New Asymmetric Catalysts with Electronically Asymmetric Heterodonor Bidentate Ligands Most palladium-catalyzed allylic substitutions give linear products; however the sterically unencumbered region in the vicinity of the sulfur stabilizes the isomer with the substituent trans to phosphorus. The electronic asymmetry promotes nucleophilic attack trans to phosphorus yielding branched products. In some cases, these ligands also promote memory effects, not often observed in Pd catalysis, wherein the stereochemistry of the starting allyl is retained.