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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

As a carboxylic acid, α-keto acid can be used as an acylating reagent by decarboxylation in organic synthesis. However, traditional methods often need transition metal catalysts or high temperatures, which limits the application of α-keto acid to a certain extent. In recent years, organic transformations induced by visible light have attracted extensive attention due to its mild conditions and simple operations. Herein, the recent advances of metal-free photocatalytic application of α-keto acids are summarized, which mainly include acylation reactions and cyclization reactions.

The photo-transition metal synergistically catalyzed coupling reaction provides a new research strategy for the development of metal-catalyzed coupling reactions. In this catalytic system, the excited state photosensitizer controls the valence state of the transition metal intermediate through a single electron transfer process, there by regulating the coupling reaction process, especially for the process that is difficult to occur in traditional transition metal catalysis. In addition, the excited photosensitizers could also promote the coupling reaction through the energy transfer process. Simultaneously, the light-promoted transition metal-catalyzed C—X bond coupling reactions without external photosensitizers have also been rapidly developed. Light and transition metals synergistically catalyzed coupling reactions provide an important tool for the construction of C-heteroatom bonds, showcasing broad application prospects in synthetic chemistry.

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.

Since C—H bond is the basic unit of organic compounds, it’s considered to be a concise synthesis method to implement direct functionalization of C—H bond. As carboxylic acids are widely found in nature, carboxyl group can act as both directing group and leaving group to drive transition metal-catalyzed controllable transformation of ortho-C—H bond functionalization of carboxylic acid that not only avoids the extra introduction and removal of the directing group in the process of C—H bond activation, but also highlights the simplicity of C—H bond activation and green of decarboxylation with “one stone and two birds” strategy of the carboxyl group. Therefore, basing on the strategy of “two birds with one stone”, ortho-C—H bond functionalization of carboxylic acid using carboxyl as a traceless directing group can provide a new strategy and method for controllable and directional synthesis, which has considerable significance in synthetic chemistry. According to the types of coupling partners involved in the transformations, transition metal-catalyzed ortho-C—H bond activations of carboxylic acids with multiple-bond-containing reagents, arylating compounds and heteroatom-containing chemicals are reviewed respectively based on the strategy of “two birds with one stone”, and the relevant reaction mechanisms are discussed.

Sulfoximines represent an important structural motif in organic chemistry, and have been utilized as chiral auxiliaries, chiral ligands and organocatalysts. They also serve as key intermediates for the construction of heterocyclic compounds. Attributing to their unique bioactivities, sulfoximines have been developed as previliged pharmacophores and widely used in pharmaceutical chemistry and agriculture. Considering the wide applications, the synthetic methods to afford sulfoximines have attracted increasing attention. Among them, the direct arylation of NH-sulfoximines to prepare NAr- sulfoxmines exhibites some unique advantages, including atom-economics, mild conditions and step-economics, and thus has made tremedous progress in recent years. Various methods of NH-sulfoximines to afford NAr-sulfoximines via a C—N bond formation strategy, as well as their applications in synthesis of bioactive molecules and ligands for transition-metal catalysts, are reviewed.

Benzylated quinones widely exist in natural products and drug molecules. Thus their convenient synthesis with high efficiency brings great significance. However, hard conditions are still essential among the present reports. Herein, the development of visible light-induced metal-free benzylation of quinones via cross dehydrogenation coupling reaction with methylene blue as photocatalyst, tert-butyl hydroperoxide as oxidant, and toluene derivatives as benzylation reagent is reported. The reaction exhibits many advantages, including mild conditions, a broad scope with good functional group tolerance, low cost, and avoidance of metal remaining in products. This method may bring novel inspiration and approach for synthesis of bioactive quinones.

1,3,5-Triazinanes are an important class of synthons, which could be regarded as the equivalent of formaldehyde imines in constructing various nitrogen-containing heterocyclic skeletons. In recent years, 1,3,5-triazinanes have attracted much attention in the construction of nitrogen-containing heterocyclic compounds. Based on this, the participation of 1,3,5-triazinanes as diatomic, triatomic and four-atom synthons in [2+n], [3+n], [4+n] cycloaddition reactions to construct nitrogen-containing heterocyclic compounds is systematically summarized. Its applications in cycloaddition, heterocyclic chemistry and pharmaceutical chemistry are also summarized. Moreover, the development of 1,3,5-triazinanes in the construction of nitrogen-containing heterocyclic skeletons and their future applications are also prospected.

A chiral phosphoric acid catalyzed aza-1,8-conjugate addition of isoxazol-5(4H)-ones to 6-methylene-6H-indoles formed in situ from 6-indolylmethanols has been developed for the first time. Notably, the remote stereocontrolled 1,8-addition of isoxazol-5(4H)-ones was featured by N-selectivity, affording aza-adducts in 70%~83% yields with 61%~96% ee.

Nitrones, served as one of the most important 1,3-dipoles in organic synthetic chemistry, can participate in various organic synthetic reactions to synthesize various heterocyclic compounds, such as nucleophilic addition, cycloaddition reaction, rearrangement reaction, C—H bond activation, etc. They are very important organic building blocks for the further construction of complex molecules. In recent years, α,β-unsaturated nitrone has attracted widespread attention from synthetic chemists because of its α,β-unsaturated bond containing rich chemical transformations, and can take part in various new chemical conversions to construct new structural heterocyclic compounds. The new strategies for the preparation of α,β-unsaturated nitrones in the past ten years, and their applications to construct nitrogen heterocyclic compounds, including O-transfer reaction, addition of nucleophiles and radical reagents, and various cycloaddition reactions, are reviewed.

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.

The synthesis of oxygen-substituted N-hydroxy phthalimide derivatives is essential due to their ubiquity in natural products and pharmaceuticals. Metals or peroxides are often required for most C=C/C—H bond activation methods used for olefins, ketones, esters, aldehydes and alcohols. Using cheap and safe iodobenzene diacetate as a feasible dehydrogenation agent and N-hydroxy phthalimide as free radical precursor, the dioxidation of olefins, α-oxidation of carbonyl compounds, oxidation of aldehydes, and oxidative esterification of primary alcohols were successfully realized. This method occurs via a radical mechanism and has the characteristics of mild metal-free reaction conditions, good compatibility and wide substrate scope.

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.

An iridium-catalyzed intermolecular N—N coupling reaction using various N-benzoyloxyamides as acyl nitrene precursor for hydrazide synthesis has been developed. Unlike the carboxylic acid-derived dioxazolones used in previous report, this type of precursors allows the efficient synthesis of both acyl and oxycarbonyl substituted hydrazines from readily accessible precursors. Computational chemistry studies indicated that formation of the metal-acylnitrenoid intermediates via intramolecular hydrogen bond-assisted N—O cleavage may be the rate-determining step, and the subsequent nucleophilic attack of metal-acylnitrenoid by arylamines may be assisted by Cl…HN hydrogen bond to form the N—N bond.