Gold-Catalyzed Hydroarylation Reactions: A Comprehensive Overview

The hydroarylation of alkynes, alkene, and, allene is a cost-effective and efficient way to incorporate unsaturated moieties into aromatic substrates. This review focuses on gold-catalyzed hydroarylation, which produces aromatic alkenes,...

Thermally-Induced Intramolecular [4+2] Cycloaddition of Allylamino- or Allyloxy-Tethered Alkylidenecyclopropanes

A thermally-induced intramolecular [4+2] cycloaddition reaction of allylamino- or allyloxy-tethered alkylidenecyclopropanes has been reported in this paper, giving a new protocol for the rapid construction of polycyclic skeleton molecules in moderate to excellent yields with a broad substrate scope. On the basis of control experiments and DFT calculations, we disclosed that the reaction proceeded through a [4+2] cycloaddition and trace of water assisted 1,3-H shift process to give the target product.

Divergent Gold Catalysis: Unlocking Molecular Diversity through Catalyst Control

The catalyst-directed divergent synthesis, commonly termed as "divergent catalysis", has emerged as a promising technique as it allows chartering of structurally distinct products from common substrates simply by modulating the catalyst system. In this regard, gold complexes emerged as powerful catalysts as they offer unique reactivity profiles as compared to various other transition metal catalysts, primarily due to their salient electronic and geometrical features. Owing to the tunable soft π-acidic nature, gold catalysts not only evolved as superior contenders for catalyzing the reactions of alkynes, alkenes, and allenes but also, more intriguingly, have been found to provide divergent reaction pathways over other π-acid catalysts such as Ag, Pt, Pd, Rh, Cu, In, Sc, Hg, Zn, etc. The recent past has witnessed a renaissance in such examples wherein, by choosing gold catalysts over other transition metal catalysts or by fine-tuning the ligands, counteranions or oxidation states of the gold catalyst itself, a complete reactivity switch was observed. However, reviews documenting such examples are sporadic; as a result, most of the reports of this kind remained scattered in the literature, thereby hampering further development of this burgeoning field. By conceptualizing the idea of "Divergent Gold Catalysis (DGC)", this review aims to consolidate all such reports and provide a unified approach necessary to pave the way for further advancement of this exciting area. Based on the factors governing the divergence in product formation, an explicit classification of DGC has been provided. To gain a fundamental understanding of the divergence in observed reactivities and selectivities, the review is accompanied by mechanistic insights at appropriate places.

Gold-Catalyzed Synthesis of Small Rings

Three- and four-membered rings, widespread motifs in nature and medicinal chemistry, have fascinated chemists ever since their discovery. However, due to energetic considerations, small rings are often difficult to assemble. In this regard, homogeneous gold catalysis has emerged as a powerful tool to construct these highly strained carbocycles. This review aims to provide a comprehensive summary of all the major advances and discoveries made in the gold-catalyzed synthesis of cyclopropanes, cyclopropenes, cyclobutanes, cyclobutenes, and their corresponding heterocyclic or heterosubstituted analogs.

Gold-Catalyzed Synthetic Strategies towards Four-Carbon Ring Systems

Four carbon ring systems are frequently present in natural products with remarkable biological activities such as terpenoids, alkaloids, and steroids. The development of new strategies for the assembly of these structures in a rapid and efficient manner has attracted the interest of synthetic chemists for a long time. The current research is focused mainly on the development of synthetic methods that can be performed under mild reaction conditions with a high tolerance to functional groups. In recent years, gold complexes have turned into excellent candidates for this aim, owing to their high reactivity, and are thus capable of promoting a wide range of transformations under mild conditions. Their remarkable efficiency has been thoroughly demonstrated in the synthesis of complex organic molecules from simple starting materials. This review summarizes the main synthetic strategies described for gold-catalyzed four-carbon ring formation, as well as their application in the synthesis of natural products.

Gold-Catalyzed Homogeneous (Cyclo)Isomerization Reactions

Gold is currently one of the most used metals in organometallic catalysis. The ability of gold to activate unsaturated groups in different modes, together with its tolerance to a wide range of functional groups and reaction conditions, turns gold-based complexes into efficient and highly sought after catalysts. Natural products and relevant compounds with biological and pharmaceutical activity are often characterized by complex molecular structures. (Cyclo)isomerization reactions are often a useful strategy for the generation of this molecular complexity from synthetically accessible reactants. In this review, we collect the most recent contributions in which gold(I)- and/or gold(III)-catalysts mediate intramolecular (cyclo)isomerization transformations of unsaturated species, which commonly feature allene or alkyne motifs, and organize them depending on the substrate and the reaction type.

Recent Advances in the Cycloisomerizations of Methylenecyclopropanes using Gold Catalysis

During the past decades, cycloisomerizations of methylenecyclopropanes using gold catalysis have attracted much attention from organic chemists. The different patterns of gold(I)-catalyzed cycloisomerizations of methylenecyclopropanes have been developed, and they can be classified as ring-opening and ring-expansion reaction patterns. This synthetic methodology provides a new approach to novel cyclic- or polycyclic compounds. The corresponding products have great potential for material science, medicinal chemistry and total synthesis. This Concept article will mainly focus on the recent advances in the cycloisomerizations of methylenecyclopropanes in the past four years.

Mechanistic insights into Pd(0)-catalyzed intermolecular and intramolecular hydroamination of methylenecyclopropanes: a computational study

The mechanisms of transition metal-catalyzed methylenecyclopropanes (MCPs)-involved reactions are rather complicated due to the diverse pathways for the activation of MCPs. Herein, computational studies were carried out to investigate the detailed mechanisms of Pd(0)-catalyzed intermolecular and intramolecular hydroamination of MCPs. The initial activation of the three-membered ring of MCPs readily occurs via the insertion of Pd(0) into the distal C-C bond, leading to a metallacyclobutane intermediate. The commonly proposed oxidative addition of amine/amide nucleophile (Nu-H) onto the Pd(0) center to afford a hydrido-Pd(ii) complex, however, is less favorable in comparison with the Pd(0)-mediated cleavage of the distal C-C bond of MCPs. Subsequently, for the Pd(0)-catalyzed intermolecular hydroamination of 1,1-diphenyl MCP with 2-pyrrolidone, it is more favorable for the C1 of the metallacyclobutane intermediate to undergo protonation to yield a π-allylpalladium intermediate, from which the final allylamine product is afforded via reductive elimination. For the Pd(0)-catalyzed intramolecular hydroamination of aniline-tethered MCP, the intramolecular nucleophilic attack of the amine moiety to C3/C4 of the corresponding metallacyclobutane intermediate is preferable to generate a cyclic intermediate. Subsequent proton transfer steps could occur to complete the hydroamination reaction. The different pKa values of the N-H bonds of amide/amine are mainly responsible for the mechanistic difference in the Pd(0)-catalyzed hydroamination of MCPs.

Gold- and silver-catalyzed intramolecular annulation and rearrangement of aniline-linked 1,6-enynes containing methylenecyclopropanes

A new synthetic approach for the construction of 1,2-dihydroquinolines having a methylenecyclopropane moiety or a cyclobutene moiety has been developed from gold- and silver-catalyzed annulation of N-tethered 1,6-enynes containing methylenecyclopropanes.

An isocyanide insertion approach to substituted pyrrolo[2,3-b]quinolines under metal-free and azide-free conditions

An isocyanide insertion approach to construct the pyrrolo[2,3-b]quinoline skeleton by an I₂/CHP mediated reaction of aminome-thylenecyclo-propanes (amino-MCPs) is developed.