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.

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.

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.

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.

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.

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 critical step for the synthesis of disulfide-containing peptides is the efficient construction of one or multiple disulfide bridges. Generally, the folding of disulfide bonds could be achieved by three chemical strategies,i.e. one-step oxidative folding strategy, multi-step oxidative folding strategy, and one-pot oxidative folding strategy. Because few comparative studies have been conducted on efficiencies of three strategies, the systematical research is desirable. Three folding strategies were separately applied for the preparation of centipede toxin RhTx. The results showed that the isolated yield of two-step oxidative folding strategy was higher than those of one-step and one-pot oxidative folding strategies. Besides, the one-pot oxidative folding strategy may induce severe misfoldings. The circular dichroism (CD) and activity tests indicated that disulfide bonds are critical for the structure and activity of RhTx. In addition, the efficient preparation of RhTx on tens of milligrams scale was achieved, affording molecular tools for the further biological and biophysical studies of RhTx targeting TRPV1. Overall, three mainstream oxidative folding strategies were systematically studied, which provided a valuable reference for the synthesis of disulfide-containing peptides.

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.

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.

(Hetero)Aryl boronic acids and their derivatives have been widely used in synthetic chemistry, material sciences, and drug discovery. Accordingly, the development of novel synthetic methods towards these structures has received a great deal of attention. In particular, Ir-catalyzed C—H borylation represents one of the most efficient methods. Due to the restriction of the reaction mechanism, regioselective controllable C—H borylation of Ir catalysis is a formidable challenge, and it is also an important development direction in this area. In this review, the recent progress in Ir-catalyzed remote selective C—H borylation of arenes is systematically discussed.

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.

Transition metal-catalyzed C—P bond activation provides an ecomomical and high-efficient route for the synthesis of organic phosphine compounds, and has received increasing attention in recent years. Owing to high bond energy of C—P bond and strong coordinative ability of P atom, the activation of C—P bond has been a fomidable challenge. Relying on substrate-preactivation and various catalysts, great progress has been achieved. This review will give a summary of this field, and according to different mechanisms of C—P bond activation and strategies of substrate pre-activation, a detailed description on reaction type, development, characteristics and mechanism will be made.

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.

An iron-catalyzed decarboxylative Heck-type alkylation of conjugate 1,3-dienes with alkyl diacyl peroxides andt-butyl peresters is reported. This method offers an efficient approach to alkylation of 1,3-dienes with good yields, and in some cases with high selectivities. Late-stage alkylation of bioactive compounds was also found to be effective.

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.

Metal-free electrochemical oxidation cyanation and phosphonylation reactions had been developed, in which 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) reduced the electrode potential of substrate and avoided over oxidation of some electron rich aromatic amines under electrochemical conditions. This protocol had good functional group compatibility, which made it to be a practical and efficient method to synthesize α-aminonitriles and α-amino phosphonates under mild conditions. Preliminary study indicated that the formation of the product was through the Shono oxidation of imine species.

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.

Diaryliodonium salts have been widely applied in organic transformations. According to the reaction type, the use of diaryliodonium salts in visible light induced arylation reactions is summarized from the following three parts: C—C bond formation, C—S bond formation and C—P bond formation.

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.

Dendrobine is an important sesquiterpenoid alkaloid bearing the picrotoxane carbon skeleton isolated from the traditional Chinese medicine “Chin-Shih-Hu”. Because of structural characteristics of fused polycyclic and seven contiguous stereocenters, and exhibiting analgesic, antipyretic activities, dendrobine has attracted a great deal of attentions from both synthetic organic chemists and medicinal chemists. Over the past 50 years, there has been a number of research reports on the pharmacological activities and chemical synthesis of dendrobine. This review summarizes the biosynthetic hypothesis and synthetic advances on dendrobine.

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.

Sulfoxide compounds bearing unique sulfinyl group have attracted extensive attentions due to their important application in asymmetric organic synthesis and medicinal chemistry. The utility of chiral sulfoxides as versatile auxiliaries, ligands, and catalysts and synthons has been well demonstrated. Furthermore, the sulfinyl moiety can act as a pharmaceutical core, a bioisosteric replacement of the carbonyl moiety or a modifier in drug design and drug development. In this review, their biological activities with esomeprazole, ajoene, sulforaphane, sulforaphene, cenicriviroc, arbidol sulfoxide, armodafinil and so on are exemplified. And their mechanisms of action are illustrated briefly. Since the sulfur chirality is different from carbon stereogenic center, much effort has been devoted to the preparation of chiral sulfoxides. Herein the advances in asymmetric synthesis of sulfoxide during the past decade are presented. The direct asymmetric oxidation of prochiral sulfides with cheap iron-complex catalyst, polyoxometalates, organocatalyst, biocatalyst and electrocatalyst is discussed. Moreover, the complementary strategy based on sulfenate anions and miscellaneous strategies emerged recently are described. Additionally, our recent research works in the construction of chiral sulfoxide are also mentioned.

In base-free specificN-alkylation of hydroxylN-heterocycles with organohalides producing pyridone-type products,N,N-dimethylformamide (DMF) was found to be the best solvent for having the most prominent solvent effect among the usual solvents. This not only led to milder reaction conditions and higher yields of the products, but also could broaden the substrate scope of the reaction. Mechanistic studies and the literature revealed that, in addition to the usual solvent effect, DMF can decompose to produce dimethylamine during the reaction, which then works as a base to promote the reaction.

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.

Transition-metal catalyzed C(sp²)—C(sp³) cross-coupling is of great significance in organic chemistry for synthesizing complex natural products and pharmaceutical molecules. Recently, reductive Heck reactions have emerged as one of the simple and efficient strategies for the construction of C(sp²)—C(sp³) bond. The recent advances in the reductive Heck reactions of alkenes are summarized on the basis of different hydride sources. The related mechanisms are provided, and the future development of this field is also prospected.

Due to the pivotal role of tailor-made amino acids in modern medicinal chemistry research and drug design, the interest in the development of synthetic methodology for preparation of these compounds is at an all-time high. Currently, electrochemical approaches for synthesis of amino acids are being actively pursued to take the advantage of sustainability and green chemistry facets offered by the electrochemistry. This work presents the first specially focused, comprehensive treatment of the literature data related to synthesis of amino acids via electrochemical means. Aspects of practicality, benefits and current shortcoming of this approach are critically discussed.

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.

Efficient C—C bond conversion might bring innovation to clean energy and circular economy. In the past several decades, developments of relatively chemical active carbon-carbon multibond conversion have been made. However, the research progress on effective functionalization of inert C(sp³)—C(sp³) bond is heavy going. The advances in this area from a free-radical chemistry point of view are summarized, which can help researchers who are interested in this topic to understand it quickly. The progesses as well as the corresponding mechanisms for free-radical promoted selective cleavage of saturated C—C bonds in alcohols and ethers, amines, aryl alkanes and simple alkanes are demonstrated. In each part, the explorations are depicted according to the initiating manners such as thermochemistry, photochemistry and electrochemistry.

Low-cost and high-performance materials have become more and more important in past decades. It exhibits the technology level of a country. Chemists used to find the candidate material according to property regression and quantitative structure activity relationship (QSAR). Traditional methods focus on finding new molecule from prior knowledge with trial and error experiments. They are time-consuming and low efficiency on screening molecules. The appearance of machine learning (ML) changes this embarrassing situation in two ways. One is accelerating the property prediction process to prevent wasting time on worse candidates. The other is inverse molecule design which expands the imagination of human. Lots of researches show promising results using different inverse design method such as, variational auto-encoder (VAE), generative adversarial networks (GAN), reinforcement learning (RL), and recurrent neural network (RNN). They introduce uncertainty from different level to generate new structure candidates. In any method, molecule descriptor has a great impact on the result. The descriptor converts the 3D structures in real world to a vector or a notation string to feed into all kinds of ML models. Large number of descriptors have been developed in cheminformatic, bioinformatic, quantum chemistry and natural language process (NLP). Some classical descriptors are Coulomb matrix (CM), smooth overlap of atomic positions (SOAP), weighted graph (WG), simplified molecular input line entry specification (SMILES). They show different advantages and solving problems from different aspects. CM has clear definition and good result on energy regression. SOAP is good at reflecting local environment features of an atom. However, they are easy to encode but hard to decode. That is a reason why people prefer WG and SMILES in the structure inverse design tasks. WG and SMILES express structure as a graph (an atom as a node and a bond as an edge) or string to apply massive mature GNN or NLP algorithm on them. Nowadays, most of the ML applications on chemistry and molecule science are focus on developing new model to regress properties. However, it is thought that there is still large improving space on inverse design methods and traditional descriptors. In this paper, WG and SMILES are briefly introduced firstly. Then, four generative models are presented, including VAE, GAN, RL and RNN. Further, the current progress and challenges of inverse design methods are summarized case by case. Finally, some of the author՚s understanding and explorations are given out. It is proved that SMILES with BASE64 preprocessed shows some advantages on molecular reconstruction and worth to study deeply in future.

Unique reaction modes, diverse reaction sites, and structural diversity of both substrates and products have made N-heterocyclic carbene catalysis be of great of importance in the field of organic catalysis. However, there have been a lot of barriers and challenges in terms of the reactivity of substrates and the selectivity of reactions for traditional and single catalytic systems with the deep development of organic synthesis. Recently, synergistic catalysis makes it possible for previously inaccessible transformations and can adjust the reactivity and selectivity more accurately by merging two single catalytic systems, thus has emerged as a powerful catalytic strategy in organic synthesis. In this review, the latest research progress in the field of synergistic catalysis of N-heterocyclic carbenes and transition metals in the last decade is mainly reviewed.

Dihydrobenzofuran structure units widely exist in a variety of natural products, such as alkaloids and terpenes. The total synthesis of natural products containing dihydrobenzofuran skeleton has thus emerged in recent years, because of their good biological activities and medicinal value. The application progress of oxidative [3+2] cycloaddition in the construction of dihydrobenzofuran ring skeleton and the total synthesis of various natural products in recent ten years was reviewed.

Organophosphorus reagents play very important role in organic synthesis. The development of Wittig reaction, Staudinger reaction, Appel reaction and Mitsunobu reaction mediated by phosphine compounds is of great significance in scientific research and industrial production. In recent decades, the research on the design of P(III)/P(V) redox catalysis and catalysts to realize the catalytic mode of these reactions, and avoiding the production of stoichiometric R₃P=O has developed rapidly. This review introduces the research progress of the catalytic process of each reaction in turn. The future research direction in this field about the reactions involving stoichiometric R₃P=O is prospected.

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.

Radical chemistry has gained its renaissence in the past decade and trendendous progresses have been witnessed in synthetic and material chemistry. However, mechanism studies are largely lagging behind comparing with rapid paces in the development of synthetic methodologies. On the other hand, the study of radical species remains a central theme in physial organic chemistry, and a large amount of thermodynamic and kinetic data on radicals have been generated over a century's reserch. Unfortuately, there has been no systematic compilation and curation of these quatitative data that are dispersedly distributed and buried in literature. As a result, most synthetic chemists are not acquainted with these valuable data. In this review, we aim in compiling and curating thermodynamic and kinetic parameters of radicals, that may hopefully provide a quantitative data basis for rational development and evolution of radical chemistry. The key parameters include radical stability energy (RSE), radical lifetime (τ), substituent constant (σ) and electrophilic index (ω). Fundamental concepts such as radical stability, Class S/O radical substitution effect, persistent/transient radical effect will be discussed on the basis of data.

Indole skeleton has been widely utilized in the synthesis and late-stage modification of biologically active compounds, especially in the fields of medicines and pesticides. In recent years, constructing spiro compounds by asymmetric dearomatization of indoles has become extremely promising. Meanwhile, the radical tandem reaction of unsaturated bonds has been a significant branch of organic chemistry, and this methodology has become a crucial approach to modify the indole skeleton. Therefore, the recent progress in the field of radical cascade reaction of unsaturated hydrocarbon using nitrogen heterocycle in indoles as radical acceptors is summarized. Besides, the reaction design, mechanism and prospects of this field are also discussed.

The photoredox reactions involving electron donor-acceptor (EDA) complexes have attracted significant attentions in the last decade. Very recently, the sodium iodide-triphenylphosphine-N-acyloxyphthalimide EDA complex has been discovered and employed in developing several net redox-neutral photoreactions. Herein, the EDA complex has been applied in a net reductive setup for the first time to establish a photoredox alkylation of aldimines without photosensitizer. The reaction affords not only high yields for secondary, tertiary andα-heterosubstituted alkyl radicals, but also high yields for primary alkyl radicals, and moderate to high yields for electron-rich or secondary benzylic radicals, two difficult groups of radicals in previous studies. This work provides an efficient and reliable approach for the synthesis of unnatural amino acids and amines.