Chiral Phosphoramide-Catalyzed Enantioselective Addition of Allylic Trichlorosilanes to Aldehydes. Preparative Studies with Bidentate Phosphorus-Based Amides
作者:Scott E. Denmark、Jiping Fu、Michael J. Lawler
DOI:10.1021/jo052203h
日期:2006.2.1
that more than one Lewis basic moiety (phosphoramide) is involved in the rate- and stereochemistry-determining step of enantioselectiveallylation, bidentate chiral phosphoramides were developed. Different chiral phosphoramide moieties were connected by tethers of methylene chains of varying length. The rate and enantioselectivity of allylation with allyltrichlorosilane promoted by the bidentate phosphoramides
<i>anti</i>-Diastereo- and Enantioselective Carbonyl Crotylation from the Alcohol or Aldehyde Oxidation Level Employing a Cyclometallated Iridium Catalyst: α-Methyl Allyl Acetate as a Surrogate to Preformed Crotylmetal Reagents
作者:In Su Kim、Soo Bong Han、Michael J. Krische
DOI:10.1021/ja808857w
日期:2009.2.25
catalyst generated in situ from [Ir(cod)Cl](2), 4-cyano-3-nitrobenzoic acid and the chiral phosphine ligand (S)-SEGPHOS, alpha-methyl allyl acetate couples to alcohols 1a-1j with complete levels of branched regioselectivity to furnish products of carbonyl crotylation 3a-3j, which are formed with good levels of anti-diastereoselectivity and exceptional levels of enantioselectivity. An identical set of optically
在使用由[Ir(cod)Cl](2)、4-氰基-3-硝基苯甲酸和手性膦配体(S)-SEGPHOS原位生成的邻位环金属化铱催化剂进行转移氢化的条件下,α-甲基乙酸烯丙酯与具有完全支化区域选择性水平的醇1a-1j偶联,提供羰基巴豆酰化产物3a-3j,形成的产物具有良好水平的反非对映选择性和异常水平的对映选择性。在相同的条件下,但使用异丙醇作为末端还原剂,可以从相应的醛2a-2j得到一组相同的光学富集的羰基巴豆酰化产物3a-3j。旨在探索立体选择起源的实验建立了 (R)-乙酸酯和经 (S)-SEGPHOS 修饰的铱催化剂的匹配电离模式,以及烯丙基乙酸酯的可逆电离和快速 pi 面相互转化。在CC键形成之前产生吡啶基中间体。此外,还证明了在羰基加成之前的快速醇-醛氧化还原平衡。因此,在不存在任何化学计量金属试剂或化学计量金属副产物的情况下,实现了醇或醛氧化水平的反非对映选择性和对映选择性羰基巴豆酰化。
Enhanced anti-Diastereo- and Enantioselectivity in Alcohol-Mediated Carbonyl Crotylation Using an Isolable Single Component Iridium Catalyst
作者:Xin Gao、Ian A. Townsend、Michael J. Krische
DOI:10.1021/jo200068q
日期:2011.4.1
The cyclometalated iridium complex (S)-I derived from [Ir(cod)Cl]2, 4-cyano-3-nitrobenzoic acid, allyl acetate, and (S)-SEGPHOS is conveniently isolated by precipitation or through conventional silica gel flash chromatography. This single-component precatalyst allows alcohol mediated carbonyl crotylations to be performed at significantly lower temperature, resulting in enhanced levels of anti-diastereo-
环金属铱配合物(小号) -我从物[Ir(COD)CL]衍生的2,4-氰基-3-硝基苯甲酸,乙酸烯丙酯,和(小号)-SEGPHOS方便地通过沉淀或通过传统的硅胶快速色谱法分离. 此单组分预催化剂允许醇介导的在显著较低温度下进行羰基crotylations,导致水平提高抗-diastereo-和对映选择性。最重要的是,色谱分离的预催化剂 ( S )- I使羰基巴豆酰化成为可能,这在先前报道的涉及原位生成 ( S )- 的条件下是不可能的我。
Catalytic, Enantioselective Addition of Substituted Allylic Trichlorosilanes Using a Rationally-Designed 2,2‘-Bispyrrolidine-Based Bisphosphoramide
作者:Scott E. Denmark、Jiping Fu
DOI:10.1021/ja016552e
日期:2001.9.1
Sequencing cross-metathesis and non-metathesis reactions to rapidly access building blocks for synthesis
作者:Gopal Sirasani、Tapas Paul、Rodrigo B. Andrade
DOI:10.1016/j.tet.2011.01.080
日期:2011.3
The olefin cross-metathesis reaction has been sequenced with four common organic transformations in a one- or two-pot manner to rapidly access useful building blocks. Those reactions are: (1) phosphorus-based olefination (e.g.. Wittig and Horner-Wadsworth-Emmons); (2) hydride reduction; (3) Evans propionate aldol reaction; (4) Brown allyl- and Roush crotyl-boration. The products of these reactions include stereodefined 2,4-dienoates, trans allylic alcohols, syn-propionate aldols, and chiral non-racemic homoallylic alcohols, respectively. Many of these intermediates have been carried further to natural products, demonstrating the utility of the methodology. (C) 2011 Elsevier Ltd. All rights reserved.