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

A.L.-P. thanks CSIC for a contract under the JAE-doctor
program. Financial support by PLE2009 project from MCIINN
and Consolider-Ingenio 2010 (proyecto MULTICAT) are also
acknowledged.

Gold-catalyzed carbon-heteroatom bond-forming reactions.

Recent advances in catalytic sequential reactions involving hydroelement addition to carbon-carbon multiple bonds.

Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.

Silver-catalysed reactions of alkynes: recent advances

The enantioselective synthesis of spirocycles has long been pursued by organic chemists. Despite their unique 3D properties and presence in several natural products, the difficulty in their enantioselective synthesis makes them underrepresented in pharmaceutical libraries. Since the first pioneering reports of the enantioselective construction of spirosilanes by Tamao et al., significant effort has been devoted towards the development of new promising asymmetric methodologies. Remarkably, with the advent of organocatalysis, particularly over six years, the reported methodologies for the synthesis of spirocycles have increased exponentially. The aim of this review is to summarize the latest trends and developments in the enantioselective synthesis of spirocompounds during these last six years.

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New development in the enantioselective synthesis of spiro compounds

A novel, facile approach to frondosin B and 5-epi-liphagal via a new [4 + 3]-cycloaddition.

A strategy concerning the synthesis of 2-substituted benzo[b]furan compounds from o-alkynyl phenols via a gold-catalyzed alkyne hydroxylation is described, which allows the rapid synthesis of various 2-substituted benzo[b]furan derivatives in excellent yields under mild conditions. The o-alkynyl phenol precursors were readily prepared with a Sonogashira coupling reaction.

Gold‐catalyzed Alkyne Hydroxylation: Synthesis of 2‐Substituted Benzo[b]furan Compounds

Ivorenolide B, an Immunosuppressive 17-Membered Macrolide from Khaya ivorensis: Structural Determination and Total Synthesis

A new triflate- or ZnCl2-promoted cycloaddition reaction of different substituted heterocyclic alcohols with conjugated dienes is shown (15 examples).

Jijun Xue

Papers

A novel, facile approach to frondosin B and 5-epi-liphagal via a new [4 + 3]-cycloaddition.

Gold‐catalyzed Alkyne Hydroxylation: Synthesis of 2‐Substituted Benzo[b]furan Compounds

Ivorenolide B, an Immunosuppressive 17-Membered Macrolide from Khaya ivorensis: Structural Determination and Total Synthesis

Regio- and Stereoselective [4+3] Cycloaddition Towards Fused 5,7,6-Tricyclic Skeletons

Synthesis of (±)-γ-Rubromycin via a New Hypoiodite-Catalytic Oxidative Cycloetherification