手性噻唑烷-铑(I)配合物催化的苯乙酮不对称硅氢化反应

由L-半胱氨酸甲酯与α-吡啶甲醛缩合制备了2-(α-吡啶基)-4-羧甲基-1, 3-噻唑烷手性配体。用该手性配体与[Rh(COD)]2反应原位生成的Rh(I)配合物为催化剂进行了苯乙酮的不对称硅氢化反应。反应的化学产率达91%, 光学产率达82.1%e.e.。考察了各种反应条件对催化剂性能的影响。     

手性树状分子膦配体在不对称催化氢化中的应用

树状大分子作为一类组成精确的超支化结构大分子,近十多年来引起了科学家们的广泛关注.作为一类新型可溶性载体应用于均相催化剂,尤其是手性均相催化剂的负载化研究是树状大分子的重要应用领域之一.本文主要介绍了手性树状大分子膦配体,包括膦配体位于树状分子核心、末端和表面的几种类型,重点对它们与金属配合物形成的催化剂在不对称催化氢化反应中的应用研究进行总结,同时对负载催化剂的分离与回收、树状分子载体的结构和体积对催化剂性能的影响进行了讨论.     

Novel rhodium-catalyzed reaction of thiazolidine derivatives with carbodiimides

A new, simple, and regioselective synthesis of thiazolidinimine derivatives based on the rhodium-catalyzed reaction of readily available thiazolidines with carbodiimides is described. This methodology provides direct access to a large variety of thiazolidinimine derivatives, possibly via a novel regiospecific insertion of carbodiimides into one of two ring carbon-nitrogen bonds, as well as a metal-catalyzed imine elimination process.     

Efficient asymmetric addition of diethylzinc to aldehydes using 3‐hydroxyazetidine derivatives as chiral ligands

A new series of chiral 3‐hydroxyazetidines has been prepared from (S)‐1‐(4‐methoxyphenyl)ethylamine. These ligands have shown excellent catalytic activities and enantiomeric selectivities in asymmetric addition of diethylzinc to aromatic aldehydes. Copyright © 2008 John Wiley & Sons, Ltd.     

Rh-catalyzed asymmetric hydrogenation of prochiral olefins with a dynamic library of chiral TROPOS phosphorus ligands

A library of 19 chiral tropos phosphorus ligands, based on a flexible (tropos) biphenol unit and a chiral P-bound alcohol (11 phosphites) or secondary amine (8 phosphoramidites), was synthesized. These ligands were screened, individually and as a combination of two, in the rhodium-catalyzed asymmetric hydrogenation of dehydro-alpha-amino acids, dehydro-beta-amino acids, enamides and dimethyl itaconate. ee values up to 98% were obtained for the dehydro-alpha-amino acids, by using the best combination of ligands, a phosphite [4-P(O)2O] and a phosphoramidite [13-P(O)2N]. Kinetic studies of the reactions with the single ligands and with the combination of phosphite [4-P(O)2O] and phosphoramidite [13-P(O)2N] have shown that the phosphite, despite being less enantioselective, promotes the hydrogenation of methyl 2-acetamidoacrylate and methyl 2-acetamidocinnamate faster than the mixture of the same phosphite with the phosphoramidite, while the phosphoramidite alone is much less active. In this way, the reaction was optimized by lowering the phosphite/phosphoramidite ratio (the best ratio is 0.25 equiv phosphite/1.75 equiv phosphoramidite) with a resulting improvement of the product enantiomeric excess. A simple mathematical model for a better understanding of the variation of the enantiomeric excess with the phosphite/phosphoramidite ratio is also presented.     

Mixtures of chiral and achiral monodentate ligands in asymmetric Rh-catalyzed olefin hydrogenation: reversal of enantioselectivity

The recently described method of combinatorial asymmetric transition metal catalysis based on the use of mixtures of chiral monodentate P-ligands has been extended to include mixtures of chiral and achiral monodentate P-ligands, reversal of enantioselectivity in Rh-catalyzed olefin hydrogenation being possible in appropriate cases.     

Efficient iridium and rhodium‐catalyzed asymmetric transfer hydrogenation using 9‐amino(9‐deoxy) cinchona alkaloids as chiral ligands

9‐Amino (9‐deoxy) cinchona alkaloids, derived from natural cinchona alkaloids, were applied in asymmetric transfer hydrogenation in both iridium and rhodium catalytic systems using i‐propanol as the hydrogen source. A series of aromatic ketones was examined, and good to excellent conversions and enantioselectivities were observed. The best results were achieved using 9‐amino(9‐deoxy) epicinchonine 2a as the ligand and [Ir(COD)Cl]₂ as the metal precursor, and for the isobutylphenone, the conversion and enantioselectivity were obtained in 90 and 97% e.e. respectively. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of cis-1,2-diol-type chiral ligands and their dioxaborinane derivatives: Application for the asymmetric transfer hydrogenation of various ketones and biological evaluation

Two cis-1,2-diol-type chiral ligands (T ₁ and T ₂ ) and their tri-coordinated chiral dioxaborinane (T _(1–2) B _(1–2) ) and four-coordinated chiral dioxaborinane adducts with 4-tert-butyl pyridine sustained by N → B dative bonds (T _(1–2) B _(1–2) -N) were synthesized and characterized by various spectroscopic techniques such as NMR (¹H, ¹³C, and ¹¹B), FT-IR and UV–Vis spectroscopy, LC–MS/MS, and elemental analysis. It was suggested that both ferrocene and trifluoromethyl groups played key roles in the catalytic and biological studies because they could tune the solubility of the chiral dioxaborinane complexes and adjust the strength of intermolecular interactions. To assess the biological activities of newly synthesized chiral dioxaborinane compounds, DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging, reducing power, antibacterial, DNA binding, and DNA cleavage activities were tested. Then, all chiral dioxaborinane complexes were investigated as catalysts for the asymmetric transfer hydrogenation of various ketones under suitable conditions. The results indicated that the chiral dioxaborinane catalysts performed well with high yields.     

新型手性环状胺膦配体的设计合成及在酮的不对称还原中的应用

新型手性配体的设计合成是不对称催化研究的重要内容,其中手性胺膦配体因同时含有"软"的磷原子和"硬"的氮原子而具有丰富的配位化学性能和优秀的不对称诱导能力.本文总结了本研究组最近设计合成的手性环状胺膦配体的制备、表征及其在铁催化酮的不对称还原中的应用.手性1,2-环己二胺与双(2-甲酰基苯基)苯基膦通过[2+2]环缩合反应能够顺利获得手性22元环的亚胺膦配体21,该配体经Na BH4还原后生成大环胺膦配体22.利用手性大环胺膦配体22与Fe3(CO)12原位生成的催化体系,能够高活性、高对映选择性地实现包括杂环芳香酮在内50多种酮的不对称转移氢化和不对称氢化反应,其S/C(底物与催化剂的摩尔比)最高可达5000:1,产物手性芳香醇的光学纯度高达99%ee.     

手性酒石酸二酰胺配体的合成及其锡络合物与苯甲醛的不对称加成

通过酒石酸乙酯和不同胺的酰胺化, 相应地合成到(+)N,N'-二苯基酒石酸二酰胺(2), (+)N,N'-二苄基酒石酸二酰胺(3),(+)N,N'-二环己基酒石酸二酰胺(4)和(+)N,N'-二正辛基酒石酸二酰胺(5).氯化亚锡与2当量的酒石酸二酰胺反应, 再加入烯丙基溴可制得手性锡络合物6, 锡络合物与苯甲醛反应,得到光学活性的高烯丙基化合物, 产率42～64％ , e.e.值24～62％.     

Binuclear and polynuclear rhodium complexes containing chiral dithiolate ligands derived from lactic acid

Two precursors of the chiral dithiolato ligands, di‐[(2R)‐acetylmercaptopropyl] phthalate and isophthalate, 1 and 2 respectively, were synthesized from (S)‐lactic acid. Reactions of 1 and 2 with [Rh₂(μ)‐OMe)₂(cod)₂] (cod = 1,5‐cyclo‐octtadiene) yielded rhodium thiolato complexes of different nuclearities. The mixtures of complexes were analyzed by gel‐permeation chromatography (GPC). The reaction with ligand 1 produced a mixture of oligomeric complexes, where the binuclear species was the main component. Higher‐nuclearity complexes were the main products of the reaction with ligand 2. The rhodium complexes, in the presence of PPh₃, were tested as catalyst precursors for the asymmetric hydroformylation of styrene. Moderate activity and regioselectivity were achieved in most cases, but no enantioselective discrimination was observed. Copyright © 2000 John Wiley & Sons, Ltd.     

Modular chiral bidentate phosphonites: design, synthesis, and application in catalytic asymmetric hydroformylation reactions

A new class of C(2)-symmetric chiral bidentate phosphonite ligands has been synthesized in moderate to good yields from readily available starting materials. Application of these air-stable chiral phosphonites in the Rh(I)-catalyzed asymmetric hydroformylation of styrene derivatives, vinyl acetate, and allyl cyanide afforded the corresponding chiral aldehydes with high regio- and enantioselectivities under mild reaction conditions. The modular nature of the ligands allows fine-tuning of the selectivities through judicious modifications of the substituents on the ligand backbone. X-ray structural analysis of the catalyst precursor suggested that the steric hindrance caused by the protruding remote substituents of the ligands into the vicinity of the metal center might be an important factor for the enantio-control of the reaction, whereas the sense of asymmetric induction can be rationalized on the basis of a trigonal-bipyramidal transition state diagram.     

Novel chiral thiazoline‐containing N―O ligands in the asymmetric addition of diethylzinc to aldehydes: substituent effect on the enantioselectivity

Several novel chiral thiazoline primary and tertiary alcohols were easily synthesized from commercially available l ‐cysteine in three steps and with high yield. These ligands were subsequently applied to the asymmetric addition of diethylzinc (Et₂Zn) to various aldehydes. Products with S configuration were obtained when thiazoline‐containing tertiary alcohol ligands were used as catalysts. The primary alcohol induced corresponding products with R configuration in 68% enantiomeric excess, which was a higher value relative to other N―O ligands possessing a primary alcohol unit in the literature. Furthermore, a plausible transition state model was proposed to explain the observed enantioselectivities. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel chiral ferrocenyl-imino phosphine ligands and their use in palladium catalyzed allylic alkylations

New chiral P,N-ferrocenyl imino-phosphine ligands have been synthesized and the absolute configuration of the stereocenters in each molecule has been determined by a single-crystal X-ray analysis of a common intermediate. Pd^II-allyl complexes of the new ligands have been isolated and tested as catalyst precursors in the asymmetric allylic alkylation of 1,3-diphenylprop-2-en-1-yl acetate with dimethyl malonate in different solvents. Quantitative yields and enantiomeric excesses as high as 80% have been obtained.     

Catalytic asymmetric aziridination with borate catalysts derived from VANOL and VAPOL ligands: scope and mechanistic studies

An extended study of the scope and mechanism of the catalytic asymmetric aziridination of imines with ethyl diazoacetate mediated by catalysts prepared from the VANOL and VAPOL ligands and triphenylborate is described. Nonlinear studies with scalemic VANOL and VAPOL reveal an essentially linear relationship between the optical purity of the ligand and the product suggesting that the catalyst incorporates a single molecule of the ligand. Two species are present in the catalyst prepared from B(OPh)(3) and either VANOL or VAPOL as revealed by (1)H NMR studies. Mass spectral analysis of the catalyst mixture suggests that one of the species involves one ligand molecule and one boron atom (B1) and the other involves one ligand and two boron atoms (B2). The latter can be formulated as either a linear or cyclic pyroborate and the (11)B NMR spectrum is most consistent with the linear pyroborate structure. Several new protocols for catalyst preparation are developed which allow for the generation of mixtures of the B1 and B2 catalysts in ratios that range from 10:1 to 1:20. Studies with catalysts enriched in the B1 and B2 species reveal that the B2 catalyst is the active catalyst in the VAPOL catalyzed asymmetric aziridination reaction giving significantly higher asymmetric inductions and rates than the B1 catalyst. The difference is not as pronounced in the VANOL series. A series of 12 different imines were surveyed with the optimal catalyst preparation procedure with the finding that the asymmetric inductions are in the low to mid 90s for aromatic imines and in the mid 80s to low 90s for aliphatic imines for both VANOL and VAPOL catalysts. Nonetheless, the crystallinity of the N-benzhydryl aziridines is such that nearly all of the 12 aziridine products screened can be brought to >99 % ee with a single recrystallization.     

Rh(I) complexes with new C2‐symmetric chiral diphosphoramidite ligands: Catalytic activity for asymmetric hydrogenation of olefins

The design and synthesis of three new C ₂‐symmetric chiral diphosphoramidite ligands starting from simple and cheap building blocks have been developed. Rhodium(I) cationic complexes bearing these chelate ligands have been prepared and applied in asymmetric hydrogenation of model olefins. A rhodium complex with a diphosphoramidite containing a chiral diamine configurationally stable and two fluxional chiral biphenyl units gave higher enantioselectivity with increasing hydrogen pressure (87% ee) in the hydrogenation of dimethyl itaconate.     

Recent applications of chiral ferrocene ligands in asymmetric catalysis

Despite the impressive progress achieved in asymmetric catalysis during the last decade, an increasing number of new catalysts, ligands, and applications are reported every year to satisfy the need to embrace a wider range of reactions and to improve the efficiency of existing processes. Because of their availability, unique stereochemical aspects, and wide variety of coordination modes and possibilities for the fine-tuning of the steric and electronic properties, ferrocene-based ligands constitute one of the most versatile ligand architectures in the current scenario of asymmetric catalysis. Over the last few years ferrocene catalysts have been successfully applied in an amazing variety of enantioselective processes. This Review documents these recent advances, with special emphasis on the most innovative asymmetric processes and the development of novel, efficient types of ferrocene ligands.