A series of 2,9-disubstituted-l,lO-phenanthroline type ligands have been used in palladiumcatalyzed displacement of allylic acetates. It was found that intermediate synand anti-(v3-buteny1)palladium complexes reacted with different rates and regiochemistries. Depending on the ligands, this could be used for regiocontrol as well as stereocontrol. With the parent 1,-10-phenanthroline, syn complexes were formed quickly as intermediates from both ( E ) and (2) allylic acetates, leading to nearly exclusive formation of (E) products. In contrast, complete retention of alkene stereochemistry was observed with 2,9-dimethyl-l,lO-phenanthroline which also gave a catalyst with a considerably higher activity than catalysts based on triphenylphosphine. @ (4) (a) Akermark, B.; Hansson, S.; Vitagliano, A. J. Am. Chem. SOC. 1990,112,4587. (b) Sjdgren, M.; Hansson, S.; Norrby, P.-0.; Akermark, B.; Cucciolito, M. E.; Vitagliano, A. Organometallics 1992, 11, 3954. (5) (a) Leutenegger, U.; Umbricht, G.; Fahrni, C.; von Matt, P.; Pfaltz, A.