Stereocontrol and Regiocontrol In Palladium-catalyzed Allylic Alkylation Using 1,10-phenanthrolines As Ligands

A series of 2,9-disubstituted-1,10-phenanthroline type ligands have been used in palladium-catalyzed displacement of allylic acetates. It was found that intermediate syn- and anti-(eta3-butenyl)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 (Z) allylic acetates, leading to nearly exclusive formation of (E) products. In contrast, complete retention of alkene stereochemistry was observed with 2,9-dimethyl-1,10-phenanthroline which also gave a catalyst with a considerably higher activity than catalysts based on triphenylphosphine.