Ligand-Accelerated C−H Activation Reactions: Evidence for a Switch of Mechanism
作者:Keary M. Engle、Dong-Hui Wang、Jin-Quan Yu
DOI:10.1021/ja105044s
日期:2010.10.13
Initial rate studies have revealed dramatic acceleration in aerobic Pd(II)-catalyzed C-H olefination reactions of phenylacetic acids when mono-N-protected amino acids are used as ligands. In light of these findings, systematic ligand tuning was undertaken, which has resulted in drastic improvements in substrate scope, reaction rate, and catalyst turnover. We present evidence from intermolecular competition studies and kinetic isotope effect experiments that implies that the observed rate increases are a result of acceleration in the C-H cleavage step. Furthermore, these studies suggest that the origin of this phenomenon is a change in the mechanism of C-H cleavage from electrophilic palladation to proton abstraction.
Constructing Multiply Substituted Arenes Using Sequential Palladium(II)-Catalyzed CH Olefination
作者:Keary M. Engle、Dong-Hui Wang、Jin-Quan Yu
DOI:10.1002/anie.201002077
日期:2010.8.16
in which the reactivity/selectivity balance in PdII‐catalyzed ortho‐CHolefination can be modulated to enable sequential CH functionalization for the rapid preparation of 1,2,3‐trisubstituted arenes 1. Additionally, a rare example of iterative CH activation, in which a newly installed functional group directs subsequent CH activation has been demonstrated (2).
平衡行为:描述了互补的催化系统,其中可以调节Pd II催化的邻位-C - H烯化反应中的反应性/选择性平衡,以实现连续的 C - H 官能化,从而快速制备 1,2,3-三取代芳烃1 . 此外,还演示了一个罕见的迭代 C → H 激活示例,其中新安装的功能组指导后续的 C → H 激活 ( 2 )。