“… Most transition‐metal catalysts and organocatalysts do not meet the requirements for modern industrial manufacturing processes. Their main limitation is low efficiency. The need to develop highly ...efficient catalysts and related catalytic reactions is a never‐ending challenge in synthetic chemistry …” Read more in the Editorial by Qi‐Lin Zhou.
Principals’ distributed leadership plays a critical role in teacher innovativeness; however, research evidence regarding the relationship between them is limited. This study aims at examining the ...effect of distributed leadership on teacher innovativeness as well as the mediating roles of teacher autonomy and professional collaboration. Using the data of 132,376 teachers derived from the 2018 Teaching and Learning International Survey (TALIS), the study applied a structural equation model (SEM) for analysis. The results revealed that distributed leadership had positive direct effects on teacher innovativeness, teacher autonomy, and professional collaboration. Meanwhile, teacher autonomy and professional collaboration significantly mediated the effect of distributed leadership on teacher innovativeness, respectively. Practical implications are discussed, school leaders are expected to adopt distributed leadership style and establish a supportive school environment, and individual teachers are supposed to cultivate a culture of collectivism and make effective use of autonomy in their teaching innovation.
A Ni‐catalyzed hydroarylation of styrenes and 1,3‐dienes with organoboron compounds has been developed. The reaction offers a highly selective approach to diarylalkanes and allylarenes under ...redox‐neutral conditions. In this hydroarylation reaction, a new strategy that uses the proton of methanol to generate the active catalyst species Ni−H was developed. The Ni‐catalyzed hydroarylation, combined with a Ir‐catalyzed C−H borylation, affords a very efficient and straightforward access to a retinoic acid receptor agonist.
OH yeah: A nickel(0)‐catalyzed hydroarylation of alkenes with organoboron reagents using an alcohol OH group as the H‐atom source is reported. The reaction offers a highly selective approach to diarylalkanes and allylarenes under redox‐neutral conditions.
Carbon–heteroatom bonds (C–X) are ubiquitous and are among the most reactive components of organic compounds. Therefore investigations of the construction of C–X bonds are fundamental and vibrant ...fields in organic chemistry. Transition-metal-catalyzed heteroatom–hydrogen bond (X–H) insertions via a metal carbene or carbenoid intermediate represent one of the most efficient approaches to form C–X bonds. Because of the availability of substrates, neutral and mild reaction conditions, and high reactivity of these transformations, researchers have widely applied transition-metal-catalyzed X–H insertions in organic synthesis. Researchers have developed a variety of rhodium-catalyzed asymmetric C–H insertion reactions with high to excellent enantioselectivities for a wide range of substrates. However, at the time that we launched our research, very few highly enantioselective X–H insertions had been documented primarily because of a lack of efficient chiral catalysts and indistinct insertion mechanisms. In this Account, we describe our recent studies of copper- and iron-catalyzed asymmetric X–H insertion reactions by using chiral spiro-bisoxazoline and diimine ligands. The copper complexes of chiral spiro-bisoxazoline ligands proved to be highly enantioselective catalysts for N–H insertions of α-diazoesters into anilines, O–H insertions of α-diazoesters into phenols and water, O–H insertions of α-diazophosphonates into alcohols, and S–H insertions of α-diazoesters into mercaptans. The iron complexes of chiral spiro-bisoxazoline ligands afforded the O–H insertion of α-diazoesters into alcohols and water with unprecedented enantioselectivities. The copper complexes of chiral spiro-diimine ligands exhibited excellent reactivity and enantioselectivity in the Si–H insertion of α-diazoacetates into a wide range of silanes. These transition-metal-catalyzed X–H insertions have many potential applications in organic synthesis because the insertion products, including chiral α-aminoesters, α-hydroxyesters, α-hydroxyphosphonates, α-mercaptoesters, and α-silyl esters, are important building blocks for the synthesis of biologically active compounds. The electronic properties of α-diazoesters and anilines markedly affected the enantioselectivity of N–H insertion reaction, which supports a stepwise ylide insertion mechanism. A novel binuclear spiro copper complex was isolated and fully characterized using X-ray diffraction analysis and ESI-MS analysis. The positive nonlinear effect indicated that binuclear copper complexes were the catalytically active species. The 14-electron copper centers, trans coordination model, perfect C 2-symmetric chiral pocket, and Cu–Cu interaction facilitate the performance of the chiral spiro catalysts in X–H insertion reactions.
The outbreak of the coronavirus disease-19 (COVID-19) has caused enormous stress among the public in China. Intellectual input from various aspects is needed to fight against COVID-19, including ...understanding of the public's emotion and behaviour and their antecedents from the psychological perspectives. Drawing upon the cognitive appraisal theory, this study examined three cognitive appraisals (i.e., perceived severity, perceived controllability, and knowledge of COVID-19) and their associations with a wide range of emotional and behavioural outcomes among the Chinese public.
Participants were 4607 citizens (age range: 17-90 years, Mage = 23.71 years) from 31 provinces in China and they took part in a cross-sectional survey online.
The results showed that the public's emotional and behavioural reactions were slightly affected by the outbreak of COVID-19. Moreover, the public had limited participation in the events regarding COVID-19 but actively engaged in precautionary behaviour. In addition, results of structural equation model with latent variables revealed that the three appraisals were differentially related to the outcome variables (i.e., negative emotion, positive emotion, sleep problems, aggression, substance use, mobile phone use, social participation, and precautionary behaviour).
The findings highlight the utility of cognitive appraisal, as a core process of coping stress, in explaining the public's emotion and behaviour in the encounter of public health concern. Practically, the findings facilitate the government and practitioners to design and deliver targeted intervention programs to the public.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Chiral carboxylic acid moieties are widely found in pharmaceuticals, agrochemicals, flavors, fragrances, and health supplements. Although they can be synthesized straightforwardly by ...transition-metal-catalyzed enantioselective hydrogenation of unsaturated carboxylic acids, because the existing chiral catalysts have various disadvantages, the development of new chiral catalysts with high activity and enantioselectivity is an important, long-standing challenge. Ruthenium complexes with chiral diphosphine ligands and rhodium complexes with chiral monodentate or bidentate phosphorus ligands have been the predominant catalysts for asymmetric hydrogenation of unsaturated acids. However, the efficiency of these catalysts is highly substrate-dependent, and most of the reported catalysts require a high loading, high hydrogen pressure, or long reaction time for satisfactory results. Our recent studies have revealed that chiral iridium complexes with chiral spiro-phosphine-oxazoline ligands and chiral spiro-phosphine-benzylamine ligands exhibit excellent activity and enantioselectivity in the hydrogenation of α,β-unsaturated carboxylic acids, including α,β-disubstituted acrylic acids, trisubstituted acrylic acids, α-substituted acrylic acids, and heterocyclic α,β-unsaturated acids. On the basis of an understanding of the role of the carboxy group in iridium-catalyzed asymmetric hydrogenation reactions, we developed a carboxy-group-directed strategy for asymmetric hydrogenation of olefins. Using this strategy, we hydrogenated several challenging olefin substrates, such as β,γ-unsaturated carboxylic acids, 1,1-diarylethenes, 1,1-dialkylethenes, and 1-alkyl styrenes in high yield and with excellent enantioselectivity. All these iridium-catalyzed asymmetric hydrogenation reactions feature high turnover numbers (up to 10000) and turnover frequencies (up to 6000 h–1), excellent enantioselectivities (greater than 95% ee with few exceptions), low hydrogen pressure (<12 atm), and operational simplicity. These features make chiral iridium catalysts superior or comparable to well-established chiral ruthenium and rhodium catalysts for asymmetric hydrogenation of unsaturated carboxylic acids. A number of chiral natural products and pharmaceuticals have been prepared by concise routes involving an iridium-catalyzed asymmetric hydrogenation of an unsaturated carboxylic acid as a key step. As part of a mechanistic study of iridium-catalyzed asymmetric hydrogenation of unsaturated acids, we isolated, for the first time, the migratory insertion intermediate in the iridium-catalyzed asymmetric hydrogenation of olefins, and this result strongly supports the involvement of an Ir(III)/Ir(V) catalytic cycle. The rigid, bulky scaffold of the chiral spiro-P,N-ligands of the catalysts not only prevents them from undergoing deactivating aggregation under the hydrogenation conditions but also is responsible for the efficient chiral induction. The carboxy group of the substrate acts as an anchor to ensure coordination of the substrate to the iridium center of the catalyst during the reaction and makes the hydrogenation proceed smoothly.
Transition metal-catalyzed carbene insertion into X-H bonds (X = N, O, S, and C) represents a typical carbene transfer reaction and has been widely used in organic synthesis. The ...enantioselectivity-determining step in some of these insertion reactions is the proton transfer of active intermediates such as ylides, metal enolates, or free enols. Since most of the traditional chiral transition metal catalysts tend to dissociate from these active intermediates and cannot be involved in the proton-transfer step, enantiocontrol of these insertion reactions has long been a challenging task. Since 2011, we have developed chiral spiro phosphoric acids as chiral proton-transfer shuttle (CPTS) catalysts, which have been proven to be efficient catalysts for the proton transfer of active intermediates in carbene insertion reactions. Upon combining with achiral dirhodium catalysts, the CPTS catalysts accomplish highly enantioselective insertions of N-H, S-H, and C-H bonds. Herein, a number of important chiral building blocks, including α-amino acid derivatives, α-amino ketones, α-thioesters, and α,α-diaryl acetates, were prepared with high yields and high enantioselectivities through these insertion reactions.
The development of chiral proton-transfer shuttles provides a totally new enantiocontrol strategy for transition metal-catalyzed asymmetric carbene insertion reactions.
Carbonyl ylides have proven to be powerful synthons for the efficient construction of various valuable O‐heterocycles, and the formation of carbonyl ylides by the reaction of metal carbenes with ...carbonyls has attracted increasing attention over the past decades. However, a catalyst‐controlled highly enantioselective reaction of carbonyl ylides from metal carbenes is extremely challenging. Herein, we report a novel copper‐catalyzed asymmetric formal 2+1 and 4+1 annulations of diynes with ketones via carbonyl ylides. Importantly, this protocol not only represents the first example of successful asymmetric epoxidation via carbonyl ylides, but also constitutes the first reaction of vinyl cations with carbonyl compounds. This method leads to the divergent, practical and atom‐economical synthesis of a range of chiral oxiranes and dihydrofurans in moderate to excellent yields with generally excellent enantioselectivities and diastereoselectivities via remote‐stereocontrol strategy.
A copper‐catalyzed asymmetric formal 2+1 and 4+1 annulation of diynes with ketones via carbonyl ylides is disclosed. This protocol enables the divergent, practical and atom‐economical synthesis of a range of chiral oxiranes and dihydrofurans in moderate to excellent yields with generally excellent enantioselectivities and diastereoselectivities.
Rearrangement reactions have attracted considerable interest over the past decades due to their high bond-forming efficiency and atom economy in the construction of complex organic architectures. In ...contrast to the well-established 3,3-rearrangement, 1,3 O-to-C rearrangement has been far less vigorously investigated, and stereospecific 1,3-rearrangement is extremely rare. Here, we report a metal-free intramolecular hydroalkoxylation/1,3-rearrangement, leading to the practical and atom-economical assembly of various valuable medium-sized lactams with wide substrate scope and excellent diastereoselectivity. Moreover, such an asymmetric cascade cyclization has also been realized by chiral Brønsted acid-catalyzed kinetic resolution. In addition, biological tests reveal that some of these medium-sized lactams displayed their bioactivity as antitumor agents against melanoma cells, esophageal cancer cells and breast cancer cells. A mechanistic rationale for the reaction is further supported by control experiments and theoretical calculations.
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