Intramolecular Diels−Alder Reactions of Ester Linked 1,3,9-Decatrienes: Cis/Trans Selectivity in Thermal and Lewis Acid Promoted Reactions of Ethylene-Tethered and Benzo-Tethered Systems
作者:Emma L. Pearson、Laurence C. H. Kwan、Craig I. Turner、Garth A. Jones、Anthony C. Willis、Michael N. Paddon-Row、Michael S. Sherburn
DOI:10.1021/jo0607818
日期:2006.8.1
High cis (i.e., endo) diastereoselectivities are witnessed in heat-promoted intramolecular Diels−Alder (IMDA) reactions of ethylene-tethered hexadienyl acrylates. The cis stereoselectivity is improved by promotion with Et2AlCl. The first examples of Et2AlCl catalyzed intramolecular Diels−Alder reactions of ester-activated dienophiles are reported. In contrast, the corresponding benzo-tethered hexadienyl
在由乙烯束缚的己二烯基丙烯酸酯的热促进的分子内Diels-Alder(IMDA)反应中,观察到了高的顺式(即内切)非对映选择性。通过用Et 2 AlCl的促进作用可以改善顺式立体选择性。报道了由Et 2 AlCl催化的酯激活的双亲物的分子内Diels-Alder反应的第一个例子。相反,相应的苯并束缚的己二烯基丙烯酸酯发生中等反式(即外切)选择性IMDA反应。通过ATPH的促进,可以获得很高的反式立体选择。这些反应的结果基本上对亲双烯体(C10)的几何形状和取代不敏感。DFT(B3LYP / 6-31 + G(d))计算的顺式/反式产物分布基于玻尔兹曼过渡结构总体与实验结果非常吻合。这些计算研究为这些系统中立体声选择的起源提供了有用的见解。乙烯系丙烯酸己二烯基酯所显示的立体选择性归因于稳定顺式过渡结构(TSs)中的次级轨道相互作用。在苯并束缚的系列中,通过稳定在顺式TS中比在顺式TS中更强的