Construction of Medium-Sized Rings by Gold Catalysis

Abstract

Compounds having cyclic molecular frameworks are highly regarded for their abundance and diverse utilities. In particular, medium-sized carbocycles and heterocycles exist in a broad spectrum of natural products, bioactive therapeutics, and medicinally significant synthetic molecules. Metal-mediated methods have been developed for the preparation of compounds containing a medium-sized ring (MSR) through cyclization of different classes of substrates and acyclic precursors. This review focuses on the methodologies for construction of MSRs via gold catalysis. Given the challenges in enabling the assembly of different ring sizes, we present here accounts on Au-mediated cyclization giving notable 7-membered and medium-sized (8–11-membered ring) structures. Emphasis on the pathway and mode of cyclization and the selection of precursors ranging from structurally biased compounds were outlined. Reactivity patterns and the choice of efficient Au catalysts for controlling reaction performance and selectivity in addition to mechanistic attributes are examined.

Catalytic Gold Chemistry: From Simple Salts to Complexes for Regioselective C−H Bond Functionalization

“…On the other hand, the propensity of gold catalysts to activate π‐bonded systems has created opportunities to discover numerous hitherto unknown organic reactions [6–34] . Gold catalysis in organic reactions has been generally understood and simplified through the concepts of frontier orbitals, relativistic effects, and π‐Lewis acidity [35–37] .…”

Indolizy Carbene Ligand. Evaluation of Electronic Properties and Applications in Asymmetric Gold(I) Catalysis

“…[1] Theh igh p-Lewis acidity of cationic gold(I) complexes allow them to activate various unsaturations such as alkynes,a llenes and also alkenes towards intra-or intermolecular nucleophilic addition. [2] During the process,t he ligands carried by the gold(I) center play am ajor role in terms of stability,a llowing low catalyst loadings,m odulation of activity,a nd selectivity. [3] Furthermore,t he linear coordination of gold(I) complexes that positions the ancillary ligand opposite to the substrate and thus to the outer-sphere attack of the nucleophile renders asymmetric gold catalysis achallenging goal.…”

Access to Indole‐Fused Benzannulated Medium‐Sized Rings through a Gold(I)‐Catalyzed Cascade Cyclization of Azido‐Alkynes

“…When p ‐Ns was used, no significant change in the reactivity compared with the model system was noticed ( 2 p , 66 %); thus, we concluded that spatial interaction of the nitro group is not significant to enhance the cyclization reaction. This reaction is also applicable to oxacycle formation ( 2 q , 39 %) by using an oxygen‐tethered substrate [7a] . Finally, a nucleophilic N ‐Boc protected indole was employed as a cyclization precursor.…”