Catalysts For Asymmetric Synthesis Research Articles

Reactions of carbonyl clusters with heterobidentate ligands. Synthesis and structural characterization of H4Ru4(CO)10[k2(P,S)-Ph2P(2-CH3SC6H4)] and Rh6(CO)14[k2(P,S)-Ph2P(2-CH3SC6H4)] clusters

Two new disubstituted derivatives of the clusters Rh6(CO)16 and H4Ru4(CO)12 with the heterobidentate ligand [Ph2P(2-CH3SC6H4)] were synthesized. Structures of these compounds were completely characterized both in solid phase and solution. The H4Ru4(CO)10[k2(P,S)-Ph2P(2-CH3SC6H4)] cluster is an example of a structure, in which a chelating coordination of a heterobidentate ligand results in the occurrence of a center of asymmetry associated with the substituted metal atom. This type of polynuclear complexes is of interest for obtaining essentially new catalysts for asymmetric synthesis on the basis of cluster compounds.

Short Peptides and Peptide‐Like Enzyme Mimics: Efficient Organic Catalysts in Asymmetric Synthesis

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Dynamic Kinetic Resolution Catalyzed by Ir Axially Chiral Phosphine Catalyst: Asymmetric Synthesis of anti‐Aromatic β‐Hydroxy‐α‐amino Acid Esters.

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Highlights in Organic Chemistry [ Short Peptides and Peptide-Like Enzyme Mimics - Efficient Organic Catalysts in Asymmetric Synthesis

Highlights in Organic Chemistry [ Short Peptides and Peptide-Like Enzyme Mimics - Efficient Organic Catalysts in Asymmetric Synthesis

Dynamic Kinetic Resolution Catalyzed by Ir Axially Chiral Phosphine Catalyst: Asymmetric Synthesis of anti Aromatic β-Hydroxy-α-amino Acid Esters

The anti selective hydrogenation of alpha-amino-beta-keto esters via dynamic kinetic resolution was achieved for the first time by using the iridium-MeOBIPHEP catalyst in asymmetric synthesis of anti aromatic beta-hydroxy-alpha-amino acid esters with excellent diastereo- and enantioslectivities. Acetic acid as a solvent and sodium acetate as an additive affected dramatically the yield and the enantioselectivity, respectively. The product anti aromatic beta-hydroxy-alpha-amino acid esters are useful for synthesis of pharmaceuticals and natural products.

Simple Amino Acids and Short‐Chain Peptides as Efficient Metal‐Free Catalysts in Asymmetric Synthesis

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Nucleophilic Chiral Amines as Catalysts in Asymmetric Synthesis

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Nucleophilic chiral amines as catalysts in asymmetric synthesis.

Nucleophilic chiral amines as catalysts in asymmetric synthesis.

New Chiral Organophosphorus Catalysts in Asymmetric Synthesis

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Characterization of the 310-helix in model peptides by HRMAS NMR spectroscopy.

A tetra- and a hepta-homopeptide from the C(alpha)-tetrasubstituted Aib (alpha-aminoisobutyric acid) residue were covalently linked to the POEPOP resin by the fragment-condensation approach. The conformational preferences of the two model peptides were determined for the first time on a solid support by means of high-resolution magic angle spinning NMR spectroscopy. The results obtained indicate that the Aib homopeptides adopt a regular 3(10)-helical structure even when they are covalently bound to a polymeric matrix, and thus confirm the remarkable conformational stability of the peptides rich in this amino acid. An ATR-FTIR spectroscopic investigation, performed in parallel, also confirmed that these polymer-bound peptides do indeed adopt a helical conformation. The results of this study open the possibility to exploit the peptide-resin conjugates based on C(alpha)-tetrasubstituted alpha-amino acids as helpful, structurally organized templates in molecular recognition studies or as catalysts in asymmetric synthesis.

Structural Investigation of a Configurationally Stable Seven-Membered Bridged Biaryl of Relevance for Atroposelective Biaryl Syntheses*

The atroposelective ring opening of lactone-bridged biaryl systems is the key step in the total synthesis of a series of axially chiral biaryl natural products and useful reagents or catalysts for asymmetric synthesis. For a more in-depth understanding of the mechanism and stereochemical course of this remarkable cleavage reaction, a seven-membered ether analog of such useful biaryl lactones has been investigated structurally, both experimentally, by X-ray diffraction analysis, and by ab initio calculations (B3LYP/6-31G*). In a nearly perfect agreement, both methods show that these seven-membered bridged biaryls do not constitute helicene-like distorted molecules, but ‘true’ biaryls, whose sufficiently long lactone or ether bridge allows the two aromatic systems to adopt a large dihedral angle to each other, without any noticeable deviation from planarity for the two aromatic systems - in contrast to related six-membered analogs, which can rather be considered as helicene-like twisted polycyclic systems.

Thiamin-diphosphate-dependent enzymes: new aspects of asymmetric C-C bond formation.

Starting from a thorough investigation of mechanistic aspects of ThDP-dependent (ThDP = thiamin diphosphate) enzymes in combination with mutagenesis studies and a detailed substrate screening, new general synthetic methods have been developed based on Umpolung reactions by thiamin catalysis. A selective donor-acceptor concept was established leading to the first asymmetric cross-benzoin condensation, and a kinetic racemic resolution through C-C bond cleavage was developed. With these tools and in combination with protein engineering, we approached the synthesis of new chiral building blocks on a preparative scale. An outlook is given with respect to the potential of other ThDP-dependent enzymes as catalysts in asymmetric synthesis.

Chiral Metallosalen Complexes: Structures and Catalyst Tuning for Asymmetric Epoxidation and Cyclopropanation

Optically active metallosalens are currently one of the most widely used catalysts for asymmetric synthesis. This is mainly due to the following reasons: various salen [N,N′-ethylenebis(salicyldeneaminato)] ligands form complexes with many metal ions and the resulting metallosalens adopt versatile structures, therefore, metallosalens show a variety of catalytic performances. Thus, selection of a metal ion serving the aimed reaction and regulation of ligand conformation to be suitable for the reaction are indispensable for achieving metallosalen-catalyzed asymmetric reactions. Recently, several factors controlling ligand-conformation in metallosalens have been clarified. This article provides selected examples of tuning the structures of metallosalens in compliance to the aimed reaction, by taking asymmetric oxene or carbene transfer reaction as the instance.

ChemInform Abstract: Polymer‐Bound Ligands and Catalysts for Asymmetric Synthesis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Bidentate Lewis acid catalysts in asymmetric synthesis

Abstract The chemistry of bidentate Lewis acids belongs to an unexplored field of science, and so far has been only poorly studied. This paper illustrates the design of several bidentate Al and Ti Lewis acids, and their successful application to selective organic synthesis, particularly to asymmetric synthesis. For example, a new, chiral bidentate Ti(IV) complex is successfully designed by adding commercially available Ti(OPri)4 and (S)-binaphthol sequentially to 2,2'-bis(tritylamino)-4,4'-dichlorobenzophenone in CH2Cl2, and can be utilized for simultaneous coordination to aldehyde carbonyls, thereby allowing the precise enantioface discrimination of such carbonyls for a new catalytic, practical enantioselective allylation of aldehydes with allyltributyltin. This chiral bidentate Ti(IV) catalyst exhibits uniformly high asymmetric induction as well as high chemical yields for various aldehydes. The present enantioselective allylation is highly chemoselective in the presence of other carbonyl moieties.

The Application of L-Proline as an Enzyme Mimic and Further New Asymmetric Syntheses Using Small Organic Molecules as Chiral Catalysts

Can a simple amino acid act like an enzyme? This question is reviewed and discussed herein. In addition, new contributions in which simple organic molecules are used as efficient chiral catalysts in asymmetric synthesis (see scheme) are highlighted.

Catalyst Enhances Asymmetric Ketone Synthesis Yields

Most people would be satisfied with a catalyst for asymmetric synthesis that rapidly gives good yields of chiral products in 80% enantiomeric excess (ee) and turns over millions of times before giving out. But not the researchers in chemistry professor Ryoji Noyori's laboratory at Nagoya University in Japan. Improving upon earlier successes, they've now devised a robust catalytic system for asymmetric hydrogenation that yields optically active secondary alcohols with close to 100% ee from a wide variety of ketones. Nagoya University associate professor Takeshi Ohkuma reported the group's findings last month in Honolulu at a Pacifichem symposium on discovery and development of asymmetric synthesis and chiral technology. As Ohkuma pointed out, chiral secondary alcohols are ubiquitous features of many biologically active molecules and often serve as key building blocks in syntheses. One way to make such alcohols is to hydrogenate the corresponding ketone. Using a chiral BINAP [2,2'-bis(diphenylphosphino)- 1,...

ChemInform Abstract: Novel Optically Active 1,3-Aminoalcohols Derived from D-Glucal.

A series of ethyl(phenyl) 6-amino-2,3,6-trideoxy-α-D-glucopyranosides (amino=piperidino (Pip), pyrrolidino (Pyr), azetidino (Az), Bu2N) have been prepared from tri-O-acetyl-D-glucal to obtain catalysts for asymmetric synthesis and the starting compounds for the syntheses of other bidentate ligands.

ChemInform Abstract: Application of MerCO as a Chiral Catalyst in Asymmetric Synthesis: Asymmetric Borane Reduction of Ketones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Application of MerCO as a chiral catalyst in asymmetric synthesis: asymmetric borane reduction of ketones

The borane reduction of aryl methyl ketones catalyzed by MerCO [(1 R,2 S,3 R)-3-mercaptocamphan-2-ol] produced 1-aryl ethyl alcohols in 92% e.e. at 50°C in toluene. Significant temperature and solvent effects were observed in this reaction.