Enantioselective desymmetrization of meso epoxides with anilines catalyzed by a niobium complex of a chiral multidentate binol derivative.
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Aniline Compounds↗
Biomedical subjects
Shu Kobayashi
Publications and source records attributed to Shu Kobayashi.
High turnover frequency observed in catalytic enantioselective additions of enecarbamates and enamides to iminophosphonates.
[Structure: see text] In addition reactions of enecarbamates and enamides, extremely high turnover frequency of the catalyst was observed in comparison with that of silicon enolate addition reactions. This is presumably due to fast transfer of the proton that locates on the nucleophiles.
Carbamates↗
Enecarbamates as imine surrogates: nucleophilic addition of 1,3-dicarbonyl compounds to enecarbamates.
[reaction: see text] Novel Mannich-type reactions of 1,3-dicarbonyl compounds with enecarbamates have been developed. Stable and storable enecarbamates work as surrogates of aliphatic aldehyde-derived imines, which are known to be difficult to isolate and store.
Journal Article↗
Carboxylic acid catalyzed three-component aza-Friedel-Crafts reactions in water for the synthesis of 3-substituted indoles.
[reaction: see text] The carboxylic acid catalyzed three-component aza-Friedel-Crafts reactions of aldehydes, primary amines, and indoles in water have been developed. The aza-Friedel-Crafts products could be easily transformed to various 3-substituted indoles including biologically active compounds. This system offers a novel efficient method for the synthesis of 3-substituted indoles.
Carboxylic Acids↗
Remarkably stable chiral zirconium complexes for asymmetric Mannich-type reactions.
Isolable, air-stable, storable, and highly selective chiral zirconium catalysts for asymmetric Mannich-type reactions have been developed. The reactions of imines with silicon enolates proceeded smoothly using 1-10 mol % of the powdered zirconium catalyst to afford the corresponding adducts in high yields with high stereoselectivities. The catalyst could be recovered and reused without significant loss of activity. On the other hand, zirconium single crystals for X-ray analysis were obtained, and the crystals also showed high performance in the asymmetric Mannich-type reactions. Although NMR analyses of these zirconium catalysts showed different structures in dichloromethane, the formation of the same key intermediate from the different catalysts was indicated.
Magnetic Resonance Spectroscopy↗
Enantioselective transfer aminoallylation: synthesis of optically active homoallylic primary amines.
A camphorquinone-derived chiral homoallylic amine was found to react with various aldehydes via imine formation and asymmetric 2-azonia-Cope rearrangement to give optically active homoallylic primary amines. A practical level of enantioselectivity with high functional group tolerance has been attained in this transformation.
Amines↗
New entries to water-compatible Lewis acids.
Lewis acid catalysis has attracted much attention in organic synthesis as it often affords access to unique reactivity and selectivity under mild conditions. Although various kinds of Lewis acids have been developed and applied in industry, these Lewis acids must be generally used under strictly anhydrous conditions, as the presence of even a small amount of water interferes with the reactions due to preferential reaction of the Lewis acids with water rather than the substrates. In contrast to this, rare earth and other metal complexes have been found to be water-compatible. Furthermore, Bi(OTf)(3)- and Ga(OTf)(3)-basic ligand complexes have also been found to be stable in water, and have been used as water-compatible Lewis acids. This application is particularly significant, as Bi(OTf)(3) and Ga(OTf)(3) themselves are unstable in the presence of water, but are stabilized by the basic ligands. This observation has led to the development of a new approach to Lewis acid catalysis in which Lewis acids that are generally unstable in the presence of water are rendered amenable to aqueous systems when combined with basic ligands. In particular, the use of chiral basic ligands leading to new types of water-compatible chiral Lewis acids may enable a wide range of asymmetric catalysis in aqueous media.
Aldehydes↗
Direct-type catalytic three-component mannich reactions leading to an efficient synthesis of alpha,beta-diamino acid derivatives.
[reaction: see text] The first example of the Lewis acid-catalyzed three-component direct-type Mannich reaction of simple aromatic and enolizable aliphatic aldehydes, secondary amines, and glycine derivatives is described. The procedure is highly atom economical and can be performed in a simple one-pot operation under mild conditions to afford a wide variety of synthetically important anti-alpha,beta-diamino ester derivatives in high yields with high diastereoselectivities.
Aldehydes↗
Highly anti-selective catalytic aldol reactions of amides with aldehydes.
Barium phenoxide-catalyzed, highly anti-selective direct-type aldol reactions of amides with aldehydes have been developed. In the presence of a slight excess amount of an amide, the desired reactions proceeded smoothly under mild conditions, and a wide range of aromatic, heterocyclic, alpha,beta-unsaturated aldehydes were applicable to afford the desired adducts in high yields with high anti-selectivities. A catalytic, enantioselective reaction of an amide with an aldehyde using a chiral ligand is also described.
Aldehydes↗
Novel polymer incarcerated palladium with phosphinated polymers: active catalyst for Suzuki-Miyaura coupling without external phosphines.
[reaction: see text] Immobilization of a palladium catalyst with use of new phosphinated polymers was carried out utilizing the polymer incarcerated (PI) method. This phosphinated PI Pd catalyst showed excellent activity in Suzuki-Miyaura couplings without addition of external phosphine ligands. No leaching of Pd was observed in this reaction, and the catalyst was recovered quantitatively by simple filtration and reused several times without loss of activity.
Catalysis↗
Polymer-micelle incarcerated scandium as a polymer-supported catalyst for high-throughput organic synthesis.
A novel immobilization technique for Sc(OTf)3, a polymer-micelle incarcerated (PMI) method, has been developed. PMI Sc(OTf)3 is highly active in several fundamental carbon-carbon bond-forming reactions. The catalyst is recovered quantitatively by simple filtration and reused several times without loss of catalytic activity, and no Sc leaching was observed in all reactions (<0.1 ppm). In addition, several solvents are available, and these aspects are suitable for high-throughput organic synthesis (HTOS). To the best of our knowledge, this is the first example of immobilization of Lewis acids utilizing polymer micelles.
Catalysis↗
Highly active, immobilized ruthenium catalysts for oxidation of alcohols to aldehydes and ketones. Preparation and use in both batch and flow systems.
A novel, highly active immobilized ruthenium catalyst, which can be successfully used in oxidation of alcohols to aldehydes and ketones, has been developed. In contrast to most immobilized catalysts, the Ru catalyst has activity that is higher than that of the original non-immobilized catalyst. In a batch system, the Ru catalyst was recovered and reused several times without loss of activity. The catalyst was also applied to a flow system, in which excellent conversions and yields were demonstrated. No leaching of Ru was observed in both cases.
Alcohols↗
Formation of nanoarchitectures including subnanometer palladium clusters and their use as highly active catalysts.
Subnanometer Pd clusters stabilized within micelles of random copolymers were formed by direct immobilization of Pd(0) via ligand exchange. The clusters were estimated to contain approximately seven Pd atoms on average (cluster diameter approximately 0.7 nm). Several Pd-containing micelle morphologies could be obtained by polymer cross-linking. These micelles containing Pd clusters were demonstrated to be efficient catalysts for hydrogenations and Heck reactions.
Journal Article↗
Synthesis of a new chiral source, (1R,2S)-1-Phenylphospholane-2-carboxylic acid, via a key intermediate alpha-phenylphospholanyllithium borane complex: configurational stability and X-ray crystal structure of an alpha-monophosphinoalkyllithium borane complex.
A synthetic route to enantiomerically pure (1R,2S)-1-phenylphospholane-2-carboxylic acid (1), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation-carboxylation of the 1-phenylphospholane borane complex 3 by using sBuLi/1,2-dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine-coordinated alpha-phosphinoalkyllithium borane complex 4, was investigated by employing lithiodestannylation-carboxylation of both diastereomers of the 1-phenyl-2-trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at -100 degrees C. The key intermediate, the DPE-coordinated trans-1-phenyl-2-phospholanyllithium borane complex 9, was isolated, and the structure was identified by X-ray crystal structure analysis. This is the first X-ray crystal structure determined for an alpha-monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li--C bond (2.170 A) has been confirmed. Moreover, (1)H-(7)Li HOESY and (6)Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9, its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at -100 degrees C. Finally, 1 was used as a chiral ligand in a palladium-catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity.
Boranes↗
CERT mediates intermembrane transfer of various molecular species of ceramides.
Ceramide produced at the endoplasmic reticulum is transported to the Golgi apparatus for conversion to sphingomyelin. The main pathway of endoplasmic reticulum-to-Golgi transport of ceramide is mediated by CERT, a cytosolic 68-kDa protein, in a nonvesicular manner. CERT contains a domain that catalyzes the intermembrane transfer of natural C(16)-ceramide. In this study, we examined the ligand specificity of CERT in detail by using a cell-free assay system for intermembrane transfer of lipids. CERT did not mediate the transfer of sphingosine or sphingomyelin at all. The activity of CERT to transfer saturated and unsaturated diacylglycerols, which structurally resemble ceramide, was 5-10% of the activity toward C(16)-ceramide. Among four stereoisomers of C(16)-ceramide, CERT specifically recognized the natural d-erythro isomer. CERT efficiently transferred ceramides having C(14), C(16), C(18), and C(20) chains, but not longer acyl chains, and also mediated efficient transfer of C(16)-dihydroceramide and C(16)-phyto-ceramide. Binding assays showed that CERT also recognizes short chain fluorescent analogs of ceramide with a stoichiometry of 1:1. Moreover, (1R,3R)-N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecamide, which inhibited the CERT-dependent pathway of ceramide trafficking in intact cells, was found to be an antagonist of the CERT protein. These results indicate that CERT can mediate transfer of various types of ceramides that naturally exist and their close relatives.
Biological Transport↗
alpha-Aminoallylation of aldehydes in aqueous ammonia.
alpha-Aminoallylation of aldehydes in aqueous ammonia has been developed; commercial aqueous ammonia was successfully used, and this method does not require anhydrous conditions thus leading to easy and practical operations.
Journal Article↗
Catalytic enantio- and diastereoselective aldol reactions of glycine-derived silicon enolate with aldehydes: an efficient approach to the asymmetric synthesis of anti-beta-hydroxy-alpha-amino acid derivatives.
We have developed an efficient method for the asymmetric synthesis of anti-beta-hydroxy-alpha-amino acid derivatives based on highly enantio- and diastereoselective aldol reactions of the silicon enolate derived from N-trifluoroacetylglycinate with aldehydes using a chiral zirconium catalyst. The resulting N-trifluoroacetyl group is easily cleaved under either acidic or basic conditions and can be used directly as a protecting group for further transformations.
Aldehydes↗
Enantio- and diastereoselective, stereospecific mannich-type reactions in water.
Catalytic asymmetric Mannich-type reactions in water proceeded in high yields and selectivities using a combination of ZnF2 and a chiral diamine that has the methoxy groups on the aromatic rings. In these reactions, either syn- or anti-Mannich adducts were stereospecifically obtained from (E)- or (Z)-silicon enolate, in contrast with most asymmetric Mannich-type reactions.
Journal Article↗