Gültekin Demet Demirci, Daştan Arif, Taşkesenligil Yavuz, Kazaz Cavit, Zorlu Yunus, Balci Metin
Askale Vocational College, Department of Metallurgical Program, Atatürk University 25500 Erzurum, Turkey.
Department of Chemistry, Atatürk University, 25240 Erzurum, Turkey.
Beilstein J Org Chem. 2023 Jun 2;19:764-770. doi: 10.3762/bjoc.19.56. eCollection 2023.
Previously we reported on the bromination of 7-bromonorbornene at different temperatures yielding mixtures of addition products. The structural elucidations of the formed compounds were achieved by NMR spectroscopy. Particularly, the γ-gauche effect and long-range couplings were instrumental in assigning the stereochemistry of the adducts. However, in a recent paper, Novitskiy and Kutateladze claimed that based on an applied machine learning-augmented DFT method for computational NMR that the structure of the product, (1,2,3,4,7)-2,3,7-tribromobicyclo[2.2.1]heptane was wrong. With the aid of their computational method, they revised a number of published structures, including ours, and assigned our product the structure (1,2,3,,7)-2,3,7-tribromobicyclo[2.2.1]heptane. To fit their revised structure, they proposed an alternative mechanism featuring a skeletal rearrangement without the intermediacy of a carbocation. Herein, we are not only confirming the structure originally assigned by us through crucial NMR experiments, we also present the ultimate structural proof by means of X-ray crystallography. Moreover, we disprove the mechanism proposed by the aforementioned authors based on sound mechanistic reasoning and point to an oversight by the authors that led them to an erroneous mechanistic pathway.
此前我们报道了7-溴降冰片烯在不同温度下的溴化反应，生成了加成产物的混合物。通过核磁共振光谱法对所形成化合物的结构进行了阐明。特别是，γ-邻位交叉效应和远程耦合有助于确定加合物的立体化学结构。然而，在最近的一篇论文中，诺维茨基和库塔特拉泽声称，基于一种应用机器学习增强的密度泛函理论（DFT）方法进行计算核磁共振，产物(1,2,3,4,7)-2,3,7-三溴双环[2.2.1]庚烷的结构是错误的。借助他们的计算方法，他们修正了包括我们的结构在内的一些已发表的结构，并将我们的产物指定为(1,2,3,,7)-2,3,7-三溴双环[2.2.1]庚烷的结构。为了符合他们修正后的结构，他们提出了一种替代机制，其特征是骨架重排，且没有碳正离子中间体。在此，我们不仅通过关键的核磁共振实验证实了我们最初指定的结构，还通过X射线晶体学提供了最终的结构证据。此外，我们基于合理的机理推理反驳了上述作者提出的机理，并指出作者的一个疏忽导致他们得出了错误的机理途径。
