Gold-catalyzed reactions of C–H bonds

Gold(i)-catalysed cascade reactions in the synthesis of 2,3-fused indole derivatives

Unactivated alkenes and 1,3-unsubstituted indoles in gold(i)-catalysed hydroaminative/arylative cascade cyclizations.

Gold-catalyzed cyclopropanation reactions using a carbenoid precursor toolbox

This review highlights recent advances in gold-catalyzed selective cyclopropanation divided by the type of carbenoid precursors.

Synthetic application of gold nanoparticles and auric chloride for the synthesis of 5-substituted 1H-tetrazoles

An effective one-pot, convenient gold catalyzed synthesis of 5-substituted 1H-tetrazoles has been discussed.

Regioselective gold-catalyzed oxidative C-N bond formation

A novel protocol for the regioselective intermolecular amination of various arenes has been developed. By using an I(III) oxidant in the presence of a Au(I) catalyst, a direct and novel route for regioselectively accessing a variety of substituted aniline moieties has been achieved with yields as high as 90%. Mechanistic insight suggests that regioselectivity can be predicted based on electrophilic aromatic metalation patterns.

Total syntheses of hyperforin and papuaforins A-C, and formal synthesis of nemorosone through a gold(I)-catalyzed carbocyclization

The remarkable biological activities of polyprenylated polycyclic acylphloroglucinols (PPAPs) combined with their highly decorated bicyclo[3.3.1]nonane-2,4,9-trione frameworks have inspired synthetic organic chemists over the last decade. The concise total syntheses of four natural products PPAPs; hyperforin and papuaforins A-C, and the formal synthesis of nemorosone are reported. Key to the realization of this strategy is the short and scalable synthesis of densely substituted PPAP scaffolds through a gold(I)-catalyzed 6-endo-dig carbocyclization of cyclic enol ethers for late-stage functionalization.

Merging gold and organocatalysis: a facile asymmetric synthesis of annulated pyrroles

The combination of cinchona-alkaloid-derived primary amine and Au(I) -phosphine catalysts allowed the selective C-H functionalization of two adjacent carbon atoms of pyrroles under mild reaction conditions. This sequential dual activation provides seven-membered-ring-annulated pyrrole derivatives in excellent yields and enantioselectivities.

Cyclization of gold acetylides: synthesis of vinyl sulfonates via gold vinylidene complexes

Differently substituted terminal alkynes that bear sulfonate leaving groups at an appropriate distance were converted in the presence of a propynyl gold(I) precatalyst. After initial formation of a gold acetylide, a cyclization takes place at the β-carbon atom of this species. Mechanistic studies support a mechanism that is related to that of dual gold-catalyzed reactions, but for the new substrates, only one gold atom is needed for substrate activation. After formation of a gold vinylidene complex, which forms a tight contact ion pair with the sulfonate leaving group, recombination of the two parts delivers vinyl sulfonates, which are valuable targets that can serve as precursors for cross-coupling reactions, for example.

Cationic cyclizations and rearrangements promoted by a heterogeneous gold catalyst

A heterogeneous gold catalyst with remarkable activity for promoting the electrophilic reactions of aryl vinyl ketones and aryl dienyl ketones is described. The catalyst is easy to prepare, is robust, and can be recycled. Low loadings are effective for different types of cationic reactions, including Nazarov cyclizations, lactonizations, and [1,2] shifts.

Gold-catalyzed cyclization of diynes: controlling the mode of 5-endo versus 6-endo cyclization--an experimental and theoretical study by utilizing diethynylthiophenes

Herein, a dual-gold catalyzed cyclization of 3,4-diethynylthiophenes generating pentaleno[c]thiophenes through gold-vinylidenes and C-H bond activation is disclosed. Various new heteroaromatic compounds--substrate classes unexplored to date--exhibiting three five-membered annulated ring systems could be synthesized in moderate to high yields. By comparison of the solid-state structures of the corresponding gold-acetylides, it could be demonstrated that the cyclization mode (5-endo versus 6-endo) is controlled by the electronic and not steric nature of the diyne backbone. Depending on different backbones, we calculated thermodynamic stabilities and full potential-energy surfaces giving insight into the crucial dual-activation cyclization step. In the case of the 3,4-thiophene backbone, in which the initial cyclization is rate and selectivity determining, two energetically distinct transition states could be localized explaining the observed 5-endo cyclization mode by classical transition-state theory. In the case of vinyl and 2,3-thiophene backbones, the theoretical analysis of the cyclization mode in the bifurcated cyclization area demonstrated that classical transition-state theory is no longer valid to explain the high experimentally observed selectivity. Herein, for the first time, the influence of the backbone and the aromatic stabilization effect of the 6-endo product in the crucial cyclization step could be visualized and quantified by calculating and comparing the full potential-energy surfaces.

Gold-catalyzed C(sp3)–H bond functionalization

Homogeneous gold-catalyzed sp³ C–H bond functionalization strategy opens a new avenue for economical and sustainable construction of fine chemicals.

Water-dispersible and magnetically separable gold nanoparticles supported on a magnetite/s-graphene nanocomposite and their catalytic application in the Ullmann coupling of aryl iodides in aqueous media

The water-dispersible and magnetic separable Au/Fe₃O₄/s-G nanocomposite was used as an effective and reusable heterogeneous catalyst for the Ullmann homocoupling.

A catalyst-controlled selective synthesis of pyridines and pyrroles

We have developed a dual reaction manifold that enables the selective synthesis of both pyridines and pyrroles from the common substrates α-diazo oxime ethers.

Gold nanoparticle supported on ionic liquid-modified graphene oxide as an efficient and recyclable catalyst for one-pot oxidative A3-coupling reaction of benzyl alcohols

A novel gold nanoparticle supported on graphene oxide with ionic liquid framework was used as a highly active and recyclable catalyst for novel domino oxidative A³-coupling reaction.

Strategic innovation in the total synthesis of complex natural products using gold catalysis

This review has been organized from the perspective of synthetic target families, with emphasis on the use of gold-catalyzed transformations and cascade reactions that significantly increase molecular complexity.

Dehydrogenative Meyer-Schuster-like rearrangement: a gold-catalyzed reaction generating an alkyne

Easily accessible propargylic esters are converted to the inverted alkynyl ketones in an oxidative gold-catalyzed reaction. Gagosz's catalyst in combination with PhI(OAc)2 is the best system for this conversion and 18 examples with yields up to 80 % are reported. The results indicate that the triple bond in the product is formed by elimination from a vinylgold intermediate. In a formal sense the new conversion overall is a dehydrogenative Meyer-Schuster rearrangement.

Gold(I)-catalyzed domino cyclization for the synthesis of polyaromatic heterocycles

Gold(I) complexes have emerged as powerful and useful catalysts for the formation of new C–C, C–O and C–N bonds. Taking advantage of the specificity of [IPrAuNCMe][SbF₆] complexes to favor the 5-exo-dig cyclization over the 6-endo-dig pathway, we report a high yielding and efficient method to generate substituted polyaromatic heterocycles under remarkably mild reaction conditions.

Gold(I)-catalyzed formation of bridged and fused carbocycles

For many years, despite a rich coordination chemistry, gold (Au) was judged as being catalytically inactive for the formation of carbon–carbon bonds. In mid-1970, few reports demonstrated that Au salts could be very useful reagents to catalyze organic transformations. In recent years, homogeneous catalysis by Au has received considerable attention by the scientific community. It was shown that Au(I) or (III) catalysts are specific and more reactive than most of the other soft Lewis acids such as Hg(II), Cu(II), Pt(II), and Pd(II). Taking advantage of the affinity of cationic phosphine Au complexes to triple bonds, we conceived a Au(I)-catalyzed 6-endo-dig cyclization of cyclic enol ether to prepare bridged and fused bicyclic ketone. Keeping in mind that 5-exo-dig cyclizations can be a competitive process, we surveyed various Au(I) complexes.

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III) complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I) complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II) catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh(3)). Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction.