Highly Enantioselective Hydrogenation of α-Dehydroamino Esters and Itaconates with Triphosphorous Bidentate Ligands and the Unprecedented Solvent Effect Thereof

An X-ray diffraction experiment revealed an interesting
triphosphorous bidentate coordination in a Pd(II) complex
of a phosphine-phosphoramidite ligand 1, which showed
excellent enantioselectivity (up to 99.4% ee) in Rh-catalyzed
hydrogenation of α-dehydroamino esters in acetone. A
dramatic solvent effect was found in the hydrogenation of
itaconates, which induces opposite chiralities of the product
with the same catalytic system by the use of different solvents
(e.g., 99.6% ee (R) in TFE vs 71.2% ee (S) in methyl ethyl
ketone).