Modular Phosphine-Aminophosphine Ligands Based on Chiral 1,2,3,4-Tetrahydro-1-naphthylamine Backbone: A New Class of Practical Ligands for Enantioselective Hydrogenations

A series of new chiral phosphine-aminophosphine ligands [(R)-HW-Phos] has been prepared from (R)-l.,2,3,4-tetrahydro-1-naphthylamine through a two-step procedure, and successfully applied in the rhodium-catalyzed asymmetric hydrogenation of various functionalized olefins such as alpha-enol ester phosphonates, alpha-enamido phosphonates, (Z)-beta-(acylamino)acrylates and so on. Excellent enantioselectivities have been achieved in the hydrogenation of most substrates tested, demonstrating the high potential of these newly developed phosphine-aminophosphine ligands in asymmetric catalysis. The present research also discloses that these newly developed phosphine-aminophosphine ligands are more efficient than that derived from (S)-1-phenyl ethyl amine, suggesting that the increased rigidity conferred by a cyclohexyl fragment in these phosphine-aminophosphine ligands has a positive effect in the asymmetric induction.