A mild and fully catalytic aryl–aryl cross coupling via gold-catalysed C–H activation has been achieved by merging gold and photoredox catalysis. The procedure is free of stoichiometric oxidants and additives, which were previously required in gold-catalysed C–H activation reactions. Exploiting dual gold and photoredox catalysis confers regioselectivity via the crucial gold-catalysed C–H activation step, which is not present in the unselective photocatalysis-only counterpart.

A dual visible light photoredox and gold-catalysed C(sp2)–C(sp2) cross coupling is described. The success of this mild, oxidant- and base-free cross coupling is highly dependent on the amount of water added. Mechanistic studies show two distinct pathways depending on the gold catalyst employed: transmetallation of the arylboronic acid with gold(I) occurs prior to oxidation of gold(I) to gold(III) using cationic gold(I) catalysts, whereas oxidation of gold(I) to gold(III) precedes transmetallation using neutral gold(I) catalysts.

This review highlights the use of the oxidative boron Heck reaction in enantioselective Heck-type couplings. The enantioselective oxidative boron Heck reaction overcomes several limitations of the traditional Pd(0)-catalysed Heck coupling and has subsequently allowed for intermolecular couplings of challenging systems such as cyclic enones, acyclic alkenes, and even site selectively on remote alkenes.

Oxidative Heck couplings have been successfully developed for 2,2-disubstituted cyclopentene-1,3-diones. The direct coupling onto the 2,2-disubstituted cyclopentene-1,3-dione core provides a novel expedient way of enantioselectively desymmetrising all-carbon quaternary centres.

A mild gold-catalyzed protodeboronation reaction, which does not require acid or base additives and can be carried out in “green” solvents, is described. As a result, the reaction is very functional-group-tolerant, even to acid- and base-sensitive functional groups, and should allow for the boronic acid group to be used as an effective traceless directing or blocking group. The reaction has also been extended to deuterodeboronations for regiospecific ipso-deuterations of aryls and heteroaryls from the corresponding organoboronic acid. Based on density functional theory calculations, a mechanism is proposed that involves nucleophilic attack of water at boron followed by rate-limiting B–C bond cleavage and facile protonolysis of a Au−σ-phenyl intermediate.

Intermolecular additions of thiols to allenols via formal SN2′ selectivity to produce functionalized dienes are described. Although this dehydrative reaction was initially developed using gold(I) catalysis, indium(III) proves to be a far superior catalyst in terms of selectivity and substrate scope.

A simple change of solvent allows controlled and efficient switching between oxidative Heck and conjugate addition reactions on cyclic Michael acceptor substrates, catalyzed by a cationic Pd(II) catalyst system. Both reactions are ligand- and base-free and tolerant of air and moisture, and the controlled switching sheds light on some of the factors which favor one reaction over the other.

Direct allylic etherification of unactivated alcohols occurs regio- and stereoselectively under mild, gold(I)-catalysed conditions.

Thiols and amines, which are common heteroatom nucleophiles in gold-catalysed reactions, are known to dampen the reactivity of gold catalysts. In this article, the identity and activity of gold(I) catalysts in the presence of thiols and amines is investigated. In the presence of thioacid, thiophenol and thiol, digold with bridging thiolate complexes [{Au(L)}2(μ-SR)][SbF6] are formed and have been fully characterised by NMR and X-ray crystallography. In the presence of amines and anilines, complexes [LAu-NH2R][SbF6] are formed instead. All new isolated gold complexes were investigated for their catalytic activity in order to compare the level of deactivation in each species.

The synthesis of a small family of six electronically and sterically modified 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene gold(I) chloride complexes is described. Additionally, the corresponding trans-[PdBr2(iPr2-bimy)(1,3,4-trisubstituted 1,2,3-triazol-5-ylidene)] complexes are also generated and used to examine the donor strength of the 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene ligands. All compounds have been characterized by 1H and 13C NMR and IR spectroscopy, high-resolution electrospray mass spectrometry (HR-ESI-MS), and elemental analysis. The molecular structures of four of the gold(I) and four of the palladium(II) complexes were determined using X-ray crystallography. Finally, it is demonstrated that these 1,2,3-triazol-5-ylidene gold(I) chloride complexes (Au(trz)Cl) are able to catalyze the cycloisomerization of 1,6-enynes, in high yield and regioselectivity, as well as the intermolecular direct etherification of allylic alcohols. Exploiting the Au(trz)Cl precatalysts allowed the etherification of allylic alcohols to be carried out under milder conditions, with better yield and regioselectivity than selected commercially available gold(I) catalysts.

Ligand-free cationic Pd(II) catalyst with NaNO3 as an additive is a highly active catalytic system for conjugate additions to sterically hindered γ-substituted cyclohexenones. More challenging γγ- and βγ-substrates also react well to produce products with quaternary centers in good dr. The conjugate additions occur in a diastereoselective fashion under mild, practical and air-stable conditions, using readily available commercial reagents.

Depending on the conditions employed, gold(I)-catalyzed addition of indoles to 3,3-disubstituted cyclopropenes can be controlled to yield either 3-(E)-vinylindoles (3) or bis-indolylalkanes (4). If the cyclopropene substituents are sterically bulky, unprecedented gold-catalyzed oxidation under air occurs to yield bis-indolylalkene (5) and epoxide (6) at room temperature.

A variety of Au(III)–oxo complexes 1 were evaluated as catalysts for the first time and shown to be active catalysts for the alkyne hydroamination reaction.

Density functional theory calculations have been employed to investigate the mechanism of gold(I)-catalysed rearrangements of cyclopropenes. Product formation is controlled by the initial ring-opening step which results in the formation of a gold-stabilised carbocation/gold carbene intermediate. With 3-phenylcyclopropene-3-methylcarboxylate, the preferred intermediate allows cyclisation via nucleophilic attack of the carbonyl group and hence butenolide formation. Further calculations on simple model systems show that substituent effects can be rationalised by the charge distribution in the ring-opening transition state and, in particular, a loss of negative charge at what becomes the β-position of the intermediate. With 1-C3H3R cyclopropenes (R = Me, vinyl, Ph), ring-opening therefore places the substituent at the β-position.

Gold(I)-catalyzed reactions of thiols, thiophenols, and thioacids with 3,3-disubstituted cyclopropenes occur in a regioselective and chemoselective manner to produce either vinyl thioethers or primary allylic thioesters in good yields. A survey of commonly used gold(I) catalysts shows Echavarren’s cationic gold(I) catalyst to be most tolerant of deactivation by sulfur. A novel digold with bridging thiolate complex is characterized by X-ray crystallography, shedding light on a possible deactivation pathway.

Gold(I)-catalysed reaction between cyclopropenes and furans produces functionalised conjugated trienes. The reaction is mild, facile and proceeds with very low catalyst loadings.

Novel gold(I) “click” carbene(1,2,3-triazolylidene) complexes have been synthesised, characterised and exploited for the self-assembly of a metallomacrocycle and as precatalysts for gold(I)-catalysed reactions.

A highly regioselective method towards tertiary allylic ethers via gold(I)-catalyzed intermolecular hydroalkoxylation of allenes is disclosed. Preventing subsequent isomerization of the tertiary allylic ether products to primary allylic ethers appears to be the key to achieving high regioselectivities.

Gold(I)-catalysed addition of alcohols to 3,3-disubstituted cyclopropenes occurs in a highly regioselective and facile manner to produce alkyl tert-allylic ethers in good yields. The reaction is tolerant of sterically hindered substituents on the cyclopropene as well as primary and secondary alcohols as nucleophiles. In this full article, we report on the substrate scope and plausible mechanism, as well as the regioselectivity issues arising from subsequent gold(I)-catalysed isomerisation of tertiary to primary allylic ethers.

Gold(I) catalyses the ring-opening addition of cyclopropenes in a mild and regioselective manner.

Gold(I) catalyses the ring-opening addition of cyclopropenes in a mild and regioselective manner.

Novel gold(I) “click” carbene(1,2,3-triazolylidene) complexes have been synthesised, characterised and exploited for the self-assembly of a metallomacrocycle and as precatalysts for gold(I)-catalysed reactions.

Direct allylic etherification of unactivated alcohols occurs regio- and stereoselectively under mild, gold(I)-catalysed conditions.

Gold(I)-catalysed reaction between cyclopropenes and furans produces functionalised conjugated trienes. The reaction is mild, facile and proceeds with very low catalyst loadings.

Density functional theory calculations have been employed to investigate the mechanism of gold(I)-catalysed rearrangements of cyclopropenes. Product formation is controlled by the initial ring-opening step which results in the formation of a gold-stabilised carbocation/gold carbene intermediate. With 3-phenylcyclopropene-3-methylcarboxylate, the preferred intermediate allows cyclisation via nucleophilic attack of the carbonyl group and hence butenolide formation. Further calculations on simple model systems show that substituent effects can be rationalised by the charge distribution in the ring-opening transition state and, in particular, a loss of negative charge at what becomes the β-position of the intermediate. With 1-C3H3R cyclopropenes (R = Me, vinyl, Ph), ring-opening therefore places the substituent at the β-position.

Oxidative Heck couplings have been successfully developed for 2,2-disubstituted cyclopentene-1,3-diones. The direct coupling onto the 2,2-disubstituted cyclopentene-1,3-dione core provides a novel expedient way of enantioselectively desymmetrising all-carbon quaternary centres.

A dual visible light photoredox and gold-catalysed C(sp2)–C(sp2) cross coupling is described. The success of this mild, oxidant- and base-free cross coupling is highly dependent on the amount of water added. Mechanistic studies show two distinct pathways depending on the gold catalyst employed: transmetallation of the arylboronic acid with gold(I) occurs prior to oxidation of gold(I) to gold(III) using cationic gold(I) catalysts, whereas oxidation of gold(I) to gold(III) precedes transmetallation using neutral gold(I) catalysts.

Gold(I)-catalysed addition of alcohols to 3,3-disubstituted cyclopropenes occurs in a highly regioselective and facile manner to produce alkyl tert-allylic ethers in good yields. The reaction is tolerant of sterically hindered substituents on the cyclopropene as well as primary and secondary alcohols as nucleophiles. In this full article, we report on the substrate scope and plausible mechanism, as well as the regioselectivity issues arising from subsequent gold(I)-catalysed isomerisation of tertiary to primary allylic ethers.

A variety of Au(III)–oxo complexes 1 were evaluated as catalysts for the first time and shown to be active catalysts for the alkyne hydroamination reaction.

Thiols and amines, which are common heteroatom nucleophiles in gold-catalysed reactions, are known to dampen the reactivity of gold catalysts. In this article, the identity and activity of gold(I) catalysts in the presence of thiols and amines is investigated. In the presence of thioacid, thiophenol and thiol, digold with bridging thiolate complexes [{Au(L)}2(μ-SR)][SbF6] are formed and have been fully characterised by NMR and X-ray crystallography. In the presence of amines and anilines, complexes [LAu-NH2R][SbF6] are formed instead. All new isolated gold complexes were investigated for their catalytic activity in order to compare the level of deactivation in each species.

This review highlights the use of the oxidative boron Heck reaction in enantioselective Heck-type couplings. The enantioselective oxidative boron Heck reaction overcomes several limitations of the traditional Pd(0)-catalysed Heck coupling and has subsequently allowed for intermolecular couplings of challenging systems such as cyclic enones, acyclic alkenes, and even site selectively on remote alkenes.

A mild and fully catalytic aryl–aryl cross coupling via gold-catalysed C–H activation has been achieved by merging gold and photoredox catalysis. The procedure is free of stoichiometric oxidants and additives, which were previously required in gold-catalysed C–H activation reactions. Exploiting dual gold and photoredox catalysis confers regioselectivity via the crucial gold-catalysed C–H activation step, which is not present in the unselective photocatalysis-only counterpart.