A Unified Explanation for Chemoselectivity and Stereospecificity of Ni-Catalyzed Kumada and Cross-Electrophile Coupling Reactions of Benzylic Ethers: A Combined Computational and Experimental Study
作者:Pan-Pan Chen、Erika L. Lucas、Margaret A. Greene、Shuo-Qing Zhang、Emily J. Tollefson、Lucas W. Erickson、Buck L. H. Taylor、Elizabeth R. Jarvo、Xin Hong
DOI:10.1021/jacs.9b00097
日期:2019.4.10
moiety. This step circumvents the competing Kumada coupling, leading to the excellent chemoselectivity of cross-electrophile coupling. These mechanisms account for the observed stereospecificity of the Kumada and cross-electrophile couplings, providing a rationale for double inversion of the benzylic stereogenic center in cross-electrophile coupling. The improved mechanistic understanding will enable
Ni 催化的 C(sp3)-O 键活化提供了一种有用的方法来从容易获得的对映体富集的苯甲醇衍生物合成对映体富集的产品。立体特异性的控制是这些转化成功的关键。为了阐明 Ni 催化的熊田和与苄醚的交叉亲电偶联反应的反向立体特异性和化学选择性,进行了计算和实验相结合的研究,以达成统一的机理理解。熊田耦合通过经典的交叉耦合机制进行。初始速率决定氧化加成伴随苄基立体中心的立体反转发生。随后用格氏试剂进行金属转移和顺式还原消除产生熊田偶联产物,在苄基位置具有整体立体反转。交叉亲电偶联反应以相同的苄基 CO 键裂解和金属转移开始,以形成常见的苄基镍中间体。然而,系链烷基氯的存在允许苄基镍部分轻松进行分子内 SN2 攻击。这一步避免了竞争性的熊田偶联,导致交叉亲电偶联的优异化学选择性。这些机制解释了观察到的熊田和交叉亲电偶联的立体特异性,为交叉亲电偶联中苄基立体中心的双重反转提供了基本原理。改进的机械理解将能够设计涉及
Iron(III)-Catalyzed Prins-Type Cyclization Using Homopropargylic Alcohol: A Method for the Synthesis of 2-Alkyl-4-halo-5,6-dihydro-2<i>H</i>-pyrans
作者:Pedro O. Miranda、David D. Díaz、Juan I. Padrón、Jaime Bermejo、Victor S. Martín
DOI:10.1021/ol034568z
日期:2003.5.1
new Prins-type cyclization between homopropargylic alcohol and aldehydes in the presence of FeX(3) to obtain 2-alkyl-4-halo-5,6-dihydro-2H-pyrans in good yield is described. Osmium-catalyzed cis dihydroxylation provided direct access to trans-2-alkyl-3-hydroxy-tetrahydro-pyran-4-ones. Anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization using homoallylic
Rapid and Efficient Protocol for the Synthesis of 4-Chlorotetrahydropyrans Using Niobium(V) Chloride
作者:J. S. Yadav、B. V. Reddy、Manoj Kumar Gupta、Swapan Kumar Biswas
DOI:10.1055/s-2004-831220
日期:——
Aldehydes undergo a rapid coupling with 3-buten-1-ol utilizing 20 mol% of niobium(V) chloride to afford 4-chlorotetrahydropyran derivatives under extremely mild conditions within short reaction times in excellent yields with high selectivity. The similar halogenated tetrahydropyrans are also obtained using gallium(III) halides.
One-pot synthesis and SAR study of cis-2,6-dialkyl-4-chloro-tetrahydropyrans
作者:Pedro O. Miranda、Leticia G. León、Víctor S. Martín、Juan I. Padrón、José M. Padrón
DOI:10.1016/j.bmcl.2006.03.064
日期:2006.6
A series of cis-2,6-dialkyl-4-chloro-tetrahydropyrans were prepared by means of an iron(III)-catalyzed process. The in vitro antiproliferative activities were examined in the human solid tumor cell lines A2780, SW1573, and WiDr. The results show that the presence of bulky substituents favors the Prins cyclization leading to new products with better activity profile against all cell lines tested. (c) 2006 Elsevier Ltd. All rights reserved.
An Efficient Prins Cyclization for Stereoselective Synthesis of Tetrahydropyran from Imines and Homoallyl Alcohols
作者:Congrong Liu、Daojuan Cheng、Fulai Yang
DOI:10.1002/cjoc.201400450
日期:2014.11
An unprecedented protocol has been developed for the efficientsynthesis of substituted tetrahydropyrans via a bismuth‐promoted Prinscyclization of imines with homoallylalcohols. In the presence of 40 mol% BiCl3, a wide variety of imines react smoothly with homoallylalcohols at room temperature to give the corresponding 4‐chlorotetrahydropyran derivatives in good to excellent yields.