1.1. General Reactivity of Alkyne-Gold(I) Complexes
For centuries, gold had been considered a precious, purely decorative inert metal. It was not until 1986 that Ito and Hayashi described the first application of gold(I) in homogeneous catalysis.1 More than one decade later, the first examples of gold(I) activation of alkynes were reported by Teles2 and Tanaka,3 revealing the potential of gold(I) in organic synthesis. Now, gold(I) complexes are the most effective catalysts for the electrophilic activation of alkynes under homogeneous conditions, and a broad range of versatile synthetic tools have been developed for the construction of carbon–carbon or carbon–heteroatom bonds.

Gold(I) complexes selectively activate π-bonds of alkynes in complex molecular settings,4−10 which has been attributed to relativistic effects.11−13 In general, no other electrophilic late transition metal shows the breadth of synthetic applications of homogeneous gold(I) catalysts, although in occasions less Lewis acidic Pt(II) or Ag(I) complexes can be used as an alternative,9,10,14,15 particularly in the context of the activation of alkenes.16,17 Highly electrophilic Ga(III)18−22 and In(III)23,24 salts can also be used as catalysts, although often higher catalyst loadings are required.

In general, the nucleophilic Markovnikov attack to η2-[AuL]+-activated alkynes 1 forms trans-alkenyl-gold complexes 2 as intermediates (Scheme 1).4,5a,9,10,12,25−29 This activation mode also occurs in gold-catalyzed cycloisomerizations of 1,n-enynes and in hydroarylation reactions, in which the alkene or the arene act as the nucleophile.



Scheme 1

Anti-Nucleophilic Attack to η2-[AuL]+-Activated Alkynes

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Gold(I)-Catalyzed Activation of Alkynes for the Construction of Molecular Complexity

This review covers the formation of N- and S-containing heterocycles, initiated by gold-catalyzed nucleophilic attack of N- or S-nucleophiles onto alkynes. These types of nucleophiles have been somewhat overlooked as compared to their C- or O-counterparts in other reviews. In this particular work, their intramolecular gold-mediated attack onto alkynes is reviewed in depth. It is structured in such a fashion that the reader will get a clear view of which substrates react in which cyclization mode.

Homogeneous Gold-Catalyzed Cyclization Reactions of Alkynes with N- and S-Nucleophiles

The allylation reaction is a well-established and indispensable tool for the development of chemical complexity and diversity in organic synthesis. Over several decades, this unique transformation has undergone several developments to establish a more simple, selective, and sustainable variant. Moving from stoichiometric amounts of metal additives to sub-stoichiometric amounts, and more recently to catalytic loadings is only one of the chemical revolutions faced by the allylation reaction. In this context, homogeneous gold catalysis has played a pivotal role, resulting in unexpected reaction pathways, concerning unactivated unsaturated hydrocarbons, feasible. Among them, [AuI]- and [AuIII]-assisted allylation reactions deserve particular mention owing to their impact in the synthesis of key organic building blocks and value-added compounds. An unprecedented survey across the development of allylation methodologies based on this coinage metal is documented in the present Minireview.

Gold‐Catalyzed Allylation Reactions

3-Imidoallenylphosphonates: In Situ Formation and β-Alkoxylation.

Herein we demonstrate a gold-catalyzed regio- and stereo-selective cycloisomerization of bis(o-alkynyl benzyl alcohols). By this protocol, the synthesis of dihydroisobenzofuran derivatives can be achieved in good yields. The reaction features a continuous alkyne/alkene-directed 5-exo-dig cyclization and a Prins-type cyclization for the formation of three cycles.

Gold-catalyzed π-directed regioselective cyclization of bis(o-alkynyl benzyl alcohols): rapid access to dihydroisobenzofuran derivatives

Gold superacid-catalyzed preparation of benzo[c]thiophenes

A new synthesis of benzothiophenes is presented in which the key transformation is the gold-catalyzed 5-exo-dig migratory cycloisomerization of a diallyl thioacetal.

Ruben A. J. Seigneur

Papers

Gold superacid-catalyzed preparation of benzo[c]thiophenes

Gold Superacid‐Catalyzed Preparation of Benzo[c]thiophenes.