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]

The Potential of Self-Activating Au(I) Complexes in Gold Catalysis

Gold catalysis has emerged as a groundbreaking field in synthetic chemistry, revolutionizing numerous organic transformations. Despite the significant achieved advancements, the mechanistic understanding behind many gold-catalyzed reactions remains elusive. This Concept article covers the so-called "self-activating" Au(I) complexes, sorting out their pivotal role in gold catalysis. We comment on how Au(I) complexes can undergo self-activation, triggering diverse catalytic transformations without the need for external additives. The most important examples reported so far that underlie the catalytic activity of these species are discussed. This intrinsic reactivity represents a paradigm shift in gold catalysis, offering new avenues for the design of efficient and sustainable catalytic systems. Furthermore, we explore the factors influencing the stability, reactivity, and selectivity of these Au(I) complexes, providing insights into their synthetic utility and potential applications. This area of research not only advances our fundamental understanding of gold catalysis but also paves the way for the development of novel catalytic strategies with broad implications in organic synthesis and the chemical industry.

Hydration Reactions Catalyzed by Transition Metal-NHC (NHC = N-Heterocyclic Carbene) Complexes

The catalytic addition of water to unsaturated C-C or C-N π bonds represent one of the most important and environmentally sustainable methods to form C-O bonds for the production of synthetic intermediates, medicinal agents and natural products. The traditional acid-catalyzed hydration of unsaturated compounds typically requires strong acids or toxic mercury salts, which limits practical applications and presents safety and environmental concerns. Today, transition-metal-catalyzed hydration supported by NHC (NHC = N-heterocyclic carbene) ligands has attracted major attention. By rational design of ligands, choice of metals and counterions as well as mechanistic studies and the development of heterogeneous systems, major progress has been achieved for a broad range of hydration processes. In particular, the combination of NHC ligands with gold shows excellent reactivity compared with other catalytic systems; however, other systems based on silver, ruthenium, osmium, platinum, rhodium and nickel have also been discovered. Ancillary NHC ligands provide stabilization of transition metals and ensure high catalytic activity in hydration owing to their unique electronic and steric properties. NHC-Au(I) complexes are particularly favored for hydration of unsaturated hydrocarbons due to soft and carbophilic properties of gold. In this review, we present a comprehensive overview of hydration reactions catalyzed by transition metal-NHC complexes and their applications in catalytic hydration of different classes of π-substrates with a focus on the role of NHC ligands, types of metals and counterions.

External Catalyst- and Additive-Free Photo-Oxidation of Aromatic Alcohols to Carboxylic Acids or Ketones Using Air/O2

We present an environment-friendly and highly efficient method for the oxidation of aromatic alcohols to carboxylic acids or ketones in air via light irradiation under external catalyst-, additive-, and base-free conditions. The photoreaction system exhibits a wide substrate scope and the potential for large-scale applications. Most of the desired products are easily obtained via recrystallization and separation from low-boiling reaction medium acetone in good yields, and the products can be subsequent directly transformed without further purification.

Activation of metal-involved halogen bonds and classical halogen bonds in gold(I) catalysis

In gold(I) catalysis, the activation of Au(I) chloride catalysts via chloride abstraction and noncovalent interactions has become a research focus in organometallic catalysis. In this work, taking halogen bond donors (C₄H₂INO₂, C₆F₅I, C₈H₉O₂I) as activators for a Au(I) chloride catalyst (Ph₃PAuCl), the mechanism of the cyclization reaction of propargylic amide was investigated. It was found that there are two activation modes as design principles to obtain the catalytically active species Ph₃PAu⁺: the halogen bond donors activate the Cl atoms of Ph₃PAuCl to form X-I⋯Cl (X = C, N) classical halogen bonds and activate the Au atoms of Ph₃PAuCl to form X-I⋯Au (X = C, N) metal-involved halogen bonds. For the two activation modes, the mechanism of the cyclization reaction of propargylic amide has pathways: the chloride abstraction process of the first step and the 5-exo/6-endo cyclization process of the second step. Both activation modes show good activity for the cyclization reaction with the activation ability of classical halogen bonds being slightly stronger than that of the metal-involved halogen bonds, which is consistent with the strength of the X-I⋯Cl halogen bonds being slightly stronger than that of the X-I⋯Au halogen bonds. Therefore, both metal-involved halogen bonds and classical halogen bonds have important development prospects for the activation of catalysts in gold(I) catalysis.

Integrated Cobaloxime and Mesoporous Silica-Supported Ruthenium/Diamine Co-Catalysis for One-Pot Hydration/Reduction Enantioselective Sequential Reaction of Alkynes

This study developed a cost-efficient hydration/asymmetric transfer hydrogenation (ATH) process for the one-pot synthesis of valuable chiral alcohols from alkynes. During this process, the initial homogeneous cobaloxime-catalyzed hydration of alkynes was followed by heterogeneous Ru/diamine-catalyzed ATH transformation of the in-situ generated ketones, which provided varieties of chiral alcohols in good yields with up to 99% ee values. The immobilized Ru/diamine catalyst could be recycled at least three times before its deactivation in the sequential reaction system. This work shows a general method for developing one-pot asymmetric sequential catalysis towards sustainable organic synthesis.

Advances in Green Catalysis for the Synthesis of Medicinally Relevant N-Heterocycles

N-heterocycles, both saturated and unsaturated, are ubiquitous biologically active molecules that are extremely appealing scaffolds in drug discovery programs. Although classical synthetic methods have been developed to access many relevant N-heterocyclic scaffolds, representing well-established and reliable routes, some do not meet the needs of sustainability. In this context, several advances have been made towards the sustainable synthesis of N-heterocycles. This review focuses on the most recent examples from the last five years of catalytic synthesis of several heterocyclic compounds of medicinal relevance. Thus, the synthesis of isoindoloquinazolines, quinazolines and azaindoles, among others, are covered. The synthetic methods selected include the use of homogeneous and heterogeneous catalysts and the use of alternative and sustainable methods such as, for example, metal-catalyzed acceptorless coupling and one-pot reactions. The green aspects of the individual synthetic approaches are highlighted, and the scope of each methodology is described.

Photoinduced Acetylation of Anilines under Aqueous and Catalyst-Free Conditions

A green and efficient visible-light induced functionalization of anilines under mild conditions has been reported. Utilizing nontoxic, cost-effective, and water-soluble diacetyl as photosensitizer and acetylating reagent, and water as the solvent, a variety of anilines were converted into the corresponding aryl ketones, iodides, and bromides. With advantages of environmentally friendly conditions, simple operation, broad substrate scope, and functional group tolerance, this reaction represents a valuable method in organic synthesis.

Integrated experimental/computational approaches to characterize the systems formed by vanadium with proteins and enzymes

An integrated instrumental/computational approach to characterize metallodrug–protein adducts at the molecular level is reviewed. A series of applications are described, focusing on potential vanadium drugs with a generalization to other metals.

An Efficient Hydration and Tandem Transfer Hydrogenation of Alkynes for the Synthesis of Alcohol in Water

A practical and efficient method for the synthesis of alcohols in one pot from readily available alkynes via a tandem process by formic acid promoted hydration and metal-ligand bifunctional iridium-catalyzed­ transfer hydrogenation under mild conditions has been described. This transformation is simple, efficient, and can be performed with a variety of alkynes in good yields and with excellent stereoselectivities. Experimental results showed high catalytic activity, and turnover frequency (TOF) up to 25000. Importantly, this transformation can be conducted in water, and is thus green and environmentally friendly.

Recent advances in metal-catalysed asymmetric sequential double hydrofunctionalization of alkynes

Recent advances in various metal-catalysed asymmetric sequential double hydrofunctionalizations of alkynes have been highlighted in this feature article.

Tandem Wittig Reaction-Ring Contraction of Cyclobutanes: A Route to Functionalized Cyclopropanecarbaldehydes

An original tandem reaction consisting of a Wittig reaction-ring contraction process between α-hydroxycyclobutanone and phosphonium ylides has been developed. Highly functionalized cyclopropanecarbaldehydes are obtained in good to high yield.

Synthesis of a Novel Magnetically Retrievable Nanocomposite with Au Nanocatalysts for Hydration Reaction

Developing efficient catalysts with good recyclability is of great importance for its practical applications. In this study, a novel magnetically retrievable nanocomposite (Au-SiO2@Fe3O4-RGO) was synthesized for catalyzing hydration reaction. Active Au nanoparticles are deposited on core-shell SiO2@Fe3O4, which are further supported by a two-dimensional reduced graphene oxide (RGO) platform. The prepared Au-SiO2@Fe3O4-RGO was proven to be efficient as well as recyclable. An excellent catalytic performance, with 97% yield towards the hydration of phenylacetylene, was achieved for the catalyst in dioxane. Remarkably, the catalyst can be readily recycled through magnetic separation and achieved superior catalyst recovery and stability after seven cycles without any metal leaching. This work provides a strategy to fabricate recyclable and durable catalysts for industrial applications.

Gold Catalysis in (Supra)Molecular Cages to Control Reactivity and Selectivity

Gold catalysis has experienced a tremendous development over the past decades, and is nowadays widely used in organic synthesis to perform chemical transformations of π-bond-containing molecules. Catalyst development has been based mostly on ligand development and counter-ion strategies. More recently, the encapsulation of gold catalysts in (supra)molecular cages was explored as a new way to control selectivity and reactivity of gold catalysts. In this review, we describe the cages that have been employed as hosts for gold complexes, along with their impact on the catalytic performance. Covalent and supramolecular approaches to encapsulate single metal complexes will be described and the impact on the catalytic performance will be discussed. Also, recent strategies to pre-organize multiple metal centers will be discussed.

One catalyst, multiple processes: ligand effects on chemoselective control in Ru-catalyzed anti-Markovnikov reductive hydration of terminal alkynes

The ligand effect through kinetic and thermodynamic control on the chemoselectivity of one-catalyst multi-step catalysis.

In(III) and Hf(IV) Triflate-Catalyzed Hydration and Catalyst-free Hydrohalogenation of Aryl Acetylenes in Liquid Sulfur Dioxide

The use of liquid sulfur dioxide as a reaction solvent to promote chemical transformations of alkynes has been explored. First, a combination of liquid SO2 and In(OTf)3 or Hf(OTf)4 as a catalyst allows to perform hydration of aryl alkynes under mild conditions without a direct addition of Brønsted acid. Second, novel catalyst-free conditions for the synthesis of α-vinyl iodides, bromides, and chlorides from aryl alkynes have been developed in liquid SO2 using group I and II metal halides and ammonium iodide as the halide ion sources.

Dynamic Kinetic Resolution for Construction of Three Transannular Stereocenters of Dihydrobenzofuranols

A handy and effective method was established to obtain the cis-2,3-dihydrobenzofuranols having three stereocenters, involving asymmetric transfer hydrogenation of benzofuranones via dynamic kinetic resolution. The general applicability of this method was examined with different benzofuran-3-(2 H)-ones, and stereoselectivities of 85-99% ee and up to 98/2 dr were obtained.

Formal Total Synthesis of Actinoranone: Synthesis Approaches and Cytotoxic Studies

This article describes our efforts toward the total synthesis of actinoranone. Our synthesis strategies rely on a convergent route to connect the terpenoid and polyketide fragments, employing catalysis and powerful classical reactions for the assembly of these key fragments. A new transformation was disclosed during this work, a domino ring-opening and esterification. Initial cytotoxic studies for the selected synthesis intermediates are also presented.

Cobaloxime-catalyzed hydration of terminal alkynes without acidic promoters

Cobaloxime (Co(dmgBF₂)₂·2H₂O), an inexpensive first-row transition-metal complex, catalyzed hydration of terminal alkynes gave the corresponding methyl ketones in good to excellent yields under neutral conditions (additional protic acids and silver salts are not required). A wide range of functional groups, such as allyl ether, benzyl ethers, carboxylic esters, imides, amides, nitro, and halogens, were tolerated. The mild reaction conditions together with the inexpensive feature and easy availability of the catalyst well address the current challenges in the field of alkyne hydration.

PMO-Immobilized AuI -NHC Complexes: Heterogeneous Catalysts for Sustainable Processes

A stable periodic mesoporous organosilica (PMO) with accessible sulfonic acid functionalities is prepared via a one-pot-synthesis and is used as solid support for highly active catalysts, consisting of gold(I)-N-heterocyclic carbene (NHC) complexes. The gold complexes are successfully immobilized on the nanoporous hybrid material via a straightforward acid-base reaction with the corresponding [Au(OH)(NHC)] synthon. This catalyst design strategy results in a boomerang-type catalyst, allowing the active species to detach from the surface to perform the catalysis and then to recombine with the solid after all the starting material is consumed. This boomerang behavior is assessed in the hydration of alkynes. The tested catalysts were found to be active in the latter reaction, and after an acidic work-up, the IPr*-based gold catalyst can be recovered and then reused several times without any loss in efficiency.

PtO2/PTSA system catalyzed regioselective hydration of internal arylalkynes bearing electron withdrawing groups

A highly efficient PtO₂/PTSA catalyst system for the hydration of a wide array of alkynes was developed. This method proved to be compatible with a large range of functional groups and the ketone products were obtained in high yields. The scope of this methodology was also extended to the synthesis of 3-aryl-isochromenones, -indoles and -benzofurans.

A highly efficient PtO₂/PTSA catalyst system for the hydration of a wide array of alkynes was developed.

One-pot synthesis of chiral alcohols from alkynes by CF3SO3H/ruthenium tandem catalysis

A practical one-pot synthesis of chiral alcohols from readily available alkynes via tandem catalysis by the combination of CF₃SO₃H and a fluorinated chiral diamine Ru(ii) complex in aqueous CF₃CH₂OH is described. Very interestingly, the combination of fluorinated catalysts and solvent exhibits a positive fluorine effect on the reactivity and enantioselectivity. A range of chiral alcohols with wide functional group tolerance was obtained in high yield and excellent stereoselectivity under simple and mild conditions.

A simple and compatible catalytic system for one-pot transformation of alkynes into chiral alcohols was developed.