Substrate-selective aqueous organometallic catalysis. How small water-soluble organic molecules enhance the supramolecular discrimination

Selective decarboxylation of two alkylallylurethane isomers into alkylallylamines has been performed in a biphasic system by using randomly hydroxypropylated and methylated cyclodextrins as discriminating agents. Surprisingly, the presence of small organic hydrosoluble molecules such as amine or alcohol derivatives appeared to be crucial in the discriminating process. Indeed, it was clearly proved that the presence of such additives enhances greatly the substrate selectivity. For instance, the addition of triethylamine to the reaction medium allows to improve the discriminating power of methylated-β-cyclodextrin by a factor 7. These unexpected results were explained by considering the formation of ternary cyclodextrin/substrate/additive complexes.