Methylated-β-cyclodextrins:: useful discriminating tools for substrate-selective reactions in aqueous organometallic catalysis

The biphasic palladium catalyzed cleavage of water-insoluble N-substituted-O-allylic urethanes in the presence of randomly methylated beta-cyclodextrins has been investigated with the aim of performing substrate-selective catalytic reactions. By using different pairs of structural isomers, it was found that the substrate selectivity depends strongly on the water solubility and the structure of isomers. So, a high substrate selectivity can only be observed with highly water-insoluble isomers that present pronounced structural differences. Furthermore, the size-fit concept which postulates the highest reactivity for the best size-matched host-guest pair provides a very useful tool for predicting the values of substrate selectivity. (C) 2004 Elsevier B.V. All rights reserved.