Acid Catalysis vs. Electron-Transfer Catalysis via Organic Cations or Cation-Radicals as the Reactive Intermediate. Are These Distinctive Mechanisms?
摘要:
Proton transfer to aromatic and olefinic donors (D) lends to the facile interchange of transient carbocations (DH+) and cation-radical (D+.). The same types of cation and cation-radical are reactive intermediates in the acid catalysis and the electron-transfer catalysis of such organic transformations as benzylic coupling, epoxide.-pinacol rearrangements and cis-trans isomerization of stilbenes when they are both carried out under otherwise identical reaction conditions, However, the rapid exchange of diamagnetic cations and paramagnetic cation-radicals blurs the traditional view of sepal ate electrophilic and homolytic processes, and rigorous experimental evidence is required to establish whether acid catalysis and electron-transfer catalysis actually represent distinct mechanistic categories.
Langlebige α-metallierte methylradikale und deren dimere
作者:Horst Hillgärtner、Wilhelm P. Neumann、Winfried Schulten、Antonios K. Zarkadis
DOI:10.1016/s0022-328x(00)92576-2
日期:1980.11
Persistent radicals R'2C.MR3(I), R'C.(MR3)2 (II) and RC???(MR3)OMR3 (III), R' mostly Ph but also t-Bu, H, R'2 also 9-fluorenyl or 9-xanthenyl, M Si, Ge, Sn, have been generated from the corresponding CH or CHal compounds or by addition of R3M. to ketones. Radicals I, II and III are investigated by ESR spectroscopy. A temperature-dependent equilibrium has been found between these radicals and
Pinacol Cross‐Coupling Promoted by an Aluminyl Anion
作者:Andrea O'Reilly、Matthew J. Evans、Claire L. McMullin、J. Robin Fulton、Martyn P. Coles
DOI:10.1002/chem.202302999
日期:2024.1.2
The potassium aluminyl K[Al(NON)] (NON=[O(SiMe2NDipp)2]2−) is a suitable platform for the pinacol coupling of aldehydes and ketones. Isolating an intermediate allows unsymmetrical examples to be accessed via a sequential addition strategy. A rare example of a p-block ketyl complex was isolated, and DFT was used to confirm a carbon-based radical. Product release was achieved using an iodosilane, demonstrating