Reversible C–C Bond Activation Enables Stereocontrol in Rh-Catalyzed Carbonylative Cycloadditions of Aminocyclopropanes

Upon exposure to neutral or cationic
Rh­(I)-catalyst systems, amino-substituted
cyclopropanes undergo carbonylative cycloaddition with tethered alkenes
to provide stereochemically complex N-heterocyclic scaffolds. These
processes rely upon the generation and trapping of rhodacyclopentanone
intermediates, which arise by regioselective, Cbz-directed insertion
of Rh and CO into one of the two proximal aminocyclopropane C–C
bonds. For cyclizations using cationic Rh­(I)-systems, synthetic and
mechanistic studies indicate that rhodacyclopentanone formation is
reversible and that the alkene insertion step determines product diastereoselectivity.
This regime facilitates high levels of stereocontrol with respect
to substituents on the alkene tether. The option of generating rhodacyclopentanones
dynamically provides a new facet to a growing area of catalysis and
may find use as a (stereo)­control strategy in other processes.

当与中性或阳离子型铑(I)（Rh(I)）催化体系接触时，氨基取代环丙烷可与连有锚定链的烯烃发生羰基化环加成反应，生成具有复杂立体化学特征的氮杂环骨架。此类反应依赖于铑环戊酮中间体的生成与捕获：该中间体通过区域选择性、Cbz（苄氧羰基）导向的铑与一氧化碳（CO）对两个近端氨基环丙烷C-C键之一的插入反应形成。针对采用阳离子型铑(I)催化体系的环化反应，合成与机理研究表明，铑环戊酮的生成过程为可逆过程，且烯烃插入步骤决定了产物的非对映选择性。该反应体系可对烯烃锚定链上的取代基实现高水平的立体调控。通过动态生成铑环戊酮的可选路径，为蓬勃发展的催化研究领域开辟了全新的研究维度，且有望在其他反应中作为（立体）调控策略得到应用。