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An asymmetric dearomative tandem annulation between 3-nitroindoles and 7-oxo-5-heptenals was developed by using modularly designed organocatalysts self-assembled from cinchona-squaramide and d-proline.

The first example of palladium-catalysed [3 + 2] annulation of VECs and ketones has been developed, allowing the efficient synthesis of indoloquinazolinones in generally excellent yields with good stereoselectivity.

A formal (2 + 1) annulation and three-component (1 + 1 + 1) cascade cyclisation via sulphur ylide cyclopropanation under mild conditions is described, with the spiro-cyclopropyl iminoindoline moiety transformed into pyrrolo[3,4-c]quinoline through a novel rearrangement process.

Oxidative N-heterocyclic carbene (NHC) organocatalysis, typically leading to the formation of acyl azolium reactive intermediates, constitutes one of the most important activation strategies for the NHC-catalyzed chemical transformations. Here, we report an unprecedented oxidative radical NHC catalysis by using peroxyester as the external single-electron oxidant to realize divergent difunctionalization of olefins. The key to success of this chemistry is the catalytic generation of oxygen radicals that could trigger an intermolecular hydrogen atom transfer to activate the inert C-H bonds, thereby enabling the productive radical relay process. With this protocol, commonly used general chemicals could serve as radical precursors to allow efficient synthesis of value-added products in a straightforward and cost-effective manner. Preliminary mechanistic investigations, including control experiments and DFT calculations, shed light on the NHC organocatalytic radical reaction mechanism.

Allyl and propargyl sulfonium salts are readily available reagents that have recently emerged as versatile building blocks for the assembly of cyclic skeletons. As an alternative to classical sulfonium salts, allyl and propargyl sulfonium salts can be converted into the corresponding vinyl sulfur ylide or allenic sulfonium salt intermediates that contain diverse nucleophilic or electrophilic reactive positions, thereby enabling a great variety of annulation reactions. In this short review, we provide a comprehensive overview of the recent developments in this growing field by summarizing annulation reactions involving allyl and propargyl sulfonium salts. 1 Introduction2 Annulations with Allyl Sulfonium Salts3 Annulations with Propargyl Sulfonium Salts4 Conclusion

The heat recovery steam generator (HRSG) of copper smelting generates a large number of arsenic−copper- containing particles, and the in-situ separation of arsenic and copper is of importance for cutting off environmental risk and realizing resource recovery. The formation of arsenic−copper-containing particles was simulated, the method of in-situ decomposition of arsenic−copper-containing particles by pyrite was proposed, and the decomposition mechanism was confirmed. It was found that particles with high arsenic content were formed in the simulated HRSG, and copper arsenate was liable for the high arsenic content. Pyrite promoted the sulfation of copper, leading to the in-situ decomposition of copper arsenate. In this process, gaseous arsenic was released, and thus the separation of arsenic and copper was realized.

Oxindoles and β-lactams are attractive structural motifs because of their unique biological importance. However, the fusion of the two moieties featuring 3,3'-spirocyclic scaffolds is a challenging task in organic synthesis. Herein we designed a novel type of oxindole-based azaoxyallyl cation synthons, which could readily participate in the [3 + 1] cyclization with sulfur ylides. With this protocol, a collection of 3,3-spiro[β-lactam]-oxindoles were facilely produced in up to 94% yield with perfect diastereoselectivity.

A Lewis acid-promoted [6+1] annulation between sulfur ylides and modified vinyl benzoxazinanones was described. In this reaction, the newly designed vinyl benzoxazinanones could serve as a novel six-atom synthon, and the key to success is the installation of an electron-withdrawing group on the alkene moiety of the benzoxazinanones. A broad range of substrates are compatible with this mild reaction system, thereby providing a facile and practical approach for constructing a benzo[b]azepine skeleton.

The palladium-catalysed diastereoselective (3 + 2) cyclisation of 5-alkenyl thiazolones with vinylethylene carbonates features unique chemoselectivity. Nevertheless, the detailed mechanisms of this cyclisation together with the origins of the unusual chemoselectivity and outstanding diastereoselectivity remain unknown. Herein, density functional theory calculations are performed to reveal a ligating-atom-dependent mechanistic pathway for this Pd-catalysed transformation. The reaction proceeds preferentially via C2′-selectivity through a unique Pd−N chelation-assisted inner-sphere pathway, producing the experimentally observed bicyclic product. Turnover frequency analysis shows that C–C bond formation for the intramolecular annulation is involved in the rate-determining step. The distortion/interaction model, non-covalent interaction and atom-in-molecule analyses reveal that the chelation effect and non-covalent interactions are key factors for the observed high selectivity. The strong chelation, favourable π-stacking and H-bonding interactions stabilise the selectivity-determining transition states for the C2′-selectivity and syn-selectivity pathways, facilitating the chemo- and diastereo-differentiation of several competing pathways for the experimentally observed selectivity.

Asymmetric construction of α-carbolinones with easily available starting materials has recently attracted considerable attention from the synthesis community, and the development of effective catalysis for this target is in great demand. Here, a bifunctional Brønsted base catalyzed asymmetric [3 + 3] cyclization of indolin-2-imines and α,β-unsaturated

Hydrocarbazolone and its derivatives are attractive organic molecules, which have been widely applied in the synthesis of natural products and pharmaceuticals. Herein, we describe a novel intermolecular dearomative [4 + 2] annulation of 3-nitroindoles and enals under oxidative N-heterocyclic carbene catalysis. With this organocatalytic strategy, a variety of dearomatised hydrocarbazolone products were obtained in high yields. This protocol was also suitable for the oxidative cyclisation of 2-nitrobenzothiophenes with enals, thereby affording a collection of 4-hydroxyldibenothiophenes.

Efficient construction of medium-sized lactones has attracted considerable interest over several decades, but remains a formidable challenge in synthetic chemistry. Here, we describe an unprecedented palladium-catalysed regioselective [5 + n] cyclisation (n = 5, 6, and 7) between vinylethylene carbonates and various anhydrides. Catalytic transformation occurs under mild, room-temperature conditions and offers an exceptional substrate scope. A broad spectrum of medium-sized bislactones with skeletal diversity can be obtained easily.

The direct functionalization of inert C(sp

An acylative Suzuki-type cross-coupling of alkyl trifluoroborates and acid fluorides was developed by merging NHC organocatalysis with photoredox catalysis. A broad spectrum of ketones could be facilely synthesised under mild reaction conditions.

We report a highly chemo- and diastereoselective [3 + 2] cyclization of vinylethylene carbonates and 5-alkenyl thiazolones through palladium catalysis. The previously inert aza-thioester moiety on the thiazolone substrates is reacted selectively with the zwitterionic π-allylpalladium species. A variety of amide monothioacetals (AMTA) with two quaternary stereocenters are facilely synthesized. An additional spirocyclic quaternary stereocenter could be further installed by Rh-catalyzed metal-carbene insertion into the C-S bond on the AMTA moiety in a highly stereoselective manner.

The 6,8-dioxabicyclo[3.2.1]octane (6,8-DOBCO) architecture widely exists in a broad spectrum of bioactive natural products, and the development of efficient and convenient protocols to construct th...

The [2 + 1], formal-[4 + 1] and [5 + 1] annulations of electron-deficient dienes with ambiphilic nitrogen reagents were developed on the basis of a similar vinylogous aza-Michael addition. These synthetic approaches enable the divergent synthesis of several interesting heterocyclic skeletons, such as vinylaziridines, pyrroline and 2-aminopyridines, from easily accessible starting materials under mild conditions.

A highly efficient cyclopropanation of diazo compounds and electron-deficient alkenes under metal- and catalyst-free conditions was developed. The use of water as the sole solvent dramatically increased the efficiency of the reaction. This on-water synthesis approach featured numerous advantages, including high yield, broad substrate scope and environmentally friendly conditions. Moreover, a simple substrate-engineering strategy was used in the reaction system to realise the unprecedented diastereodivergent synthesis of functionalised cyclopropane derivatives with remarkable stereoselectivities.

A Lewis acid-promoted [6+1] annulation between sulfur ylides and modified vinyl benzoxazinanones was described. In this reaction, the newly designed vinyl benzoxazinanones could serve as a novel six-atom synthon, and the key to success is the installation of an electron-withdrawing group on the alkene moiety of the benzoxazinanones. A broad range of substrates are compatible with this mild reaction system, thereby providing a facile and practical approach for constructing a benzo[

Over the past decades, N-heterocyclic carbene (NHC) organocatalysis has undergone a flourish of development on the basis of closed-shell reaction paths. By contrast, the emerging area of single-electron transfer (SET) reactions enabled by NHC catalysis still remain underdeveloped, but offer plenty of opportunities to develop new catalytic modes and useful synthetic methods. A number of interesting transformations were triggered by the SET process from the electron-rich Breslow intermediates to various single-electron acceptors. In additions, recent studies revealed that the Breslow radical cations could also be generated by single-electron reduction of the electron-deficient acyl azolium intermediates. These discoveries open a new avenue for NHC organocatalysis to harness radical reactions. The present review will focus on the exciting advancements in the dynamic area of radical NHC organocatalysis.

Heterocycles are the fundamental structural motifs found in natural products and biologically active compounds. The construction of these structures is therefore an important task in organic chemistry. Vinylethylene carbonates (VECs) are versatile building blocks that can undergo transition metal catalysed decarboxylation to enable various kinds of interesting transformations. This review provides an overview of the significant achievements of VECs in palladium-catalysed annulations over the past five years. The flexible reactivity of VECs is demonstrated by various [3 + 2], [5 + n] and other types of annulations, which could offer powerful protocols for accessing diverse functionalised heterocycles.

Direct sulfide organocatalysis is an emerging topic in research on synthetic chemistry. Here, an unprecedented sulfide-catalyzed diastereoselective [4+1] annulation of (in situ generated) ortho-quinone methides and bromides is reported. Notably, the robustness of such sulfide organocatalysis was demonstrated by performing the catalytic reaction under oxidative conditions without significantly affecting the reaction outcome. Various dihydrobenzofurans with diverse substituents were obtained with high isolated yields of up to 98% and remarkable diastereoselectivity (>19:1 dr in general).

The construction of a chiral halogenated cyclic quaternary carbon center through various catalytic strategies is an emerging hot topic in the field of asymmetric synthesis. Herein, we give a summary of recently developed synthetic methods for preparing such structures. In addition, a novel enolate activation mode of aldehydes is highlighted, which provides an elegant pathway to access enantiopure heterocycles featuring a halogenated quaternary stereocenter through organocatalytic [4+2] cycloaddition.

Scorodite (FeAsO4·2H2O) is the most popular phase for arsenic (As) immobilization while the reductive dissolution of Fe(III) to Fe(II) will promote As release. In the present study, an equilibrium between Fe(III) and Fe(II) was achieved in scorodite preparation system by introducing certain alcohol (methanol, ethanol, isopropanol or tert-butanol), and thus a new mixed-valent iron arsenate black crystal formulated as Fe(II)5.2Fe(III)8.8(HAsO4)4(AsO4)8·H2O was prepared. In comparison with scorodite, the black crystal has higher As content (36.4%, mass fraction) and lower crystal water content (0.73%, mass fraction). Additionally, the leaching concentration of As can be lower than the threshold value (5 mg/L) regulated by identification standards for hazardous wastes of China (GB 5080.3–2007). Therefore, this new mixed-valent iron arsenate crystal could be classified as a non-hazardous and promising As-bearing phase in environmental applications.

Asymmetric construction of halogenated quaternary carbon centers under mild reaction conditions remains challenging. Reported here is an unprecedented and highly stereoselective Bronsted base catalyzed [4+2] cycloaddition between either α-chloro- or α-bromoaldehydes and cyclic enones. The key intermediate, an α-halogenated enolate, is susceptible to dehalogenation and can be stabilized and stereochemically controlled using bifunctional tertiary amines. This method provides facile access to a collection of optically pure bicyclic dihydropyrans having three contiguous stereocenters, including a halogen-bearing quaternary carbon center. Of note, the product can be transformed in situ into densely functionalized spirocyclopropanes in a highly efficient and stereoselective manner.

Here we report a secondary amine-catalyzed, highly enantioselective [3+3] cyclization reaction of α-alkylidene pyrazolinones and α,β-unsaturated aldehydes, which facilely delivers a variety of enantioenriched spiropyrazolones showing structural and stereochemical complexity. The reaction uses an iminium ion activation strategy to activate both the β- and ipso-positions of the enals as dielectrophilic sites. A broad range of substrates are compatible with this mild reaction system.

Arsenic (As) removal from smelting acidic wastewater is an urgent task. The most common method is oxidation of trivalent As(III) to pentavalent As(V) subsequently precipitated by ferric (Fe(III)) salts. Foundations of redox behavior and chemical species are of great importance for understanding As removal. In this work, cyclic voltammetry (CV) and UV-Vis spectroscopy were used for laboratory observation; meanwhile HSC and MINTEQ software were employed for theoretical analyses. It is found that As(III) oxidation, a multiple electron transfer reaction, is diffusion-controlled. The oxidation over-potential is very high (about 0.9 V) in sulfuric acid solutions (pH 1.0). In addition, Fe(III)-As(V) complexes are evidenced by UV-Vis spectra and chemical species analyses in series of Fe(III)-As(V)-H2SO4-H2O solutions. Therefore, the Fe(III) and As(V) species distribution against pH values are determined and a new φ–pH diagram with inclusion of Fe-As complexes is consequently compiled based on thermodynamic data predicted by other researchers.

Zinc leaching residue (ZLR), produced from traditional zinc hydrometallurgy process, is not only a hazardous waste but also a potential valuable solid. The combination of sulfate roasting and water leaching was employed to recover the valuable metals from ZLR. The ZLR was initially roasted with ferric sulfate at 640 °C for 1 h with ferric sulfate/zinc ferrite mole ratio of 1.2. In this process, the valuable metals were efficiently transformed into water soluble sulfate, while iron remains as ferric oxide. Thereafter, water leaching was conducted to extract the valuable metals sulfate for recovery. The recovery rates of zinc, manganese, copper, cadmium and iron were 92.4%, 93.3%, 99.3%, 91.4% and 1.1%, respectively. A leaching toxicity test for ZLR was performed after water leaching. The results indicated that the final residue was effectively detoxified and all of the heavy metal leaching concentrations were under the allowable limit.

Fluorinated ketones are widely prevalent in numerous biologically interesting molecules, and the development of novel transformations to access these structures is an important task in organic synthesis. Herein, we report the multicomponent radical acylfluoroalkylation of a variety of olefins in the presence of various commercially available aromatic aldehydes and fluoroalkyl reagents through N-heterocyclic carbene organocatalysis. With this protocol, over 120 examples of functionalized ketones with diverse fluorine substituents have been synthesized in up to 99 % yield with complete regioselectivity. The generality of this catalytic strategy was further highlighted by its successful application in the late-stage functionalization of pharmaceutical skeletons. Excellent diastereoselectivity could be achieved in the reactions forging multiple stereocenters. In addition, preliminary results have been achieved on the catalytic asymmetric variant of the olefin difunctionalization process.

A series of iminoindoline-derived alkenes was found to be a new class of excellent aza-diene electrophiles in NHC-catalyzed asymmetric [4 + 2] cyclizations. This transformation is mainly characterized by excellent compatibility, which allows aza-diene substrates to incorporate various substituents and functionalities, including (hetero)aryl, (linear or branched)alkyl, alkenyl, alkynyl, and ester groups. Forty examples of the desired tetrahydro-α-carbolinones were facilely synthesized using this method, with up to 99% yield and >99% ee.