799764-79-7Relevant academic research and scientific papers
Chiral monooxazolines as modular copper(I)-heterocomplex building blocks: Investigations on the catalytic asymmetric cyclopropanation of alkenes
Carreiro, Elisabete P.,Ramalho, J.P. Prates,Burke, Anthony J.
, p. 4640 - 4648 (2011)
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 α-methylstyrene, giving moderate to good enantioselectivities (up to 74% ee for the trans-cyclopropane 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 pin-pointing the identity of the active chiral catalyst and only afforded a very weak conclusion. In order to ascertain the importance of the π-π 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 π-π interactions at work.
Hetero-Diels-Alder and pyroglutamate approaches to (2S,4R)-2-methylamino-5- hydroxy-4-methylpentanoic acid
Tarver Jr., James E.,Terranova, Kristen M.,Joullié, Madeleine M.
, p. 10277 - 10284 (2007/10/03)
The stereoselective syntheses of fully protected (2S,4R)-2-methylamino-5- hydroxy-4-methylpentanoic acid, a non-coded amino acid of cyclomarin A, and its diastereomer are reported. A pyroglutamate template was employed in the key diastereoselective alkylation used for introducing the 4-methyl stereochemistry. In addition, the first diastereoselective intramolecular hetero-Diels-Alder of a 2-cyano-1-azadiene with an electron deficient dienophile is described. Graphical Abstract
