Enantioselektive Katalyse, VIII. Neue 1,2‐Bisphosphanliganden mit vier stereogenen Zentren und zusätzlichen Methoxygruppen für die asymmetrische katalytische Hydrierung

Enantioselective Catalysis, VIII[1]. – New 1,2‐Bisphosphane Ligands with Four Stereogenic Centers and Additional Methoxy Groups for Asymmetric Catalytic Hydrogenation* The synthesis of N‐acyl derivatives of all possible diastereomers of [P(R,S), 3R, 4R,P′(R,S)]‐3,4‐bis[(benzyl)phenylphosphanyl]‐pyrrolidine and [P(R,S), 3R, 4R,P′(R,S)]‐3,4‐bis[(2‐methoxybenzyl)phenylphosphanyl]pyrrolidine in optical pure form is described. Palladium and rhodium complexes with these ligands were prepared. The enantioselective hydrogenation of acetamidocinnamic acid with these rhodium complexes was studied at H2 pressures between 1 and 75 bar. There is only a small influence of the 2‐methoxy group in the ligand on the catalytic hydrogenation when compared with the respective unsubstituted diastereomer. The structure of {[PR,3R, 4R,P′R)‐1‐(tert‐butoxycarbonyl)‐3,4‐bis[(2‐methoxybenzyl)phenylphosphanyl]pyrrolidine‐P,P′}diiodopalladium was determined by X‐ray diffraction.