A domino 1,4-addition/alkyne carbozincation sequence based on a radical zinc-atom transfer process is disclosed. Two efficient multicomponent approaches to 3-alkylidenetetrahydrofurans from β-(propargyloxy)enoates bearing pendant alkynes (including ynamides) have been established: one involving the direct addition of dialkylzincs, and the second involving the dimethylzinc-mediated addition of alkyl
The silylzincation of terminal ynamides is achieved through a radical‐chain process involving (Me3Si)3SiH and R2Zn. A potentially competing polar mechanism is excluded on the basis of diagnostic control experiments. The unique feature of this addition across the CC bond is its trans selectivity. One‐pot electrophilic substitution of the CZn bond by CuI‐mediated CC bond formation and subsequent manipulation
Development of a Radical Silylzincation of (Het)Aryl‐Substituted Alkynes and Computational Insights into the Origin of the
<i>trans</i>
‐Stereoselectivity
Aryl- and hetaryl-substituted acetylenes undergo regio- and stereoselective silylzincation by reaction with [(Me3Si)3Si]2Zn in the presence of Et2Zn (10–110 mol%) as additive. The distinctive feature of this addition across the C−C triple bond is its trans stereoselectivity. The radical nature of the silylzincation process is supported by diagnostic experiments and DFT calculations, which also corroborate
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。
Radical‐Polar Crossover Domino Reaction Involving Alkynes: A Stereoselective Zinc Atom Radical Transfer