Nitro-Substituted Hoveyda−Grubbs Ruthenium Carbenes: Enhancement of Catalyst Activity through Electronic Activation
摘要:
The design, synthesis, stability, and catalytic activity of nitro-substituted Hoveyda-Grubbs metathesis catalysts are described. The highly active and stable meta- and para-substituted complexes are attractive from a practical point of view. These catalysts operate in very mild conditions and can be successfully applied in various types of metathesis [ring-closing metathesis, cross-metathesis (CM), and enyne metathesis]. Although the presence of a NO2 group leads to catalysts that are dramatically more active than both the second-generation Grubbs's catalyst and the phosphine-free Hoveyda's carbene, enhancement of reactivity is somewhat lower than that observed for a sterically activated Hoveyda-Grubbs catalyst. Attempts to combine two modes of activation, steric and electronic, result in severely decreasing a catalyst's stability. The present findings illustrate that different Ru catalysts turned out to be optimal for different applications. Whereas phosphine-free carbenes are catalysts of choice for CM of various electron-deficient substrates, they exhibit lower reactivity in the formation of tetrasubstituted double bonds. This demonstrates that no single catalyst outperforms all others in all possible applications.
Regioselective Aromatic Perfluoro-<i>tert</i>-butylation Using Perfluoro-<i>tert</i>-butyl Phenyl Sulfone and Arynes
作者:Zhiqiang Wei、Lixian Wen、Kaidi Zhu、Qian Wang、Yanchuan Zhao、Jinbo Hu
DOI:10.1021/jacs.2c10479
日期:2022.12.7
synthetic protocol to realize aromatic perfluoro-tert-butylation. The key to the success is the identification of PFtB phenyl sulfone as a new source of PFtB anion, which reacts with arynes in a highly regioselective manner to afford perfluoro-tert-butylated arenes in high yields. The application of the method is demonstrated by the preparation of sensitive 19F-labeled NMRprobes with an extraordinary resolving