Indole-based chiral heterocycles constitute a class of important heterocyclic compounds that are found in numerous natural products, pharmaceuticals, pesticide, and functional materials. The efficient and highly enantioselective synthesis of chiral indole derivatives has become one of the most important issues in organic chemistry. Due to the simple reactivity of the traditional indoles, their involved catalytic asymmetric reactions are very limited, resulting in the limited types of constructed indole-based frameworks. To solve these challenging issues, chemists devised a strategy of introducing simple functional groups to the indole ring, so as to obtain a series of functionalized indole derivatives, namely indole-based platform molecules, as efficient building blocks for constructing chiral indole-related frameworks. Among them, 2-indolylmethanols are a class of important platform molecules, which were designed on the consideration that the introduction of a hydroxymethyl group to C2-position of the indole ring would change the reactivity and the reactive site of the indole ring. This class of platform molecules can act as either electrophiles or nucleophiles, and can act as multi-carbon building blocks in catalytic asymmetric reactions. Therefore, the design and development of 2-indolylmethanols as platform molecules have provided a new strategy for the efficient and highly enantioselective synthesis of chiral indole derivatives. The advances in catalytic asymmetric reactions using 2-indolylmethanols as platform molecules are summarized, which will open a new window for designing and application of new types of indole-based platform molecules.

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.

Fluoro-containing heterocyclics play an important role in many fields, such as organic chemistry, pharmaceutical chemistry and material science due to their excellent physical and chemical properties. However, there are few natural fluoro-containing heterocyclics in nature, so it is particularly important to develop efficient synthesis methods of fluoro- containing heterocyclics. With the rapid development of transition metal catalyzed, photocatalyzed and electrocatalyzed radical reactions, radical chemistry has made a breakthrough in the field of synthesis and stimulated the interest of organic chemists in constructing fluoro-containing heterocyclics by using radical chemistry. In this paper, monofluoroalkylation, difluoroalkylation, trifluoromethylation, trifluoroalkoxy/sulfur/selenylation, perfluoroalkylation of unsaturated hydrocarbons and direct C—H fluoroalkylation of heterocycles are classified, and the construction of fluorine-containing side chain heterocycles mediated by free radicals is discussed from the aspects of transition metal catalysis, photocatalysis and electrocatalysis.

The importance of azaarene derivatives in many arenas, especially pharmaceutical and material industry, has attracted increasing attention of chemists to develop highly efficient synthetic methods. To date, functionalization of commercially available azaarenes and their simple derivatives as feedstocks by exploiting the electronic properties of azaarenes to trigger transformations has been appreciated as a powerful tool. Among them, due to the advantages of mild reaction conditions, good functional group tolerance and diverse reaction types, the methods via visible light-driven photocatalysis have been extensively explored. Notably, a number of asymmetric manifolds towards the synthesis of enantioenriched imine-containing azaarene derivatives have been established with satisfactory results. The advances of this important area are summarized and discussed according to the relative positions of the formed stereocenters to azaarenes.

Diazo compounds are important synthons which have attracted condirable attentions by synthetic chemists. They can server as carbene precursors, 1,3-dipoles, C-nucleophiles, terminal N-electrophiles and radical intermediates. In recent years, the photocatalytic generation of radicals from diazo compounds has made remarkable development. In this review, the recent developments in this research field are summarized which mainly focus on the generation of diazomethyl radical, carbon radicals, carbyne radicals and allene radicals from diazo compounds. Moreover, the future development direction, as well as challenges in this field is prospected.

Ortho-quinone methides (o-QMs) belong to a class of highly reactive organic intermediates, which play an important role in catalytic asymmetric formations of carbon-carbon bond and carbon-heteroatom bond. However, o-QMs are highly unstable, which led to the underdevelopment of catalytic asymmetric reactions involving o-QMs. The utilization of some precursors for in situ generating o-QMs is a solution to address this challenging issue. Therefore, the development of catalytic asymmetric reactions involving in situ generated o-QMs has absorbed great attention from the chemists. The key to develop such reactions is to exploit easily available and stable precursors of o-QMs. Ortho-hydroxybenzyl alcohols are a kind of o-QM precursors with unique advantages. Hence, the catalytic asymmetric [4+n] cycloadditions, tandem cyclizations and nucleophilic additions of o-hydroxybenzyl alcohols have developed very rapidly in recent years, which have become efficient strategies for the synthesis of chiral oxygen-containing heterocycles and arylmethane derivatives. The catalytic asymmetric reactions involving o-hydroxybenzyl alcohols are summarized, which will open a new window for the design of new type of o-hydroxybenzyl alcohols and their involved catalytic asymmetric reactions.

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.

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.

Alkenes are cheap and easily available bulk industrial feedstocks. Difunctionalization of alkenes can rapidly construct complex molecules, which have broad applications in organic synthesis. Compared with traditional redox-neutral alkene difunctionalization, the reductive difunctionalization of alkenes can introduce two different electrophiles to both sides of the carbon-carbon double bond, which has the advantages of mild reaction conditions, high functional group tolerance, and no need for pre-prepared organometallic reagents. The latest research progress in nickel-catalyzed reductive difunctionalization of alkenes is summarized. The development prospect of the reaction is prospected.

Chiral heterocyclic compounds are an important class of chiral substances, which are widespread in many chiral drugs, pesticides and catalysts. Therefore, the efficient asymmetric synthesis of these compounds becomes a research hotspot in organic synthesis. Transition metal-catalyzed asymmetric cyclization with heteroatom-dipole precursors is an important method to construct these frameworks. Among them, the heteroatom-dipole precursors designed based on transition metal-catalyzed allyl or propargyl substitutions have been extensively studied in the past two decades and occupied an important role in this field. The transition metal-catalyzed asymmetric cyclizations with allyl or propargyl heteroatom-dipole precursors are introduced in detail. The advantages and existing problems of the current methods are analyzed, which would provide useful reference for the researchers in asymmetric synthesis and related fields.

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.

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.

Sulfonium salts are one of the most important class of organosulfur (IV) compounds which have a positive charge on the sulfur center with three C—S bonds. Because of their bench-stable, easy synthesis, broad structural diversity, and rich reactivity, sulfonium salts are playing a significant role in synthetic chemistry. In recent years, visible-light promoted photoredox catalysis is rapidly developing into a powerful tool for organic synthesis. In this paper, the recent advances of different sulfonium salts in the radical type reactions induced by visible light are summarized. The formation reactions of C—C bond and C—X (X=B, N, O, S, Se, Te, F, Cl, I) bonds are introduced, and the applicable scope and mechanism of some reactions are also discussed.

In recent years, visible-light photocatalytic asymmetric synthesis has shown considerable potential in the mild and rapid construction of optically active organic molecules with structural diversity. Chiral Lewis acids (CLA), including chiral borane compounds, lanthanum complexes, first-row transition metal complexes, and chiral-at-iridium or rhodium complexes, have been established as one class of the most effective catalysts being capable of controlling the stereochemistry in photo-induced chemical transformations. The recent advances in this emerging field were presented by classifying the reactions into bifunctional CLA photocatalytic reactions and reactions enabled by dual catalysis with a CLA catalyst and an external photosensitizer, expecting that these studies will stimulate progress in organic synthesis, photocatalysis and asymmetric catalysis.

Organoboron compounds are important and versatile synthetic building blocks in synthetic chemistry. Owing to the unique characteristics, they manifest great value in organic synthesis. In view of the versatile transformations, migration reactions of organoboron compounds have attracted great attention from chemists in recent years due to their high efficiency and mild reaction conditions, which are widely utilized for rapid constructions of carbon-carbon and carbon-heteroatom bonds. Recent progress on 1,2-migration reactions based on tetracoordinate boron intermediates is summarized according to various reaction conditions and bond formations.

2H-Indazole is a privileged scaffold widely existing in drugs and bioactive molecules. The C—H functionalization of 2H-indazole is the cutting edge in medicinal chemistry and organic chemistry. Compared with traditional synthetic methods, the visible light/electrochemical-promoted synthetic method has mild conditions and is an environmentally friendly synthetic strategy. The C—H functionalization of 2-aryl-2H-indazoles at the C-3 position catalyzed by photochemical/electrochemical strategies in recent years is summarized in terms of catalytic systems, with special emphasis on the corresponding reaction mechanism, which might inspire the further development of new catalytic methods.

Near-ultraviolet and visible light-induced organic synthesis without photosensitizer has attracted much attention for the organic chemists. Since no photosensitizer is needed in the reaction, it makes the reaction system more simple and feasible, and indicates the future development direction for visible-light-induced organic transformations. Visible-light-promoted organic synthesis without photosensitizer is reviewed in this paper. It covers organic photosyntheses in which the substrate/product as a light-absorbing substance, the electron donor acceptor (EDA) complex as a light-absorbing substance, and the homolysis of weak covalent chemical bonds under the visible-light irradiation conditions. Moreover, other organic photosynthetic reactions without external photocatalyst are also discussed.

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.

A novel method for the synthesis of pyrazine and ketone derivatives was developed by using asymmetric ligand-based catalyst TNP-Cu@rGO. The screening of reaction bases, solvents, reaction temperatures and time was conducted to determine optimal reaction conditions. The reaction scope and generality of this methodology for the synthesis of pyrazines were tested and the results showed that this catalytic system had good functional tolerance. More than twenty substrates experiments were successfully set up, and pyrazines with moderate to high yields were isolated. Additionally, this catalytic system could also be used to the systhesis of ketones in good yields. Furthermore, the mechanism investigations were conducted for the synthesis of pyrazine derivatives to better understand the synthesis of pyrazines. The recycling test of TNP-Cu@rGO for the synthesis of pyrazines was investigated and the experiments showed that the catalyst could still maintain high catalytic activity for five times.

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.

The N—N bond is widely found in natural products and bioactive compounds. The atropisomerism of N—N bond, however, has been dismissed for a long time due to the stereotype that N—N axis is unstable. The electronic barrier stemming from the repulsive interaction between the lone pairs on the two nitrogen atoms leads to a rotationally hindered axis, resulting in stable N—N atropisomers. Since the first report in 2021, the catalytic asymmetric synthesis of N—N atropisomers has been developed rapidly into an emerging area. These reactions include asymmetric N—H bond functionalization, asymmetric desymmetrization and atroposelective de novo construction of (hetero-)aromatic rings. The N—N axially chiral compounds are valuable molecules, in terms of their potential application in chiral ligand/catalysts design and biological activity evaluation. Herein, the state-of-the-art catalytic asymmetric synthesis of N—N atropisomers is summarized.

Alkenes and their functionalized derivatives represent a versatile class of building blocks in organic synthesis. The traditional synthetic methods include Wittig olefination, Peterson olefination, Horner-Wadsworth-Emmons reaction and others, and many of these classic reactions have also become textbook knowledge. Most of these methods are based on ionic pathways and some still require pre-functionalization at the sites where C—C double bonds are formed, resulting some limitations on substrate scope or functional group tolerance. Over the past few years, photoredox catalysis has become a powerful platform for new reaction design owing to its green chemistry characteristics and unique activation modes. The recently developed and representative methods for the synthesis of alkenes under photochemical conditions are summarized. Moreover, the prospects of further developments are also discussed.

The difunctionalization of unsaturated hydrocarbons (alkenes or alkynes) is an important strategy to introduce functional groups, and is also an important method to synthesize polysubstituted hydrocarbons, which is widely used in the fields of total synthesis of natural products and drug synthesis. The latest research progress on the electrochemically enabled difunctionalization of alkenes or alkynes in recent five years is summarized. According to the classification of difunctionalization of alkenes and cyclization of unsaturated hydrocarbon, the application and the related reaction mechanism are introduced. It is hoped that this review can be referred to the future application in organic synthesis of electrochemic- mediated difunctionalization of alkenes/alkynes.

A practical method for the synthesis of various thiocyanated 5-membered aromatic heterocycles through electrochemical cross-coupling of heterocycles (pyrazoles, pyrroles, furans and thiophenes) with NH₄SCN under chemical oxidant- and exogenous electrolyte-free conditions was developed. NH₄SCN played dual roles of a supporting electrolyte and a thiocyanated reagent, and thus simplify the reaction system.

Transition metal catalyzed asymmetric hydroboration of alkenes is one of the most powerful methods to prepare chiral organoboronates, which has attracted extensive attention of chemists due to its simple raw materials, high atomic economy, diverse structure of borated products, etc. The transition metal catalyzed enantioselective hydroboration of internal alkenes including strained internal alkene, β-substituted styrenes and internal alkenes bearing a coordinating group is summarized.

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.