Asymmetric dihydroxylation using heterogenized cinchona alkaloid ligands on mesoporous silica

Cinchona alkaloids have been successfully grafted on mesoporous silica. Asy mmetric dihydroxylation using the heterogenized chiral ligands procceded wi th varying degrees of enantioselection depending upon the nature of the chi ral ligands. High asymmetric induction (up to > 99.5% enantiomeric excess) almost equal to that obtained from the homogeneous, catalyst system could b e achieved using a dimeric alkaloid ligand with a six-carbon link between t he ligand and the Support (L3). while inferior results were obtained when a monomeric alkaloid ligand system vas used. Reduced enantioselectivites wer e observed upon repeated recycling of the immobilized ligand system. (C) 20 01 Elsevier Science Ltd. All rights reserved.