21592-97-2Relevant articles and documents
Bismuth-substituted "sandwich" type polyoxometalate catalyst for activation of peroxide: Umpolung of the peroxo intermediate and change of chemoselectivity
Amanchi, Srinivasa Rao,Khenkin, Alexander M.,Diskin-Posner, Yael,Neumann, Ronny
, p. 3336 - 3341 (2015/06/16)
The epoxidation of alkenes with peroxides by WVI, MoVI, VV, and TiIV compounds is well established, and it is well accepted that the active intermediate peroxo species are electrophilic toward nucleophilic substrates. Polyoxotungstates, for example, those of the "sandwich" structure, [WZn(TM-L)2(ZnW9O34)2]q- in which TM = transition metal and L = H2O, have in the past been found to be excellent epoxidation catalysts. It has now been found that substituting the Lewis basic BiIII into the terminal position of the "sandwich" polyoxometalate structure to yield [Zn2BiIII2(ZnW9O34)2]14- leads to an apparent umpolung of the peroxo species and formation of a nucleophilic peroxo intermediate. There are two lines of evidence that support the formation of a reactive nucleophilic peroxo intermediate: (1) More electrophilic sulfoxides are more reactive than more nucleophilic sulfides, and (2) nonfunctionalized aliphatic alkenes and dienes showed ene type reactivity rather than epoxidation pointing toward "dark" formation of singlet oxygen from the nucleophilic intermediate peroxo species. Allylic alcohols reacted much faster than alkenes but showed chemoselectivity toward C-H bond activation of the alcohol and formation of aldehydes or ketones rather than epoxidation. This explained via alkoxide formation at the BiIII center followed by oxidative β-elimination.
Enantioselective opening of cyclic vinyl epoxides with organoaluminium reagents catalysed by copper salts
Equey, Olivier,Alexakis, Alexandre
, p. 1531 - 1536 (2007/10/03)
Herein we report conditions for the enantioselective conjugate addition of trialkylaluminium reagents to cyclic vinyl epoxides catalysed by copper salts and chiral phosphorus-based ligands. The reaction must be carried out in THF, otherwise we observed only oligomeric products. The best ees have been obtained with CuTC as the copper salt and a 2,2′-binaphthyl-based phosphorus ligand. Both opening products (SN2 and SN2 ′ pathways) were obtained with good enantioselectivity and moderate to good regioselectivity.
Regioselectivity in the palladium-catalyzed addition of carbon nucleophiles to carbocyclic derivatives
Hoke, Molly E.,Brescia, Marc-Raleigh,Bogaczyk, Suzanne,DeShong, Philip,King, Bryan W.,Crimmins, Michael T.
, p. 327 - 335 (2007/10/03)
The regioselectivity of Pd-catalyzed malonate additions and arylations to cycloalkenyl esters can be predicted by completing a stereochemical analysis of the Pd-π-allyl complex. The Pd-catalyzed malonate additions which have the greatest degree of regioselectivity are in which substituents have a steric influence in blocking the incoming nucleophile. Cyclopentenyl substrates displayed lower regioselectivity than the cyclohexyl counterparts presumably due to increased planarity of the system. Arylations using tin and hypervalent silicon reagents were compared.
