A comparison of electron transfer reagents in the reductive opening of epoxides: reasons for the superiority of titanocene based complexes
摘要:
Several commonly used electron transfer reagents were compared in their reactivity towards three epoxides. These substrates were designed to allow for a distinction between competing courses of the reaction. It was found that titanocene reagents were clearly superior due to their low Lewis acidity, high reduction tendency towards epoxides, and low reduction tendency towards the pivotal P-metal oxy radical intermediates. (C) 2002 Elsevier Science Ltd. All rights reserved.
Sustainable radical reduction through catalyzed hydrogen atom transfer reactions (CHAT-reactions)
作者:Andreas Gansäuer、Matthias Otte、Frederik Piestert、Chun-An Fan
DOI:10.1016/j.tet.2009.03.088
日期:2009.6
system with coupled catalytic cycles is described that allows radicalreduction by catalyzed hydrogenatomtransfer (CHAT) from transition metal hydrides. These intermediates are generated through H2 activation. Radical generation is carried out by titanocene catalyzed electron transfer to epoxides. The reaction provides a novel entry into the atom-economical reduction of radicals that has long been
Sustainable Radical Reduction through Catalytic Hydrogen Atom Transfer
作者:Andreas Gansäuer、Chun-An Fan、Frederik Piestert
DOI:10.1021/ja801232t
日期:2008.6.1
A system with coupled catalytic cycles is described that allows radicalreduction by hydrogenatom abstraction from rhodium hydrides. These intermediates are generated from H2 activation by Wilkinson's catalyst. Radical generation is carried out by titanocene-catalyzed electron transfer to epoxides.
A rationally designed titanium(III) catalyst allows the opening of epoxides with high enantioselectivity. This reaction [Eq. (1)] constitutes the first example of an enantioselective transitionmetalcatalyzedradicalreaction that proceeds by electrontransfer.
A comparison or different titanium catalysts in the enantioselective opening of meso-epoxides has been carried out. The best catalyst is readily available in both enantiomers from menthol and allows for a highly enantioselective reaction.