Recent advances in the gold-catalyzed additions to C-C multiple bonds

Gold-Catalyzed Addition of β-Ketoesters to Alkenes: Influence of Electronic and Steric Effects in the Reaction Outcome

The gold-catalyzed intermolecular hydroalkylation of olefins with β-ketoesters represents a conceptually attractive and useful synthetic tool; however, it has been scarcely applied, remaining a challenge for chemists. The aim of the current study was to investigate the addition of these 1,3-diketo-compounds to alkenes under gold catalysis conditions, in order to establish the electronic and steric effects of the alkenyl substrates in the reaction outcome. The screening of different catalyst systems and diverse olefins enabled defining the alkenyl requirements and the best reaction conditions to efficiently achieve the coupled products.

Gold-Catalyzed Synthesis of 2-Sulfenylspiroindolenines via Spirocyclizations

2-Phenylsulfenyl-N-propargyl tryptamines have been prepared by electrophilic sulfuration of the corresponding tryptamines. These compounds undergo gold-catalyzed spirocyclizations to the corresponding 2-phenylthiospiroindolenines in good yields. The compounds were analyzed by NMR experiments, infrared, mass spectra and X-ray diffraction. This method provides a new efficient entry to the synthesis of 2-sulfenyl spiroindolic compounds.

Dissecting the Gold(I)-Catalyzed Carboaminations of N-Allyl Tetrahydro-β-carbolines to Allenes

N-Allyl tetrahydro-β-carbolines undergo gold-catalyzed cyclizations that lead to tetracyclic compounds, resulting from both ring closure and the transfer of the allylic group from the nitrogen to the carbon backbone. The final skeleton obtained depends on the nature of both the R² group of the allene and the R³ group of the allylic residue. Mechanistic studies and DFT calculations allowed the determination of all the mechanistic pathways involved in these processes, stemming from a common intermediate that evolves differently according to the substituents nature.

Reactions of secondary propargylamines with heteroallenes for the synthesis of diverse heterocycles

This focused review aims to summarize recent developments in the processes involving additions of secondary propargylamines to various heteroallenes and subsequent transition metal-catalyzed or electrophile-mediated cyclizations.

Gold catalyzed Heck-coupling of arenediazonium o-benzenedisulfonimides

An efficient gold catalyzed Heck coupling of arenediazonium o-benzenedisulfonimides is proposed. An o-benzenedisulfonimide anion enables a radical pathway that does not require the presence of photocatalysts or external oxidants.

Gold(I)-Catalyzed Direct Stereoselective Synthesis of Deoxyglycosides from Glycals

Au(I) in combination with AgOTf enables the unprecedented direct and α-stereoselective catalytic synthesis of deoxyglycosides from glycals. Mechanistic investigations suggest that the reaction proceeds via Au(I)-catalyzed hydrofunctionalization of the enol ether glycoside. The room temperature reaction is high yielding and amenable to a wide range of glycal donors and OH nucleophiles.

Bonding Situation of Bis-gold Chloride Complexes with N-heterocyclic Carbene-Analogues [(AuCl)2-NHEMe] (E=C – Pb) based on DFT Calculations

We computationally investigated the structure and bonding situation of bis-gold chloride complexes, (AuCl)2, containing N-heterocyclic carbenes and analogues, called tetrylenes [(AuCl)2-NHEMe] (Au2-NHE) with E=C to Pb, using density functional theory (DFT) at the BP86 level with the basis sets def2-SVP, def2-TZVPP, and TZ2P+. The nature of the (AuCl)2-NHEMe bond in the Au2-NHE complexes was analyzed using charge and energy decomposition methods. The calculated equilibrium structures of the Au2-NHE complexes showed that the tetrylene ligands, NHEMe (E=C to Ge), are bonded in a head-on fashion to the bis-gold chloride fragment, (AuCl)2, and that the structure of Au2-NHSn contains a distorted head-on NHSn ligand, and the NHPb ligand is bonded in a side-on mode to the bis-gold chloride fragment, (AuCl)2. The theoretical calculation of bond dissociation energy (BDE) suggests that the bis-gold chloride-NHEMe bond strength increases from Au2-NHC to Au2-NHSi and then significantly decreases from Au2-NHSi to Au2-NHSn, and the strongest bond is exhibited for Au2-NHPb. The EDA-NOCV results and NOCV pairs indicate that the NHEMe ligand in the Au2-NHE complexes is a strong σ-donor and a weak π-acceptor, as well as a very weak π-donor (AuCl)2←{NHEMe}. The trend in the Au-E bond strength resulted from the increase in (AuCl)2←NHEMe donation. The results of this study may establish an interesting class of compounds worthy of further study.

N-2-Selective gold-catalyzed alkylation of 1-sulfonyl-1,2,3-trizoles

An efficient new method was developed to synthesis N-2-alkyl-1,2,3-trizoles via gold catalyzed alkylation of 1-sulfonyl-1,2,3-trizoles with vinyl ethers.

Gold catalysis: synthesis of spiro, bridged, and fused ketal natural products

This review summarises the application of gold catalysis for the syntheses of spiro, bridged and fused ketal natural products.

Magnetically recoverable graphene-based nanocomposite material as an efficient catalyst for the synthesis of propargylamines via A3 coupling reaction

The magnetically separable Au NPs–Fe₃O₄–rGO catalyst provides a robust and efficient route for the A³ coupling reaction of secondary amines, terminal alkynes and aldehyde with tolerance of diverse functional groups for the synthesis of propargylamine in high yields.

Gold(I)-Catalyzed N-Desulfonylative Amination versus N-to-O 1,5-Sulfonyl Migration: A Versatile Approach to 1-Azabicycloalkanes

Valuable 1-azabicycloalkane derivatives have been synthesized through a novel gold(I)-catalyzed desulfonylative cyclization strategy. An ammoniumation reaction of ynones substituted at the 1-position with an N-sulfonyl azacycle took place in the presence of a gold cation by intramolecular cyclization of the disubstituted sulfonamide moiety onto the triple bond. Depending on the size of the heterocyclic ring and substitution of the substrates, two unprecedented forms of nucleophilic attack on the sulfonyl group were exploited, that is, a N-desulfonylation in the presence of an external protic O nucleophile (37-87 %, 10 examples) and a unique N-to-O 1,5-sulfonyl migration (60-98 %, 9 examples).

Mutual Cooperation in the Formal Allyl Alcohol Nucleophilic Substitution and Hydration of Alkynes for the Construction of γ-Substituted Ketones

Mutual cooperation in the formal allyl alcohol nucleophilic substitution reaction and hydration of an alkyne has been utilized in the presence of a gold catalyst to give a series of γ-functionalized ketones with high to excellent yields. This reaction actually involved an intramolecular O-H insertion cyclization of an alkyne to form the dihydrofuran intermediate, which was followed by the nucleophilic addition ring-opening of a dihydrofuran to give the target compound.

A direct access to isoxazoles from ynones using trimethylsilyl azide as amino surrogate under metal/catalyst free conditions

A general access to isoxazoles with outstanding functional group compatibility from the readily available ynones using trimethylsilyl azide as an amino surrogate under exceptionally simple conditions is described.

Copper-catalyzed tandem reaction in ionic liquid: an efficient reusable catalyst and solvent media for the synthesis of fused poly hetero cyclic compounds

Herein we report a copper catalyzed tandem reaction for the therapeutically important pyrrolo-/pyrido[2,1-b] benzo[d][1,3]oxazin-1-ones using 2-aminobezyl alcohols, green solvent medium, alkynoic acids, under ligand and base free conditions.

Pyridylidene ligand facilitates gold-catalyzed oxidative C-H arylation of heterocycles

Triaryl-2-pyridylidene effectively facilitates the gold-catalyzed oxidative C-H arylation of heteroarenes with arylsilanes as a unique electron-donating ligand on gold. The employment of the 2-pyridylidene ligand, which is one of the strongest electron-donating N-heterocyclic carbenes, resulted in the rate acceleration of the C-H arylation reaction of heterocycles over conventional ligands such as triphenylphosphine and a classical N-heterocyclic carbene. In situ observation and isolation of the 2-pyridylidene-gold(III) species, as well as a DFT study, indicated unusual stability of gold(III) species stabilized by strong electron donation from the 2-pyridylidene ligand. Thus, the gold(I)-to-gold(III) oxidation process is thought to be facilitated by the highly electron-donating 2-pyridylidene ligand.

When Phosphosugars Meet Gold: Synthesis and Catalytic Activities of Phostones and Polyhydroxylated Phosphonite Au(I) Complexes

The synthesis and characterization of P-chiral phosphonite-, phosphonate- and thiophosphonate-Au(I) complexes are reported. These novel ligands for Au(I) are based on glycomimetic phosphorus scaffolds, obtained from the chiral pool. The catalytic activities of these complexes are shown in the cyclization of allenols and the hydroamination of 2-(2-propynyl)aniline combined with an organocatalyzed reduction to the corresponding 2-phenyl tetrahydroquinoline. All described gold complexes present excellent catalytic activities.

Diversity Oriented Synthesis of Indoloazepinobenzimidazole and Benzimidazotriazolobenzodiazepine from N(1)-Alkyne-1,2-diamines

A one-pot protocol for the diversity oriented synthesis of two N-polyheterocycles indoloazepinobenzimidazole and benzimidazotriazolobenzodiazepine from a common N(1)-alkyne-1,2-diamine building block is described. The approach involves sequential formation of benzimidazole through cyclocondensation and oxidation, which is followed by the formation of either an azepine ring (through alkyne activation and 6-endo-dig cyclization, 1,2-migration with ring expansion, and re-aromatization), or diazepine and triazole rings through 1,3-dipolar cycloaddition.

MediaChrom: Discovering a Class of Pyrimidoindolone-Based Polarity-Sensitive Dyes

A small library of six polarity-sensitive fluorescent dyes, nicknamed MediaChrom, was prepared. This class of dyes is characterized by a pyrimidoindolone core fitted out with a conjugated push-pull system and a carboxy linker for a conceivable coupling with biomolecules. The optimized eight-step synthetic strategy involves a highly chemo- and regioselective gold-catalyzed cycloisomerization reaction. The photophysical properties of MediaChrom dyes have been evaluated in-depth. In particular, the MediaChrom bearing a diethylamino as an electron-donating group and a trifluoromethyl as an electron-withdrawing group displays the most interesting and advantageous spectroscopic features (e.g., absorption and emission in the visible range and a good quantum yield). Promising results in terms of sensitivity have been obtained in vitro on this dye as a membrane/lipophilic probe and as a peptide fluorescent label.

Gold(I)-catalyzed asymmetric desymmetrization of meso-alkynyl diols and kinetic resolution of the corresponding DL-diols: effects of celite filtration and silver salts

The asymmetric desymmetrization of meso-2-alkynylbenzenediols through the use of a combination of axially chiral diphosphine(AuCl)2 precatalysts and silver salt co-catalysts gave optically active isochromene compounds with high enantioselectivities in good yields. The corresponding DL-diol isomers underwent efficient kinetic resolution to give the cyclized isochromenes and recovered diols with high enantioselectivities under similar conditions. The high reactivity and selectivity in the desymmetrization of the meso-diols is independent of the combination of axially chiral diphosphine(AuCl)2 precatalyst and silver salt co-catalyst, whereas the corresponding tricarbonylchromium complexes of alkynylbenzenediols were affected by the combination of the diphosphine(AuCl)2 and silver salt. The reactivity was largely dependent on the nature of the gold(I) species.

A general catalytic reaction sequence to access alkaloid-inspired indole polycycles

A general two-step catalytic reaction sequence affording a range of indole alkaloid-inspired complex molecular frameworks is presented.

Regioselectivity in the Au-catalyzed hydration and hydroalkoxylation of alkynes

The issue of regioselectivity in the Au-catalyzed hydration and hydroalkoxylation of alkynes is a perpetual challenge that essentially remains an unsolved problem with respect to general solutions.