P‐Modular Homochiral Bis(phosphanes) with 1,2‐Disubstituted Cyclopentane Backbones in Asymmetric Hydrogenation

The review surveys synthetic aspects of a class of bidentate phosphanes based on the trans‐1,2‐disubstituted cyclopentane framework and the application of such ligands in transition‐metal‐catalyzed enantioselective hydrogenation. In particular, we address the preparative potential of the isomerically pure multi‐purpose P−H and P−Cl reagents (R,R)‐ and (S,S)‐C5H8(PX2)2 (X = H, Cl), which can serve to construct a family of optically active bis(phosphanes) with structural components (“modules”) that are easily and systematically interchanged. The so‐designed chelate ligands allow access to rhodium catalysts with stereodiscriminating properties, depending on parameters such as (i) presence of P‐substituents that are equal or pairwise different in steric demand, (ii) spatial orientation of such substituents as defined by the endo‐ and exo‐chelate P−C−C−P and P−Rh−P−C torsion angles, and (iii) existence of C‐ and P‐chirogenic stereoelements in matched (or mismatched) combination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)