A Highly Diastereoselective Dioxetane Formation by the Hydroxy-Directed [2+2] Cycloaddition of Singlet Oxygen to a Chiral Allylic Alcohol
作者:Waldemar Adam、Chantu R. Saha-Möller、Simon B. Schambony
DOI:10.1021/ja9835077
日期:1999.3.1
with singlet oxygen in CDCl3 to yield the dioxetane threo-2a, accompanied by the dioxolane 4, which is formed as a subsequent product of an initial ene reaction. In the more polar CD3OD/CCl4 solvent mixture, the diastereoselectivity drops to 89:11, but the ene mode (dioxolane 4) is completely suppressed. In contrast, the photooxygenation of the acetate 1b in CDCl3 and in CD3OD yielded only ene product
金刚烷基取代的烯丙醇 1a 与 CDCl3 中的单线态氧发生非对映选择性反应,生成二氧杂环丁烷 threo-2a,同时生成二氧戊环 4,后者作为初始烯反应的后续产物形成。在极性更大的 CD3OD/CCl4 溶剂混合物中,非对映选择性下降到 89:11,但烯模式(二氧戊环 4)被完全抑制。相比之下,醋酸盐 1b 在 CDCl3 和 CD3OD 中的光氧化仅产生烯产物 3b。观察到的苏式选择性羟基方向性是根据单线态氧和羟基之间的激基复合物中的氢键来解释的,后者通过 1,3-烯丙基应变在基底中适当地构象排列。