New Perfluoroalkyl‐Substituted Bisoxazolines as Chiral Ligands in Asymmetric CuII‐Catalyzed Reactions

Abstract

AbstractTwo new enantiomerically pure perfluoroalkyl‐substituted bisoxazolines (F‐Box) have been prepared by a reaction sequence that involves formation of the properly functionalized Box followed by introduction of one or two n‐C8F17 residues. These ligands were employed for the first time in the Mukaiyama aldol addition of silylketene thioacetals to methylpyruvate promoted by Cu(OTf)2 (up to 85% ee) and in the ene reaction between α‐methylstyrene and ethylglyoxalate in the presence of Cu(OTf)2 (up to 74% ee). We compared the reactivities of the new ligands with those of two other chiral fluorous bisoxazolines that we have reported previously. In both cases, the F‐Box that has the lower fluorine content performed better, in terms of chemical yield and enantioselectivity, than the more‐fluorinated one. The recovery and recycling of the ligands is realized either by phase separation of the reaction solvents or by filtration through a short plug of fluorous silica gel. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)