the dioxolane ring had a small effect on the asymmetric induction by DIOP in the hydrogenation. Modification at the phosphino group affected the stereocontrol by the ligand and the unsymmetrical DIOP with di-2-naphthylphosphino group gave higher optical yields than (−)-DIOP for the hydrogenation of α-acetamidocinnamic acid and dehydrodipeptides.
New chiraldiphosphinites were prepared starting from (+)-diethyl tartrate. The asymmetrichydrogenation of dehydroamino acids, itaconic acid and dehydrodipeptides was studied using Rh(I)-diphosphinite catalysts. In the hydrogenation of dehydroamino acid derivatives, an introducion of ω-(dimethylamino)alkyl group in the ligands did not raise the optical yield. By the use of Rh(I)-diphosphinite having
Asymmetric Hydrogenation of Dehydrodipeptides with Rhodium(I)–Chiral Diphosphinites. Selective (<i>S</i>,<i>S</i>)- and (<i>R</i>,<i>R</i>)-Product Formation by Double Asymmetric Induction
stereoselectivities, depending on the chiral center of the substrates. This result was ascribed to the electrostaticinteractionbetween the ligand and substrate. POP’s without ω-(dimethylamino)alkyl group gave (R,R)-product for (R)-substrate in a high stereoselectivity by the steric effect between the ligand and substrate, while for (S)-substrate, (S,S)-product was obtained in a low stereoselectivity.