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.