Non-linear effects operate and dynamic ligand exchange occurs when chiral BINOL-boron Lewis acids are used for asymmetric catalysis

Non-linear effects reveal that the use of chiral BINOL-boron reagents for aza-Diels-Alder reactions results in an enantioselective catalytic species containing at least 2 equiv. of BINOL. Dynamic ligand exchange and ligand accelerated catalysis occurs in these reactions, consistent with the formation of a cyclic borate ester of BINOL with enhanced Lewis acidity. (C) 2003 Elsevier Science Ltd. All rights reserved.