Gold Complexes in Asymmetric Catalysis

Transition metal compounds containing gold were once considered as being catalytically inert just in the past few years gold has emerged as a powerful homogeneous catalyst for the electrophilic activation of alkynes towards a variety of nucleophilic additions. 

The strong Lewis acidity of cationic Au(l) and/or Au(lll) as well as their ability to stabilize cationic reaction intermediates imparts unique reactivity to such catalysts and makes them important tools in the development of new synthetic methods in organic chemistry. Thus there are an impressive number of reports on the use of gold catalysts to carry out a variety of catalytic transformations of alkynes towards (a) nucleophiles, 

More recently, Echavarren and coworkers performed a detailed investigation of the enantioselective alkoxycyclization of functionalized enynes with gold (1) complexes in the presence of a variety of chiral ligands such as BEMAP, chiral 1,2-ferrocenyl phosphines and chiral 1,2-ferrocenyl-P N bidentate ligands. Interestingly the authors 

Hayashi-Ito asymmetric Aldol reaction with chiral ferrocenylphosphine-gold complex. 

The use of gold complexes with chiral phosphines to promote asymmetric cyclization reactions remains the most studied approach of several groups.However, Toste and coworkers pushed this chemistry further, when they combined the additive elfects of a chiral phosphine ligand and a chiral counter ion which forms an ion pair with the active species [L Au] X 3 (L = chiral phosphine ligand X = chiral counter ion). Thus a dramatic increase in Au(I)-catalysed enantioselective intramolecular hydroalkylation of 

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