Chiral aggregates and asymmetric induction of the reduction of prochiral ketones

The aim of this work was to establish structure-reactivity relationships be tween chiral aggregates (micelles, vesicles, and "pseudo-micelles" of amphi philic dendrimers) and asymmetric induction. In water, micelles or vesicles formed with sugar-headed surfactants gave less than 10% ee in the reductio n of prochiral ketones by NaBH4, in contrast with dendrimers bearing the sa me types of sugar moieties, which gave more than 50% ee under the same reac tion conditions. Moreover, in the presence of neoglycodendrimers in THF we have been able to improve reduction of prochiral ketones to give very high stereoselectivity, near 100% in many cases. Comparison of these results sug gests that to improve high stereoselectivity it is necessary to work with r igid, well-organized colloidal objects. (C) 2000 Wiley-Liss, Inc.