Synthesis of chiral tridentate oxazolines with thioether and heteroaryl donor groups and their application in the catalysis of asymmetric Michael reactions

Four chiral amino alcohols 1 derived from the natural a-amino acids L-cysteine and L-methionine have been converted with 2-thiophene and 2-pyridine carboxylic acid derivatives 2 to give eight tridentate oxazoline ligands 3a-d and 4a-d with a heteroaryl and a thioether donor function. In one case the coordination geometry at copper(II) was established by X-ray single crystal structure analysis. All ligands have been screened with 13 metal compounds 8 with regard to the asymmetric catalysis of the Michael reaction of a beta-keto ester 6 with methyl vinyl ketone (7) to give an optimal result of 19% ee. (C) 1999 Elsevier Science Ltd. All rights reserved.