A diastereoselective ring contraction of the diastereomixture of 2,4-disubstituted 1,3-dioxepins to 2,5-cis-2,3,5-trisubstituted tetrahydrofurans was achieved using TfOH in DMF. The reaction appears to proceed via a chair-like transition state, in which stereomutation of the oxocarbenium occurred, followed by an aldol-type cyclization.
在
DMF 中使用 TfOH 实现了 2,4-二取代 1,3-
二氧杂环庚烷的非对映选择性环收缩为 2,5-顺式-2,3,5-三取代
四氢呋喃。该反应似乎是通过一个类似椅子的过渡态进行的,在该过渡态中,氧代羰基发生了立体变异,随后发生了醛醇型环化反应。