Overall 5-endo-trig iodocyclisations of all isomers of the 2-alkenylcyclopentan-1-ols and -cyclohexan-1-ols 11, 12, 14 and 16 have been examined. Only in the cases of the trans-alkenylcyclopentanols 11a and 12a are the reactions either unsuccessful or low yielding, by reason of formation of a relatively strained trans-fused 5/5 ring system. In contrast, iodocyclisations of cis-alkenylcyclopentanols work well but only show useful stereoselection in the case of the cis-(Z)-alkenylcyclopentanol 16a. All examples involving the cyclohexanols 14 and 16 are high yielding and generally lead to single isomers of perhydro-3-iodobenzofurans 18, 20, 23 and 26. Transition state conformations are proposed which account for these observations and which should be useful in applying this type of cyclisation to related substrates.
对 2-烯基环戊-1-醇和环己-1-醇 11、12、14 和 16 的所有异构体进行了全面的 5-内-三
碘环化研究。只有在反式烯基
环戊醇 11a 和 12a 的情况下,由于形成了相对紧张的反式融合 5/5 环系统,反应要么不成功,要么产量低。相反,顺式-烯基
环戊醇的
碘环化反应效果很好,但只有在顺式-(Z)-烯基
环戊醇 16a 的情况下才显示出有用的立体选择性。所有涉及
环己醇 14 和 16 的例子产量都很高,一般都能得到过氢-3-
碘苯并呋喃 18、20、23 和 26 的单一异构体。提出的过渡态构象解释了这些观察结果,并有助于将这种环化方法应用于相关底物。