Carbon Gold -Catalyze

Hydrothiolation of Allenes The first example of a gold-catalyzed carbon-sulfur bond formation was published by Kraus et al. who synthesized 2,5-dihydrothiophenes by allenyl thiocarbinols [38]. The best results were obtained with AuCI in CH2C12, providing an impressive diastereoselectivity. In the same study, other coin-metal precatalysts were tested but only gold afforded the cydization product. 

Gold-Catalyzed Oxidation of Carbon Monoxide. The oxidation of gold electrodes in alkaline media has been discussed in Chapter 10 and the electrochemical oxidation of CO, in Chapter 11. Because the intermediate involves... 

As for the aUcynes, the reactions here are arranged by the nature of the nucleophile. Thus heteronucleophiles, mainly nitrogen- and oxygen-based, and carbon nucleophiles are discussed. However, first of all, a gold-catalyzed enantioselective synthesis of axially chiral allenes will be... 

A number of ferrocenylphosphines containing chiral carbon center(s) on the side chain have been also prepared and examined for the gold-catalyzed aldol reaction [16, 75]. The enantioselectivity is strongly dependent on the configurations of the chiral carbons. A few of the good results obtained for the aldol reaction of benzaldehyde are shown in Scheme 2-53. 

Bond, G.C. Thompson, D.T. Gold catalyzed oxidation of carbon monoxide. Gold Bull. 2000, 33 (2), 41-51. 

The influence of the support on the gold catalyzed oxidation of ethane-1,2-diol is very relevant. In fact a comparison of the results in Table 2 shows carbon (entry 1) to be peculiar in its high activity, with respect to AI2O3, Ce02, Si02 and a-Fe203 (entries 2-5). 

Bollinger, M.J., R.E. Sievers, D.W. Fahey, and F.C. Fehsenfeld. 1983. Conversion of nitrogen dioxide, nitric acid, and w-propyl nitrate to nitric oxide by gold-catalyzed reduction with carbon monoxide. Anal. Chem. 55 1980-1986. 

Gold-catalyzed intramolecular [4+2] cycloaddition of furans with alkynyl substituents led to the formation of phenol derivatives, A mechanistic study showed that a transposition of the oxygen from the carbon atoms of furan to the former terminal carbon of the alkynes seemed to occur through an intramolecular mode and the epoxide depicted below was presumably an intermediate <01OL3769>. 

The first gold-catalyzed addition reactions of carbon nucleophiles to allenes were only first disclosed in 2006, and the number of examples is still small. Toste and co-workers showed that allenic silyl enol ethers undergo a 5-endo- ng cyclization to hexahydroindenone derivatives in the presence of a cationic gold catalyst (Scheme 4-10). In these transformations, water or methanol is used as an external proton source for protodeauration of an intermediate vinylgold species. In an analogous manner, cyclopentenes were obtained in good yields from allenic P-ketoesters. In the presence of a palladium catalyst and an allylic halide, these substrates afford functionalized 2,3-dihydroflirans. 

Several examples of gold-catalyzed addition reactions of carbon nucleophiles to unactivated alkenes have been reported in recent years. Yao and Li obtained adducts with high regioselectivity from 3-diketones and various alkenes (styrene derivatives, conjugated dienes, enol ethers) in the presence of cationic gold species prepared in situ from AuCls and AgOTf (Scheme 4-15). This hydroalkylation is... 

Not only simple, unactivated olefins but also a,P-unsaturated carbonyl compounds undergo gold-catalyzed addition reactions. Electron-rich arenes or heteroarenes (e.g., indoles) are suitable carbon nucleophiles for these Michael additions. For the 1,4-addition of indoles to enones, enals, and related Michael acceptors, simple gold(III) catalysts like NaAuCl4-2 or AuCU can be used... 

The gold-catalyzed formation of a carbon-sulfur bond is not an easy task, given the high strength of Au-S bonds that renders sulfides potent poisons for gold catalysts. Nevertheless, the first example for a gold-catalyzed C-S bond formation was reported in 2006 when Morita and Krause converted various a-thioallenes into the corresponding 2,5-dihydrothiophenes (Scheme 4-118). In this transformation. 

Krause has reported the gold-catalyzed intramolecular endo-hydroalkoxylation of (3-hydroxyallenes to form dihydropyrans [103]. For example, treatment of a 70 30 diastereomeric mixture of (3-hydroxyallene 61 with a catalytic 1 1 mixture of AuCl and pyridine in dichloromethane led to isolation of dihydropyran 62 in 84% yield as a 70 30 mixture of diastereomers (Eq. (12.32)). This transformation was also catalyzed effectively by a 1 1 mixture of (PPh3)AuCl and AgBp4 in toluene. (3-Hydroxyallenes that possessed substitution at the internal allenyl carbon atom also underwent gold-catalyzed cycloisomerization with selective transfer of chirality from the allenyl... 

Scheme 16.17 Effect of an acyclic carbone ligand on selectivity in gold-catalyzed rearrangements.

GOLD-CATALYZED ACTIVATION OF MULTIPLE CARBON-CARBON BONDS FUNCTIONALIZATION BY ADDITION OF OXYGEN, NITROGEN, SULFUR, OR CARBON NUCLEOPHILES... 

GOLD-CATALYZED ACTIVATION OF MULTIPLE CARBON-CARBON BONDS 215... 

Besides alkenes, several other carbon nucleophiles, as for instance, diketones and aryl groups, can participate in gold-catalyzed reactions. Selected examples of intermolecular reactions are displayed in Scheme 16.17 [17c, 21],... 

A series of other structurally different cationic intermediates, generated following a gold-catalyzed cyclization step, are also susceptible to be trapped by an oxygen, nitrogen, or even carbon-centered nucleophile (Scheme 16.19) [23]. 

Gold-Catalyzed Addition of Carbon-and Heteronucleophiles to Alkynes... 

---