Synthesis of monodentate chiral spiro phosphonites and the electronic effect of ligand in asymmetric hydrogenation

New monodentate chiral phosphonites were synthesized from enantiomerically pure 1,1'-spirobiindane7,7'-diol. The phosphonites 2 were efficient ligands for the Rh-catalyzed asymmetric hydrogenation of alpha- and beta-dehydroamino acid derivatives, providing the amino acids in high enantioselectivities. The study of electronic effect showed that the electron-withdrawing substitutent on the P-phenyl ring of the phosphonite ligand dramatically decreased both the reactivity and enantioselectivity of the ligand.