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Role of Planar Chirality of S,N- and P,N-Ferrocene Ligands in Palladium-Catalyzed Allylic Substitutions

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posted on 21.05.2002, 00:00 by Shu-Li You, Xue-Long Hou, Li-Xin Dai, Yi-Hua Yu, Wei Xia
Palladium-catalyzed asymmetric allylic substitutions using thioether and phosphino derivatives of ferrocenyloxazoline as ligands have been investigated with a focus on studying the role of planar chirality. In allylic alkylation, up to 98% ee and 95% ee were achieved with S,N- and P,N-ligands, respectively. In allylic amination, 97% ee was realized with P,N-ligands in the presence of TBAF. Several palladium allylic complexes were characterized by X-ray diffraction and/or solution NMR. Thioether derivatives of ferrocenyloxazolines with only planar chirality showed lower enantioselectivity in the allylic alkylation except 5c because of the formation of a new chirality on sulfur atom during the coordination of sulfur with palladium. On the other hand, in the planar chiral P,N-ligands without central chirality, (Sp)-11ac there was no such disturbance and comparatively higher enantioselectivity in both palladium-catalyzed allylic alkylation and amination was provided.