Preparation of new C2-symmetric tetraphosphine ligands for Rh-catalyzed asymmetric hydrogenation of arylenamides

A new type of chiral tetraphosphine ligands 1 were prepared from enantiopure anti-head-to-head coumarin dimer 5 and then utilized in Rh-catalyzed asymmetric hydrogenation reaction of arylenamides, affording the corresponding amides with up to 85% ee. Some chiral bisphosphine ligands derived from coumarin dimer 5 were also evaluated in the same reaction.