<i>C</i>₂-Symmetric Diphosphinite Ligands Derived from Carbohydrates. The Strong Influence of Remote Stereocenters on Asymmetric Rhodium-Catalyzed Hydrogenation

Modular ligands of C2 symmetry (13a−e, 14a,b,d, and ent-9), systematically modified at positions 2 and 5, were easily prepared from d-glucosamine, d-glucitol, and tartaric acid, respectively. The application of these ligands in the rhodium-catalyzed hydrogenation of methyl acetamidoacrylate, methyl acetamidocinnamate, and dimethyl itaconate shows that both the configuration and the substituents at positions 2 and 5 of the tetrahydrofuran backbone have a strong influence on the enantioselectivty of the processes.