During the past several decades, Suzuki-Miyaura cross-coupling reaction has emerged and flourished as one of the most remarkable and practical methods to construct C—C bond. The substrates, organoboronic compounds, are usually more stable, less toxic and easier to obtain compared with other metal or metalloid alternatives. Suzuki-Miyaura cross-coupling reaction possesses extraordinary merits of demonstrated efficiency, broad functional group compatibility and mild reaction conditions. It has been the premier method to construct C—C bond for organic synthetic chemists and has been widely applied in the industrial syntheses. The rapid development of Suzuki-Miyaura cross-coupling reaction is accompanied with the progress of mechanism studies. It is well accepted that the catalytic cycle of Suzuki-Miyaura cross-coupling reaction contains three main steps: oxidative addition of organic halides to Pd catalysts, transmetalation between oxidative addition intermediates and organoboronic compounds, and reductive elimination from transmetalation intermediates to form C—C bond along with regenerating Pd catalysts. However, these three main steps can be influenced by diverse reaction conditions, and different reaction pathways may occur within each single step. Furthermore, beyond the oxidative addition and transmetalation intermediates, other transient but crucial intermediates may exist. To figure out these issues and discover more insights into Suzuki- Miyaura cross-coupling reaction, numerous researchers have designed and conducted systematic investigations. Herein, the recent progress of mechanism studies is summarized and discussed. The steps of oxidative addition, transmetalation and reductive elimination are discussed in detail. Moreover, a brief introduction of transition-metal-free and base-free Suzuki- Miyaura cross-coupling reactions which show more possibilities of the reaction mechanism is given. Besides summary of precedent research works, our opinions about future development of the mechanism studies are also given. Although breakthroughs have been made in the mechanism studies, further investigations are needed to bring comprehensive knowledge of this reaction and help us further optimize the reaction conditions.

Proton-coupled electron transfer (PCET) reactions are a kind of unconventional redox reactions, which exhibit special reactivities and selectivities due to their unique interdependent electron-proton transfer mechanisms. There are three possible pathways of PCET processes, including stepwise electron transfer followed by proton transfer (ETPT), proton transfer followed by electron transfer (PTET), and concerted pathway in which electron and proton transfer synchronously (CEPT), avoiding intermediates with high energy. These reactions have been playing a key role in numerous areas in organic chemistry, inorganic chemistry, bioorganic chemistry, organometallic and material chemistry, including the redox processes in natural and artificial systems, such as the activation for small molecules. Recently, the application of PCET reactions in organic synthesis has received a great deal of attentions and interests. Being accompanied by the development of electrochemical methods and photocatalysts, more and more novel reactions in electrochemistry and photochemistry involve PCET processes have been reported. Applying these electrochemical and photochemical methods, the activation of X—H bond has been achieved via PCET processes, including C—H bond, N—H bond, P—H bond, S—H bond or O—H bond. Thus, based on these crucial processes, a number of vital structures and fundamental frameworks can be synthesized, and various synthetic building blocks and natural products have been attained. For example, pharmaceutical building blocks like 2°-piperidines can be cyanated at their α-position; substituted dimeric pyrroloindolines such as (–)-calycanthidine, (–)-chimonanthine, and (–)-psychotriasine have also been successfully synthesized via PCET mechanism. Moreover, not only the products of reduction of multiple bonds (C=Y bond such as C=C bond, C=N bond and C=O bond), but also the products of self/cross-coupling have been achieved via PCET mechanism. In this review, the recent applications and developments of PCET mechanism in organic synthesis are summarized, including new catalyst systems and new reagents, especially with electrochemical and photochemical methodologies. The future of this area has also been demonstrated from both experimental and theoretical aspects.

The merger of visible-light photoredox catalysis and nickel catalysis makes it possible to forge challenging chemical bonds under mild conditions. Nevertheless, most of these transformations only construct a single carbon-carbon bond or carbon-heteroatom bond in one operation. In recent years, photoredox/nickel dual catalysis has attracted widespread attention in the field of catalytic difunctionalization of alkenes and alkynes. The synergistic cascade mode enables the construction of multiple chemical bonds in one single pot, providing a mild, efficient and selective protocol for the rapid assembly of complex structural motifs. The latest progress in the photoredox/nickel dual-catalyzed difunctionalization reactions of olefins and alkynes is summarized.

Most of the traditional organic fluorescent molecules have notorious aggregation-induced quenching (ACQ) effect, which limits their application in many fields. Therefore, how to achieve the transition from ACQ to aggregation-induced emission (AIE) while maintaining the functional properties of traditional conjugated molecules is of great significance. In recent years, many research groups have done a lot of breakthrough works in this field. According to the construction method and structural characteristics of AIE luminogen (AIEgen), the ACQ to AIE transformation strategy can be divided into two types. Based on the restriction of intramolecular motion (RIM) mechanism, the first one is to decorate ACQphore with typical AIEgen (e.g. tetraphenylethene unit). As the second one, some functional units (e.g. triphenylamine and cyanoethylene moiety) are introduced to realize the construction of AIE molecules from zero starting point as the RIM mechanism. In the latter, the construction of other AIEgen systems involving isomerism and excited-state intramolecular proton transfer (ESIPT) mechanisms has also been prominent recently. Thus, according to these classifications, the new progress on the construction strategy of ACQ-to-AIE transformation in the past five years is summarized from the four aspects of AIEgens’ structure, performance, mechanism and application.

Organochlorides have been widely used in medicine, pesticides, materials and other fields. In addition, organochlorides are also important synthetic building blocks. They have participated in a variety of reactions, such as free radical reactions, substitution reactions and cross-coupling reactions. The hydrochlorination of olefins is one of the most direct and efficient methods for the synthesis of organochlorides, and remakable breakthroughs have been made in the past thirty years. The research progress of olefin hydrochlorination in the past three decades is introduced. According to whether metal catalysis is involved, it is mainly classified into two categories: metal-free alkene hydrochlorination and metal-catalyzed alkene hydrochlorination. Different type of hydrochlorination reactions and related mechanisms are summarized. In addition, the future development direction of alkene hydrochlorination is prospected.

In recent years, a series of novel organic reactions, named “ionic transfer reaction”, has received much attention. This kind of reaction has a characteristic mechanism and avoids the use of inflammable, explosive, highly toxic and other difficult to operate reagents. It provides a new powerful tool for transfer functionalizations of unsaturated compounds, such as transfer hydrosilylations, transfer hydrogenations, transfer hydrohalogenations, and transfer hydrocyanations. Herein, the recent progress of ionic transfer reactions and related mechanisms are summarized. Furthermore, the future developments of ionic transfer reactions are prospected.

In recent years, multi-resonance thermally activated delayed fluorescence (MR-TADF) materials have attracted wide attention because of their excellent photophysical properties and electroluminescent performance. By introducing electron-deficient and electron-rich centers (such as boron and nitrogen atoms) in the framework of polycyclic aromatic hydrocarbons (PAHs), the HOMO and LUMO can be separated on different atoms due to the opposite resonance effects, which can reduce the singlet-triplet energy gap (ΔE_ST) to achieve TADF properties. Compared with conventional donor-acceptor type TADF materials, MR-TADF materials have rigid skeletons and show short-range charge transfer characteristics, which are conducive to realizing narrowband luminescence with high color purity and high quantum efficiency, making them ideal luminescent materials and widely used in organic light-emitting diodes (OLEDs). Since the first report of MR-TADF materials based on B,N-heteroarenes in 2016, significant progress has been achieved in the development of new materials. However, a timely summary on this topic is still lacking. In this review, the design strategy and synthetic method of MR-TADF materials based on B,N-heteroarenes are summarized, and the recent advances in the development of new molecular skeletons, the backbone modification strategy to tune the properties, and a novel type of chiral MR-TADF materials are discussed. It is expected that the current review would further promote the development and application of MR-TADF materials in the future.

Coupling reagents mediate the formation of amide bonds and play a key role in solid phase peptide synthesis. The novel N,N-diisopropylcarbodiimide (DIC)/ethyl cyanoglyoxylate-2-oxime (Oxyma) condensation system has the advantages of low cost, operational safety, higher coupling efficiency and lower rate of racemization. The DIC/Oxyma condensation system has been widely used in manual and automated synthesis of peptides. However, the ideal reaction ratio in DIC/Oxyma condensation system at mild reaction temperature remains to be further investigated. GsMTx4 is a cysteine rich peptide toxin identified from the venom of Grammostola spatulata spider, which consists of 34 amino acid residues and three pairs of disulfide bonds. GsMTx4 is the only inhibitor specifically targeting piezo channel, which is a multifunctional mechanically sensitive cation channel and associated with a variety of hereditary diseases. Herein, the synthetic efficiencies of different reaction ratios of DIC and Oxyma at moderate reaction temperature were systematically evaluated. The efficiency and robustness of DIC/Oxyma condensation system were validated by the rapid manual synthesis of linear GsMTx4. The one-step oxidative folding strategy was applied for the construction of three pairs of disulfide bridges, affording the active GsMTx4. The circular dichroism and patch-clamp electrophysiology tests were conducted to evaluate the structure and activity of synthetic GsMTx4. In summary, a fast, robust and safe synthetic method based on DIC/Oxyma is established, which is particularly useful for the manual synthesis of peptides.

Chiral tertiary alcohol is widely present in a series of bioactive compounds, natural products and pharmaceuticals. Consequently, the development of efficient asymmetric catalytic methods for their syntheses is highly important. Kinetic resolution (KR) is an important strategy to access enantioenriched alcohols from racemic alcohols. However, due to the requirement to distinguish three none-hydrogen substituents at the α-position of tertiary alcohols, it is challenging to develop highly efficient kinetic resolution protocols for tertiary alcohols with broad substrate scope. Nevertheless, significant progress has been made in the field of nonenzymatic kinetic resolution of tertiary alcohols in recent years, and a number of novel asymmetric reactions and catalytic systems have been successfully applied in the KR of tertiary alcohols. The tremendous advances in the kinetic resolution of tertiary alcohols are comprehensively reviewed, the substrate scope, characteristics, mechanisms and limitations of these methods are summarized, and our perspective on this research field is also provided.

N-Heteroarenes are present in a wide variety of natural products, small-molecule drugs, organic materials, and ligands. Therefore, the methods for selective C—H functionalization of N-heteroarenes are highly sought-after for late-stage modification of pharmaceuticals. A useful tool for the synthesis of alkyl-substituted nitrogen-containing aromatic rings is the Minisci reaction, in which a protonated N-heteroarene is attacked by an alkyl radical under oxidative and acidic conditions. Classic Minisci reactions often require the use of excess oxidant, excess acid, and high temperature, which greatly limits the scope of the substrates. With the rapid development of photocatalysis in organic synthesis, in recent years, a variety of photocatalytic Minisci reactions have been reported, and successfully been applied to the synthesis of drugs. In this paper, the visible light mediated Minisci reactions in recent years are briefly reviewed.

Starting from commercially available simple olefins, alkene isomerization could realize the efficient construction of multi-substituted alkenes, which might be difficult to access with other synthetic methods, in an atom-economic manner via the stereoselective or positional-selective modulation of the carbon-carbon double bonds. The palladium catalyzed stereoselective (Z/E) and the positional selective isomerization reactions of alkenes are summarized. The mechanistic perspectives, and their synthetic applications in the synthesis of drug molecules and natural products are discussed in detail.

Copper-catalyzed Chan-Lam reaction represents an important and highly efficient method for the synthesis of organic molecules containing carbon-heteroatom (C—N, C—O, C—S) bonds, which has many advantages such as mild conditions, wide substrates range and high yields. Therefore, the Chan-Lam coupling reactions are extensively applied in organic synthesis, medicinal chemistry and material science, etc. Although many catalytic systems using different copper salt alone or in combination with various ligands for Chan-Lam coupling reaction have been extensively reported by different groups, the studies on the Chan-Lam coupling reaction employing well-defined copper complexes as catalysts were underdeveloped. In recent years, the Chan-Lam reactions catalyzed by copper complexes with different ligands have attracted more special attention from synthetic chemist and made many achievements. Some novel copper complexes have been designed and synthesized, which were further used as efficient catalysts for Chan-Lam coupling reactions of arylboronic acids with various nucleophiles. The recent progresses on Chan-Lam coupling reactions catalyzed by well-defined copper(II) complexes are summarized from two aspects of homogeneous catalysis and heterogeneous catalysis in detail. Then the homogeneous Chan-Lam reactions are classified by the different coordination mode of copper complexes, and the heterogeneous Chan-Lam reactions are described according to chronological order. The reaction mechanism on Chan-Lam coupling proposed by different research groups is also straightened out and discussed. Finally, the development prospects of this research field are pointed out.

Molecular nanocarbon materials with well-defined structures constructed through organic synthesis have attracted much attention in recent years, exhibiting unique properties and broad applications in many areas. The combination of helicenes and molcular nanocarbons generates a fancinating type of chiral molecular nanocarbons with potential applications in the fields of chiral optics, chiral optoelectronics and spintronics etc. However, it is of greart challenge to synthesize these molecules due to the large intramolecular strain and the special helical structure. Among various synthetic strategies, the Scholl reaction possesses the advantages of mild conditions and high efficiency. In this review, recent advances in the syntheses of helicene-based molecular nanocarbons via the Scholl reaction are summarized, and our perspectives to stimulate further development of the chiral nanocarbon materials are also provided.

Proteins are the most abundant biomolecules in nature and are involved almost in all living processes. Chemical modification of proteins is an efficient strategy to mediate and study the physical and chemical properties and biological functionalities of proteins. Most protein chemical modifications are based on the bioorthogonal reactivities of the side chain functional groups of certain amino acid residues. Among 20 proteinogenic amino acids, cysteine has become the best choice for chemical protein modification, owning to its relative low abundance in proteins, the unique nucleophilicity and low redox potential of its mercaptan group. The recent advances in chemical protein modification via cysteine are comprehensively reviewed and the challenges and applications for future development are discussed.

Berberine is an important natural drug and a kind of benzyl isoquinoline alkaloid, which has unique four-ring structure. In recent years, pharmacological research has found berberine is expected to be used in the clinical treatment of cancer, diabetes and other frequently occurring diseases. Based on the Woodward’s biosynthetic hypothesis, a schematic review on the synthetic studies towards berberine is provided.

In recent years, vinyl radical-mediated hydrogen atom transfer (HAT) has received increasing attention. This protocol provides an efficient pathway for radical cyclization and regioselective C(sp³)—H bond functionalization including vinylation, alkynylation, halogenation, arylation, etc. Generally, vinyl radicals are generated from single electron reduction of vinyl halides or the addition of extra radical to alkynes. The reaction pathways depend on substrates. For example, the resulting alkyl radical arising from vinyl radical-mediated HAT process is prone to be intramolecularly re-added to alkene, leading to cyclic products. When employing specific propargyl alcohols as substrates, the cyclic alkyl radical intermediate undergoes β-scission of C—C bond to realize vinyl migration. In addition, intermolecular radical trapping usually occurs by using internal alkynes. The transformation based on vinyl radical-mediated HAT features high regioselectivity, good atom-economy, and broad diversity of reaction modes. The recent advances in this research area are summarized.

Boron dipyrromethene (BODIPY) dyes are widely used in the fields of life sciences, chemical analysis and optoelectronic materials due to its excellent photophysical properties, favorable biocompatibility, facile synthesis and modification etc. The synthesis and derivative strategies of BODIPY provide the basis for its wide application and have attracted great attention from researchers. In this review, the modification strategies for different reaction positions of BODIPY have been discussed, and Pd-catalyzed cross-coupling reactions and oxidative coupling reactions about BODIPY are discussed individually. Finallly, the development of this field is prospected.

Carbene is one of the most important synthetic intermediates in organic synthesis. In the past few decades, transition-metal catalyzed carbene transfer reactions have made remarkable development. Recently, visible light-promoted transformation of diazo compounds through the formation of free carbene as key intermediate begun to rise. The reaction only need visible light as the sole energy source which meets the concept of green chemistry. Since the pioneering works developed by the groups of Diaves and Zhou, photo-promoted transformation of diazo compounds has attracted more and more attentions. On the basis of previous work, the latest progress in this field is further improved, which mainly focuses on the recent new transformation reactions of diazo compounds under visible light irradiation and the contributions reported from Chinese research group. The future development direction, as well as challenges in this field is prospected.

Medium-sized rings (8~11 membered ring) and macrocycles (12-membered rings and above) are extremely important parts of drug and natural products. Meanwhile, they are widely used in the field of medicinal chemistry, organic chemistry and other fields. Developing simple, green and efficient protocol to synthesize medium-sized rings and macrocycles has attracted great interests from chemists in the recent years. The latest ring expansion/cyclization reaction in the synthesis of medium-sized ring and macrocyclic compounds in the past five years is reviewed, and the prospect of their future and development is also outlined.

N-Hydroxyphthalimide (NHP) esters are easily available, stable, inexpensive, and highly photoactive compounds, which are derived from the corresponding carboxylic acids. In recent years, the application of NHP esters in photocatalytic decarboxylative reactions has captured huge attention. Herein, the vigorous development of photocatalytic alkylation reactions using alkyl NHP esters as alkylating reagents is summarized based on the classification of photocatalysts.

Minisci reaction, an important method for the construction of new carbon-carbon bonds, refers to one kind of the radical substitution reactions between a nucleophilic carbon radical and an electron-deficient nitrogen-containing aromatic heterocycle. Besides, organic electrosynthesis is experiencing a renaissance as a green synthesis technology and means. This review focuses on the recent advances in Minisci reactions under electrochemical conditions.

Aniline and its derivatives, as the basic aromatic amine compounds, are widely used in different fields such as chemistry, biology, medicine, dyes, polymer materials and agriculture. Moreover, hydrogenation reduction of nitrobenzene is a simple method for the synthesis of aniline. According to the difference of proton/electron donor, the reduction of nitrobenzene can be divided into Bechamp reduction, catalytic hydrogenation, catalytic hydrogen transfer and Zinin reduction. Zinin reduction is a method for preparing aniline by reducing nitro group by using sulfide as electron donor and protic solvent as hydrogen source, which is widely used in the laboratory research and industrial production. In this review, Zinin reduction method is systematically summarized. The principle of reduction of nitro group by sulfide is clarified from the types of sulfide reductants, the reduction mechanism of nitro group, and the application of nitro group reduction. Additionally, the reduction mechanism of nitro group by elemental sulfur, sulfide, polysulfide and hydrosulfide is detailly elucidated, and the regulatory mechanism of OH^- and H₂O in the reduction of nitro group by sulfide is explained in detail. Finally, the ability and application effect of different sulfides as reductants to reduce nitro group are analyzed in terms of atom economy.

Molnupiravir is an oral drug against SARS-CoV-2 infection approved by Britain and America in 2021. Currently, the reported synthetic methods of molnupiravir have disadvantages, such as long steps, limited yield and high cost. Efficient methods for the synthesis of molnupirovir through direct acylation of low-price cytidine are developed. In different proportions of aqueous tetrahydrofuran solution, selective isobutyrylation of hydroxyl of cytidine and further 2',3'-deprotection of 2',3',5'-tri-O-isobutyrylcytidine could be realized, which successfully gave 5'-O-isobutyrylcytidine. Finally, N⁴-hydroxylation of 5'-O-isobutyrylcytidine yielded molnupirovir. Using this straightforward and high-yielding three-step approach, molnupirovir was obtained from cytidine in 82% overall yield.

The cyano substitution reaction is an important method for introducing cyano functional groups in organic synthesis. In this paper, a series of cyano compounds were synthesized by nucleophilic substitution reaction using acetone cyanohydrin as cyanation reagent and aliphatic haloalkanes R—X (X=Cl, Br, I) as substrates. The results show that the cyanation product can be obtained by reacting the acetone cyanohydrin with the corresponding halogenated alkanes at 50 ℃, and the yield can reach 70%~99%. The reaction solvent is the mixture of tetrahydrofuran (THF) and 1,3-dime- thylimidazolinone (DMI) (volume ratio of 3:1), and the base is LiOH?H₂O. This reaction uses cheap and low toxicity acetone cyanohydrin instead of highly toxic sodium cyanide or other expensive cyanide reagents requiring harsh conditions and it also does not require precious metals as catalysts. The reaction conditions is mild so that it has extensive application and great value of practical application.

Nitrogen-containing organic compounds are ubiquitous in natural products, drug molecules and organic intermediates. Therefore, the introduction of nitrogenous functional groups into organic compounds is of great significance. Despite transition metal-catalyzed C—N coupling reaction provided an effcient strategy to access these ntrogen-containing compounds, extra steps are generally required to obtain the pre-functionalized starting materials. Recently, transition metal-catalyzed C—H amination has emerged as a more atom- and step-economical strategy to construct C—N bonds. Compared to the noble metals (e.g. palladium and rhodium), base metal catalysts, such as copper, cobalt and nickel, have attracted dramatic attentions, due to their earth abundance, cost effectiveness, and unique catalytic activities. Herein, the recent advances in copper-, cobalt- and nickel-catalyzed C—H amination reactions assisted by directing groups were summmarized according to the types of base metals, C—H bonds, and amination reagents with an emphasis on the discussion of various amination reagents and their application. Finally, the limitations and development trend of this research field are analyzed and prospected.

The absolute configuration (AC) assignment of chiral molecules is crucial to the research and application of chiral chemistry. In recent years, various methods for the AC determination for chiral compound fall mainly into three categories according to their principles. The first is the nuclear magnetic resonance (NMR)-based method for determining the AC of chiral compound by exciting the nucleus of the chiral compound in the chiral environment, including the NMR-based method using aromatic ring diamagnetic shielding effect and the NMR method using sugar shift effect. The second is X-ray diffraction (XRD) methods based on atomic resonance scattering, including single crystal and powder XRD. The third is based on the enantiomer refraction and absorption of polarized light, including optical rotation spectroscopy, electronic circular dichroism, vibration circular dichroism and vibration Raman spectroscopy. In addition, other methods such as enzyme-based and homobenzotetramisole (HBTM)-based methods are supplementary. Based on our research experiences in chiral fluorescent recognition and chiral drugs, the principles and application of these methods, aiming to afford beneficial references for chiral chemists and related workers are reviewed.

The reaction of naphthol and paraformaldehyde in acetic acid solution with ammonium acetate as a catalyst resulted in the synthesis of a series of hydroxynaphthalenes in yields of up to 86%. Several phenols were also transformed into the corresponding salicylaldehydes under the same reaction conditions in moderate yields of 42%~58%. A rational mechanism was also proposed based on the facts of experimental observations. This metal-free process has the advantages of mild reaction conditions, simple operation and low cost.

gem-Difluoroalkenes are important fluorine-containing compounds with structural superiority in organic synthetic chemistry and medicinal chemistry. For instance, the gem-difluoroethylene moiety could be converted to monofluoroalkenyl, difluoroalkyl, trifluoromethyl moiety, and many other fluorine-containing structures conveniently. The gem-difluoroethylene moiety is also an ideal carbonyl group bioisostere and has already been widely used in drug design. Herein, a nickel-promoted electrochemical reductive cross-coupling to access functionalized and substituted gem-difluoroalkenes is reported. This reaction enables the combination of allylic defluorination of trifluoromethyl alkenes and decarboxylation of redox-active esters or dehalogenation of alkyl halides under mild electrochemical reduction conditions and in an undivided cell, therefore obviates the use of stoichiometric amount metal powder or organic reductants. Furthermore, this reaction provides efficient access to biologically interesting molecules containing gem-difluoroethylene moiety.

Following the renaissances of organic electrochemistry and photochemistry, photoelectrochemical approach was arising as one of hot research areas by combination advantages of photocatalysis and electrocatalysis. The photoeletrocatalysis was widely applied in redox reactions, coupling reactions and beyond. The development of photoelectrochemical transformations during past five years is summarized and the related reactions are classified according to mechanism and catalyst. The current progresses and future outlooks of such method are also discussed.

α-Chiral primary amine subunits are widespread structural units in a large number of pharmaceutical molecules and are key intermediates toward the preparation of numerous amine-containing drugs. Versatile functionalizations on the NH₂ group also supply a quick way to construct molecular complexity. Additionally, chiral primary amines can serve as ligands or organocatalysts which can be applied in organic synthesis. Therefore, efficient synthetic routes toward chiral primary amines have attracted tremendous attention. Asymmetric chemo-catalytic reactions that are capable of directly preparing chiral primary amines remain scarce. Transition-metal-catalyzed asymmetric reductive amination (ARA), a reaction type that transforms easily available ketones and amines into chiral amines in the presence of a chiral metal-catalyst and reductant, is among the most straightforward methods to access chiral amines. However, studies on ARA are still limited compared to that on imine hydrogenation, probably due to the presence of competitive ketone reduction as the side reaction. ARA using ammonium salts as the amine sources can directly yield chiral primary amines from prochiral ketones and are thus highly attractive and of great significance. In addition to competition with ketone reduction process, this reaction also faces some other challenges, including: (1) NH₃ or the produced primary amines can coordinate to the metal center which results in catalyst poisoning effect; (2) the coordination of amine ligand to the metal center may lead to ligand exchange that enhances the challenge on asymmetric control; (3) the produced primary amines may undergo further alkylation process via double reductive amination, thus providing more complicated outcome. The existing problems and challenges in ARA require urgent development of applicable catalytic systems. Aiming to solve some challenges in the field of ARA with ammonium salts, we have carried out systematic studies and will present the latest progress achieved from our team in this account.

2-Aminopyridine is a significant synthetic synthon, with unique dual nucleophilic structure. It can react with ketones, aldehydes, acids, multifunctional esters, halogenated aromatics and other compounds to synthesize five- and six-member azaheterocycles. In recent years, the cyclization reactions based on 2-aminopyridines have been under the spotlight. According to the different types of substrates, the research progress on the synthesis of imidazo[1,2-a]pyridines and pyrido[1,2-a]pyri- midines based on 2-aminopyridines in the past 5 years is reviewed, and its applications in organic synthesis methodology, drug synthesis and fluorescent probes are summarized. Furthermore, the development trend of green cyclization and its application based on 2-aminopyridines in the future are prospected.

C—N bonds are widely existed in drugs, natural products, and functional materials. Thus, the construction of C—N bonds is one of the most important research areas in academia and industry. Recently, the renaissance in organic electrochemistry has promoted the electrochemical C—N bond formations to be a special branch of organic synthesis. The most recent advances in the electrochemical C—N bond formations since 2015 are summarized. The reaction mechanisms of these transformations are discussed, and the challenges and future directions of this important filed are included. We hope that this review can give references to the researchers, graduate students and other related people.

Ynamides are a class of special ynamines bearing an electron-withdrawing group on the nitrogen atom. The electron-withdrawing group endows ynamides an optimal balance between the stability and activity, and thus enabling ynamides to be versatile synthons widely used in organic synthetic chemistry. The ynamide chemistry has witnessed a rapid development over the past two decades. As a consequence, its synthetic methods have attracted widespread attention. In this context, the recent advances in the synthesis of ynamides are reviewed herein. According to the structure of the main starting materials, the contents are classified as the synthesis with haloenamides, alkynes or its derivatives, and dihalo-substituted alkenes. The representative mechanisms are also discussed.

Transition metal-catalyzed cross-coupling reactions for building carbon-carbon bonds have received extensive attention due to their high efficiency and selectivity. In recent years, electrophiles which containing C(sp³)—O bonds have been used to replace organic halides in cross-coupling reactions for the construction of C(sp³)—C bonds, due to their advantages of commercial availability or facile synthesis, high reaction selectivity, and environmental friendliness. Among those reported highly efficient catalysts, nickel catalysts have been gradually applied to such reactions and achieved remarkable advances due to their earth-abundant, cheap, unique catalytic activities and selectivity. Because of the small radius of the nickel atom, C(sp³)—Ni can inhibit and/or manipulate β-H elimination reactions, which reduces the formation of by-products. Nickel has several variable valence states and can flexibly participate in redox-neutral coupling reactions and reductive cross-coupling reactions. The latest research progress in nickel-catalyzed coupling reactions employing alcohol derivatives as electrophiles is reviewed. It is separated into four sections including nickel-catalyzed cross-coupling reactions involving methanol or primary alcohol derivatives, nickel-catalyzed cross-coupling reactions involving secondary alcohol derivatives, nickel-catalyzed cross-coupling reactions involving acetal and N,O-acetal derivatives, and nickel-catalyzed cross-coupling reactions involving tertiary alcohol derivatives.

Over the past few decades, transition metal-catalyzed reactions have been developed into a powerful tool for building various chemical bonds. At the same time, non-metal-promoted chemical bond construction reactions have attracted more and more attention of synthetic chemists because of the avoiding of using expensive metal catalysts and ligands, resulting in the reduce of reaction costs and environmental pollution. It conforms to the concept of green chemistry development. Among them, potassium tert-butoxide-promoted cyclization and coupling reactions have been rapidly developed. The intramolecular cyclization and intermolecular coupling reactions involving potassium tert-butoxide since 2000 are summarized, and the possible reaction mechanisms are elucidated, which can help chemists better understand the development of this field and promote the development of this field.

The seven-membered rings represent an important structural motif and have found wide presence in natural products, biologically active molecules and drugs. In contrast to the five- and six-membered rings, the construction of seven- membered ring remains challenging. Thus, the developing efficient strategies for the synthesis of seven-membered rings is very desirable. N-Heterocyclic carbene (NHC) organocatalysis has been recognized as a powerful and unique tool for the quick construction of complex molecular architectures. Nevertheless, whereas significant advances have been made using NHC as catalysis. However, most of these works concentrated on the assembly of five or six-membered rings. This review highlights the developments and new advances for the construction of seven-membered rings catalyzed by NHC. The aim of this review is to provide an overview of this area and inspire synthetic chemists to develop more efficient and novel strategies for the construction of seven-membered rings.

Diazo compounds have rich reactivity and are important synthetic intermediates in organic synthesis. Diazo compounds are commonly used as the precursors of transition metal carbenes, and the relative transition metal catalyzed reactions have achieved many important progresses in the past decades. In sharp contrast, radical reactions with diazo compounds as a key component are still less explored. Owing to the easy generation of diverse radical intermediates under mild conditions, visible-light photoredox catalysis has emerged as a powerful tool for organic synthesis. By the combination of visible light photoredox catalysis and diazo compounds, some novel reactions that different from the classical carbene processes have been developed, which further extend the synthetic applications of these reagents. The progresses of radical reactions of diazo compounds enabled by visible light photoredox catalysis in the past five years are summarized, including: (1) diazo compounds as the nucluophiles, (2) diazo compounds as the equivalents of carbyne precursors, (3) diazo compounds as the radical acceptors, and (4) diazo compounds as the radical precursors. We wish that the detailed discussion on the mechanism of the reactions would help the audiences to understand the features of radical reactions of diazo compounds and the realative visible light chemistry.

Carbon dioxide (CO₂) is the main greenhouse gas, the excessive burning of fossil fuels leads to the increasing of CO₂ concentration, resulting in global warming. On the other hand, CO₂ is regarded as an ideal C₁ source due to its nontoxicity, abundance and availability. Hence, the transformation of CO₂ into fine chemicals and hydrocarbon fuels in organic synthesis is becoming one of hot research fields. Among them, the transition-metal catalyzed CO₂ hydrogenation is an appealing and promising approach for CO₂ utilization with wide potential applications, thus leading to selective fromation of 2e, 4e, and 6e reductive products including formic acid, formamide, formate, formaldehyde, methanol and C₂₊ alcohols under mild reaction conditions. In this review, the recent advances on transition metal complexe-catalyzed CO₂ hydrogenation are in detail summarized on the basis of the molecular structures, activities of the homogeneous catalysts, and product selectivity controlling. This review also gives an overview on the in situ catalytic hydrogenation corresponding to the recently developed CCU (CO₂ capture and utilization) strategy. Furthermore, the challenges and perspectives in homogeneous catalytic hydrogenation field are also given in this article.