Gold(I)-Catalyzed Intramolecular Cyclization/Intermolecular Cycloaddition Cascade: Fast Track to Polycarbocycles and Mechanistic Insights

Abstract

Herein we report a gold-catalyzed cascade protocol for the assembly of polycarbocyclic frameworks in high yields under mild reaction conditions. Mechanistic studies indicate that the unique β-aryl gold-carbene species, generated via gold-promoted 6-endo-dig diazo-yne cyclization, is the key intermediate in this reaction, followed by a [4 + 2]-cycloaddition with external alkenes. In comparison to the well-documented metal carbene cycloadditions, this is the first example of the carbene intermediate to serve as a 4-C synthon in a cycloaddition reaction. A variety of elusive π-conjugated polycyclic hydrocarbons (CPHs) with multiple substituents are readily accessible from the initially generated products by a mild oxidation procedure.

Keteniminium Induced Dienone‐Phenol Rearrangement and Intramolecular 6‐endo‐dig Cyclization Cascade of Yne‐Dienone

“…Interestingly, the catalyst combination of PPh 3 AuCl (5.0 mol-%) or JohnPhosAuCl (5.0 mol-%) with AgNTf 2 (10 mol-%) in CHCl 3 (0.05 M) at 60 °C for 12 h delivered 3a in 20 % and 78 % yield, respectively with better Z/E selectivity (entries 5 and 6). To examine the effect of counter anion, various silver salts, for example: AgSbF 6 , AgBF 4 , and AgOTf in combination with JohnPhosAuCl (5.0 mol-%) were tested (entries [7][8][9]; in all such cases, 3a was formed only in a trace amount. The reaction didn't proceed in the absence of either AgNTf 2 or JohnPhosAuCl (entries 10 and 11).…”

“…[1 -4] In one hand, the π-acidic and carbophilic Au(I)-catalysts are being successfully employed for various cascade cyclization and cycloisomerization of unsaturated systems for the construction of polyfused carbo-and heterocycles. [5][6][7][8][9] While in other hand, the Au-catalyzed hydrofunctionalization and difunctionalization of unsaturated alkynes provides access to highly functionalized olefin derivatives. [10 -12] In this context, Au-catalyzed hydrophenoxylation of phenol with alkyne leading directly to aryl-vinyl ethers is well-studied (Scheme 1,a), [13 -18] by contrast, the identical process with ynamide is so far less explored.…”