Ene–Diene Transmissive Cycloaddition Reactions with Singlet Oxygen: The <i>Vinylogous Gem Effect</i> and Its Use for Polyoxyfunctionalization of Dienes
作者:Angelika Eske、Bernd Goldfuss、Axel G. Griesbeck、Alan de Kiff、Margarethe Kleczka、Matthias Leven、Jörg-M. Neudörfl、Moritz Vollmer
DOI:10.1021/jo5000434
日期:2014.2.21
trimethylated substrates 1k and 1l, respectively. The vinylogous gem effect favors the formation of 1,3-dienes from the substrates, and thus, secondary singlet oxygen addition was observed to give hydroperoxy-1,2-dioxenes 19 and 20 in an ene–diene transmissive cycloaddition sequence. These products were reduced to give alcohols (16, 17, and 18) or furans (24 and 25), respectively, or treated with titanium(IV) alkoxides
将模型化合物1b – d的单重态氧反应性和区域选择性与双(选择性)钛酸乙酯(1a)的单线态氧反应性和区域选择性进行了比较。tiglate / angelate系统1a / 1a'的动力学顺式效应为k E / k Z = 5.2,而高宝石区域选择性没有变化。与乙烯基的进一步缀合使得能够进行模式选择过程,即,[4 + 2]环加成对烯反应。对于二烯1e – g,研究了甲基化对烯键反应的模式选择性和区域选择性的位点特异性影响。。分别对γ,δ-二甲基化和α,γ,δ-三甲基化的底物1h和1i观察到乙烯基类宝石效应。相应的苯基化底物1j - 1显示出相似的模式选择性,因为单甲基化1j仅表现出[4 + 2]反应性,而串联产物12和14分别从二甲基化和三甲基化底物1k和1l中分离出来。乙烯基类宝石效应有利于从底物形成1,3-二烯,因此,观察到二次单线态氧的添加产生了氢过氧-1,2-二氧六环19和20以烯-二