Stereochemistry as a Tool in Deciphering the Processes of a Tandem Iminium Cyclization and Smiles Rearrangement
作者:Jinbao Xiang、Tong Zhu、Qun Dang、Xu Bai
DOI:10.1021/jo101798p
日期:2010.12.3
isomer. The former was rationalized by the postulation of a Cram’s chelate transition state leading to the cis product as kinetically favored. The latter was due to the equilibration between the trans/cis pair involving a carbocation intermediate and the steric hindrance, which prevented the cis isomer from undergoing the intramolecular nucleophilic substitution. This hypothesis was further supported
为了了解最近报道的串联亚胺基亚胺环化和Smiles重排的详细机理,通过监测手性底物的立体化学过程研究了手性底物的反应过程。在串联反应条件下,衍生自1-脯氨醇的手性醛1导致两个令人惊讶的结果。首先,亚胺基环化得到非对映异构体混合物,其中以顺式构型产物为主。第二,两者的重排微笑顺-和反式- 2导致了同样的产物3A从直接导出反异构体。前者是通过假设Cram的螯合物过渡态合理化而导致顺式产物在动力学上受到青睐的。后者是由于涉及碳正离子中间体的反式/顺式对与空间位阻之间的平衡,这阻止了顺式异构体进行分子内亲核取代。竞争实验的结果进一步支持了该假设,在竞争实验中,在重排步骤中添加1当量的对甲氧基苯胺导致大量的苯胺基交换的重排产物。