Synthesis of new chiral monodentate phosphines and their use in asymmetric hydrogenation

A general synthesis of chiral 4,5-dihydro-3H-dinaphthophosphepines 1a–g is described. The resulting ligands represent a new class of monodentate chiral phosphines. First applications of 1a–g in the rhodium-catalyzed asymmetric hydrogenation of unsaturated carboxylic acid derivatives demonstrate the usefulness of our ligands. Enantioselectivities up to 95% ee for the hydrogenation of methyl α-acetamidocinnamate were obtained in the presence of 1d. This result represent the highest enantioselectivity reported for asymmetric hydrogenation in the presence of monodentate phosphines.