Gold-Catalyzed Heck Reaction.

Herein, we report a gold-catalyzed Heck reaction facilitated by the ligand-enabled Au(I)/Au(III) redox catalysis. The elementary organometallic steps such as migratory insertion and ß-hydride elimination have been realized in the catalytic fashion for the first time in gold chemistry. The present methodology not only overcomes the limitations of previously known transition metal-catalyzed Heck reactions such as the requirement of specialized substrates and formation of a mixture of regioisomeric products as a result of the undesirable chain-walking process but also offers complementary regioselectivity as compared to other transition metal catalysis.

Enantioselective Au(I)/Au(III) Redox Catalysis Enabled by Chiral (P,N)-Ligands.

Presented herein is the first report of enantioselective Au(I)/Au(III) redox catalysis, enabled by a newly designed hemilabile chiral (P,N)-ligand (ChetPhos). The potential of this concept has been demonstrated by the development of enantioselective 1,2-oxyarylation and 1,2-aminoarylation of alkenes which provided direct access to the medicinally relevant 3-oxy- and 3-aminochromans (up to 88% yield and 99% ee). DFT studies were carried out to unravel the enantiodetermining step, which revealed that the stronger trans influence of phosphorus allows selective positioning of the substrate in the C2-symmetric chiral environment present around nitrogen, imparting a high level of enantioselectivity.

The interplay of carbophilic activation and Au(I)/Au(III) catalysis: an emerging technique for 1,2-difunctionalization of C-C multiple bonds.

Gold complexes have emerged as the catalysts of choice for various functionalization reactions of C-C multiple bonds due to their inherent carbophilic nature. In a parallel space, efforts to realize less accessible cross-coupling reactivity have led to the development of various strategies that facilitate the arduous Au(I)/Au(III) redox cycle. The interplay of the two important reactivity modes encountered in gold catalysis, namely carbophilic activation and Au(I)/Au(III) catalysis, has allowed the development of a novel mechanistic paradigm that sponsors 1,2-difunctionalization reactions of various C-C multiple bonds. Interestingly, the reactivity as well as selectivity obtained through this interplay could be complementary to that obtained by the use of various other transition metals that mainly involved the classical oxidative addition/migratory insertion pathways. The present review shall comprehensively cover all the 1,2-difunctionalization reactions of C-C multiple bonds that have been realized by the interplay of the two important reactivity modes and categorized on the basis of the method that has been employed to foster the Au(I)/Au(III) redox cycle.

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.

Ligand-enabled gold-catalyzed 1,2-heteroarylation of alkenes.

By adopting the interplay between ligand-enabled Au(i)/Au(iii) catalysis and the unique π-activation mode of gold complexes, a highly coveted 1,2-heteroarylation of alkenes has been accomplished. The present ligand-enabled approach not only circumvents the requirement for strong sacrificial oxidants or photocatalysts but also operates under mild reaction conditions by utilizing simple and non-prefunctionalized aryl coupling partners.

Gold-Catalyzed 1,2-Diarylation of Alkenes.

Herein, we disclose the gold-catalyzed 1,2-diarylation of alkenes through the interplay of ligand-enabled AuI /AuIII catalysis with the idiosyncratic π-activation mode of gold complexes. Unlike the classical migratory-insertion-based approach to 1,2-diarylation, the present approach not only circumvents the formation of direct Ar-Ar' coupling and Heck-type side products but more intriguingly demonstrates reactivity and selectivity complementary to those of previously known metal catalysis (Pd, Ni, or Cu). Detailed investigations to underpin the mechanistic scenario revealed oxidative addition of aryl iodides to an AuI complex to be the rate-limiting step owing to the non-innocent nature of the aryl alkene.

Gold-Catalyzed Cycloisomerization of Pyridine-Bridged 1,8-Diynes: An Expedient Access to Luminescent Cycl[3.2.2]azines.

Gold-catalyzed diyne cycloisomerizations involving carbene/alkyne metathesis have been the focal point of attention for the past few years as it offers great potential to build complex polycyclic architectures. However, the design of novel cycloisomerizations has been mostly limited to 1,5/1,6- diynes and has remained very challenging to apply for higher 1,n-diynes. Herein, we disclose an unprecedented cycloisomerization of pyridine-bridged 1,8-diynes involving carbene/alkyne metathesis to access luminescent cycl[3.2.2]azines.

Gold(i)-catalyzed cross-coupling reactions of aryldiazonium salts with organostannanes.

Gold(i)-catalyzed cross-coupling reactions of aryldiazonium salts with organostannanes are described. This redox neutral strategy offers an efficient approach to diverse biaryls, vinyl arenes and arylacetylenes. Monitoring the reaction with NMR and ESI-MS provided strong evidence for the in situ formation of Ph3PAuIR (R = aryl, vinyl and alkynyl) species which is crucial for the activation of aryldiazonium salts.