Easily recoverable BINOL ligand with ionic tag for asymmetric catalysis

A new chiral task specific ionic species containing chiral (S)-binaphthyl unit was synthesized and used as an auxiliary in the Ti-promoted addition of diethylzinc to benzaldehyde. The utilization of the ionic ligand containing the (S)-BINOL substructure led to enantioselectivities similar to those of the related non-ionic Counterpart. The ionic substructure allowed an appropriate tuning of the solubility of the BINOL ligands in order to ensure reaction in a homogeneous medium and recovery of the chiral auxiliary. The reaction was performed in CH,Cl, while the chiral ionic auxiliary was re-used in three catalytic cycles without a loss in activity or enantioselectivity. (c) 2005 Elsevier Ltd. All rights reserved.