Gold complexes hydroarylation reactions

Hydroarylations of alkynes are catalyzed by gold complexes and these bear some resemblance to the Fujiwara Pd-catalyzed reaction. In general, when using gold chemistry, better Z/E selectivities are observed compared with palladium, lower catalyst loadings and milder conditions (neutral not TFA) are used. The mechanism involves the attack of ArH on the Au-coordinated alkyne. Flowever, electron-poor acetylenes only appear to work with palladium chemistry (Equations (75) and (76)).72... 

Hydroarylation can also be mediated by Au(I) and Au(III) (Scheme 33) (384). In the case of aryl substituted alkynes, the Au(III) Ji complex undergoes electrophilic aromatic substitution with the electron-rich arene to give aLkenyl-Au(III) complex, which is immediately protonated by the H generated upon C C bond formation. For the Au(I)-catalyzed hydroarylation, the cationic gold complex k coordinates the alkyne, with subsequent nucleophilic attack by the arene from the opposite face leading to an alkenyl-gold complex, which is protonated to the desired products. The nature of the reaction causes the regioselectivity of this reaction to be sensitive to electronic rather than steric factors. 

Study on this allene hydroarylation reaction, the presence of dinuclear gold-gold and gold-silver intermediates was suggested (Scheme 18.19), together with vinyl gold complex, in the gold(I)-catalyzed hydroarylation [18],... 

Che has reported the tandem hydroamination/hydroarylation of aromatic amines wirh terminal alkynes to form dihydroquinolines in which 1 equiv of aniline combines with 2 equiv of alkyne [23]. For example, reaction of 3-methoxyanilme with pheny-lacetylene (5 equiv) and a catalytic 1 1 mixture of the gold(I) N-heterocydic carbene complex (IPr)AuCl (IPr= l,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) and AgOTf at 150 °C under microwave irradiation led to isolation of dihydroquinoline 21 in 82 % yield (Eq. (11.15)). Alternatively, reaction of o-acetylaniline with pheny-lacetylene catalyzed by a mixture of (IPr)AuCl and AgOTf at 150 °C led to isolation of the quinoline derivative 22 in 93% yield via incorporation of a single equivalent of alkyne (Eq. (11.16)). Arcadi has reported the gold(IlI)-catalyzed hydroamination/ hydroarylation of 2-alkynylanilines with a,p-enones to form C3-alkyl indoles [24]. As an example of this transformation, treatment of 2-(phenylethynyl)aniline with 4-phenyl-3-buten-2-one and a catalytic amount of sodium tetrachloroaurate dihydrate in ethanol at 30°C formed 1,2,3-trisubstituted indole 23 in 88% yield (Eq. (11.17)). 

Indenes can be synthesized via intramolecular hydroarylation of propargyl acetates catalyzed by NHC gold(I) complexes [127, 128]. The formation of the indenes proceeds via a 1,3-shift to form an allene, followed by the hydroarylation (Scheme 1.8). Notably, this reaction requires strictly anhydrous conditions, because conjugated enones and enals are isolated in the presence of water [129]. Related transformations include reaction with propagyl sulphides or dithioacetals. 

As part of our investigation of the hydroarylation of alkynes (or alkenylation of arenes) catalyzed by electrophilic transition metal complexes, our group reported the intra- and intermolecular reaction of indoles with alkynes catalyzed by gold (see Ref. [118, 133] in Chap. 1). Thus, alkynyUndole III-l cycUzes readily in the presence of a cationic gold(I) complex to give azepino[4,5-h]indole derivative III-2, whereas the use of AuCls leads to indoloazocine III-3 by a S-endo-dig process, this cyclization mode has not been observed in other hydroarylation of alkynes (Scheme 4.7). Under certain forcing conditions, aUenes and tetracyclic compounds were also obtained (see Refs. [118, 133] in Chap. 1). 

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