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.
Aerobic epoxidation of hindered olefins and enol ethers catalyzed by a polymerizable β-ketoesterate complex of iron(III)
作者:Luigi Lopez、Piero Mastrorilli、Giuseppe Mele、Cosimo F. Nobile
DOI:10.1016/s0040-4039(00)73259-x
日期:1994.5
Peculiar hindered olefins and derivatives have been epoxidized, under Mukaiyama's conditions, using iron(III) catalytic centres. The experimental results allow to rule out the involvement of singlet oxygen and free peroxyacids as active species.
Catalytic Epoxidation of Hindered Olefins with Dioxygen. Fast Oxygen Atom Transfer to Olefin Cation Radicals from Nitrogen Oxides
作者:Eric Bosch、Jay K. Kochi
DOI:10.1021/ja953786n
日期:1996.1.1
efficiently converted to epoxides by dioxygen at 25 °C in dichloromethane containing catalytic amounts of nitrogen oxides (NO2, NO+, NO, etc.). Nitrogen dioxide also effects the direct (stoichiometric) epoxidation of the same hindered olefins. Olefin cation radicals are spectrally identified as the first observable intermediate, and separate experiments confirm the facile transfer of an oxygen atom from nitrogen
Lopez Luigi, Mastrorilli Piero, Mele Giuseppe, Nobile Cosimo F., Tetrahedron Lett, 35 (1994) N 21, S 3633-3636
作者:Lopez Luigi, Mastrorilli Piero, Mele Giuseppe, Nobile Cosimo F.
DOI:——
日期:——
Acid Catalysis vs. Electron-Transfer Catalysis via Organic Cations or Cation-Radicals as the Reactive Intermediate. Are These Distinctive Mechanisms?
作者:Rajendra Rathore、Jay K. Kochi、Augusto Canavesi、Larry L. Miller、Giovanni V. Sebastiani、George W. Francis、József Szúnyog、Bengt Långström
DOI:10.3891/acta.chem.scand.52-0114
日期:——
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.
Aerobic oxidations of unsaturated substrates under mukaiyama's conditions: The role of the metal and of the sacrificial aldehyde
作者:Piero Mastrorilli、Cosimo F. Nobile、Gian P. Suranna、Luigi Lopez
DOI:10.1016/0040-4020(95)00410-a
日期:1995.7
Aerobic epoxidation of unsaturated substrates has been achieved under Mukaiyama's conditions (atmospheric pressure of dioxygen, in the presence of an excess of sacrificial aldehyde) with or without metal catalyst. The influence of light in non-catalysed reactions and the possible role of the aldehyde and of the metal complex in catalysed reactions are discussed. Two mechanistic pathways are proposed for Co(II) and Fe(III) [Ni(II)] catalytic centres.