Chiral gold complexes

Worth mentioning are chiral gold complexes [20d, e] as well as chiral quaternary ammonium fluorides [21], which are used successfully as catalysts in the asymmetric aldol reaction. 

Scheme 930 Enantioselective alkoxycyclization catalyzed by chiral gold complexes.

Scheme 933 Axially chiral gold complex-catalyzed enantioselective intermolecular [4-1-2] cycloaddition of allenamides and dienes [61].

Water and alcohols can act as nucleophiles in the gold-catalyzed intra- " and intermolecular " reaction with 1,6-enynes. The asymmetric version of the reaction proceeds with good to excellent enantioselectivity using chiral gold complexes [208-210]. The hydroxy- and alkoxycyclization of 1,7-enynes takes place in a similar way [211]. Furthermore, this methodology has been extended to other... 

With the C—C double bond fully substituted at the end proximal to the alkyne, the enyne moiety tends to cyclize in a 6-exo-dig manner, forming a relatively stable tertiary carbocation-containing intermediate (i.e., 20, Scheme 4.6), which can be trapped by nucleophiles in a cascade process. This is exemplified in elegant work by Sethofer et al. [10], where the cascade leads to the formation of three fused rings with high enantiomeric access when a chiral gold complex is used. 

One of the earliest examples of an asymmetric catalytic aldol reaction in which the enolate component is generated in situ in the presence of an aldehyde is to be found in the pioneering work by Hayashi and Ito. In 1986, these investigators reported enantioselective addition reactions of a-isocyanoacetate to aldehydes catalyzed by chiral gold complexes (Scheme 4.23 see also Scheme 4.3) [18, 40). Several features of the catalyst and the process are important to note (1) the isocyanoester is a C-H acid (pfC 13), which is significantly further acidified upon its chelation to the Au center, (2) the presence of the tertiary amine in the ligand likely assists the enolization event, and (3) turnover of the... 

Munoz MP, Adrio J, Carretero JC, Echavarren AM (2005) Ligand effects in gold- and platinum-catalyzed cyclization of enynes chiral gold complexes for enantioselective alkoxycyclization. Organometallics 24 1293-1300... 

The gold(I) complex of a chiral ferrocenylphosphine complex promotes asymmetric aldol reactions of a-isocyanocarboxylates to form chiral oxazolines in high diastereo- and enantio-selectivities (Scheme 52).225,226 In these reactions, the analogous silver(I) ferrocenylphosphine complex also works well. 

Figure 8.1 Gold complex used as catalyst for the hydroamination of axially chiral allenes.

Ferrocenylphosphine-gold complexes, 225 Formaldehyde oligomerization, 332 Formic acid, transfer hydrogenation, 123 Formulas, chiral compounds, xiii-xvii Four-dimensional chemistty. See Asymmetric catalysis... 

In 1986 Ito, Sawamura, and Hayashi [4] reported that gold(I) complexes prepared from cationic gold complex 1 and chiral ferrocenylphosphine ligands (2) bearing a tertiary amino group at the terminal position of a pendant chain are effective catalysts for asymmetric aldol reaction of... 

Scheme 3.39 Enantioselective relay catalysis by gold complex/chiral phosphoric acid bina system.

Table 11 Enantioselectivity and Diastereoselectivity in the Aldol Reactions of Methyl Isocyanoacetate Under Catalysis by Chiral Ferrocenylphosphine-Gold Complexes (equation 22)...

Catalysis by Chiral Ferrocenylphosphine-Gold Complexes (equation 22)... 

Abstract Progress in the field of metal-catalyzed redox-neutral additions of oxygen nucleophiles (water, alcohols, carboxylic acids, and others) to alkenes, alkynes, and allenes between 2001 and 2009 is critically reviewed. Major advances in reaction chemistry include development of chiral Lewis acid catalyzed asymmetric oxa-Michael additions and Lewis-acid catalyzed hydro-alkoxylations of nonacti-vated olefins, as well as further development of Markovnikov-selective cationic gold complex-catalyzed additions of alcohols or water to alkynes and allenes. 

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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