity of transition metal catalyst, which meets the requirements of green chemistry. Therefore, iodine catalysis has attracted much attention of the synthetic chemists. The research progress on low-valence iodine-catalyzed oxidative coupling from 2010 to now is summarized, and outlook of this field is also prospected.

Palladium catalyzed cross-coupling of 3,6-(Bpin)₂-o-carborane (Bpin=pinacolatoboryl) with aryl bromides has been achieved, leading to the formation of a series of B(3,6)-diarylated-o-carborane derivatives in moderate yields. In this reaction, PdCl₂(cod)/tricyclohexylphosphine was used as catalyst to avoid the formation of palladium-catalyzed aryl-aryl exchange and direct B-H arylation by-products. A possible mechanism is proposed, involving a tandem sequence of oxidative addition, anion exchange, transmetalation, and reductive elimination.

Heterocyclic compounds are not only important intermediates in organic synthesis and medicine synthesis, but also the basic building framework of biologically active natural products. In recent years, Pd-catalyzed C(sp³)-H bonds activation has been demonstrated as one of the hot topics in the field of heterocyclic compound synthesis because of its high atomic economic characteristics. Herein, the recent research progress in the construction of heterocyclic compounds via Pd-catalyzed C(sp³)-H bond activation is summarized according to the classification of the ring number of heterocyclic compounds (mainly including N, O heterocycles). The reaction selectivity, substrate compatibility, reaction mechanism, advantages and disadvantages as well as an outlook in this field are also discussed.

A simple and practical visible-light-induced protocol has been developed for the construction of 3-arylquinoxa-lin-2(1H)-ones via Eosin Y-catalyzed direct C-H 3-arylation of quinoxalin-2(H)-ones with aryl diazonium salts at room temperature in air. The present reaction provides a cost-effective and operationally straightforward approach to the target products in moderate to good yields, and does not require any metal reagents, bases, acids, and strong oxidants.

Direct synthesis of the hydroxymethylated arene derivatives via ruthenium(Ⅲ)-catalyzed nitrogen atom directed C-H activation is described. The reaction proceeds smoothly at room temperature and generates the corresponding products in moderate to excellent yields. Meanwhile, it has a broad substrate scope and opens up an attractive avenue for the application of direct hydroxymethylation in the synthesis of biologically active compounds.

A catalyst system combined of PdCl₂ with 1,3-bis(diphenylphosphion)propane (dppp), which was simple and from commercially available materials, was reported for the highly efficient arylation of benzoxazoles at C-2 position with aryl bromides. This catalytic system could tolerate a great number of functional groups in benzoxazole and bromobenzene. With a low PdCl₂ loading of 0.01 mol%, aryl bromides could be completely converted into the desired products for 24 h. If the loading of catalyst was up to 0.10 mol%, most of substrates could give more than 90% yields in 6 h. The exploration of the reaction mechanism discovered that Pd nanoparticles were formed during this reaction. The morphology and composition analysis of the Pd nanoparticles with transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) indicated that dppp played a key role to block the aggregation of palladium particles. In addition, the ring-opening pathway of benzoxazoles in the reaction process was proved by control experiments. Hot filtration experimental and high resolution mass spectrum (HRMS) analysis of filtrate suggested that the real active species were Pd(0)-Pd(Ⅱ)/dppp complexes.

Aromatic nitro compounds are of great importance as chemical raw materials and organic synthesis intermediates. Traditional electrophilic nitration is difficult to achieve regioselective nitrification. In recent years, transition-metal-catalyzed C-H bond activation has developed rapidly. Most functional groups can be introduced into specific sites of aromatics through the chelation of transition metals with directing groups. Directing-group assisted C-H nitration, which is catalyzed by palladium, rhodium, ruthenium and other transition-metal, has made important progress due to its less byproducts, good regioselectivity and environmental protection. According to different transition metal catalysts, the research progress on transition-metal-catalyzed directing-group assisted C-H nitration is summarized, and the limitations of the research field and prospects for future develop-ment are presented.

Construction of C-N bond is one of the most important areas in synthetic organic chemistry and medical chemistry. Many synthetic methods for the construction of C-N bond have been reported over the past few years. Copper-catalyzed Chan-Lam reactions represent one of the most powerful and straightforward tools to construct C-N bonds. In this paper, the recent progress in Chan-Lam coupling of N-compounds with (hetero) aryl boronates to construct C-N bond based on the reaction mechanism, reaction system, the scope of substrates, etc., is reviewed.

Recent years the great progress in transition metal-catalyzed direct aromatic C—H oxidation has been witnessed, which has been utilized in the preparation of various phenolic compounds. These transformations employ inter alia palladium, copper, ruthenium, iridium, etc. as the transition metal catalysts, and hypervalent iodine, persulfate, or oxygen as the oxidants. There have been several reviews in which the C—H oxidations with specific transition metal or oxidant was discussed. This review focuses specifically on transition metal-catalyzed aromatic C—H oxidations with ortho-, meta-, or para-selectivity, and rationalizes the possible generation mechanism of regio-selectivities, which might be controlled by the directing group via chelation-assistance, the ligand, or intrinsic properties of the substrate. The discussion section indicated the existing problems of transition metal-catalyzed aromatic C—H oxidations, as well as the possible limiting factors for the development and application of this strategy.

Imines are very important class of compounds and have been widely utilized in fine chemicals, pharmaceuticals and chemical industry. The C=N double bond in imine is an important nitrogen source in different types of reactions due to its high reactive activity. Due to its high atom economy, catalytic direct coupling of alcohols and amines to imines based on metal catalysts has attracted much attention and maken great progress in recent years. In this paper, the advances in direct coupling of alcohols and amines to imines catalyzed by metal catalysts are reviewed.

A novel copper-catalyzed oxidative cross-coupling reaction between N-arylglycine esters and Silyl enol ethers for the synthesis of β-acyl-α-amino acid esters has been developed. The features of this reaction are high reaction yields, mild reaction conditions (such as room temperature environments and inexpensive catalysts, etc.) and smooth operation in aqueous medium.

An electrochemical synthesis of tetrasubstituted hydrazines through dehydrogenative dimerization of secondary amines has been developed. The reactions are conducted in a simple undivided cell with constant current. The use of electricity to promote the reactions obviates the need for transition metal catalysts and oxidizing reagents, providing an efficient and sustainable access to tetrasubstituted hydrazines with diverse electronic properties.

Trifluoromethylation using Togni reagents usually releases one equivalent of iodobenzoats as wasteful byproducts. A visible-light-mediated, atom-and step-economical hydrotrifluoromethylation of aromatic alkynes and remote benzoyl-oxylation of α-C(sp³)-H bond of ether with Togni reagent as a bifunctional reagent by means of hydrogen atom transfer strategy was disclosed. The combination of two organic transformations into one reaction not only brings 100% atom economy but also addresses the challenge of stereoselective hydrotrifluoromethylation of aromatic alkynes. This unprecedented protocol offers an important access to a wide range of highly functionalized CF₃-containing alkenes with great potential for post-modification.

A dehydrative cross coupling of ketone-stabilized phosphorus ylides with the readily available allylic alcohols followed by an one-pot Wittig reaction is developed. A range of functional 1,4-dienes could be obtained in 52%~95% isolated yields in the presence of 5 mol% Pd(PPh₃) ₄ and 20 mol% B(OH) ₃. The same method can be extended to ester or nitrile-stabi-lized phosphorus ylides, affording the corresponding 1,4-dienes in moderate yields.