Alkenes, gold-catalyzed reactions

Most gold-catalyzed reactions involve this pattern of reactivity that has been studied since the eighties. The first examples were found with allenes as substrates and subsequently alkenes and alkynes started to be used, the latter being the most popular in the last five years. 

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],... 

From the encouraging results obtained in the reactions of a series of gold(III) oxo complexes with olefins [56], Cinellu et al. tried to achieve the supposed oxametalla-cyclic intermediate, which had never been isolated before [25]. In the reaction of 8 and norbornene 56, if the - atoms were considered to be equivalents of coordinated water, and it was therefore possible to talk about the gold-catalyzed addition of water to an alkene. The metallaoxetane 58 was separated from the gold-alkene complex 57 and characterized by X-ray crystal structure analysis. The subsequent stoichiometric reaction yielded epoxide 59 (Scheme 8.5). 

Reactions by Arenes In 2000, the first evidence of a gold-catalyzed hydroarylation of a, 3-unsaturated alkenes was reported by Hashmi et al. in their research with furans. In this publication, they proposed two possible mechanisms for the process ... 

After compiling many results obtained in similar studies of different substrates (alkenes, dienes, alkynes and so on), the results cannot be correlated to draw definitive conclusions due to the wide variety of parameters that can influence the reaction (substrates, catalyst precursors, supports, pressure, temperature and so on) [9, 208-214]. This is maybe the main reason why there are no clear mechanistic explanations for this simple reaction, unlike homogeneous gold-catalyzed processes. 

Alkenylboron compounds cyclopropanations, 9, 181 haloetherification, 9, 182 hydrogenation and epoxidation, 9, 182 metal-catalyzed reactions, 9, 183 metallic reagent additions, 9, 182 via radical addition reactions, 9, 183 5-Alkenylboron compounds, cross-coupling reactions, 9, 208 Alkenyl complexes with cobalt, 7, 51 with copper, 2, 160, 2, 174 with Cp Re(CO) (alkene)3 , 5, 915-916 with dicarbonyl(cyclopentadienyl)hydridoirons, 6, 175 with gold, 2, 255... 

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... 

The corresponding intermolecular addition of cyclic ureas to terminal alkenes is catalyzed by Au[P(/-Bu)2(o-biphenyl)]Cl and AgOTf, and it provided alkylated ureas in high yield at 100 °C. The reaction even works with ethylene and other gaseous olefins. In the presence of chiral gold(I) pre-catalyst [Au2 (S)-3,5-r-Bu-4-MeO-MeOBIPHEP Cl2] and silver triflate, the hydroamination products were obtained with 71-76% ee (Scheme 4-68). Treatment of cyclic ureas with allylic alcohols in the presence of cationic gold(I) catalysts afforded allylated ureas with... 

Iwasawa has reported the gold(III)-catalyzed reaction of N-(o-ethynylphenyl)imi-nes with electron-rich alkenes to form polycyclic indole derivatives [26]. As an example, reaction of N-[l-(l-pentynyl)phenyl]imine 28 and tert-butyl vinyl ether with a catalytic amount of AuBrs in toluene at room temperature led to isolation of the polycyclic indole 29 in 80% yield as a mixture of diastereomers (Scheme 11.3). Conversion of 28 to 29 presumably occurs via initial intramolecular hydroamination to form the gold carbene containing azomethine ylide 30 that undergoes intermo-lecular [3 + 2] cydoaddition with tert-butyl vinyl ether to form the carbene complex 31. 1,2-Migration of the 7t-propyl group to the metal-bound carbon atom coupled with deauration then forms 29. This transformation is also catalyzed efficiently by PtCl2 [26]. 

In contrast to the hydroamination of alkenes with sulfonamides, the potential of an acid-catalyzed reaction pathway in the hydroamination of alkenes with carboxamide derivatives appears less likely. Hartwig found that the intramolecular hydroamination of alkenes with N-arylcarboxamides was only realized in the presence of stoichiometric amounts of triflic add [50]. In contrast, He reported that triflic add catalyzes the intramolecular hydroamination of an N-4-methyl-4-pentenyl carbamate in toluene at 85 °C [55]. However, in the corresponding gold(I)-catalyzed transformation, the intramolecular hydroamination of an N-4-methyl-4-pentenyl carbamate was markedly slower than was the intramolecular hydroamination of an N-4-pentenyl carbamate [52], which is inconsistent with the antidpated behavior of an acid-catalyzed pathway. Furthermore, control experiments firmly ruled out the presence of an acid-catalyzed reaction pathway in the gold(I)-catalyzed intramolecular hydroamination of alkenes with carboxamide derivates and ureas [53, 54]. 

In an effort to extend tins reactivity to alkenes from allenes, the Toste group [300] performed the cyclohydroamination reaction with their preferred gold catalyst systems using diene-substituted suhbnylamides. Such substrates are prone to proton-mediated reactivity profiles, as discussed earlier, and generation of an acidic species has been postulated for catalytic turnover in Au(I)-catalyzed reactions [300],... 

A new intermolecular gold(I)-catalyzed reaction of terminal alkynes with functionalized alkenes led to 8-oxabicyclo[3.2.1]oct-3-enes by a [2 + 2 + 2] cycloaddition process in which two C—C bonds and one C—O... 

In addition, the gold-catalyzed intermolecular reaction of alkynes with alkenes leads to cyclobutene compounds (Scheme 1.27) [201]. This transformation shows that in the absence of constrains imposed by the tethers in the intramolecular processes, a [2-I-2] cycloaddition is the predominant mechanism. 

In addition to the gold-catalyzed chemistry described in the preceding section, ruthenium complexes also catalyzed the addition of carboxylic acids to alkenes (Scheme 2.20) [25]. A common air-stable ruthenium compound served as the catalyst for the reaction along with silver(I) triflate as an additive. While a range of monosubstituted terminal alkenes were successfully converted into esters in moderate to excellent yields (up to 95%), analogous reactions with internal or disubstituted alkenes were less successful. Both the gold- and ruthenium-catalyzed additions were attractive due to the availability of the catalysts used for the reactions. 

There are several approaches for this transformation. The direct addition of phenols and alcohols to unactivated alkenes has been accomplished using a range of methods. Practical approaches include a gold-catalyzed process [22] as well as an acid-promoted reaction [23]... 

The gold-catalyzed benzannulation of o-alkynylbenzaldehydes 11 proceeded not only with alkynes or alkenes, but also with carbonyl compounds 47 (Scheme 15.19) [32], The reaction proceeded even with conjugated enyne aldehydes 20. Paraldehyde 49 can be used as a masked acetaldehyde in this reaction. 

Garcia-Garcia et al. reported that the gold-catalyzed cycloisomerization of 1,3-dien-5-ynes 128 afforded penta-substituted benzenes 129 (Scheme 27.43) [55]. The reaction is initiated by an intramolecular nucleophilic attack of the terminal alkene, leading to intermediate 130, which is represented as the contribution of several resonance structures, such as ISC and 130". [l,2]-Migration of one of the methyl groups... 

Zhang et al. recently reported on a Au-catalyzed carboamination reaction of the A-tosyl amino alkene substrate. They developed a gold-catalyzed intermolecular carboamination reaction toward the synthesis of substituted pyrrolidines in excellent yield in racemic form (Scheme 40.21)." This report was the first to convert the C(Sp )-Au bond into the C(Sp )-C(Sp ) bond. 

Abstract In this chapter, we review the synthetic and mechanistic aspects of addition reactions of water and alcohols to alkynes, alkenes, and allenes in the presence of gold catalysts. In addition, gold-catalyzed hydroxy- and alkoxycy-clizations of 1, n-enynes n = 5-7) are also covered. 

Despite the successes of the gold-catalyzed addition of O-nucleophiles to alkynes, the corresponding catalyzed reactions involving nucleophilic addition to olefins are very limited. Mild, metal-catalyzed additions of O-H bonds across olefins have been studied for decades, and efforts to develop such processes have intensified in the last years. Results of the hydroalkoxylation of alkenes are collected in different reviews [1, 94-96, 161]. 

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