Advances in Phase-Transfer Catalysis [New synthetic methods (20)]

Phase-transfer catalysis (PTC) has grown into a versatile preparative method in the last few years. The most notable new developments include the use of crown ethers as phase-transfer catalysts and the introduction of solid-liquid PTC. Some representative examples have been selected from the large number of new PTC reactions and some of them are summarized in tables.     

New chiral phase-transfer catalysts possessing a 6,6′-bridged ring on the biphenyl unit: application to the synthesis of α,α-dialkyl-α-amino acids

A new chiral phase-transfer catalyst possessing a 6,6′-bridged ring on the biphenyl unit has been developed for the practical synthesis of α,α-dialkyl-α-amino acids. This catalyst shows very high activity for the asymmetric alkylation of an alanine derivative to give α,α-dialkyl-α-amino acid derivatives with high enantioselectivities.     

Versatile Ligands for Palladium-Catalyzed Asymmetric Allylic Alkylation

Palladium complexes of the chiral diphosphanes 1 and 2 which possess a rigid backbone and a large bite angle catalyze the alkylation of allyl compounds with both high enantioselectivities and reaction rates, particularly with less sterically demanding substrates. 1 : R=Me, X=S; 2 : R=H, X=C(CH₃)₂.     

Towards Perfect Asymmetric Catalysis: Additives and Cocatalysts

Make your catalyst more enantioselective! The enantiomeric excess of a catalytic reaction system can sometimes be enhanced from below 10 to over 90 % by the use of suitable achiral additives. Since completely different mechanisms can influence the catalyst and reaction outcome, there is a range of additives that can be applied to improve the catalyst efficiency for a variety of organic reactions.     

微通道反应器在不对称催化中的应用

不对称催化是合成手性化合物的重要手段,针对该领域已开展了大量的研究工作并获得了引人瞩目的研究成果。相比于传统的釜式反应器,微通道反应器具有传质/传热效率高、反应时间短、易于自动化和提高安全性等优势。因此,将微通道反应器应用于不对称催化领域已成为当前的研究热点,并且在耦合在线分析、多相催化和光催化等领域已展现出良好的应用前景。本文对近年来微通道反应器在不对称催化领域中的最新研究进展进行总结和综述,并对未来的发展方向进行展望。     

Proline-Based P,N Ligands in Palladium-Catalyzed Asymmetric π-Allyl Additions

Excellent yields and at least 95 % ee can be achieved for the addition of dimethyl malonate to cycloalkenyl acetates by using a palladium complex of the new phosphanyldihydrooxazole ligand L as a catalyst (see scheme). The ligand L can be synthesized from commercially available trans 4-hydroxy-L -proline in four steps. BOC=tert-butoxycarbonyl.     

Asymmetric Catalysis with Heterobimetallic Compounds

This review focuses on a new concept in catalytic asymmetric reactions that was first realized for the use of heterobimetallic complexes. As these heterobimetallic complexes function as both a Brønsted base and as a Lewis acid, just like an enzyme, they make possible a variety of efficient catalytic asymmetric reactions. This heterobimetallic concept should prove to be applicable to a variety of new asymmetric catalyses. The first part of this review describes the development of rare-earth–alkali metal complexes such as LnM₃tris(binaphthoxide) complexes (LnMB, Ln = rare-earth metal, M = alkali metal), which are readily prepared from the corresponding rare-earth trichlorides or rare-earth isopropoxides, and their application to catalytic asymmetric synthesis. By using a catalytic amount of LnMB complexes several asymmetric reactions proceed efficiently to give the corresponding desired products in up to 98% ee: LnLB-catalyzed asymmetric nitroaldol reactions (L = Li), LnSB-catalyzed asymmetric Michael reactions (S ? Na), and LnPB-catalyzed asymmetric hydrophosphonylations of either imines or aldehydes (P ? K). Applications of these heterobimetallic catalysts to the syntheses of several biologically and medicinally important compounds are also described. Spectral analyses and computational simulations of the asymmetric reactions catalyzed by the heterobimetallic complexes reveal that the two different metals play different roles to enhance the reactivity of both reaction partners and to position them. From mechanistic considerations, a useful activation of the heterobimetallic catalyses was realized by addition of alkali metal reagents. The second part describes the development of another type of heterobimetallic catalysts featuring Group 13 elements such as Al and Ga as the central metal. Among them, the AlLibis(binaphthoxide) complex (ALB) is an effective catalyst for asymmetric Michael reactions, tandem Michael–aldol reactions, and hydrophosphonylation of aldehydes.     

辛可宁季铵盐的合成及催化不对称烷基化研究

探索了辛可宁季铵盐的通用合成方法, 确定辛可宁与取代苄溴在四氢呋喃中回流为最优反应途径, 合成了11个羟基保留的辛可宁季铵盐, 收率57%~88%, 并合成了4种羟基保护季铵盐, 羟基成醚过程在生成季铵盐前后均可进行, 总收率62%~71%; 羟基酯化只能在生成季铵盐之后进行, 总收率78%. 本文共合成了15个季铵盐(Cn-1~Cn-15), 其中5个为新化合物, 另有4个的合成方法未见文献报道. 选用该类季铵盐催化剂催化二苯亚甲基甘氨酸叔丁酯的不对称苄基化反应, 结果发现, 催化剂苄基具有4-Br取代或羟基成醚均有助于提高反应产物的对映选择性. Cn-9可得到最优的反应结果, 产率93%, e.e.值91%.     

Phase-Transfer Catalyzed Two-Phase Reactions in Preparative Organic Chemistry

Quaternary ammonium and phosphonium salts catalyze reactions between substances located partly in an aqueous and partly in an organic phase. Use of such phase-transfer catalysts simplifies and accelerates numerous reactions traditionally conducted in nonaqueous media. These reactions include carbene reactions, nucleophilic substitutions, alkylations of ketones and nitriles, Wittig and Darzens reactions, formation of ethers and esters. Other reactions such as hydrolysis and oxidation can be accelerated.     

C3 Symmetry in Asymmetric Catalysis and Chiral Recognition

Rotational symmetry can be an important factor in the design of highly selective receptors for chiral recognition. This is well known for C₂-symmetric compounds, but the concept can be extended to chiral compounds of higher symmetry such as 1 .     

手性高分子金属络合物在不对称催化中的应用

综述了手性高分子金属络合物（人工合成）在不对称催化中的应用及最新进展,参考文献５３篇。     

Asymmetric phase-transfer reactions under base-free neutral conditions

Although quaternary onium salt-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles proceeded smoothly in the presence of lipophilic quaternary onium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate additions, aldol reaction, sulfenylation, and chlorination under the influence of chiral bifunctional onium bromides as key catalysts.     

高分子支载的金鸡纳生物碱催化剂在不对称催化反应中的应用进展

综述了近年来高分子支载的金鸡纳生物碱催化剂在不对称双羟基化反应、不对称Michael加成反应、活性亚胺的不对称烷基化反应以及潜手性酮的不对称还原反应中的应用及最新进展。     

手性原子簇合物与不对称催化反应

以骨架手性原子簇合物为催化剂的不对称催化反应一直认为是极富挑战性的课题，一旦实现，将是一种理想和概念上的突破，回顾原子簇合物的不对性及不对称催化反应的进展，阐述了我们的目标和一些相关的问题。     

光学活性四面体过渡金属簇合物的诱导合成

报导了用手性季铵盐诱导合成SFeCoMo等手性四面体过渡金属簇合物的新方法。发现,苄基辛可宁对四面体簇合成有手性诱导作用;在不同溶剂中,手性簇产物的绝对构型不同,而且含钌簇的含光度比含铁簇的旋光度小。     

Asymmetric Catalysis with Chiral Frustrated Lewis Pairs

The chemistry of frustrated Lewis pairs (FLPs) provides the most important approach for the metal‐free hydrogenation and hydrosilylations. Great progress has been achieved in this area for the past decade. Some promising results have also been obtained. This perspective article mainly focuses on the recent advances for the synthesis of chiral Lewis acidic boranes in category of three protocols, 1) hydroboration of chiral internal alkenes with Piers’ borane HB(C₆F₅)₂; 2) in situ hydroboration of chiral alkenes or alkynes without any purification; 3) and substitution reaction of (C₆F₅)_nBCl_3–n with chiral organometallic reagents, as well as their applications in the metal‐free asymmetric hydrogenations and hydrosilylations.

     

A Novel Synthesis of Cyclic Polythioethers Using Liquid-Liquid Phase-Transfer Catalysis

The synthesis of cyclic polythioethers has been achieved by the reactions of dithiols with alkyl dihalides. Thiols are not only hard to handle owing to their unpleasant smell, but also they are easily oxidizable, thus it is not easy to obtain various dithiols. However, we have developed a procedure for the preparation cyclic polythioethers by the reaction of dithioiminium salts with alkyl dihalides using phase-transfer catalyst without the use of dithiols, and have examined the ion recognition of these compounds.     

反应控制相转移催化研究的进展

反应控制相转移催化是近年来发展起来的一类新的催化体系.该催化体系在反应过程中具有均相催化的本征,当反应结束后,催化剂发生相的变化而从反应介质中析出,从而可实现催化剂的分离和循环使用.本文就反应控制相转移催化原理及其在烯烃环氧化、醇氧化、烯烃断键氧化、苯羟基化、硒催化羰基化和酯化反应等方面应用的最新进展进行了综述.     

相转移催化在高分子化合物合成中的应用

 综述了相转移催化用于高分子化合物合成的主要研究进展．介绍了季铵盐类及冠醚类相转移催化剂在高聚物的亲核取代反应、阴离子开环聚合反应及自由基聚合反应中的应用．重点总结了亲核取代反应中聚苯乙烯类化合物的功能化及化学修饰，包括合成路线、反应机理、温度以及催化剂和溶剂的种类与用量等因素对反应的影响．冠醚类化合物的催化效果略优于季铵盐类化合物，而后者的成本低、毒性小、应用更广泛，其催化的反应应作为今后研究的重点，以期将相转移催化技术尽早用于工业化生产．     

基于大环主体化合物的不对称超分子催化

超分子化学与催化的不断渗透融合催生了超分子催化这一挑战性的前沿研究热点。作为超分子化学的主要研究对象,大环化合物因具有可以和不同客体分子通过非共价相互作用可逆结合的识别位点,模拟酶催化中对底物分子的预组织过程,在超分子催化发展之初就备受关注,并在近二十年来取得了可喜的发展。本综述主要介绍了近十年来发展的基于冠醚、环糊精和杯芳烃等大环主体分子的代表性手性超分子催化剂,以及它们在不对称催化反应中的应用,重点阐述了主-客体等弱相互作用对催化剂活性和对映选择性的超分子调控作用,同时对这一研究领域目前存在的局限性和不足进行了总结,并展望了不对称超分子催化的发展前景。