Application In Asymmetric Catalysis Research Articles

Chiral catalysts derived from biomass: design, synthesis and applications in asymmetric catalysis

AbstractThe development of new and more efficient catalytic systems is the subject of increasing attention from both academic and industrial research. Moreover, biomass is an endless supply of hydrocarbon materials that can be used as renewable raw materials for the development of new organic compounds. In this context, many research groups have devoted their works to products with a natural chirality source, non‐toxic, biodegradable and usually cost effective for the development of new chiral catalysts. Some new chiral molecules derived from biomass such as carbohydrates and natural amino acids have been synthesized and used as chiral ligands or organocatalysts for asymmetric transformations leading to the formation of expected products in good yields with high enantioselectivities

Carbohydrate-Based Chiral Iodoarene Catalysts: A Survey through the Development of an Improved Catalyst Design.

Iodoarene catalysts can be applied in versatile reactions, for instance in the construction of complex chiral molecules via dearomatization of simple aromatic compounds. Recently, we reported the synthesis of the first carbohydrate-based chiral iodoarene catalysts and their application in asymmetric catalysis. Here we describe the synthesis of some new and improved catalysts. An account on how we got to the improved catalyst design, as well as the X-ray structure of one of the carbohydrate-based iodoarenes, is given.

Chirality Transfer in Galvanic Replacement Reactions.

Demand for the transfer of chirality from a pre-engineered nanoparticle to any other metal is of fundamental importance for developing a wide range of chirality-related applications. Herein, we show that binary alloy chiral nanoparticles (CNPs) with an engineerable composition can be formed from metallic CNPs with intrinsic structural chirality serving as sacrificial templates (STs), via a galvanic replacement reaction (GRR). This GRR-mediated chirality transfer is a general phenomenon and results in the formation of Cu-Ag CNPs with solid morphology and mesoporous CNPs made of Ag-Au, Ag-Pt, and Ag-Pd. Our study imposes a new component, i.e., structural chirality, on the GRR. The insights from our study improve our fundamental understanding of the GRR principle and devise a versatile method to generate mesoporous alloy CNPs for developing prominent chirality-related applications in asymmetric catalysis, enantiodifferentiation, enantioseparation, biodetection, and bioimaging.

N-Substituted Benzene-1-Urea-3,5-Biscarboxamide (BUBA): Easily Accessible C2 -Symmetric Monomers for the Construction of Reversible and Chirally Amplified Helical Assemblies.

Non-C3 -symmetric supramolecular helices are gaining interest for the design of hierarchical assemblies, for the compartmentalisation or the self-assembly of polymer chains and for application in asymmetric catalysis. Herein, N-substituted benzene-1-urea-3,5-biscarboxamide (BUBA) monomers, which consist of one urea and two carbon-connected amide functions linked to an aromatic ring, are introduced as an easily accessible class of C2 -symmetric supramolecular synthons. In apolar solvents, BUBA monomers assemble into long helical assemblies by means of hydrogen-bonding and aromatic interactions, as assessed by several analytical techniques. To probe the influence of the urea function, BUBA and related benzene-1,3,5-tricarboxamide (BTA) helical polymers have been compared, in terms of their thermodynamics of formation, stability, reversibility and chiral amplification properties. Similar to BTA, BUBA monomers form long helices reversibly through a highly cooperative mechanism and the helicity of their assemblies is governed by chiral amplification effects. However, precise quantification of their properties reveals that BUBA monomers assemble in a more cooperative manner. Also, chiral amplification operates to a higher extent in BUBA helices, as probed by both sergeants-and-soldiers and majority-rules experiments. Compatibility between urea and amide functions also allows the formation of co-assemblies that incorporate both BUBA and BTA monomers. Importantly, a small amount of chiral BUBA monomers in these co-assemblies is sufficient to obtain single-handed helices; thus paving the way towards the development of functional supramolecular helices.

Selective Synthesis of Interlocked Molecules with Topological Chirality

Mechanically interlocked molecules can be chiral if each of the rings has no bilateral symmetry. Although chiral catenanes have been isolated from racemic mixtures via chromatographic techniques, these optically active molecules have not been directly synthesized until now. In this issue of Chem, Goldup and co-workers describe an auxiliary approach for the stereoselective synthesis of the topological enantiomers of chiral [2]catenanes. This methodology enables exploration of the potential applications of these chiral molecules in areas such as medicine and materials science.

Synthesis of Crosslinked Chiral Polysiloxanes of Cinchona Alkaloid Derivatives and their Applications in Asymmetric Catalysis

AbstractCrosslinked chiral polysiloxanes containing cinchona alkaloid derivatives were synthesized from poly(methylhydrosiloxane) by hydrosilylation reaction. The C3‐vinyl group of cinchona alkaloid derivatives were easily hydrosilylated with Si−H functional groups of poly(methylhydrosiloxane) by using Pt catalyst. The reaction between cinchona alkaloid dimers and poly(methylhydrosiloxane) and afforded the crosslinked chiral polysiloxanes. Partial hydrolysis of Si−H bonds with Pt catalyst during reaction resulted in a formation of extra crosslinkages of chiral polysiloxanes. Mixed solvent (toluene and DMF) system was employed for a successful immobilization of C6′−OH free cinchona alkaloid derivatives into poly(methylhydrosiloxane). Both cinchona alkaloid C9‐ester and C9‐urethane derivatives were incorporated into poly(methylhydrosiloxane) through Si−C bond. The resulted crosslinked chiral polysiloxanes were insoluble in common organic solvents. Their catalytic performance was evaluated in asymmetric Michael addition reactions. The chiral polysiloxanes of cinchona alkaloid having C6′−OH showed higher enantioselectivities (up to 99% ee) with sufficient catalytic activities in the Michael addition reactions. The chiral polysiloxanes were easily recovered by filtration or centrifugation method and could be reused for several times without losing their catalytic performance.

Chiral zeolite beta: structure, synthesis, and application

Pure polymorph-A of zeolite beta with chiral pore structure has potential applications in asymmetric catalysis and chiral separations.

P-Chiral 1,7-diphosphanorbornenes: from asymmetric phospha-Diels-Alder reactions towards applications in asymmetric catalysis.

A straightforward synthesis of P-chiral polycyclic phosphines by an asymmetric Diels-Alder reaction of 1-alkyl-1,2-diphospholes and (5R)-(l-menthyloxy)-2(5H)-furanone (MOxF) is presented. The [4 + 2] cycloaddition reaction of 1,2-diphospholes 1-3 with MOxF (4) proceeded with high diastereoselectivity (de up to 90%) resulting in the corresponding enantiopure anti-endo-1,7-diphosphanorbornenes 5a-7a. The absolute configuration of 5-7 was proved by a variety of 1D/2D NMR correlation methods. The use of the anti-endo-1,7-diphosphanorbornene 5a in the Pd-catalyzed asymmetric allylic alkylation of cinnamyl acetate 8 with cyclic β-ketoesters 9a,b provided up to 52% ee.

Applications of N'-monofunctionalised TsDPEN derivatives in asymmetric catalysis.

This review contains an account of recent developments in the applications of N'-monoalkylated or N'-mono(thio)acylated(N-sulfonyl)-1,2-diphenylethylene-1,2-diamine (TsDPEN) derivatives to asymmetric catalysis. The coverage features examples of applications of derivatives as ligands in organometallic complexes for use in asymmetric reduction and oxidation reactions. The use of TsDPEN derivatives as catalysts in a diverse range of C-C and C-S bond formation reactions is also described in detail.

A Cooperative Hydrogen Bond Donor-Brønsted Acid System for the Enantioselective Synthesis of Tetrahydropyrans.

Carbocations stabilized by adjacent oxygen atoms are useful reactive intermediates involved in fundamental chemical transformations. These oxocarbenium ions typically lack sufficient electron density to engage established chiral Brønsted or Lewis acid catalysts, presenting a major challenge to their widespread application in asymmetric catalysis. Leading methods for selectivity operate primarily through electrostatic pairing between the oxocarbenium ion and a chiral counterion. A general approach to new enantioselective transformations of oxocarbenium ions requires novel strategies that address the weak binding capabilities of these intermediates. We demonstrate herein a novel cooperative catalysis system for selective reactions with oxocarbenium ions. This new strategy has been applied to a highly selective and rapid oxa-Pictet-Spengler reaction and highlights a powerful combination of an achiral hydrogen bond donor with a chiral Brønsted acid.

A Cooperative Hydrogen Bond Donor–Brønsted Acid System for the Enantioselective Synthesis of Tetrahydropyrans

AbstractCarbocations stabilized by adjacent oxygen atoms are useful reactive intermediates involved in fundamental chemical transformations. These oxocarbenium ions typically lack sufficient electron density to engage established chiral Brønsted or Lewis acid catalysts, presenting a major challenge to their widespread application in asymmetric catalysis. Leading methods for selectivity operate primarily through electrostatic pairing between the oxocarbenium ion and a chiral counterion. A general approach to new enantioselective transformations of oxocarbenium ions requires novel strategies that address the weak binding capabilities of these intermediates. We demonstrate herein a novel cooperative catalysis system for selective reactions with oxocarbenium ions. This new strategy has been applied to a highly selective and rapid oxa‐Pictet–Spengler reaction and highlights a powerful combination of an achiral hydrogen bond donor with a chiral Brønsted acid.

Chiral organobases: Properties and applications in asymmetric catalysis

Chiral organobases occupy a significant position in asymmetric organocatalysis. The general types of chiral organobases include tertiary amines, amidines, guanidines, cyclopropenimines, and iminophosphoranes, etc. These organobases are demonstrated to be effective organocatalysts to promote divers kinds of base-initiated reactions in excellent yields and stereoselectivities. In previous reports, several groups have summarized each kind of chiral organobases in different reviews. To the aim of understanding the whole of them in one review, herein, we provide a brief introduction of these chiral organobases in asymmetric catalysis.

Stereoselective and Stereospecific Reactions of Cobalt Sandwich Complexes: Synthesis of a New Class of Single Enantiomer Bulky Planar Chiral P-N and P-P Ligands.

Starting from (η5 -acetylcyclopentadienyl)(η4 -tetraphenylcyclobutadiene)cobalt(I), highly enantioselective (99 % ee) (S)-CBS catalysed ketone reduction followed by stereospecific alcohol-azide exchange, azide reduction and dimethyllation gave (R)-(η5 -α-N,N-dimethylaminoethylcyclopentadienyl)(η4 -tetraphenylcyclobutadiene) cobalt(I) (Arthurs' amine). This underwent highly diastereoselective cyclopalladation to give di-μ-acetate-bis-(R)-[(η5 -(Sp )-2-(α-N,N-dimethylaminoethyl)cyclopentadienyl, 1-C, N)(η4 -tetraphenylcyclobutadiene)cobalt(I)]dipalladium, and highly diastereoselective lithiation to give (R)-(η5 -(Sp )-1-(α-N,N-dimethylaminoethyl)-2-(diphenylphosphino)cyclopentadienyl)(η4 -tetraphenylcyclobutadiene)cobalt(I) (PPCA) following the addition as electrophile of chlorodiphenylphosphine. This PN-ligand was converted into (R)-(η5 -(Sp )-1-(α-dicyclohexylphosphinoethyl)-2-(diphenylphosphino)cyclopentadienyl)(η4 -tetraphenylcyclobutadiene)cobalt(I), a PP-ligand (Rossiphos), by stereospecific amine-phosphine exchange using HPCy2 . These air-stable P-N and P-P complexes are the first examples of a new class of bulky planar chiral ligands for application in asymmetric catalysis.

Renaissance of pyridine-oxazolines as chiral ligands for asymmetric catalysis.

Oxazoline-containing ligands have been widely employed in numerous asymmetric catalytic reactions. Pyridine-oxazoline-type ligands, a class of hybrid ligands, were designed earlier than bisoxazoline and phosphine-oxazoline ligands; however, their unique properties have only been discovered recently. Pyridine-oxazoline-type chiral ligands are rapidly becoming popular for use in asymmetric catalysis, especially for several new and efficient asymmetric methodologies. Several types of challenging asymmetric reactions have been discovered recently using pyridine-oxazoline-type ligands showing their special properties and potential for future application in a wide range of new catalytic methodologies. This review provides an overview of this field, with the aim of highlighting both ligand design and synthetic methodology development.

均一系オレフィン・メタセシス反応による面不斉遷移金属錯体のエナンチオ選択的合成法の開発と不斉触媒反応への応用

均一系オレフィン・メタセシス反応による面不斉遷移金属錯体のエナンチオ選択的合成法の開発と不斉触媒反応への応用

Efficient and Stereoselective Synthesis of the Chiral Dihydroxy-bisquinazoline-dione Derivatives and Their Application in Asymmetric Catalysis

探索了手性苯并噁嗪-2-酮二酚衍生物的高效合成，以甲氧基取代的2-羟基苯甲醛衍生物和手性环己二胺为起始原料合成手性双亚胺，后经低价钛促进下还原、偶联与固体光气作用，构建了含有甲氧基的手性苯并噁嗪-2-酮衍生物，通过官能团转化，利用三溴化硼还原得到相应的手性苯并噁嗪-2-酮二酚衍生物.在此基础上，考察了手性苯并噁嗪-2-酮二酚催化剂在醛与二乙基锌不对称加成中的应用.此方法为合成手性苯并噁嗪-2-酮二酚衍生物提供了一条有效途径.

Synthesis of MeO-PEG2000-supported chiral ferrocenyl oxazoline carbinol ligand and its application in asymmetric catalysis

A simple method for the synthesis of a MeO-PEG-supported chiral ferrocenyl oxazoline carbinol ligand has been developed. The chiral ligand was successfully applied to the catalytic asymmetric addition of diethylzinc to aryl aldehydes, affording secondary alcohols in high yields and with excellent enantioselectivities (up to 94% ee). The chiral ligand can be recovered and reused twice with no apparent loss of catalyst efficiency.

Features and Application in Asymmetric Catalysis of Chiral Phosphine-Phosphite Ligands.

Chiral phosphine-phosphites are a class of ligands for asymmetric catalysis characterized by two coordinating functionalities with different electronic properties. These ligands also possess a highly modular structure and, due to versatile synthetic processes, they can be tuned precisely in the catalyst optimization process. Research regarding the application of these ligands in several enantioselective catalytic processes has provided outstanding results in a good number of them. These processes include not only Rh catalyzed reactions, such as olefin hydrogenation and hydroformylation, but also other reactions, such as hydrogenation of olefins and imines by Ru complexes, of imines and N-heterocycles by Ir derivatives, allyl alkylation or conjugate addition by Cu catalysts, or hydrocyanation of olefins by Ni ones. Overall, the use of these ligands has led to the preparation of a wide variety of chiral building blocks with high enantiomeric excess. Therefore, phosphine-phosphites have become in an important class of ligands in asymmetric catalysis.

ChemInform Abstract: Chirality and Catalysis with Aromatic N‐Fused Heterobicyclic Carbenes

AbstractReview: 33 refs.

Synthesis of titanium-containing helical silicates for catalytic oxidation of alkenes

A new series of titanium-containing helical silicates were prepared by doping of chiral sodium lactate in a sol–gel process. Characterizations revealed that the present titanium materials had good porosities, hexagonal symmetries, helical morphologies, as well as right-handed internal chiralities. Loading of chiral sodium lactate in preparation facilitated internal chiralities of synthetic products. In catalysis, the titanium materials showed moderate-to-excellent conversions, moderate-to-high stereoselectivities, and satisfactory recyclings for oxidation of aliphatic and aromatic alkenes by using solid oxidants such as iodobenzene diacetate and iodosylbenzene. Furthermore, both using ionic liquid as solvent and leaching of catalyst were studied. In general, titanium-containing chiral silicates were provided, and their applications in asymmetric catalysis were discussed too, which showed values on design of new efficient chiral catalysts.