Chiral dendritic bis(oxazoline) copper(II) complexes as Lewis acid catalysts for enantioselective aldol reactions in aqueous media

A series of copper(II) complexes, with chiral bis(oxazoline) ligands disubstituted at the carbon atom linking the two oxazolines by Fréchet-type polyether dendrimers, have been designed and synthesized. These complexes were used as Lewis acid catalysts in enantioselective aldol reactions in aqueous media. Good yields and moderate enantioselectivities were achieved, which are comparable with those resulting from the corresponding smaller catalysts.     

手性双噁唑啉配体在不对称合成中的应用

双噁唑啉手性配体已广泛用于不对称Henry反应、环丙烷化反应、Aldol反应、烷基化反应、环加成反应中,并表现出很高的对映选择性和催化活性,成为最有用的手性配体之一。文章综述了近10年来双噁唑啉手性配体及高分子受载手性双噁唑啉在不对称合成中的研究进展。     

Effective binuclear Pd(II) complexes for Suzuki reactions in water

A series of new ionic binuclear Pd(II) complexes supported by water‐soluble bis(α‐diimine) ligands were prepared and employed as catalysts for the palladium‐catalyzed Suzuki reaction in aqueous media. The binuclear nature of the complexes increased the reaction rate, while electronic and steric modification of the ligand frameworks had a remarkable influence upon the catalytic activity of the palladium complexes. The catalysts were shown to be homogeneous through mercury poisoning experiments and complexes could be recycled more than 10 times without loss of catalytic activity. Copyright © 2013 John Wiley & Sons, Ltd.     

三氟甲基磺酸铜(II)手性衍生物:不对称合成中的一类高效催化剂

三氟甲基磺酸铜 [Cu(OTf) 2 ]与各种手性磷氮配体络合催化不对称合成已取得了巨大进展 .详细评述了近五年来该类手性铜催化剂在各种不对称催化反应中的最新应用     

手性双唑啉铜配合物在不对称合成中的应用

综述了手性双E唑啉配体的主要结构类型,并讨论了手性双E唑啉铜配合物在不对称Diels-Alder反应、Ene反应、Mukaiyama adol反应、烯丙基氧化、环丙烷化、氮杂环丙烷化等反应中的应用。     

Reversal of enantioselection in an aldol reaction catalyzed by sterically congested bis(oxazoline)–Cu(II) complexes

The use of sterically congested C₂-symmetrical bis(oxazoline) ligands with methylene and ethylene spacers between the oxazoline rings results in the reversal of the enantioselection for aldol reactions catalyzed by bis(oxazoline)–Cu(II) complexes.     

Surface-enhanced stereoselectivity in Mukaiyama aldol reactions catalyzed by clay-supported bis(oxazoline)-copper complexes

Surface effects on a laponite-exchanged bis(oxazoline)-copper complex modify the stereochemical course of the Mukaiyama aldol reaction between 2-(trimethylsilyloxy)furan and alpha-ketoesters, leading up to 90% ee (dr 86 : 14) becoming the best overall result obtained for this reaction and significantly improving the homogeneous process.     

m-Carborane-based chiral NBN pincer-metal complexes: synthesis, structure, and application in asymmetric catalysis

We have succeeded in synthesizing m-carborane-based chiral NBN-pincer ligands, 1,7-bis(oxazolinyl)-1,7-dicarba-closo-dodecaborane (Carbox) (7-9). The combination of bis(hydroxyamides) and 3 equiv of diethylaminosulfur trifluoride (DAST) is a key step for cyclization to form oxazoline rings in excellent yields. X-ray crystal structures of these ligands confirmed three donor sites, one central B and two flanking N atoms in fixed positions. The electrophilic halogenation of the Carbox pincer ligands with iodine and a catalytic amount of Lewis acid led to ring-opening of the oxazolines and afforded bis(haloamides) (13 and 14). The air- and moisture-stable Carbox pincer complexes of rhodium(III), nickel(II), and palladium(II) were synthesized by the oxidative addition of RhCl(3)·3H(2)O, Ni(COD)(2), and Pd(CH(3)CN)(4)[BF(4)](2) to the Carbox pincer ligands (7-9), respectively. The catalytic activity of the rhodium(III) complexes (18-20) was examined for the asymmetric conjugate reduction of α,β-unsaturated esters and reductive aldol reaction. Among these catalysts, [(S,S)-Carbox-iPr]Rh(OAc)(2)·H(2)O (18) showed the highest enantioselective catalytic ability for both asymmetric conjugate reduction and reductive aldol reaction.     

Catalytic reactions in ionic liquids

The chemical industry is under considerable pressure to replace many of the volatile organic compounds (VOCs) that are currently used as solvents in organic synthesis. The toxic and/or hazardous properties of many solvents, notably chlorinated hydrocarbons, combined with serious environmental issues, such as atmospheric emissions and contamination of aqueous effluents is making their use prohibitive. This is an important driving force in the quest for novel reaction media. Curzons and coworkers, for example, recently noted that rigorous management of solvent use is likely to result in the greatest improvement towards greener processes for the manufacture of pharmaceutical intermediates. The current emphasis on novel reaction media is also motivated by the need for efficient methods for recycling homogeneous catalysts. The key to waste minimisation in chemicals manufacture is the widespread substitution of classical 'stoichiometric' syntheses by atom efficient, catalytic alternatives. In the context of homogeneous catalysis, efficient recycling of the catalyst is a conditio sine qua non for economically and environmentally attractive processes. Motivated by one or both of the above issues much attention has been devoted to homogeneous catalysis in aqueous biphasic and fluorous biphasic systems as well as in supercritical carbon dioxide. Similarly, the use of ionic liquids as novel reaction media may offer a convenient solution to both the solvent emission and the catalyst recycling problem.     

Reusable catalysts for the asymmetric Diels-Alder reaction

A new method for recycling chiral bis(oxazoline)-copper complexes is described based on the formation of charge-transfer complexes, their subsequent precipitation, and reuse after addition of new substrates. The conditions to perform this procedure were optimized in the presence of three bis(oxazoline)-based ligands. When associated with copper salts, these ligands efficiently catalyzed the Diels-Alder reaction between cyclopentadiene and alpha,beta-unsaturated acyloxazolidinones. These catalysts were successfully recycled up to ten times while maintaining their high activities and enantioselectivities.     

Novel chiral gallium Lewis acid catalysts with semi-crown ligands for aqueous asymmetric Mukaiyama aldol reactions

Asymmetric Mukaiyama aldol reactions in aqueous media (water-ethanol = 9:1) were catalyzed by chiral gallium catalysts with semi-crown ligands to give aldol products with good yields, syn-diastereoselectivities and enantioselectivities.     

Asymmetric Diels—Alder Reaction Catalyzed by Novel Chiral Dibenzo[a,c] cycloheptadiene Bis（oxazoline） Metal Complexes

A series of novel chiral C2-symmetric bis (oxazoline) ligands have been synthesized.The copper and magnesium complexes,prepared in situ from copper(Ⅱ)-triflate of magnesium triflate with the new enantiopure oxazoline ligands,were evaluated as chiral catalysts in the enantioselective Diels-Alder reaction of cyclopentadiene with N-crotenoyl-oxazolidin-2-one.Primary results showed that diastereoselectivity up to 94% and enantioselectivity up to 68% ee for endo products were observed respectively with these ligands.     

Chiral iridium(I) bis(NHC) complexes as catalysts for asymmetric transfer hydrogenation

The common use of NHC complexes in transition‐metal mediated C–C coupling and metathesis reactions in recent decades has established N‐heterocyclic carbenes as a new class of ligand for catalysis. The field of asymmetric catalysis with complexes bearing NHC‐containing chiral ligands is dominated by mixed carbene/oxazoline or carbene/phosphane chelating ligands. In contrast, applications of complexes with chiral, chelating bis(NHC) ligands are rare. In the present work new chiral iridium(I) bis(NHC) complexes and their application in the asymmetric transfer hydrogenation of ketones are described. A series of chiral bis(azolium) salts have been prepared following a synthetic pathway, starting from L ‐valinol and the modular buildup allows the structural variation of the ligand precursors. The iridium complexes were formed via a one‐pot transmetallation procedure. The prepared complexes were applied as catalysts in the asymmetric transfer hydrogenation of various prochiral ketones, affording the corresponding chiral alcohols in high yields and moderate to good enantioselectivities of up to 68%. The enantioselectivities of the catalysts were strongly affected by the various, terminal N‐substituents of the chelating bis(NHC) ligands. The results presented in this work indicate the potential of bis‐carbenes as stereodirecting ligands for asymmetric catalysis and are offering a base for further developments. Copyright © 2010 John Wiley & Sons, Ltd.     

A new class of substituted aryl bis(oxazoline) ligands for highly enantioselective copper-catalyzed asymmetric aldol addition of dienolsilane to pyruvate and glyoxylate esters

[reaction: see text] A new class of bis(oxazoline) ligands are introduced that feature o-alkoxyaryl substituents and provide the highest enantioselectivities yet reported for the copper-catalyzed asymmetric dienosilane aldol addition to pyruvate and glyoxylate esters. Enantioselectivities up to 98% ee (before recrystallization) and isolated yields up to 91% were observed. Additionally, chloride counterions were found to be superior to triflate for this reaction.     

Bis(oxazoline)copper complexes covalently bonded to insoluble support as catalysts in cyclopropanation reactions.

Chiral bis(oxazolines) are readily dialkylated in the methylene bridge, opening the way to immobilization at that position, keeping the C(2) symmetry of the chiral ligand. Bis(oxazolines) functionalized with two allyl or vinylbenzyl groups are easily grafted onto mercaptopropylsilica. Another approach to immobilization is the polymerization of the ligands bearing vinylbenzyl groups to yield insoluble polymers. The Cu(OTf)(2) complexes of the immobilized ligands promote the enantioselective cyclopropanation reaction between styrene and ethyl diazoacetate. The results depend on the nature of the support and the method of immobilization. With regard to the type of solid, the best results, which are similar to or even better than those obtained with the corresponding dibenzylated homogeneous catalysts, are obtained with homopolymers. With regard to the bis(oxazoline), that bearing indan groups leads to good results both onto silica and polymers, whereas with the ligand bearing tert-butyl groups good enantioselectivities are only obtained with homopolymeric catalysts. Some of the heterogeneous catalysts can be easily recovered and reused, as much as five times, with the same yield and stereoselectivities.     

全氟烷基磺酸盐和全氟烷基磺酰亚胺盐的多相化催化研究

传统的Lewis酸催化剂在环境的压力下受到挑战,全氟烷基磺酸盐和全氟烷基磺酰亚胺盐作为均相、高效的Lewis酸催化剂在有机合成中受到人们的关注.为了简化分离操作,人们对全氟烷基磺酸盐和全氟烷基磺酰亚胺盐的多相化进行了研究,并已取得巨大进展.本文综述了全氟烷基磺酸盐和全氟烷基磺酰亚胺盐分别负载在有机载体、无机载体以及离子液体上的多相化催化最新研究进展,简要概括了其制备方法和催化活性,并对其催化应用前景进行了展望.     

First Pre‐Functionalised Polymeric Aromatic Framework from Mononitrotetrakis(iodophenyl)methane and its Applications

Starting from mononitrotetrakis(iodophenyl)methane as monomer, we report the preparation of the first pre‐functionalised porous aromatic frameworks (PAFs) and their application as supports for organometallic catalysts. Neutral coordinate imino‐pyridine Schiff base ( PAF‐NPy ) or chiral bis‐amino ( PAF‐NPro ) ligands were obtained by post‐synthetic treatment of PAF‐NH₂ and treated with copper(I) or rhodium(I) to yield the corresponding supported transition‐metal catalysts. The as‐prepared PAF‐NN‐M catalysts exhibited activity and selectivity similar to that of the corresponding homogeneous catalysts and were easily removed from reaction media and recycled without loss of activity or selectivity.     

C1-symmetric versus C2-symmetric ligands in enantioselective copper-bis(oxazoline)-catalyzed cyclopropanation reactions

A thorough experimental and theoretical study of the enantioselective cyclopropanation of alkenes catalyzed by chiral bis(oxazoline)- and azabis(oxazoline)-copper complexes, which comprise a new family of ligands that lack C2 symmetry, has been conducted. Surprisingly high enantioselectivities were observed with some of these ligands, which were rationalized on the basis of molecular modeling studies. The course of the asymmetric induction in connection with ligand symmetry and the implications for supported enantioselective catalysts are discussed.     

Synthesis of new C1-symmetric bis(oxazoline) ligands with a chelating sidearm for stereoselective Mukaiyama aldol condensations

Novel C₁-symmetric bis(oxazoline) ligands with a secondary binding sidearm were prepared in enantiomerically pure form in good yields, in only four steps starting from commercially available reagents. These new chiral ligands were tested in the enantioselective Mukaiyama aldol condensation between the trimethylsilyl keteneacetal of methyl isobutyrate and a non-chelating substrate such as benzaldehyde to afford the product in up to 55% ee.     

金催化剂及其在有机反应中的应用研究进展*

本文综述了金催化剂在选择氧化、选择加氢、不对称醇醛缩合、C-N键生成等多相和均相催化反应中的应用研究,并讨论了各种影响金催化剂催化活性的因素,最后展望了金催化剂的应用前景.