Catalytic Enantioselective Functionalizations of C-H Bonds by Chiral Iridium Complexes.

The development of catalytic enantioselective transformations, enabling the construction of complex molecular scaffolds from simple precursors, has been a long-standing challenge in organic synthesis. Recent achievements in transition-metal catalyzed enantioselective functionalizations of carbon-hydrogen (C-H) bonds represent a promising pathway toward this goal. Over the last two decades, iridium catalysis has evolved as a valuable tool enabling the stereocontrolled synthesis of chiral molecules via C-H activation. The development of iridium-based systems with various chiral ligand classes, as well as studies of their reaction mechanisms, has resulted in dynamic progress in this area. This review aims to present a comprehensive picture of the enantioselective functionalizations of C-H bonds by chiral iridium complexes with emphasis on the mechanisms of the C-H activation step.

Tethered Counterion-Directed Catalysis: Merging the Chiral Ion-Pairing and Bifunctional Ligand Strategies in Enantioselective Gold(I) Catalysis.

Tethering a metal complex to its phosphate counterion via a phosphine ligand enables a new strategy in asymmetric counteranion-directed catalysis (ACDC). A straightforward, scalable synthetic route gives access to the gold(I) complex of a phosphine displaying a chiral phosphoric acid function. The complex generates a catalytically active species with an unprecedented intramolecular relationship between the cationic Au(I) center and the phosphate counterion. The benefits of tethering the two functions of the catalyst are demonstrated here in a tandem cycloisomerization/nucleophilic addition reaction, by attaining high enantioselectivity levels (up to 97% ee) at an unusually low 0.2 mol % catalyst loading. Remarkably, the method is also compatible with a silver-free protocol.