Chiral Benzoquinones as a New Class of Ligands for Asymmetric Catalysis:  Synthesis and Application to the Palladium(II)-Catalyzed 1,4-Dialkoxylation of 1,3-Dienes

Chiral C 2 -symmetric 2,5-bisamide hydroquinone ligands, with β-amino alcohols as chiral building units, were synthesized in excellent overall yields. The ligands gave up to 54.4% ee in the palladium-catalyzed 1,4-dialkoxylation of 1,3-dienes. These findings demonstrate the potential of asymmetric induction utilizing chiral benzoquinones as ligands in palladium(II) catalysis, albeit with modest enantiomeric excesses. Weakly coordinating hydroxyl groups of the ligand appear to be crucial for the success of the reaction. Mechanistic aspects and the origin of enantioselectivity are also discussed.