Asymmetric Catalysis by Architectural and Functional Molecular Engineering: Practical Chemo- and Stereoselective Hydrogenation of Ketones

Hydrogenation is a core technology in chemical synthesis. High rates and selectivities are attainable only by the coordination of structurally well-designed catalysts and suitable reaction conditions. The newly devised [RuCl(2)(phosphane)(2)(1,2-diamine)] complexes are excellent precatalysts for homogeneous hydrogenation of simple ketones which lack any functionality capable of interacting with the metal center. This catalyst system allows for the preferential reduction of a C=O function over a coexisting C=C linkage in a 2-propanol solution containing an alkaline base. The hydrogenation tolerates many substituents including F, Cl, Br, I, CF(3), OCH(3), OCH(2)C(6)H(5), COOCH(CH(3))(2), NO(2), NH(2), and NRCOR as well as various electron-rich and -deficient heterocycles. Furthermore, stereoselectivity is easily controlled by the electronic and steric properties (bulkiness and chirality) of the ligands as well as the reaction conditions. Diastereoselectivities observed in the catalytic hydrogenation of cyclic and acyclic ketones with the standard triphenylphosphane/ethylenediamine combination compare well with the best conventional hydride reductions. The use of appropriate chiral diphosphanes, particularly BINAP compounds, and chiral diamines results in rapid and productive asymmetric hydrogenation of a range of aromatic and heteroaromatic ketones and gives a consistently high enantioselectivity. Certain amino and alkoxy ketones can be used as substrates. Cyclic and acyclic alpha,beta-unsaturated ketones can be converted into chiral allyl alcohols of high enantiomeric purity. Hydrogenation of configurationally labile ketones allows for the dynamic kinetic discrimination of diastereomers, epimers, and enantiomers. This new method shows promise in the practical synthesis of a wide variety of chiral alcohols from achiral and chiral ketone substrates. Its versatility is manifested by the asymmetric synthesis of some biologically significant chiral compounds. The high rate and carbonyl selectivity are based on nonclassical metal-ligand bifunctional catalysis involving an 18-electron amino ruthenium hydride complex and a 16-electron amido ruthenium species.     

Selective hydrogenation by polymer-encapsulated platinum nanoparticles prepared by an easy single-step sonochemical synthesis

Polypyrrole-encapsulated platinum nanoparticles (PPy/Pt-NPs) prepared by an easy single-step sonochemical synthesis were used as catalysts for the liquid phase hydrogenation of substituted alkenes in methanol or methanol/water mixtures. Polypyrrole (PPy) coatings on the nanoparticles were able to act as nanoscopic filters for substrates molecules, and consequently substrate selectivity could be controlled in the catalytic processes.     

Enantioselective hydrocyanation of aldehydes catalyzed by [Li{Ru(phgly)2(binap)}]X (X = Cl, Br)

Novel bimetallic complexes [Li{Ru[(S)-phgly](2)[(S)-binap]}]X (X = Cl, Br) are readily synthesized by mixing Ru[(S)-phgly](2)[(S)-binap] and LiX. A single-crystal X-ray analysis reveals the structure. These bimetallic complexes efficiently catalyze asymmetric hydrocyanation of aldehydes with a substrate-to-catalyst molar ratio of 500-2000 at -78 to -60 °C. A range of aromatic, heteroaromatic, and α,β-unsaturated aldehydes as well as a tert-alkyl aldehyde is converted to the cyanohydrins in high enantiomeric excess (up to 99%).     

Search for anomalous top–gluon couplings at LHC revisited

Through top-quark pair productions at LHC, we study possible effects of nonstandard top–gluon couplings yielded by SU(3)×SU(2)×U(1) invariant dimension-6 effective operators. We calculate the total cross section and also some distributions for $pp\to t\bar{t}X$ as functions of two anomalous-coupling parameters, i.e., the chromoelectric and chromomagnetic moments of the top, which are constrained by the total cross section $\sigma(p\bar{p}\to t\bar{t}X)$ measured at Tevatron. We find that LHC might give us some chances to observe sizable effects induced by those new couplings.     

Stereoselective preparation of methylenecyclobutane-fused angular tetracyclic spiroindolines via photosensitized intramolecular [2+2] cycloaddition with allene

Irradiation of 3-(hexa-4,5-dienyl)indole derivatives in the presence of 3′,4′-dimethoxyacetophenone by a high-pressure mercury lamp through Pyrex glass gave the corresponding [2+2] cycloaddition products stereoselectively in high yields. The major product was a methylenecyclobutane-fused angular tetracyclic spiroindoline derivative produced by the [2+2] cycloaddition through a parallel orientation. The minor product was a hexahydromethanocarbazole derivative through a crossed orientation. Electron-withdrawing substituents, such as acyl or alkoxycarbonyl, on the indole nitrogen were suitable for this reaction.     

Luminescence-based colorimetric discrimination of single-nucleotide transversions by the combined use of the derivatives of DOTA-conjugated naphthyridine and its terbium complex

We newly synthesized a nucleobase-binding ligand, ND-DOTA, in which 2-amino-5,7-dimethyl-1,8-naphthyridine (ND) was conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DOTA) via an amide linker, and found that its terbium(III) complex (ND-DOTA-Tb) showed green emission based on an energy transfer from the naphthyridine moiety to Tb³⁺. The blue emission of ND-DOTA was selectively quenched by adding abasic site-containing DNA duplexes that have pyrimidine bases opposite to the abasic site. In contrast, at the same excitation wavelength, ND-DOTA-Tb showed green emission independently of the bases opposite to the abasic site. Thus, a mixed solution of ND-DOTA and ND-DOTA-Tb enabled the luminescence-based colorimetric discrimination of single-nucleotide transversions with the naked eye at a single excitation wavelength.     

Dynamical system related to quasiperiodic Schrödinger equations in one dimension

A dynamical map is obtained from a class of quasiperiodic discrete Schrödinger equations in one dimension which include the Fibonacci system. The potentials are constant except for steps at special points.