Correlations Between Nucleophilicities and Selectivities in the Substitutions of Tetrahydropyran Acetals
作者:Jennifer R. Krumper、Walter A. Salamant、K. A. Woerpel
DOI:10.1021/jo901639b
日期:2009.11.6
Selectivities that deviate from SN1 stereoelectronic models in the nucleophilic substitutions of tetrahydropyran acetals were investigated. When weak nucleophiles were employed, stereoselectivities conformed to known SN1 stereoelectronic models. In contrast, stereoselectivities in the substitutions of acetals with strong nucleophiles depended on reaction conditions. Erosions in selectivities were observed when
研究了在四氢吡喃缩醛的亲核取代中偏离 S N 1 立体电子模型的选择性。当使用弱亲核试剂时,立体选择性符合已知的 S N 1 立体电子模型。相反,用强亲核试剂取代缩醛的立体选择性取决于反应条件。当在没有配位反离子的情况下使用强亲核试剂时,观察到选择性的侵蚀。这些选择性的降低归因于接近扩散极限的氧代碳鎓离子中间体的亲核加成速率。然而,当三氟甲磺酸盐反离子存在时,S N2-like 通路可以通过强亲核试剂获得。在检查的大多数情况下,通过 S N 2 样途径进行的反应形成的主要立体异构体与通过 S N 1 途径进行的类似反应形成的主要立体异构体相反。