A REMARKABLE ANION EFFECT ON THE ENANTIOSELECTIVITY OF THE PD-CATALYZED ALLYLIC AMINATION USING FERROCENYL LIGANDS

The effect of several anions on the enantioselectivity of the Pd-catal yzed substitution reaction of 1,3-diphenylprop-2-enylethyl carbonate 1 with benzylamine, utilizing chiral ferrocenyl ligands such as R)-1-[( S)-2-(diphenylphosphino)-ferrocenyl]ethyl}- 3-(1-adamantyl)-1H-pyrazol e 3a, was investigated. Small hard anions such as F- and BH4-, added i n co-catalytic amounts to the catalyst, were found to enhance the ee t o >99.5%. On the other hand, non-coordinating anions, e.g. PF6-, had a detrimental effect on the enantioselectivity (<10% ee). The beneficia l effect of fluoride is discussed in terms of its establishing Curtin- Hammett conditions, by virtue of its coordination to Pd. (C) 1997, Els evier Science Ltd. All rights reserved.