作者:Yan Xu、Jonathan J. Wong、Adrian E. Samkian、Jeong Hoon Ko、Shuming Chen、K. N. Houk、Robert H. Grubbs
DOI:10.1021/jacs.0c11334
日期:2020.12.16
cyclometalated ruthenium catalysts with bulky N-heterocycliccarbene (NHC) ligands. Superior reactivity and stereoselectivity are realized for the first time in this challenging transformation, allowing streamlined access to an important class of cis-Michael acceptors from readily available feedstocks. The kinetic preference for cross-metathesis is enabled by a pivalate anionic ligand, and the origin
通过使用具有庞大 N-杂环卡宾 (NHC) 配体的新型环金属化钌催化剂,开发了丙烯酰胺和普通末端烯烃之间的高效 Z 选择性交叉复分解。在这一具有挑战性的转化中首次实现了卓越的反应性和立体选择性,允许从现成的原料中简化获得一类重要的顺式迈克尔受体。交叉复分解的动力学偏好是由新戊酸盐阴离子配体实现的,这种效应的起源通过密度泛函理论计算得到阐明。
Asymmetric Construction of an Aryl‐Alkene Axis by Palladium‐Catalyzed Suzuki–Miyaura Coupling Reaction
The construction of axially chiral acyclic aryl-alkene skeletons via classic Suzuki–Miyaurareaction has been challenging compared to the biaryls. Rational optimization established an enabling 3,3′-triphenylsilyl-substituted phosphite ligand for asymmetric coupling of hindered aryl halides and vinyl boronates under mild conditions, affording the acyclic aryl-alkenes in good yield, atroposelectivity
A new class of easily accessible and stable imidazolin-2-ylidenes has been synthesized where the side chains are comprised of substituted naphthyl units. Introduction of the naphthyl groups generates C-2-symmetric (rac) and C-s-symmetric (meso) atropisomers, and interconversion between the isomers is studied in detail both experimentally and computationally. Complete characterization of the carbenes includes rare examples of crystallographically characterized saturated NHC structures. Steric properties of the ligands and an investigation of their stability are also presented. In catalysis, the new ligands show versatility comparable to the most widely used NHCs IMes/SIMes or IPr/SIPr. Excellent catalytic results are obtained when either the NHC salts (ring-opening alkylation of epoxides), NHC-modified palladium compounds (C-C and C-N cross-couplings), or NHC-ruthenium complexes (ring-closing metathesis, RCM) are employed. In several cases, this new ligand family provides catalytic systems of higher reactivity than that observed with previously reported NHC compounds.