Selective Propargylation of Carbonyl Compounds and Imines with Barium Reagents

A Barbier‐type regioselective propargylation of aldehydes and ketones with (3‐bromobut‐1‐ynyl)trimethylsilane has been achieved using reactive barium as a low‐valent metal in THF. Especially in the case of ketones, the corresponding homopropargylic alcohols form almost exclusively. In the reaction of α,β‐unsaturated carbonyl compounds, only 1,2‐adducts have been observed. This method is also applicable to propargylation of imines, and the corresponding homopropargylic amines are obtained regiospecifically in good yields with diastereomeric ratios of up to 87:13.     

Ξ Resonances in Ξ− Be interactions II. Properties of Ξ(1820) and Ξ(1960) in the\Lambda \bar K^0 and\Sigma ^0 \bar K^0 channels

In an experiment at the CERN-SPS charged hyperon beam, we have investigated the inclusive \(\Lambda \bar K^0 \) and \(\Sigma ^0 \bar K^0 \) final states formed in Ξ^? Be interactions. In the \(\Lambda \bar K^0 \) channel, we observe a signal at 1826 MeV/c² which can be identified with the known Ξ(1820) resonance. We determine its mass and width to be:M=1826±4 MeV/c², Г=12±14 MeV/c². A moment analysis is consistent with a spin of 3/2 and indicates a negative parity for this spin assignment. Also in the \(\Lambda \bar K^0 \) channel, we observe a 3.6σ signal with the following parameters:M=1963±5 MeV/c², Г=25±15 MeV/c². This state, which we call Ξ(1960), is not observed in the \(\Sigma ^0 \bar K^0 \) channel, leading to an upper limit on the ratio of partial widths \(\Sigma \bar K/\Lambda \bar K\) of 2.3 (90% confidence level). A moment analysis of the \(\Lambda \bar K^0 \) final state indicates a spin of 5/2 or greater in the natural spin-parity series 5/2⁺, 7/2^?, etc.     

Regiospecific α-dialkoxymethylation of preformed enolates

Reaction of a preformed lithium enolate and trimethyl orthoformate with added boron trifluoride leads to the corresponding α-dimethoxymethyl ketone.     

Important role of molecular permanent dipoles of the Alq3/Al interface studied from first-principles

We have studied the atomic geometries and electronic properties of the tris-(8-hydroxyquinoline) aluminum (Alq₃)/Al interface using density functional calculations. The calculated interface dipoles agree reasonably well with the experiments and the origin of the interface dipole formation mainly comes from the alignment of the permanent dipoles of Alq₃ molecules. The HOMO levels of the Alq₃ molecules significantly depend on the orientation of the molecular permanent dipoles and the interfacial gap state observed by experiments is ascribed to the co-existence of the two orientations of the molecular dipoles.     

BINAP/AgOTf/KF/18-crown-6 as new bifunctional catalysts for asymmetric Sakurai-Hosomi allylation and Mukaiyama aldol reaction

A catalytic amount of KF.18-crown-6 complex is effective as a soluble fluoride source to activate an asymmetric Sakurai-Hosomi allylation with BINAP and silver(I) triflate catalyst. The allylation of a variety of aromatic, alpha,beta-unsaturated and aliphatic aldehydes with allylic trimethoxysilane resulted in high yields and remarkable enantioselectivities. In addition, the asymmetric Mukaiyama-type aldol reaction is achieved by using trimethoxysilyl enol ethers in the presence of the same catalysts. High anti selectivity is obtained from E-silyl enol ether, while Z-silyl enol ether gives syn selectivity.     

Hyperfine quantum beat of short-lived beta-emitter8Li polarized by the tilted foil technique

To disclose the basic mechanisms of nuclear polarization creation realized by the tilted foil technique, hyperfine quantum beats of the nuclear polarization of the short-lived beta-emitter⁸Li(I =2⁺,T _1/2=840 ms) were measured as a function of the distance between two tilted foils. From the observed beats of the⁸Li nuclear polarization, it was found that the Fermi-contact interaction of the⁸Li nucleus with the ground 1s-electron in LiIII plays a main role in the final stage of polarization transfer from polarized orbital electrons to the⁸Li nucleus.     

Nuclear spin dependence of polarization enhancement by multi-tilted foils studied by short-lived beta-emitters8B and12B

In order to study the basic mechanism of polarization enhancement realized by the multitilted foil technique, nuclear polarization of short-lived beta-emitter⁸B(T_1/2=769 ms,I =2⁺) was induced. Utilizing up to ten tilted foils, the polarization enhancement was measured as a function of the foil numbers. The observed enhancement for⁸B was combined with the previous results for¹²B(I =1⁺,T _1/2=20 ms) which has the same atomic configurations but different nuclear spin. Analyzing these results in the framework of the classical vector model, the essential features of the enhancement depending on the nuclear spin was disclosed.     

A long-range-corrected time-dependent density functional theory

We apply the long-range correction (LC) scheme for exchange functionals of density functional theory to time-dependent density functional theory (TDDFT) and examine its efficiency in dealing with the serious problems of TDDFT, i.e., the underestimations of Rydberg excitation energies, oscillator strengths, and charge-transfer excitation energies. By calculating vertical excitation energies of typical molecules, it was found that LC-TDDFT gives accurate excitation energies, within an error of 0.5 eV, and reasonable oscillator strengths, while TDDFT employing a pure functional provides 1.5 eV lower excitation energies and two orders of magnitude lower oscillator strengths for the Rydberg excitations. It was also found that LC-TDDFT clearly reproduces the correct asymptotic behavior of the charge-transfer excitation energy of ethylene-tetrafluoroethylene dimer for the long intramolecular distance, unlike a conventional far-nucleus asymptotic correction scheme. It is, therefore, presumed that poor TDDFT results for pure functionals may be due to their lack of a long-range orbital-orbital interaction.