排序方式: 共有100条查询结果,搜索用时 15 毫秒
91.
Tang Z Jiang F Yu LT Cui X Gong LZ Mi AQ Jiang YZ Wu YD 《Journal of the American Chemical Society》2003,125(18):5262-5263
Novel organic molecules containing an l-proline amide moiety and a terminal hydroxyl for catalyzing direct asymmetric aldol reactions of aldehydes in neat acetone are designed and prepared. Catalyst 3d, prepared from l-proline and (1S,2S)-diphenyl-2-aminoethanol, exhibits high enantioselectivities of up to 93% ee for aromatic aldehydes and up to >99% ee for aliphatic aldehydes. A theoretical study of transition structures demonstrates the important role of the terminal hydroxyl group in the catalyst in the stereodiscrimination. Our results suggest a new strategy in the design of new organic catalysts for direct asymmetric aldol reactions and related transformations because plentiful chiral resources containing multi-hydrogen bond donors, for example, peptides, might be adopted in the design. 相似文献
92.
立体选择合成是当今有机合成中一个较新的,极其活跃的研究领域。而利用手性模板进行不对称诱导反应,则是立体选择合成的一种重要方法。近年来,国外报道了许多利用手性模板获得高光学纯度的氨基酸的事例。1981年,Schoellkopf 等用环烯状的双内酰亚胺作手性模板获得了高光学纯度的α-氨基酸。1986年,Williams 用亲电性的甘氨酸内酯作为手性模板进行不对称诱导反应,得到了光学纯度96.5~99.5%的一系列α-取代氨基酸。因此,选择一个好的手性模板是获得高光学纯度产物的关键。较理想的手性模板必须满足以下条 相似文献
93.
三尖杉碱具有五元稠环结构,围绕着五环组建的先后顺序不同,产生各种拼合策略和设计。本文简要介绍近几年全合成三尖杉碱的新路线。参考文献19篇。 相似文献
94.
A series of new 7,7′-disubstituted BINAPs were readily prepared starting with an asymmetric catalytic oxidative coupling. They were applied as ligands to rhodium catalyzed 1,4-addition of arylboronic acids to enones, resulting in enantioselectivities of up to 99% ee. The enantioselectivity was found to be dependent on the size of achiral substituents. 相似文献
95.
设计合成了系列:唑啉-Ti(OiPr)4配合物催化剂,首次成功地用这类催化剂催化一系列硫醚的不对称氧化,获得了e.e.值为70%~96%的亚砜;考察了溶剂、催化剂用量、抗衡离子等因素对反应的影响. 相似文献
96.
The formal hetero-Diels-Alder reaction between 1-methoxy-3-(trimethyl-silyl)oxy-1,3-butadiene and aldehydes provides useful access to dihydropyrones, a class of compounds with extensive utility in organic synthesis. Asymmetric catalysis of this reaction has been previously reported by a number of investigators. Herein we wish to describe that chiral 5,5',6,6',7,7',8,8'-octahydro-1, 1'-bi-2-naphthol (H8-BINOL)/Ti(O-i-Pr)4 complexes are more effective catalysts than BINOL/Ti(O-i-Pr)4 and others for the asymmetric hetero-Diels-Alder reactions. 相似文献
97.
98.
[reaction: see text]A new rhodium-catalyzed highly enantioselective nitroallylation of 2-nitrocyclohex-2-enol esters with arylboronic acids is described. A rhodium complex of [RhOH(COD)]2 and optically pure BINAP is the optimal catalyst that provides good yields and high enantioselectivities ranging from 90 to 99% ee for various arylboronic acids at 50 degrees C. A concise total synthesis of optically pure (+)-gamma-lycorane in overall 38% yield was achieved on the basis of this new method. 相似文献
99.
100.
Yao-Zhong Zhang 《Letters in Mathematical Physics》1992,26(3):219-226
A four-dimensional affine Yang-Mills theory, i.e. Yang—Mills gauge theory with values in an affine Kac-Moody algebra, is constructed which can give rise to a spontaneous breakdown of the affine symmetry. The affine self-dual Yang-Mills equation (which is a special kind of affine YM theory) in four dimensions is dimensionally reduced to the affine self-dual Chem-Simons equation in two dimensions. The latter is shown to have soliton solutions which satisfy the conformal affine Toda equations.K. C. Wong Research Award Winner; address after 28 October 1992: Department of Mathematics, University of Queensland, Brisbane, Queensland 4072, Australia. 相似文献