Gold-Catalyzed Regioselective Hydration of Propargyl Acetates Assisted by a Neighboring Carbonyl Group: Access to α-Acyloxy Methyl Ketones and Synthesis of (±)-Actinopolymorphol B

Theoretical insight into the Au(i)-catalyzed hydration of halo-substituted propargyl acetate: dynamic water-assisted mechanism

Three possible hydration pathways, including 1,5-exo-dig cycloaddition, 1,6-endo-dig cycloaddition, and direct water attack, have been considered and investigated by using DFT method and the cluster-continuum solvent model.

Stable yet reactive cationic gold catalysts with carbon based counterions

Widely applicable cationic gold catalysts with a carbon based counterion.

Visible light promoted hydration of alkynes catalyzed by rhodium(III) porphyrins

Visible light promoted hydration of a wide scope of alkynes to ketones catalyzed by rhodium(III) porphyrin complexes was described. The key intermediate β-carbonyl alkyl was observed and independently synthesized. The rate of photolysis is over two orders of magnitude faster than that of the thermal process.

Regioselective hydration of terminal alkynes catalyzed by a neutral gold(I) complex [(IPr)AuCl] and one-pot synthesis of optically active secondary alcohols from terminal alkynes by the combination of [(IPr)AuCl] and Cp*RhCl[(R,R)-TsDPEN]

A neutral gold(I) complex [(IPr)AuCl] (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene) was found to be a highly effective catalyst for the hydration of terminal alkynes, including aromatic alkynes and aliphatic alkynes. The desired methyl ketones were obtained in high yields with complete regioselectivities. Furthermore, a series of optically active secondary alcohols could be obtained in high yield with good to excellent enatioselectivities via one-pot sequential hydration/asymmetric transfer hydrogenation (ATH) from terminal alkynes by the combination of of [(IPr)AuCl] and Cp*RhCl[(R,R)-TsDPEN] (Cp* = pentamethylcyclopentadienyl, TsDPEN = N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine). Notably, this research exhibited the potential of the direct use of neutral gold(I) complexes instead of cationic ones as catalysts for the activation of multiple bonds for organic synthesis.

Au(i) π-bis(tert-butyldimethylsilyl)acetylene triphenylphosphine complex, an effective pre-catalyst for Au(i)-catalyzed reactions

A [Ph₃PAu]⁺ η²-alkyne π complex is found to be shelf-stable and effective for a range of the Au(i)-catalyzed alkyne π activation reactions.

Efficient hydration of alkynes through acid-assisted Brønsted acid catalysis

The combined acid catalyzed hydration of alkynes is an efficient one-step synthesis of carbonyl compounds.

Cationic gold catalyst poisoning and reactivation

High gold affinity impurities (halides, bases) in solvents, starting materials, filtration, or drying agents could affect the reactivity of gold catalyst adversely, which may significantly reduce the TON of cationic gold-catalyzed reactions. Use of a suitable acid activator (e.g., HOTf, In(OTf)3) reactivates the gold catalyst and makes the reaction proceed smoothly at low gold catalyst loading.

Iron(III) sulfate as terminal oxidant in the synthesis of methyl ketones via Wacker oxidation

An efficient and environmentally benign method using Fe(III) sulfate as a terminal oxidant in the synthesis of methyl ketones from terminal olefins via the Wacker process is developed. The methodology offers high selectivity for a Markonikov product, shows good functional group compatibility, involves mild reaction conditions, and is operationally simple. Fe2(SO4)3 is the sole terminal oxidant in this process. The method holds potential for future applications in organic synthesis.

Formation and stability of 3-5 atom gold clusters from gold complexes during the catalytic reaction: dependence on ligands and counteranions

Gold complexes and salts decompose to catalytically active 3-5 atom gold clusters during the one-pot acylation-hydration of propargyl alcohols. Kinetic and spectroscopic studies show that released ligands and counteranions exert a direct effect on the formation and stability of the clusters.

Generation of gold carbenes in water: efficient intermolecular trapping of the α-oxo gold carbenoids by indoles and anilines

The efficient intermolecular reaction of gold carbene intermediates, generated via gold-catalyzed alkyne oxidation, with indoles and anilines has been realized in aqueous media.

NHC–gold(i) catalysed [4 + 2] cycloaddition–acyclic addition of dialkyl substituted propargylic esters with 1,3-diphenylisobenzofuran: synthesis of novel benzo[c]fluorenols and substituted dienes

A new class of benzofluorenols is generated via a novel gold carbene complex [IPrAuCl/AgSbF₆] catalysed cycloaddition of propargylic esters with 1,3-diphenylisobenzofuran.

Gold-catalyzed glycosidation for the synthesis of trisaccharides by applying the armed-disarmed strategy

The synthesis of oligosaccharides is still a challenging task as there is no universal glycosyl donor for the synthesis of all oligosaccharides. The gold catalysis for glycosidation reactions, in which alkynylated glycosides are used, has emerged as one of the versatile options in this regard. A cleavage of the interglycosidic bond that was thought to be due to the higher reaction temperature and the acidic medium was observed during the synthesis of trisaccharides. In addition, a very little percentage of deprotection of benzyl protecting groups at the C-6 position was observed and no deprotection of benzyl ethers in aliphatic molecules was noticed. In order to overcome this fact, a collection of leaving groups that contain an alkynyl moiety were screened. It was found that 1-ethynylcyclohexanyl (Ech) glycosides are suitable for carrying out the glycosidation at 25 °C in the presence of 5 mol % each of AuCl₃ and AgSbF₆. Subsequently, Ech-glycosides were observed to be suitable for the synthesis of trisaccharides under gold catalysis conditions.

Small gold clusters formed in solution give reaction turnover numbers of 10(7) at room temperature

Very small gold clusters (3 to 10 atoms) formed from conventional gold salts and complexes can catalyze various organic reactions at room temperature, even when present at concentrations of parts per billion. Absorption and emission ultraviolet-visible spectroscopy and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry revealed that, for example, the ester-assisted hydration of alkynes began only when clusters of three to five gold atoms were formed. The turnover numbers and turnover frequencies associated with these catalyzed reactions can be as high as 10(7) and 10(5) per hour, respectively.

Hydration of terminal alkynes catalyzed by water-soluble cobalt porphyrin complexes

Water-soluble cobalt(III) porphyrin complexes were found to promote the hydration of terminal alkynes to give methyl ketones. The alkyne hydration proceeded in good to excellent yield with 0.1 to 2 mol % cobalt catalyst 1 and was compatible with the presence of acid/base- or redox-sensitive functional groups such as alkyl silyl ethers; allyl ethers; trityl ethers; benzyl ethers; carboxylic esters; boronic esters; carboxamides; nitriles; and nitro, iodo, and acetal groups. Some of the alkyne substrates tested here are otherwise difficult to hydrate. The alkyne hydration can be performed on a gram scale, and the catalyst can be recovered by aqueous workup.