Two 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 a-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.
New perfluoroalkyl-substituted bisoxazolines as chiral ligands in asymmetric Cu-II-catalyzed reactions / B. Simonelli, S. Orlandi, M. Benaglia, G. Pozzi. - In: EUROPEAN JOURNAL OF ORGANIC CHEMISTRY. - ISSN 1434-193X. - 2004:12(2004), pp. 2669-2673. [10.1002/ejoc.2004000335]
New perfluoroalkyl-substituted bisoxazolines as chiral ligands in asymmetric Cu-II-catalyzed reactions
S. OrlandiSecondo
;M. BenagliaPenultimo
;
2004
Abstract
Two 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 a-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.Pubblicazioni consigliate
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