Asymmetric dihydroxylation using heterogenized cinchona alkaloid ligands on mesoporous silica

Abstract

Cinchona alkaloids have been successfully grafted on mesoporous silica. Asymmetric dihydroxylation using the heterogenized chiral ligands procceded with varying degrees of enantioselection depending upon the nature of the chiral ligands. High asymmetric induction (up to > 99.5% enantiomeric excess) almost equal to that obtained from the homogeneous, catalyst system could be achieved using a dimeric alkaloid ligand with a six-carbon link between the ligand and the Support (L3). while inferior results were obtained when a monomeric alkaloid ligand system vas used. Reduced enantioselectivites were observed upon repeated recycling of the immobilized ligand system. (C) 2001 Elsevier Science Ltd. All rights reserved.