Chiral Crown Conformation of Rh2(S-PTTL)4: Enantioselective Cyclopropa nation with α-Alkyl-α-diazoesters
Chiral Crown Conformation of Rh2(S-PTTL)4: Enantioselective Cyclopropa nation with α-Alkyl-α-diazoesters
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DOI：
10.1021/ja9026852
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发表时间：
2009-06-03
影响因子：
15
通讯作者：
Fox, Joseph M.
中科院分区：
文献类型：
--
作者：
DeAngelis, Andrew;Dmitrenko, Olga;Fox, Joseph M.
本文提供了晶体学和计算证据，证明Hashimoto的Rh-2(s - ptl)(4)催化剂采用具有反应性手性面和非反应性手性面的“手性冠”构象。在Rh-2(s - ptl)(4)中，所有四个叔丁基都在催化剂的同一面上排列，并且每个C-(t-Bu)键大致平行。和中间的Rh-Rh键相连。这使得四个邻苯二胺基团在催化剂的相反面上定向。还描述了使用α -烷基- α -重氮酯催化的分子间Rh-2(s - ptl)(4)环丙烷化的对映选择性和非对映选择性方案。分子间环丙烷化在两个相互竞争的分子内途径中是选择性的：碳氢插入和b氢化物消除。在密度泛函理论计算和davis - singleton模型的基础上，提出了环丙烷反应的不对称诱导模型。
Herein, we provide crystallographic and computational evidence that Hashimoto's Rh-2(S-PTTL)(4) catalyst adopts a "chiral crown" conformation with a reactive chiral face and an unreactive achiral face. In Rh-2(S-PTTL)(4), all four tert-butyl groups are aligned on the same face of the catalyst, and each C-(t-Bu) bond is roughly parallel. to the central Rh-Rh bond. This orients the four phthalimido groups on the opposite face of the catalyst. Also described is an enantioselective and diastereoselective protocol for intermolecular Rh-2(S-PTTL)(4)-catalyzed cyclopropanation using alpha-alkyl-alpha-diazoesters. Intermotecular cyclopropanation is selective over two competing intramolecular pathways: C-H insertion and B-hydride elimination. On the basis of density functional theory calculations and the Davies-Singleton model, for cyclopropanation, a model for asymmetric induction is proposed.