Gold Catalyzed Asymmetric Transformations

Abstract

In this chapter, the strategies developed to attain asymmetric reactions with gold are disclosed. Because of its preferred linear arrangement, to induce asymmetry, gold(I) needs to fulfill one of the following requirements: a) the use of bulky chiral ligands, that create a chiral pocket around the active site, b) the coordination to bifunctional ligands capable to establish secondary interactions with substrates, or c) tight ion pairing with chiral counteranions. On the other hand, gold(III) profits of a square-planar coordination mode, which approaches chiral ligands to substrates. However, its tendency to be reduced leads to difficulties for its applications in catalytic asymmetric transformations. Pioneering works using cyclometaled structures, have found the balance between stability and activity, showing its potential in asymmetric transformations.

H-Bonded Counterion-Directed Enantioselective Au(I) Catalysis

“…Various bi- and tricyclic structures were accessed in good to excellent yield and enantioselectivity from 1,6-enynes, via 5- exo -dig and 6- endo -dig cyclizations with or without external nucleophiles. 14 To overcome the reactivity 8 and enantiocontrol 15 challenges described above, we envisioned to prepare gold(I) complexes with bifunctional phosphine ligands 16 incorporating dual H-bond donor groups 17 such as (thio)ureas 18 and combine them with BINOL-derived chiral anions 19 ( Scheme 2 ). The pendant H-bond donor would serve two purposes: (1) remove the chiral anionic ligand from the Au(I) coordination sphere, thus enabling substrate coordination and subsequent catalysis at the metal center; (2) place the chiral anion close to the substrate, ensuring good transmission of the stereochemical information.…”