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Asymmetric Ligand
In homogeneous catalysis, ''C''2-symmetric ligands refer to ligands that lack mirror symmetry but have ''C''2 symmetry (two-fold rotational symmetry). Such ligands are usually bidentate and are valuable in catalysis. The ''C''2 symmetry of ligands limits the number of possible reaction pathways and thereby increases enantioselectivity, relative to asymmetrical analogues. ''C''2-symmetric ligands are a subset of chiral ligands. Chiral ligands, including ''C''2-symmetric ligands, combine with metals or other groups to form chiral catalysts. These catalysts engage in enantioselective chemical synthesis, in which chirality in the catalyst yields chirality in the reaction product. Examples An early ''C''2-symmetric ligand, diphosphine catalytic ligand DIPAMP, was developed in 1968 by William S. Knowles and coworkers of Monsanto Company, who shared the 2001 Nobel Prize in Chemistry. This ligand was used in the industrial production of -DOPA. : Some classes of ''C''2-symmetric lig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homogeneous Catalysis
In chemistry, homogeneous catalysis is catalysis where the catalyst is in same phase as reactants, principally by a soluble catalyst in a solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid and gas, respectively. The term is used almost exclusively to describe solutions and implies catalysis by organometallic compounds. Homogeneous catalysis is an established technology that continues to evolve. An illustrative major application is the production of acetic acid. Enzymes are examples of homogeneous catalysts. Examples Acid catalyst The proton is a pervasive homogeneous catalyst because water is the most common solvent. Water forms protons by the process of self-ionization of water. In an illustrative case, acids accelerate (catalyze) the hydrolysis of esters: :CH3CO2CH3 + H2O CH3CO2H + CH3OH At neutral pH, aqueous solutions of most esters do not hydrolyze at practical rates. Transition met ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asymmetric Hydrogenation
Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen to a target (substrate) molecule with three-dimensional spatial selectivity. Critically, this selectivity does not come from the target molecule itself, but from other reagents or catalysts present in the reaction. This allows spatial information (what chemists refer to as chirality) to transfer from one molecule to the target, forming the product as a single enantiomer. The chiral information is most commonly contained in a catalyst and, in this case, the information in a single molecule of catalyst may be transferred to many substrate molecules, amplifying the amount of chiral information present. Similar processes occur in nature, where a chiral molecule like an enzyme can catalyse the introduction of a chiral centre to give a product as a single enantiomer, such as amino acids, that a cell needs to function. By imitating this process, chemists can generate many novel synthetic molecules that inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sharpless Asymmetric Dihydroxylation
Sharpless asymmetric dihydroxylation (also called the Sharpless bishydroxylation) is the chemical reaction of an alkene with osmium tetroxide in the presence of a chirality (chemistry), chiral quinine ligand to form a Vicinal (chemistry), vicinal diol. The reaction has been applied to alkenes of virtually every substitution, often high enantioselective, enantioselectivities are realized, with the chiral outcome controlled by the choice of dihydroquinidine (DHQD) vs dihydroquinine (DHQ) as the ligand. Asymmetric dihydroxylation reactions are also highly site selective, providing products derived from reaction of the most electron-rich double bond in the substrate. It is common practice to perform this reaction using a catalytic amount of osmium tetroxide, which after reaction is regenerated with reoxidants such as potassium ferricyanide or N-Methylmorpholine N-oxide, ''N''-methylmorpholine ''N''-oxide. This dramatically reduces the amount of the highly toxic and very expensive osm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dihydroquinine
Dihydroquinine, also known as hydroquinine or DHQ, is an organic compound and as a cinchona alkaloid closely related to quinine. The specific rotation is −148° in ethanol. A derivative of this molecule is used as chiral ligand in the AD-mix for Sharpless dihydroxylation. DHQ also inhibits growth of the parasite ''Toxoplasma gondii'' by inducing mitochondrial membrane damage, but does not disrupt host mitochondrial membrane potential, as well as reactive oxygen species In chemistry and biology, reactive oxygen species (ROS) are highly Reactivity (chemistry), reactive chemicals formed from diatomic oxygen (), water, and hydrogen peroxide. Some prominent ROS are hydroperoxide (H2O2), superoxide (O2−), hydroxyl ... (ROS) generation. See also * Dihydroquinidine References {{Other drugs for disorders of the musculo-skeletal system Secondary alcohols Phenol ethers Quinoline alkaloids Quinuclidine alkaloids Methoxy compounds ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AD-mix
In organic chemistry, AD-mix is a commercially available mixture of reagents that acts as an asymmetric catalyst for various chemical reactions, including the Sharpless asymmetric dihydroxylation of alkenes. The two letters AD, stand for asymmetric dihydroxylation. The mix is available in two variations, "AD-mix α" and "AD-mix β" following ingredient lists published by Barry Sharpless. Sharpless, K. B., ''et al.'' '' J. Org. Chem.'' 1992, ''57'', 2768-2771. () The mixes contain: * Potassium osmate K2OsO2(OH)4 as the source of Osmium tetroxide * Potassium ferricyanide K3Fe(CN)6, which is the re-oxidant in the catalytic cycle * Potassium carbonate * A chiral ligand: **AD-mix α contains (DHQ)2PHAL, the phthalazine adduct with dihydroquinine ::: :*AD-mix β contains (DHQD)2PHAL, the phthalazine Phthalazine, also called benzo-orthodiazine or benzopyridazine, is a heterocyclic organic compound with the molecular formula C8H6N2. It is isomeric with other naphthyridines including ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TADDOL
In organic chemistry, TADDOL is an acronym for . These compounds are easily accessed and are often used as chiral auxiliaries. TADDOLs consist of a dioxolane ring substituted with two mutually groups. They are derived from d,l-tartaric acid, an inexpensive C2-symmetric molecule. Condensation of dimethyl ester of d,l-tartaric acid with acetone gives the acetonide, a particular kind of dioxalane. The ester groups are susceptible to reaction with aryl Grignard reagents, leading after hydrolysis to the diol.Albert K. Beck, Peter Gysi, Luigi La Vecchia, and Dieter Seebach "(4R,5R)-2,2-Dimethyl-α,α,α',α'-tetra(naphth-2-yl))-1,3-dioxalane-4,5-dimethanol from Dimethyl Tartrate and 2-Naphthyl-Magnesium Bromide" Org. Synth. 1999, 76, 12. References {{Reflist Diols Dioxolanes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
BINAP
BINAP (2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) is an organophosphorus compound. This Optical isomerism, chiral diphosphines, diphosphine ligand is widely used in chiral synthesis, asymmetric synthesis. It consists of a pair of 2-diphenylphosphinonaphthalene, naphthyl groups linked at the 1 and 1′ positions. This C2-Symmetric ligands, C2-symmetric framework lacks a stereocenter, stereogenic atom, but has axial chirality due to restricted rotation (atropisomerism). The barrier to racemization is high due to steric hindrance, which limits rotation about the bond linking the naphthyl rings. The dihedral angle between the naphthyl groups is approximately 90°. The natural bite angle is 93°. Use as ligand in asymmetric catalysis BINAP is used in organic synthesis for enantioselective transformations catalyzed by its complex (chemistry), complexes of ruthenium, rhodium, and palladium. As pioneered by Ryōji Noyori and his co-workers, rhodium complexes of BINAP are usefu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Synthesis
Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the general subject of organic synthesis, there are many different types of synthetic routes that can be completed including total synthesis, Enantioselective synthesis, stereoselective synthesis, automated synthesis, and many more. Additionally, in understanding organic synthesis it is necessary to be familiar with the methodology, techniques, and applications of the subject. Total synthesis A total synthesis refers to the complete chemical synthesis of molecules from simple, Precursor (chemistry), natural precursors. Total synthesis is accomplished either via a linear or convergent approach. In a Linear synthesis, ''linear'' synthesis—often adequate for simple structures—several steps are performed sequentially until the molecule is com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bisoxazoline Ligand
Bis(oxazoline) ligands (often abbreviated BOX ligands) are a class of chiral ligand, privileged chiral ligands containing two oxazoline rings. They are typically molecular symmetry, C2‑symmetric and exist in a wide variety of forms; with structures based around Methylene bridge, CH2 or pyridine linkers being particularly common (often generalised BOX and PyBOX respectively). The coordination complexes of bis(oxazoline) ligands are used in asymmetric catalysis. These ligands are examples of C2-Symmetric ligands, C2-symmetric ligands. Synthesis The synthesis of oxazoline rings is well established and in general proceeded via the cyclisation of a 2‑amino alcohol with any of a number of suitable functional groups. In the case of bis(oxazoline)s, synthesis is most conveniently achieved by using bi-functional starting materials; as this allows both rings to be produced at once. Of the materials suitable, dicarboxylic acid, carboxylic or dinitrile compounds are the most commonly av ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Salen Ligand
Salen refers to a tetradentate C2-Symmetric ligands, C2-symmetric ligand synthesized from salicylaldehyde (sal) and ethylenediamine (en). It may also refer to a class of compounds, which are structurally related to the classical salen ligand, primarily bis-Schiff bases. Salen ligands are notable for coordinating a wide range of different metals, which they can often stabilise in various oxidation states. For this reason salen-type compounds are used as metal deactivators. Metal salen complexes also find use as catalysts. Synthesis and complexation H2salen may be synthesized by the condensation reaction, condensation of ethylenediamine and salicylaldehyde. : Complexes of salen with metal cations can often be made in situ, i.e., without isolating the H2salen.{{cite journal , doi = 10.1039/B307853C , journal = Chem. Soc. Rev. , title = Metal-Salen Schiff base complexes in catalysis: Practical aspects , year = 2004 , author = Pier Giorgio Cozzi, volume = 33 , issue = 7 , p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jacobsen's Catalyst
Jacobsen's catalyst is the common name for N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride, a coordination compound of manganese and a salen-type ligand. It is used as an asymmetric catalyst in the Jacobsen epoxidation, which is renowned for its ability to enantioselectively transform prochiral alkenes into epoxides. Before its development, catalysts for the asymmetric epoxidation of alkenes required the substrate to have a directing functional group, such as an alcohol as seen in the Sharpless epoxidation. This compound has two enantiomers, which give the appropriate epoxide product from the alkene starting material. Enantiomerically pure epoxides are desirable as building blocks for complex molecules with specific chirality. Biologically active compounds can exhibit radically different activity based on differences in chirality and therefore the ability to obtain desired stereocenters in a molecule is of great importance to the pharm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
