Can a Ketone Be More Reactive than an Aldehyde? Catalytic Asymmetric Synthesis of Substituted Tetrahydrofurans

O‐heterocycles bearing tetrasubstituted stereogenic centers are prepared via catalytic chemo‐ and enantioselective nucleophilic additions to ketoaldehydes, in which the ketone reacts preferentially over the aldehyde. Five‐ and six‐membered rings with both aromatic and aliphatic substituents, as well as an alkynyl substituent, are obtained. Moreover, 2,2,5‐trisubstituted and 2,2,5,5‐tetrasubstituted tetrahydrofurans are synthesized with excellent stereoselectivities. Additionally, the synthetic utility of the described method is demonstrated with a three‐step synthesis of the side chain of anhydroharringtonine.     

On the lattice defects in Nasicon compounds

Summary  Samples of Nasicon compounds (Na super ionic conductor) with different silicon and phosphorus contents were investigated by performing radioluminescence experiments. In all samples examined, the Frenkel pairs, originated by the displacements of sodium ions in lacunar sites, were found to be the dominant defects. Some useful information on sodium ion mobility was obtained from the analysis of radioluminescence spectra.     

A modified layered-step interior-point algorithm for linear programming

The layered-step interior-point algorithm was introduced by Vavasis and Ye. The algorithm accelerates the path following interior-point algorithm and its arithmetic complexity depends only on the coefficient matrixA. The main drawback of the algorithm is the use of an unknown big constant in computing the search direction and to initiate the algorithm. We propose a modified layered-step interior-point algorithm which does not use the big constant in computing the search direction. The constant is required only for initialization when a well-centered feasible solution is not available, and it is not required if an upper bound on the norm of a primal—dual optimal solution is known in advance. The complexity of the simplified algorithm is the same as that of Vavasis and Ye. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.Research supported in part by ONR contract N00014-94-C-0007 and the Grant-in-Aid for Scientific Research (C) 08680478 and the Grant-in-Aid for Encouragement of Young Scientists (A) 08780227 of the Ministry of Science, Education and Culture of Japan. This research was partially done while S. Mizuno and T. Tsuchiya were visiting IBM Almaden Research Center in the summer of 1995.     

Defect evolution and photoluminescence in anion-defective alumina single crystals exposed to high doses of gamma-rays

A method of luminescent UV and VUV spectroscopy was used to study the evolution of color centers in anion-defective alumina single crystals exposed to high doses of gamma-radiation. A sharp drop in the intensity of the emission bands and, therefore, the concentration of F⁺ and F-centers associated with the formation of aggregate F₂-type centers was found. The aggregate centers create an additional emission band in the range of (1.8–2.8) eV. When the crystals are exposed to middle and high doses, the photoluminescence (PL) intensity is the highest in the emission band of F₂²⁺-centers, which indicates a high concentration of the aggregates from singly charged oxygen vacancies (of F⁺-centers). When PL of the crystals exposed to high doses is excited with synchrotron radiation of the VUV range, a wide emission band in the red and near infrared (NIR) regions is registered. The centers related presumably to impurity defects, their aggregates and clusters consisting of several oxygen vacancies are responsible for this emission band.     

An interpolation formula of the derivatives of higher order

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手性螺-环丙烷双内酯化合物的合成与结构

本文进一步研究了5-(l-孟氧基)-3-溴-2(5H)-呋喃酮(1)与氧的亲核试剂,如二苯甲醇、苯甲醇、α-甲基苯甲醇、薄荷醇、冰片醇发生新颖的串联不对称双Michael加成/分子内亲核取代反应,合成了一般方法难以合成的含有多个手性中心的螺[1-溴-4-l-孟氧基-5-氧杂-6-氧代双环[3.1.0]己烷-2,3'-(4'-亲核基-5'-孟氧基丁内酯)](4a-4e)。通过元素分析,IR,UV,^1HNMR,^1^3CNMR,MS,[α]~D^2^0波谱分析数据以及X四圆衍射确定了4a-4e的化学结构和绝对构型。     

Principles of the theory of adsorption of large molecules in pores with nonuniform walls

Principles of the theory of adsorption of large molecules blocking more than one adsorption center on a surface in slit-like pores are proposed. The theory takes into account lateral adsorbate—adsorbate interactions and nonuniformity of the pore walls. The equations of adsorption isotherms are derived using the cluster approach. The lateral interactions are taken into account in the quasi-chemical approximation, preserving effects of direct correlations, and in the mean field approximation without effects of correlations. The following problems are discussed: 1) distinguishing of partial contributions of nonuniform adsorption centers on the pore walls; 2) exact solution for dimer adsorption in a two-layer pore with uniform walls; 3) basic types of adsorption isotherms, for which the differences are due to various orientations of the adsorbate in micropores with uniform walls; 4) estimates of the pressure responsible for volume filing of micropores; and 5) the effect of nonuniformity of the pore walls on the pressure values. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1467–1478, August, 1999.     

Optical and Luminescence Properties of YAlO3 ‐Tm Crystals

The results on optical absorption, photoluminescence and thermoluminescence of YAP‐Tm crystals of 1 at.% and 4 at.% of Tm are presented as well as influence of UV‐, γ‐radiation and thermal treatments on optical and luminescence properties of the crystals. The blue‐green luminescence of defect centers was observed in YAP‐Tm crystals at Ar⁺‐laser excitation. The possibility of energy transfer processes between defect centers and Tm³⁺ ions was shown.     

Crystal structure of a new precursor of radical-clock based on the norbornenyl framework

The crystal of 5-phenyl-2-endo-(propane-2-sulfonyl)-bicyclo[2-2-1]hept-5-ene-2-carbonitrile1, a new radical-clock is described. The structure has confirmed the configuration for the positions of the phenyl and sulfonyl groups. In the crystal, the radical precursor carbon atom of the propane group is not neighbouring with the double bond of the norbornene. Nevertheless, in solution, it may be expected an ideal conformation with a short intergroup distance leading to a cyclization process. Crystal data: C₁₇H₁₉NO₂S, triclinic, space group P−1,a=6.567 (3),b=10.407(5),c=12.610(6), α=110.48(2), β=95.88(2), λ=102.67(3).     

分子束外延生长赝配高电子迁移率超高速微结构功能材料里深中心识别

应用深能级瞬态谱(DLTS)技术研究分子束外延(MBE)生长的highelectronmobilitytransistors(HEMT)和Pseudomorphichighelectronmobilitytransistors(PHEMT)结构深中心行为.样品的DLTS谱表明,在HEMT和PHEMT结构的nAlGaAs层里存在着较大浓度(1015-1017cm-3)和俘获截面(10-16cm2)的近禁带中部电子陷阱.它们可能与AlGaAs层的氧含量有关.同时还观察到PHEMT结构晶格不匹配的AlGaAsInGaAsGaAs系统在AlGaAs里产生的应力引起DX中心(与硅有关)能级位置的有序移动.其移动量可作为应力大小的一个判据,表明DLTS技术是定性识别此应力的可靠和简便的工具. 关键词： 分子束外延生长 高电子迁移率超高速微结构功能材料 深中心