Hydroboration of bi(cyclopent-1-ene) (1) or 3,3'-biindene (2) with borane, thexylborane or (-)-isopinocampheylborane afforded, regardless of reaction conditions, meso-isomers of polycyclic 1,4-diols 3a, 4a as the main products. No reaction was observed with 9-BBN. The structure of the major product 4a, as well as of the minor racemic product 4b was assigned based on 1H NMR spectra of the corresponding Mosher's diesters 5a-5c. Finally, the stereochemistry of the product 4a was confirmed by a single-crystal X-ray analysis of the corresponding dimesylate 6. To elucidate preferential formation of the meso-isomers, complexes of monohydroborated intermediate with borane were studied theoretically by DFT methods.
使用硼烷、thexylborane或(-)-isopinocampheylborane对双(环戊-1-烯)(1)或3,3'-联吡啶(2)进行氢硼化反应,无论反应条件如何,都会得到多环1,4-二醇的meso-异构体3a和4a作为主要产物。9-BBN没有反应。主要产物4a以及次要的外消旋产物4b的结构是基于对应的Mosher's二酯5a-5c的1H NMR谱进行判定的。最后,通过相应的二甲基硫酸酯6的单晶X射线分析证实了产物4a的立体化学。为了阐明meso-异构体的优先形成,使用DFT方法理论研究了单氢硼中间体与硼烷的配合物。