手性催化剂负载的一种新方法: 自负载策略

较系统地介绍了手性催化剂负载的一种新方法(即“自负载”策略)及其在非均相不对称催化反应中应用的最新进展. 与传统的负载模式不同, “自负载”策略中利用含双或多官能团的配体与金属通过自组装形成的有机-无机聚合物做为催化剂, 因此不需使用任何载体. “自负载”手性催化剂在若干非均相不对称催化反应中显示了优秀的催化活性和对映选择性并且能够简单回收再利用, 为手性催化剂的负载化提供了一个新的策略.     

Self-supported chiral catalysts for heterogeneous enantioselective reactions

The development of heterogeneous chiral catalysts for enantioselective reactions is highly desirable in order to overcome some drawbacks of homogeneous catalysts. Different from the conventional approaches by using various types of supports or biphasic systems for the recovery and reuse of homogeneous catalysts, a conceptually new strategy for heterogenization of homogeneous chiral catalysts, that is, a "self-supporting" approach, has been developed to use homochiral metal-organic coordination polymers generated by the self-assembly of chiral multitopic ligands with metal ions, and thus obviates the use of any support. In this concept article, the success of this "self-supporting" strategy will be exemplified in heterogeneous catalysis of asymmetric carbonyl-ene, sulfoxidation, epoxidation, and asymmetric hydrogenation reactions.     

Copper(II)‐Catalyzed Nitroaldol (Henry) Reactions: Recent Developments

Self‐assembled copper(II) complexes are described as effective catalysts for nitroaldol (Henry) reactions on water. The protocol involves a heterogeneous process and the catalysts can be recovered and recycled without loss of activity. Further, C2‐symmetric N,N′‐substituted chiral copper(II) salan complexes are found to be more effective catalysts than chiral copper(II) salen complexes for reactions in homogeneous catalysis, with high enantioselectivities. The reactions involve bifunctional catalysis, bearing the properties of a Brønsted base, as well as a Lewis acid, to effect the reaction in the absence of external additives.     

In Operando Analysis of Diffusion in Porous Metal-Organic Framework Catalysts

The potential to exert atomistic control over the structure of site-isolated catalyst sites, as well as the topology and chemical environment of interstitial pore spaces, has inspired efforts to apply porous metal-organic frameworks (MOFs) as catalysts for fine chemical synthesis. In analogy to enzyme-catalyzed reactions, MOF catalysts have been proposed as platforms in which substrate confinement could be used to achieve chemo- and stereoselectivities that are orthogonal to solution-phase catalysts. In order to leverage the tunable pore topology of MOFs to impact catalyst selectivity, catalysis must proceed at interstitial catalyst sites, rather than at solvent-exposed interfacial sites. This Minireview addresses challenges inherent to interstitial MOF catalysis by 1) describing the diffusional processes available to sorbates in porous materials, 2) discussing critical factors that impact the diffusion rate of substrates in porous materials, and 3) presenting in operando experimental strategies to assess the relative rates of substrate diffusion and catalyst turnover in MOF catalysis. It is anticipated that the continued development of in operando tools to evaluate substrate diffusion in porous catalysts will advance the application of these materials in fine chemical synthesis.     

稀土金属在不对称催化中的应用:从均相催化到异相催化

稀土金属的配位数较高,可通过容纳大型手性配体,构筑手性环境,催化不对称反应的定向发生,在工业生产特别是制药工程中具有重要应用价值.本文以Henry反应、Mannich反应和Strecker反应为例,总结回顾了稀土金属催化剂在此类反应中的设计思路、性能特点与应用前景,旨在展现稀土金属催化剂兼具融合均相催化与异相催化的优势...     

Modulating the acidity: highly acidic Brønsted acids in asymmetric catalysis

Recently, chiral highly acidic Brønsted acids have emerged as powerful catalysts for enantioselective C C and C X bond‐forming reactions. Their strong acidity renders them valuable tools for the activation of imines, carbonyl compounds, and other weakly basic substrates. As a result, new perspectives are opened and highly stereoselective transformations based on the concept of chiral contact‐ion‐pair catalysis can be realized. This Minireview gives an overview of the design and application of these new organocatalysts and presents recent results in this rapidly growing field.     

Homochiral porous metal-organic frameworks: Why and how?

This paper highlights the most significant recent advances in the synthesis, characterization, and applications of single-crystalline homochiral porous metal-organic frameworks (MOFs). The motivations for the synthesis of homochiral porous solids and the strategies on how they can be designed are provided. The latest examples of chiral separation and Lewis acid heterogeneous asymmetric catalysis using homochiral porous MOFs are presented.     

Catalysis in Single Crystalline Materials: From Discrete Molecules to Metal-Organic Frameworks

Catalysis is one of the key techniques for people's modern life. It has created numerous essential chemicals such as biomedicines, agricultural chemicals and unique materials. Heterogeneous catalysis is the new emerging method with reusable catalysts. Among heterogenous catalysis patterns developed so far, single crystalline catalysis has become the promising one owing to its high catalytic density and selectivity resulted by the inherent porosity, orderliness of the lattices and permeability. These crystalline catalysts could be used in various reactions such as photo-dimerization, Diels-Alder reaction, CO₂ transformation and so on. In this review, we highlighted the reported works about the single crystalline catalysts. Both discrete small molecules and metal-organic frameworks (MOFs) have been used to prepare single crystals for catalysis. For discrete molecules based crystalline catalysts, coordinated and covalent molecules have been used. There were more catalytic modes in crystalline MOF catalysts. Three patterns were identified in this review: single crystalline MOFs i) without catalytic sites, ii) with inherent catalytic features and iii) with introducing catalytic units by post synthetic modification. Based on these examples, this review committed to provide the inspirations for the further design and application of single crystalline materials.     

Enantioselective Carbonyl Catalysis Enabled by Chiral Aldehydes

Organocatalytic methods have achieved spectacular advancements for the preparation of chiral molecules in highly enantioenriched forms. The fast development of this field can mainly be attributed to the evolution of general and reliable activation modes. The discovery and identification of new activation modes are therefore highly desirable to push the boundaries of asymmetric reactions. In this Minireview, recent advances in enantioselective carbonyl catalysis, one useful subbranch of organocatalysis for the efficient activation of simple amines, will be summarized. With elegantly designed chiral aldehyde catalysts, highly enantioselective and efficient asymmetric reactions can be developed. Continued development of enantioselective carbonyl catalysis is expected in the future.     

Development of Chiral Organosuperbase Catalysts Consisting of Two Different Organobase Functionalities

In the field of chiral Brønsted base catalysis, a new generation of chiral catalysts has been highly anticipated to overcome the intrinsic limitation of pronucleophiles that are applicable to the enantioselective reactions. Herein, we reveal conceptually new chiral Brønsted base catalysts consisting of two different organobase functionalities, one of which functions as an organosuperbase and the other as the substrate recognition site. Their prominent activity, which stems from the distinctive cooperative function by the two organobases in a single catalyst molecule, was demonstrated in the unprecedented enantioselective direct Mannich‐type reaction of α‐phenylthioacetate as a less acidic pronucleophile. The present achievement would provide a new guiding principle for the design and development of chiral Brønsted base catalysts and significantly broaden the utility of Brønsted base catalysis in asymmetric organic synthesis.     

Chiral Iminophosphoranes—An Emerging Class of Superbase Organocatalysts

Chiral Brønsted base catalysis is a fascinating and highly explored field of research. For many years catalysts based on chincona alkaloid chiral scaffolds have constituted privileged systems widely employed in numerous base‐promoted organic transformations. Recently, a novel group of chiral base catalysts has been successfully introduced. The application of organosuperbases, namely cyclopropenimines, guanidines, and iminophosphoranes, as chiral catalysts is receiving increasing attention. The aim of this Concept article is to summarize recent progress in the field of chiral iminophosphorane superbase organocatalysis. Catalysts design, different approaches to their synthesis, and applications in asymmetric synthesis are outlined and discussed in detail.     

手性自负载催化剂研究新进展

催化剂的负载和回收再利用是提高其使用效率、降低反应成本和减少金属离子对产物污染的一条有效途径。与传统的负载模式不同, 手性自负载催化剂通过含双或多官能团的手性配体与金属通过自组装形成一类有机-无机聚合物,因此无需使用任何载体,即能够有效地实现手性催化剂的回收和再利用。近年来,手性自负载催化剂作为一种新的负载模式,已经成功地应用于一些非均相催化的不对称反应中。本文概述了手性自负载催化剂的在一些不对称催化反应研究中取得的新进展。     

Asymmetric Syntheses with the Aid of Homogeneous Transition Metal Catalysts

The progress made in the field of homogeneous catalysis during the last five to six years has led, inter alia, to the development of highly selective catalysts for asymmetric syntheses. Homogeneous asymmetric hydrogenation, using well defined transition metal catalysts, may be achieved with optical yields of 85 to 90% or more. Catalytic reactions, in which the chiral centers are generated by C? C bond formation, can result in optical yields of 70 to 80%. The hydrogenation catalysts consist primarily of rhodium(I) complexes containing “Homer phosphanes”, phosphanes with chiral C atoms, or optically active amides. Catalysts which induce optical activity through the formation of C? C bonds have been developed from π-allylnickel halides, Lewis acids, and phosphanes containing chiral C atoms. The results obtained signify a breakthrough in an area of catalysis previously restricted to syntheses involving enzymes.     

Recent topics in dual hydrogen bonding catalysis

Dual hydrogen bonding donors have received much attention in the area of organocatalysis after the discovery of chiral thiourea derivatives that act as asymmetric catalysts. This digest focuses on recent advances in this area categorized in the following three topics: 1) enhanced hydrogen bonding donor catalysis; new scaffolds with improved reactivity and selectivity are introduced and compared with established catalysts; 2) anion binding catalysis; recent advances in terms of catalysts and their applications is addressed; 3) multiple catalysis involving dual hydrogen bonding catalysts; a relatively new field of dual hydrogen bonding donor catalysis combined with other catalysis is introduced.     

Stereogenic‐Only‐at‐Metal Asymmetric Catalysts

Chirality is an essential feature of asymmetric catalysts. This review summarizes asymmetric catalysts that derive their chirality exclusively from stereogenic metal centers. Reported chiral‐at‐metal catalysts can be divided into two classes, namely, inert metal complexes, in which the metal fulfills a purely structural role, so catalysis is mediated entirely through the ligand sphere, and reactive metal complexes. The latter are particularly appealing because structural simplicity (only achiral ligands) is combined with the prospect of particularly effective asymmetric induction (direct contact of the substrate with the chiral metal center). Challenges and solutions for the design of such reactive stereogenic‐only‐at‐metal asymmetric catalysts are discussed.     

Recent Advances in the Development of Chiral Gold Complexes for Catalytic Asymmetric Catalysis

Asymmetric gold catalysis has been rapidly developed in the past ten years. Breakthroughs have been made by rational design and meticulous selection of chiral ligands. This review summarizes newly developed gold-catalyzed enantioselective organic transformations and recent progress in ligand design (since 2016), organized according to different types of chiral ligands, including bisphosphine ligands, monophosphine ligands, phosphite-derived ligands, and N-heterocyclic carbene ligands for asymmetric gold(I) catalysis as well as heterocyclic carbene ligands and oxazoline ligands for asymmetric gold(III) catalysis.     

Multiple catalysis with two chiral units: an additional dimension for asymmetric synthesis

This Minireview focuses on asymmetric reactions mediated by two distinct chiral catalysts (chiral multiple catalysis). Initially, this approach appears unconventional, but indeed it allows a fast multidimensional optimization and fine-tuning of the catalytic system required to perform a given transformation. Herein, this emerging concept is presented and its potential applications are highlighted.     

Recent advances in asymmetric phase-transfer catalysis

The use of chiral nonracemic onium salts and crown ethers as effective phase-transfer catalysts have been studied intensively primarily for enantioselective carbon-carbon or carbon-heteroatom bond-forming reactions under mild biphasic conditions. An essential issue for optimal asymmetric catalysis is the rational design of catalysts for targeted reaction, which allows generation of a well-defined chiral ion pair that reacts with electrophiles in a highly efficient and stereoselective manner. This concept, together with the synthetic versatility of phase-transfer catalysis, provides a reliable and general strategy for the practical asymmetric synthesis of highly valuable organic compounds.     

Synthetic strategies for chiral metal-organic frameworks

By direct synthesis route, chiral metal-organic frameworks are synthetized with enantiopure ligands or spontaneous resolution; by indirect method, post-synthetic method and chiral inductionare introduced to construct chiral metal-organic frameworks.     

聚合物负载的手性联二萘酚的合成及其在不对称催化中的应用进展

作为一种有机配体, 手性1,1'-联二萘酚(BINOL)被广泛应用于过渡金属催化的均相不对称有机反应. 为克服均相催化剂不易回收重复使用等缺陷, 人们深入研究了聚合物负载手性BINOL催化剂的方法. 总结了近年来聚合物负载手性BINOL催化剂的合成及其在不对称有机催化中的应用, 并对负载型BINOL催化剂进行了展望.