Asymmetric C–H Bond Functionalization of Ferrocenes: New Opportunities and Challenges

Chiral Catalysts for Pd0‐Catalyzed Enantioselective C−H Activation

“…Another major application of CÀHa ctivation using chiral phosphoramidites is found in the synthesis of planar chiral ferrocenes. [32] This reactivity was simultaneously discovered by the Gu [33] (discussed later) and Liu-Zhao [34] groups in 2014 (Scheme 6). The approach undertaken by Zhao and co-workers utilized again the simple phosphoramidite L 4 ,w hich provided high enantioselectivities across abroad scope of aryl and nitrogen substituents (12 a-d).…”

Enantioselective C–H Alkenylation of Ferrocenes with Alkynes by Half-Sandwich Scandium Catalyst

“…Ferrocene and its derivatives have been the subject of extensive studies since the discovery of ferrocene in the early 1950s, because of their fascinating structural features and properties. − In particular, ferrocenes possessing planar chirality are of great interest and importance in the fields of asymmetric catalysis and materials science. Therefore, the development of efficient protocols to introduce planar chirality into the ferrocene backbone has attracted intense attention over the past decades. − In view of the high potential of chiral hybrid olefin ligands containing both a heteroatom and an olefin unit in asymmetric catalysis, − planar-chiral ferrocenes bearing both N -heterocycle and alkene functionalities are of great interest. In principle, the asymmetric C–H addition of N -heterocycle-substituted ferrocenes to alkynes could be a straightforward and 100% atom-efficient route for the synthesis of planar-chiral ferrocenes bearing N /alkene functionalities .…”

“…In principle, the asymmetric C–H addition of N -heterocycle-substituted ferrocenes to alkynes could be a straightforward and 100% atom-efficient route for the synthesis of planar-chiral ferrocenes bearing N /alkene functionalities . However, despite extensive studies and recent advances in C–H activation and transformations, − the enantioselective C–H alkenylation of ferrocenes with alkynes has remained a challenge to date because of the lack of suitable chiral catalysts. It has been previously reported that the reaction of amine-substituted ferrocenes with diphenylacetylene in the presence of a chiral palladium catalyst gave the corresponding alkyne-annulated ferrocene products, while a straightforward C–H alkenylation product was not obtained (Scheme a, i) .…”

Synthesis of Atropisomers by Transition-Metal-Catalyzed Asymmetric C–H Functionalization Reactions

“…New stereocenters can be introduced with simple C–H bond-containing molecules, thereby quickly generating complex structures. Although methods for generating central or planar chirality are well documented, significant advances in the enantio­selective synthesis of axially chiral compounds through C–H functionalization have only been made more recently, likely due to the facile racemization of atrop­isomers under relatively vigorous conditions. In addition, the steric hindrance inherently encountered during the synthesis of compounds with stable axial chirality makes the C–H functionalization process more difficult.…”