O.N‐bis(diphenylphosphino) derivatives of chiral trans‐ and cis‐2‐aminocyclohexanols: Synthesis and enantioselective behaviour as ligands in Rh‐based homogeneous hydrogenation catalysts

Abstract trans‐ and cis‐2‐Methylamino cyclohexanols (MAC) were prepared in enantiomerically pure forms and transformed into O.N‐bis(diphenylphosphino) derivatives (“PONP”). An analogous trans‐1 R; 2 R‐aminocyclohexanol PONP could only be isolated in an impure form, whereas the attempted synthesis of PONP's of diastereoisomeric trans‐2‐(N‐α‐phenylethylamino)‐cyclohexanols failed. Cationic Rh(I)‐chelates of the new PONP's catalyzed the enantioselective hydrogenation of dehydro‐α‐acylamino acids with ≦97% ee. A comparison of the enantiodiscriminating properties of the MAC‐PONP's with structurally related chiral ligands leads to surprising conclusions.