Role of Planar Chirality of <i>S,N-</i> and <i>P,N-</i>Ferrocene Ligands in Palladium-Catalyzed Allylic Substitutions
2002-05-21T00:00:00Z (GMT) by
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 <i>S</i>,<i>N</i>- and <i>P</i>,<i>N</i>-ligands, respectively. In allylic amination, 97% ee was realized with <i>P</i>,<i>N</i>-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 <b>5c</b> 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 <i>P</i>,<i>N</i>-ligands without central chirality, (<i>Sp</i>)-<b>11a</b>−<b>c</b> there was no such disturbance and comparatively higher enantioselectivity in both palladium-catalyzed allylic alkylation and amination was provided.