Correlation between Functionality Preference of Ru Carbenes and <i>exo</i>/<i>endo</i> Product Selectivity for Clarifying the Mechanism of Ring-Closing Enyne Metathesis
Functionality preferences of metathesis Ru carbenes to various alkenes and alkynes with electronic and steric diversity were determined by using time-dependent fluorescence quenching. The functionality preferences depend not only on the properties of multiple bonds but also on the ligands on Ru. There was a good correlation between functionality preference and the metathesis reaction outcome. The correlation between functionality preference and exo/endo product ratio offers a solution to resolve the mechanistic issue related with alkene- vs alkyne-initiated pathway in ring-closing enyne metathesis. The correlation indicates the preference is likely to dictate the reaction pathway and eventually the outcome of the reaction. The Ru catalyst favoring alkyne over alkene provides more endo product, indicating that the reaction mainly initiates at the alkyne. By changing the substitution pattern, the preference can be reversed to give an exclusive exo product.
Conjugated Diene-Assisted Allylic C−H Bond Activation: Cationic Rh(I)-Catalyzed Syntheses of Polysubstituted Tetrahydropyrroles, Tetrahydrofurans, and Cyclopentanes from Ene-2-Dienes
作者:Qian Li、Zhi-Xiang Yu
DOI:10.1021/ja100409b
日期:2010.4.7
activation of allylic C-H bonds and their subsequent insertion into the alkene moieties of conjugateddienes. This novel C-H activation/alkene insertionreaction provides an efficient way to synthesize polysubstituted tetrahydropyrroles, tetrahydrofurans, and cyclopentanes with quaternary carbon centers. Preliminary mechanistic studies using D-labeling experiments have revealed that allylic C-H activation
Enantioselective Rhodium-Catalyzed Allylic CH Activation for the Addition to Conjugated Dienes
作者:Qian Li、Zhi-Xiang Yu
DOI:10.1002/anie.201005215
日期:2011.2.25
Easy and efficient: By applying the title transformation, two adjacent sp3 stereogenic centers, one of which is a quaternary carbon center, can be easily formed. This asymmetric reaction provides easy and efficient access to multifunctionalized tetrahydropyrrole, tetrahydrofuran, and cyclopentane compounds (see scheme; coe=cyclooctene, DME=1,2‐dimethoxyethane, Tf=trifluoromethanesulfonyl).