Stereoselective ring expansion via bicyclooxonium ion. A novel approach to oxocanes

[reaction: see text] The stereoselective 1,4-rearrangement-ring expansion of tetrahydrofurans via bicyclo[3.3.0]oxonium ions was developed to synthesize oxocanes. On the basis of this rearrangement, the stereoselective synthesis of 2,8-syn-2,8-dimethyloxocane was accomplished.     

Synthesis and properties of the first stable germabenzene

The first stable germabenzene (1a) bearing an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, was successfully synthesized by the reaction of the corresponding chlorogermane (4) with lithium diisopropylamide in THF. The molecular structure and aromaticity of 1a were discussed on the basis of its NMR, UV-vis, and Raman spectra, X-ray crystallographic analysis, and theoretical calculations. All (1)H and (13)C NMR chemical shifts of the germabenzene ring of 1a were in good agreement with those calculated. UV-vis and Raman spectra of 1a showed patterns similar to those of benzene, suggesting the structural similarity between germabenzene and benzene. X-ray crystallographic analysis of 1a revealed that the germabenzene ring was almost planar, indicating the delocalization of pi-electrons. Theoretical calculations (NICS(1) and ASE(isom)) also indicated the ring current effects and aromatic stabilization of the germabenzene. While germabenzene 1a reacted as a Ge[bond]C double-bond compound (germene) with mesitonitrile oxide and 2,3-dimethyl-1,3-butadiene, 1a also reacted as a 1-germabuta-1,3-diene with C[bond]C double- and triple-bond compounds. Furthermore, 1a reacted with water and MeOH to give both 1, 2- and 1, 4-adducts.     

Growth mechanism of ZnO nanorods from nanoparticles formed in a laser ablation plume

We have succeeded in synthesizing ZnO nanorods by pulsed-laser ablation at comparatively high gas pressures without using a catalyst. The nanorods had an average size of 300 nm and a length of about 6 m. Stimulated emission was observed from the nanorods at 388 nm by optical pumping. As a catalyst was not used in our method, nanorod growth was not controlled by the vapor-liquid-solid (VLS) mechanism. We found that nanoparticles formed by condensation of ablated particles in the laser ablation plume play an important role in nanorod growth. PACS 61.46.+w; 81.07.Bc; 78.66.Hf; 78.67.Bf; 81.16.Mk     

Total synthesis of a cytotoxic acetogenin,pyranicin

[structure: see text] The first total synthesis of a new cytotoxic acetogenin, pyranicin (1), is described. SmI(2)-induced reductive cyclization of beta-alkoxy acrylate 4 proceeded stereoselectively to give 16,20-syn-19,20-trans-THP derivative 14, which was efficiently transformed into the 19,20-cis-THP derivative 18 through Mitsunobu lactonization. Wittig reaction of the phosphonium salt 2 obtained therefrom with butenolide 3 at -78 degrees C followed by reduction and deprotection afforded 1 in good overall yield.     

Exploiting sparsity in semidefinite programming via matrix completion II: implementation and numerical results

 In Part I of this series of articles, we introduced a general framework of exploiting the aggregate sparsity pattern over all data matrices of large scale and sparse semidefinite programs (SDPs) when solving them by primal-dual interior-point methods. This framework is based on some results about positive semidefinite matrix completion, and it can be embodied in two different ways. One is by a conversion of a given sparse SDP having a large scale positive semidefinite matrix variable into an SDP having multiple but smaller positive semidefinite matrix variables. The other is by incorporating a positive definite matrix completion itself in a primal-dual interior-point method. The current article presents the details of their implementations. We introduce new techniques to deal with the sparsity through a clique tree in the former method and through new computational formulae in the latter one. Numerical results over different classes of SDPs show that these methods can be very efficient for some problems. Received: March 18, 2001 / Accepted: May 31, 2001 Published online: October 9, 2002 RID="⋆" ID="⋆"The author was supported by The Ministry of Education, Culture, Sports, Science and Technology of Japan. Key Words. semidefinite programming – primal-dual interior-point method – matrix completion problem – clique tree – numerical results Mathematics Subject Classification (2000): 90C22, 90C51, 05C50, 05C05     

Asymmetric epoxidation with a photoactivated [Ru(salen)] complex

(Nitrosyl)(salen)ruthenium(II) complex 1 was found to serve as an efficient catalyst for the epoxidation of conjugated olefins under photoirradiation, with 2,6-dichloropyridine N-oxide (2) or tetramethylpyrazine N,N'-dioxide as a stoichiometric oxidant. High enantioselectivity was achieved irrespective of the substitution pattern of olefins. The choice of solvent depends on stability of the resulting epoxides: high enantioselectivity is generally observed in the reaction with ethereal solvents, but use of benzene is recommended when the resulting epoxides are acid-sensitive.     

Development of optical pickup for mini disc drives

In order to miniaturize optical disc drives, it is important to miniaturize and thin the optical pickup. We have developed two new optical parts: the hologram laser and the actuator. By optimizing the hologram pattern of the hologram laser, optical path length is shortened. The frequency characteristics of the actuator have been stabilized by improving the damping characteristics. Thus, we have developed a compact optical pickup for Mini Disc drives, and the pickup shows high performance when it reads out an optical disc.     

Molecular structure of phosgene as studied by gas electron diffraction and microwave spectroscopy: The rz structure and isotope effect

The r_z structure of phosgene has been determined by a joint analysis of the electron diffraction intensity and the rotational constants as follows: $\text{r}{}_{\mathrm{z}}\text{(}\text{CO}\text{) = 1.1785 ± 0.0026}\text{A}\text{?}$, $\text{r}{}_{\mathrm{z}}\text{(}\text{CCl}\text{) = 1.7424 ± 0.0013}\text{A}\text{?}$, ∠_z;ClCCl = 111.83 ± 0.11°, where uncertainties represent estimated limits of experimental error. The effective constants representing bond-stretching anharmonicity have been obtained from an analysis of the isotopic differences in the r_z structure: $\text{a}{}_3\text{(}\text{CO}\text{) = 2.9 ± 0.9}\text{A}\text{?}{}^{\mathrm{?1}}$, $\text{a}{}_3\text{(}\text{CCl}\text{) = 1.6 ± 0.4}\text{A}\text{?}{}^{\mathrm{?1}}$. The equilibrium bond distances have been estimated from the r_z structure for the normal species and from the anharmonic constants to be $\text{r}{}_{\mathrm{e}}\text{(}\text{CO}\text{) = 1.1756 ± 0.0032}\text{A}\text{?}$, $\text{r}{}_{\mathrm{e}}\text{(}\text{CCl}\text{) = 1.7381 ± 0.0019}\text{A}\text{?}$.