coupling method, to assign the absoluteconfiguration of the benzylic stereogenic center of 1-aryl-1,2-diols. According to this method, it is only necessary to prepare the 4-biphenylboronic esters of the diols and to record their CDspectra in the 230−300 nm range, i.e., in the range corresponding to the long-axis 1La transition of the biphenyl chromophore. From the sign of the CD couplet or Cotton effect
我们在此基于激子偶联方法描述一种简单,通用且可靠的非经验方法,以分配1-芳基-1,2-二醇的苄基立体异构中心的绝对构型。根据该方法,仅需制备二醇的4-联苯硼酸酯并记录其在230-300 nm范围内(即在对应于长轴1 L a的范围内)的CD光谱联苯发色团的过渡。从260 nm处的CD偶联或棉花效应的征兆,可以知道由芳基和联苯发色团跃迁定义的手性,然后确定苄基碳的绝对构型。通过这种方法,已经制定了简单的规则,使我们能够建立许多种类的1-芳基-1,2-二醇的绝对构型。
Design of New Modifiers for the Enantioselective Hydrogenation of Ethyl Pyruvate
synthesized and tested in the hydrogenation of ethylpyruvate. The best enantiomeric excess achieved with the new modifier was 87%, which is 12% higher than the optimized value obtained with the corresponding naphthalene derivative (4). A further advantage of the new modifier is the higher stability against self-hydrogenation. Hydrogenation of ethylpyruvate in the presence of modifier mixtures indicated the
A New Chiral Anthracene for the Asymmetric Diels−Alder/Retro-Diels−Alder Sequence
作者:Kerrie L. Burgess、Neil J. Lajkiewicz、Amitav Sanyal、Wanlin Yan、John K. Snyder
DOI:10.1021/ol047968a
日期:2005.1.1
hracene (8) is successfully employed as a chiral template in the Diels-Alder/retro-Diels-Alder sequence for the preparation of alpha,beta-unsaturated lactams. The cycloadditions proceed with complete diastereoselectivity, and regioselectivity in subsequent transformations of the carbonyl groups is also excellent. Flash vacuum pyrolysis accomplishes the cycloreversion.
Catalytic Enantioselective Allyl- and Crotylboration of Aldehydes Using Chiral Diol•SnCl<sub>4</sub> Complexes. Optimization, Substrate Scope and Mechanistic Investigations
作者:Vivek Rauniyar、Huimin Zhai、Dennis G. Hall
DOI:10.1021/ja8016076
日期:2008.7.1
induction in the allylboration of aldehydes by commercially available allylboronic acid pinacol ester 1a. The corresponding homoallylic alcohol products of synthetically useful aliphatic aldehydes are obtained in excellent yields with up to 98:2 er. This combined acid manifold is also efficient in catalyzing the diastereo- and enantioselective crotylboration of aldehydes, thus providing the propionate
我们报告了一类新的 C2 对称手性二醇,其源自对苯二酚骨架。在 Yamamoto 的路易斯酸辅助布朗斯台德酸度(LBA 催化)概念下,这些二醇与 SnCl 4 的组合导致可商购的烯丙基硼酸频哪醇酯 1a 在醛的烯丙基硼化中产生高水平的不对称诱导。合成有用的脂肪醛的相应高烯丙醇产品以高达 98:2 的产率获得。这种组合的酸歧管还可有效催化醛的非对映选择性和对映选择性巴豆基硼化反应,从而提供 >95:5 dr 和高达 98:2 er 的丙酸酯单元。最佳二醇 x SnCl4 配合物 Vivol (4m) x SnCl4 的 X 射线晶体结构,明确显示了这种 LBA 催化剂的 Brønsted 酸性特征及其高度不对称的环境。进一步的控制排除了可能的硼与手性二醇的酯交换机制,并指出频哪醇烯丙基硼酸酯 1 的 LBA 催化剂衍生的活化。由于二醇 x SnCl4 复合物的缓慢解离,需要少量过量的二醇为了抑制由游离
Corey; Noe, Mark C., Journal of the American Chemical Society, 1996, vol. 118, # 45, p. 11038 - 11053