Laali Kenneth K, Okazaki Takao, Bunge Scott D, Lenoir Dieter
Department of Chemistry, Kent State University, Kent, OH 44242, USA.
J Org Chem. 2008 Jun 6;73(11):4092-100. doi: 10.1021/jo800175d. Epub 2008 May 14.
Generation and NMR studies of novel carbocations and carboxonium ions are reported from sterically hindered stilbene 1,1'-bi(benzocyclobutenylidene) 1, its dimethoxy derivative 5, and from their skeletally rearranged derivatives, namely, the spirocyclic ketone 6, diastereomeric alcohols 7 and isomeric diols 8. Quenching experiments on the carbocations under various conditions resulted in the formation/isolation of several novel covalent adducts. Acid-catalyzed isomerization of the diols 8 produced a remarkable dimeric molecule, whose structure was confirmed by X-ray analysis. Reactions of hindered stilbenes 1 and 5 with Br 2/CDCl 3 were examined via NMR experiments. The experimentally observed carbocations were also studied computationally by GIAO-DFT and by NICS.
报道了新型碳正离子和羧鎓离子的生成及核磁共振研究，这些离子来源于空间位阻较大的芪1,1'-联(苯并环丁烯叉)1、其二甲氧基衍生物5及其骨架重排衍生物，即螺环酮6、非对映体醇7和异构体二醇8。在各种条件下对碳正离子进行猝灭实验，得到了几种新型共价加合物的形成/分离。二醇8的酸催化异构化产生了一个显著的二聚体分子，其结构通过X射线分析得到证实。通过核磁共振实验研究了受阻芪1和5与Br₂/CDCl₃的反应。还通过GIAO-DFT和NICS对实验观察到的碳正离子进行了计算研究。
