Applications of Aza‐ and Phosphaferrocenes and Related Compounds in Asymmetric Catalysis

Asymmetric Metathesis Dimerization/Kinetic Resolution of Racemic Planar-Chiral Vinylphosphaferrocenes

“…Hence, an η 5 -coordination of such an unsymmetric Cp – species to a transition-metal cation produces a chiral metallocene (or a chiral half-metallocene) whose stereogenicity is referred to as “planar chirality” . The ferrocene-based planar chirality was first recognized in 1959, and since then, various planar-chiral ferrocene derivatives were prepared and utilized as chiral ligands or chiral catalysts. ,, Although planar-chiral ferrocenes are widely accepted as one of the most effective chiral scaffolds in asymmetric synthesis, methods of preparing enantiomerically enriched planar-chiral ferrocenes are still limited, and development of such highly effective reactions has been awaited . Traditional methods of preparing optically active planar-chiral ferrocenes are based either on resolution of preformed racemates including enzymatic resolution or on diastereoselective metalation utilizing chiral ortho -directing groups .…”

Enantioselective Desymmetrization of 1,2,3-Trisubstituted Metallocenes by Molybdenum-Catalyzed Asymmetric Intraannular Ring-Closing Metathesis

“…The chirality in the substituted ferrocene originates in discrimination between the two enantiotopic faces of the unsymmetrical cyclopentadienide by the η 5 -coordination of an Fe­(II) cation and is an example of so-called “planar chirality”. Since the first enantiomeric separation of the planar-chiral ferrocene derivative in 1959, various such ferrocenes have been reported, and they have found widespread application in asymmetric synthesis as chiral ligands or chiral catalysts . Standard methods of preparing enantiomerically enriched planar-chiral ferrocenes are based either on optical resolution of racemic compounds or on diastereoselective metalation using chiral directing groups or external chiral bases .…”

Versatile and Enantioselective Preparation of Planar-Chiral Metallocene-Fused 4-Dialkylaminopyridines and Their Application in Asymmetric Organocatalysis

“…Ferrocene is a cylindrical compound with unique three-dimensional properties. , Introduction of two different substituents at the 1- and 2-positions of an Fe­(II)-bound η 5 -cyclopentadienyl ligand breaks the symmetry to induce planar chirality in the molecule (Figure , left) . The ferrocene-based planar chirality has been proven to be useful chiral scaffolds in asymmetric synthesis, and various such ferrocene derivatives have been utilized in a wide range of asymmetric reactions as chiral ligands and chiral catalysts. , …”

“…In the 1990s, Fu employed this design concept for desymmetrizing flat-shaped N -heteroarenes, and since then various ferrocene-fused 4-dialkylaminopyridines (Fc-DAAPs; 1 ; Figure , right) have been prepared and applied in asymmetric organocatalysis. Among many chiral 4-dialkylaminopyridine derivatives reported so far, , Fc-DAAPs are arguably the most successful compounds . Indeed, 1 showed excellent enantioselectivity in a variety of asymmetric transformations .…”