Enantioselective Synthesis of (E)-δ-Boryl-Substituted anti-Homoallylic Alcohols Using Palladium and a Chiral Phosphoric Acid

(E)-δ-Boryl-substituted anti-homoallylic alcohols are synthesized in a highly diastereo- and enantioselective manner from 1,1-di(boryl)alk-3-enes and aldehydes. Mechanistically, the reaction consists of 1) palladium-catalyzed double-bond transposition of the 1,1-di(boryl)alk-3-enes to 1,1-di(boryl)alk-2-enes, 2) chiral phosphoric acid catalyzed allylation of aldehydes, and 3) palladium-catalyzed geometrical isomerization from the Z to E isomer. As a result, the configurations of two chiral centers and one double bond are all controlled with high selectivity in a single reaction vessel.     

Zagreb indices of graphs

The first Zagreb index M₁(G) is equal to the sum of squares of the degrees of the vertices, and the second Zagreb index M₂(G) is equal to the sum of the products of the degrees of pairs of adjacent vertices of the underlying molecular graph G. In this paper, we obtain lower and upper bounds on the first Zagreb index M₁(G) of G in terms of the number of vertices (n), number of edges (m), maximum vertex degree (Δ), and minimum vertex degree (δ). Using this result, we find lower and upper bounds on M₂(G). Also, we present lower and upper bounds on M₂(G) +M₂(G) in terms of n, m, Δ, and δ, where G denotes the complement of G. Moreover, we determine the bounds on first Zagreb coindex M₁(G) and second Zagreb coindex M₂(G). Finally, we give a relation between the first Zagreb index and the second Zagreb index of graph G.     

High-resolution electron energy loss spectroscopy study of O-Cu(410)

We have investigated oxygen adsorption on Cu(410) by high-resolution electron energy loss spectroscopy, dosing O2 with a supersonic molecular beam at different surface temperatures and for different angles of incidence and beam energies or by backfilling. In the investigated crystal temperature range (127 < T < 570 K), adsorption is always dissociative. Depending on T, impact energy, and angle of incidence, the oxygen atoms end up in different adsorption configurations, characterized by different vibrational signatures. In particular, at grazing incidence when only the step edge is exposed to O2, the adatoms end up initially preferentially at the step edge. An ordered overlayer forms at half monolayer coverage when the adsorbate is mobile. Oxide patches develop eventually for large exposures performed by backfilling and at high crystal temperature.     

DNA capillary electrophoresis using poly(vinyl alcohol). II. Separation media

We represent the first extensive study on DNA capillary electrophoresis using various poly(vinyl alcohol) (PVAL)-related polymers as separation media. As a separation medium, PVAL homopolymer has shown poor resolutions probably due to its very strong hydrogen-bonding characteristics, resulting in extensive self-aggregation. On the other hand, poly(vinyl alcohol-co-vinyl acetate) and poly(vinyl alcohol-co-1-vinyl-2-pyrrolidone) (PVAL-VP), both with a degree of polymerization of approximately 3.0x10(3), have been found to give excellent electropherograms with good resolutions for the analysis of double-stranded (ds)DNA. PVAL-VP, with hydrolytic stability in high and low pH regions, has also yielded fair electropherograms for single-stranded (ss)DNA under neutral and alkaline conditions, although further investigation is essential in order to increase the resolutions necessary for DNA sequencing analysis. The separations obtained under alkaline conditions have shown significantly shorter retention times, one-third of that for the current commercial separation media, due to the higher ionization of phosphate groups in the DNA chains.     

Uniaxial stress effects on the 3.4 eV optical structure of silicon by schottky-barrier electroreflectance

The electroreflectance of Si under uniaxial stress has been measured in the 3.0–4.0 eV region at 77 K. The results indicate that the dominant structure in this energy region is attributed to Λ^v₃ → Λ^c₁ (or L^v_3′ → L^c₁ transition. The deformation potentials of these bands are determined to be $\text{D}{}^1{}_1\text{= -7 ± 3 eV,}\text{D}{}^3{}_3\text{= 4 ± 1 eV}\text{and}\text{D}{}^5{}_1\text{= 5 ± 2 eV}$.     

Stereocontrolled spirocyclization of exo-glucal derivatives for stereodivergent synthesis of spiro[5.5]ketals

This Letter describes a stereoselective synthetic approach to spiro[5.5]ketals from the exo-glucals, constructed from 1-(4-hydroxyalkylidene)-1,5-anhydro-d-glucitol, by spirocyclization based on intramolecular α- and β-selective glycosylation. Stereodivergent synthesis of both α- and β-glucoside of spiro[5.5]ketals was attained by combination of chiral d-glucopyranose environment and C-4′ chiral center on the side chain.     

Enantioselective,Desymmetrizing, Bromolactonization Reactions of Symmetric Olefinic Dicarboxylic Acids

The results of studies leading to the development of enantioselective desymmetrizing, bromolactonization reactions of symmetric olefinic dicarboxylic acids, which are promoted by a C₃‐symmetric trisimidazoline catalyst, are described. These processes generated carboxylic‐acid‐containing bromolactones in moderately high enantiomeric excesses. The results of optimization studies showed that reactions in a mixed solvent system of toluene and acetone proceeded with the highest levels of enantioselectivity. NMR studies probing the interactions between the catalyst and dicarboxylic acid substrates, as well as the effect of acetone on the stereochemistry of the process, are also described.     

Synthesis,Structure, and Dynamics of Chiral Eight-Membered Cyclic Molecules with Thienylene and Cyclopropylene Units Alternately Connected

A rhodium(II)-catalyzed asymmetric cyclooligomerization of bifunctional monomers possessing triazolyl and vinyl groups at 2,3- and 3,4-positions on the thiophene ring is studied. Structurally interesting cyclic dimers in which thienylene and cyclopropylene units are alternately connected are obtained as the major components. The eight-membered rings in the center are non-planar and adopt a tub-shaped conformation. We also observe the phenomenon of racemization caused by a tub-to-tub ring-flipping, the activation energy of which is determined as 108 kJ mol⁻¹ by electronic circular dichroism spectra measurement.     

Extremely low-energy projectiles for SIMS using size-selected gas cluster ions

A new cluster time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed using a size-selected gas cluster ion as a projectile. Since a large gas cluster ion can generate many low-energy constituent atoms in a collision with the surface, it causes multiple and ultra low-energy sputtering. The mean kinetic energy of constituent atoms is provided by dividing the acceleration energy of the gas cluster ion by the number of constituent atoms. Therefore, the sputtering can be controlled to minimize the decomposition of sample molecules and substrate material by precisely adjusting the number of constituent atoms (the cluster size) and/or acceleration energy of the gas cluster ion. The cluster size was selected on the basis of the time-of-flight method using two ion deflectors attached along the ion-beam line. A high resolution of 11.7 was achieved for the cluster size/size width (M/ΔM) of Ar-cluster ions.