Zinc reagents (Me2PhSi)2Zn and [(Me3Si)3Si]2Zn undergo highly regio- and stereoselectiveaddition across the carbon–carbon triple bond of nitrogen-, sulfur-, oxygen-, and phosphorus-substituted terminal alkynes in the absence of copper or any other catalyst. Both reagents yield exclusively β-isomers, and the stereoselectivity is determined by the silyl group: Me2PhSi for cis or (Me3Si)3Si for trans
Radical Germylzincation of α-Heteroatom-Substituted Alkynes
作者:Karen de la Vega-Hernández、Elise Romain、Anais Coffinet、Kajetan Bijouard、Geoffrey Gontard、Fabrice Chemla、Franck Ferreira、Olivier Jackowski、Alejandro Perez-Luna
DOI:10.1021/jacs.8b09851
日期:2018.12.19
The regio- and stereoselectiveaddition of germanium and zinc across the C-C triple bond of nitrogen-, sulfur-, oxygen-, and phosphorus-substituted terminal and internal alkynes is achieved by reaction with a combination of R3GeH and Et2Zn. Diagnostic experiments support a radical-chain mechanism and the β-zincated vinylgermanes that show exceptional stability are characterized by NMR spectroscopy
通过与 R3GeH 和 Et2Zn 的组合反应,锗和锌在氮、硫、氧和磷取代的末端和内部炔烃的 CC 三键上的区域和立体选择性加成。诊断实验支持自由基链机制,并通过 NMR 光谱和 X 射线晶体学表征显示出异常稳定性的 β-锌化乙烯基锗烷。这种新的自由基锗基锌化反应的独特之处在于,形成的 C(sp2)-Zn 键仍然可用于随后的原位 Cu(I)-或 Pd(0)-介导的 CC 或 C-杂原子键的形成,同时保留双键几何。
Stereodivergent Synthesis of β-Heteroatom-Substituted Vinylsilanes by Sequential Silylzincation–Copper(I)-Mediated Electrophilic Substitution
stereoretentive copper(I)-mediated electrophilic substitution of the intermediate C(sp2)–Zn bond. These stereodivergent protocols offer a regio- and stereoselective access to trisubstituted vinylsilanes decorated with sulfur-, oxygen-, and phosphorus substituents with either double-bond geometry. Sulfur-, oxygen-, and phosphorus-substituted terminalalkynes undergo regio- and stereoselective silylzincation
Preparation and Synthetic Transformation of Alkenyl Carbamates into Vinyl Zirconocene Derivatives
作者:Ilan Marek、Helena Chechik-Lankin
DOI:10.1055/s-2005-918436
日期:——
The carbocupration reaction of alkynyl carbamates leads to the stereospecific preparation of polysubstituted alkenyl carbamates. Subsequent treatment of these enol carbamates with the Negishi reagent gave the corresponding vinyl zirconocene species.
The asymmetric synthesis of an acyclic anti-β-alkoxy ether was achieved by the Ireland–Claisen rearrangement of Z-3-alkoxy-2-propenyl glycolate ester, prepared from Garner’s aldehyde, a glycolic acid derivative, and ethynyl N,N-diisopropylcarbamate. The resulting acyclic ether was facilely converted to seven- and eight-membered cyclic ethers via processes involving ring-closing olefin metatheses.