Mechanistic Studies of the Biomimetic Epoxy Ester−Orthoester and Orthoester−Cyclic Ether Rearrangements
作者:José-Luis Giner、Xiaoyong Li、Joseph J. Mullins
DOI:10.1021/jo034566s
日期:2003.12.1
The relative rates of acid-catalyzed rearrangements of epoxy esters to [3.2.1]bicyclic orthoesters, the subsequent rearrangements of these ortho esters to substituted tetrahydrofurans, and the rates of orthoester hydrolysis at pH 4.75 were measured in NMR kinetics experiments. The ease of formation and stabilities of these orthoesters compared favorably with the OBO-type [2.2.2]bicyclic orthoesters
在NMR动力学实验中,测量了酸催化环氧酯重排为[3.2.1]双环原酸酯的相对速率,这些原酸酯随后重排为取代的四氢呋喃的相对速率,以及在pH值为4.75时原酸酯水解的速率。这些原酸酯的形成容易性和稳定性与通常用作羧酸保护基的OBO型[2.2.2]双环原酸酯相比具有优势。用13 C NMR检测到的18 O-标记进行的研究表明,环氧酯重排优先通过6-exo环化发生,尽管当环氧化物的远端中心被双取代时,7-endo竞争。通过18 O标记显示原酸酯环醚重排仅通过五元二氧杂环鎓离子的中介发生。水解产物的结构还表明在水解过程中二氧戊酸根离子的中间性。讨论了海洋聚醚毒素的假设生物合成的意义。