Catalysis of Organic..

460Chiral BisphospholanesInteresting results were also observed when the hydrogenation of α-acylamidoacrylates being important intermediates for the synthesis of enantiopure α-aminoacids was investigated.R 1 [Rh(Ligand)(COD)]BF 4 ,H 2 (1 bar), MeOH, rt.R 1AcHNCOOR 2AcHNCOOR 290OOO%ee807060PP5040Reihe1PReihe2P3020100R 1 = MeR 2 = MeR 1 = MeR 2 = BnR 1 = EtR 2 = MeR 1 =i-PrR 2 = EtFigure 6. Comparison of DuPHOS and catASium fienantioselective hydrogenation of α-acylamido acrylatesR 1 = PhR 2 = EtM Rh-catalyst in theIn particular for the hydrogenation of the important Z-configured substratesbearing bulkier substituents in 3-position (Et, i-Pr, Ph) a catASium fi M Rh-catalystbearing the maleic anhydride backbone (1a) gave significantly higherenantioselectivities than the related DuPHOS-complex (Figure 6). Differences by upto 75 % ee were observed. A similar superiority of the catASium fi M complex wasnoted in THF as solvent.In summary, the modular synthesis of a new type of vicinal bisphospholanescalled catASium fi M have been discovered, which affords a broad array ofdiphosphine ligands with small and definite differences in the bite angle of relevantmetal complexes. Besides new applications, the new ligands can be advantageouslyemployed for the fine tuning of those enantioselective hydrogenations whereDuPHOS-type ligands need optimization. Due to the modular synthesis eachdiphosphine ligand can be easily provided in kg-quantities by Degussa AG, DegussaHomogeneous Catalysts.