Recent Progress in N-Heterocyclic Carbene Gold-Catalyzed Reactions of Alkynes Involving Oxidation/Amination/Cycloaddition

Abstract

Recent rapid development in homogeneous gold catalysis affords an alternative and particularly thriving strategy for the generation of gold carbenes through gold-catalyzed oxidation/amination/cycloaddition of alkynes, while it avoids the employment of hazardous and potentially explosive diazo compounds as starting materials for carbene generation. In addition to facile and secure operation, gold carbenes generated in this strategy display good chemoselectivity distinct from other metal carbenes produced from the related diazo approach. N-heterocyclic carbene (NHC) gold is a special metal complex that can be used as ancillary ligands, which provides enhanced stability and can also act as an efficient chiral directing group. In this review, we will present an overview of these recent advances in alkyne oxidation/amination/cycloaddition by highlighting their specificity and applicability, aiming to facilitate progress in this very exciting area of research.

Prodrug Activation by Gold Artificial Metalloenzyme‐Catalyzed Synthesis of Phenanthridinium Derivatives via Hydroamination

“…By contrast, Au‐c [Au III complex] only gave good yields and TONs for substrates 1 a , b,f . Likely, Au‐b is more stable and more reactive in phosphate buffer solution (pH 7.4) than Au‐c because the N‐heterocyclic carbene ligand in Au‐b has a stronger metal‐carbon σ bond, which provides enhanced stability and higher activities [23] . By contrast, Au‐c complexes possess high redox potential, leading to facile reduction of Au III complexes to metallic Au 0 species in the presence of electron‐rich reagents [24] .…”

Alcohol Dehydrogenases and N‐Heterocyclic Carbene Gold(I) Catalysts: Design of a Chemoenzymatic Cascade towards Optically Active β,β‐Disubstituted Allylic Alcohols

“…With that purpose and due to the large π‐acidic character of Au complexes, the selection of alkynes as benchmark substrates flourish as a wise choice based on the diverse chemical possibilities of this pair Au‐alkyne [37–41] . Interestingly, a broad number of organic transformations can be successfully accomplished such as cyclization, hydration, redox isomerization or rearrangements such as the Rupe or Meyer–Schuster ones (Scheme 1), [42–46] gold N‐heterocyclic carbenes (NHCs) playing a relevant role in the catalysis of these type of chemical processes [47–49] …”

Gold-Catalyzed Intermolecular Alkyne Hydrofunctionalizations—Mechanistic Insights

“…Reactions of this kind can also produce more complex products if the gold-vinyl intermediates that form in the course of the reaction (see below) are intercepted or undergo further evolution before the actual hydrofunctionalization product is liberated [8][9][10]. This interesting possibility is however available mostly in the case of more complex substrates, in which these evolution reactions generally take place by involving other functional group present in the same intermediate (i.e., in an intramolecular fashion); alternatively, such a possibility is provided also by the use of unprotonated nucleophiles with oxidizing character [9,10]. Since this review article is specifically focused on the factors affecting the mechanism and rates of intermolecular alkyne hydrofuncionalizations, further reactions of the type outlined above will not be specifically covered herein.…”

“…Furthermore, we do not aim at providing a comprehensive coverage of the gold-based catalytic systems proposed to date for these reactions, but rather to focus on the contributions that shed light on the mechanistic features of these reactions. For a more general coverage of hydrofunctionalization reactions, catalyzed by gold but also by other metals, the interested reader is referred to several other dedicated reviews that have recently appeared in the literature [5][6][7][8][9][10][11].…”