Application of Tridentate Bis(oxazoline) Ligands in Catalytic Asymmetric Nozaki-Hiyama Allylation and Crotylation:An Example of High Enantioselection with a Non-Symmetric Bis(oxazoline) Ligand

摘要

A series of both symmetric and non-symmetric bis(oxazoline) ligands was applied in the Nozaki-Hiyama allylation and crotylation of benzalde-hyde.It was found that both the magnitude and sense of the asymmetric induction depended strongly on the nature and combination of the oxazoline substituents.For both reactions,the non-symmetric tert-butyl/ben-zyl-substituted ligand proved to be the optimal ligand and was applied successfully in the allylation and crotylation of a range of aryl and aliphatic aldehydes.The enantioselectivities obtained in allylation were up to 91% ee and in crotylation up to 92% with typical syn:anti ratios of up to 80:20.