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Title: Chiral monooxazolines as modular copper(I)-heterocomplex building blocks: investigations on the catalytic asymmetric cyclopropanation of alkenes
Authors: Prates Ramalho, João Paulo
Carreiro, Elisabete
Burke, Anthony
Issue Date: 2011
Publisher: Elsevier
Citation: Elisabete P. Carreiro, J.P. Prates Ramalho, Anthony J. Burke, Tetrahedron 67 (2011) 4640-4648
Abstract: Novel chiral monodentate oxazoline ligands have been synthesized in good yields. The catalytic activity of these monodentate oxazoline/Cu catalysts was evaluated in the catalytic asymmetric cyclopropanation of styrene and a-methylstyrene, giving moderate to good enantioselectivities (up to 74% ee for the transcyclopropane product) and full conversions (up to 100%). In an attempt to enhance the enantioselectivities of the cyclopropanations, heterocombinations of these ligands were used. Unfortunately, with the data set that was used in this study, no improvements were observed. However, to gain an insight into the nature of the active catalyst present under these circumstances, NMR, mass spectrometric and computational studies were carried out and indicated the presence of bidentate heterocomplexes in the equilibrium mixture. Analysis of the stereoselectivities (ees and des) did not prove very useful in pinpointing the identity of the active chiral catalyst and only afforded a very weak conclusion. In order to ascertain the importance of the pi-pi interactions, the monodentate oxazoline ligands 3a and 3b were synthesized and screened in these reactions, and the resulting stereoselectivities were compared to the results obtained using ligands 1a and 1b. There seemed to be very weak pi-pi iinteractions at work.
Type: article
Appears in Collections:CQE - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica
QUI - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica

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