Cascade Skeletal Rearrangement of Gold Carbene Intermediates: Synthesis of Medium‐Sized Pyrimidine‐Fused Benzolactones

DFT rationalization of the mechanism and selectivity in a gold-catalyzed oxidative cyclization of diynones with alcohols

The mechanism, regioselectivity, and chemoselectivity in a gold-catalyzed oxidative cyclization of diynones with alcohols to give furan-3-carboxylate derivatives were explored by density functional theory (DFT). The obtained results revealed that the first step of the global reaction involves a nucleophilic attack of a pyridine-N-oxide derivative on the catalyst-ligated diynone, forming a vinyl intermediate that can isomerize to an α,α'-dioxo gold carbene upon the cleavage of the N-O bond. In the second step, a nucleophilic addition is also completed via pyridine-N-oxide instead of an alcohol proposed in the experiment. In the following steps, the selective nucleophilic addition of alcohol, 1,2-alkynyl migration, five-membered cyclization, and protodeauration lead to the furan-based products with the regeneration of the gold catalyst. The unique features of regio- and chemoselectivity were investigated in detail by the global reactivity index (GRI) and distortion/interaction analyses. Apart from fully rationalizing the experimental data, the DFT results provide an important contribution to understanding, optimizing, and further developing the related types of organic transformations.

Reagent-Free Intramolecular Hydroamination of Ynone-Tethered Aryl-sulfonamide: Synthesis of Polysubstituted 4-Quinolones

An efficient reagent-free method for the synthesis of polysubstituted 4-quinolone from 2-substituted alkynoyl aryl-sulfonamide was developed. This developed method tolerates various functional groups and gives the corresponding 4-quinolones. We have successfully extended this method to the synthesis of dihydro-4-quinolones from 2-alkenoyl aryl sulfonamide derivatives.

Transition-Metal Catalyzed Synthesis of Pyrimidines: Recent Advances, Mechanism, Scope and Future Perspectives

Pyrimidine is a pharmacologically important moiety that exhibits diverse biological activities. This review reflects the growing significance of transition metal-catalyzed reactions for the synthesis of pyrimidines (with no discussion being made on the transition metal-catalyzed functionalization of pyrimidines). The effect of different catalysts on the selectivity/yields of pyrimidines and catalyst recyclability (wherever applicable) are described, together with attempts to illustrate the role of the catalyst through mechanisms. Although several methods have been researched for synthesizing this privileged scaffold, there has been a considerable push to expand transition metal-catalyzed, sustainable, efficient and selective synthetic strategies leading to pyrimidines. The aim of the authors with this update (2017-2023) is to drive the designing of new transition metal-mediated protocols for pyrimidine synthesis.

Gold-Catalyzed Oxidative Cyclization/C-C Bond Cleavage of Ynones with External Nucleophiles: Synthesis of Linear Functionalized N-Tosylamides

A gold-catalyzed oxidative cyclization/nucleophilic addition/C-C bond cleavage reaction of ynones with various nucleophiles has been developed. This methodology allows for the formation of highly functionalized linear N-Ts amides with broad substrate scope, high efficiency, and general tolerance of functional groups. A wide range of nucleophiles such as alcohols, water, and amines including aryl and alkyl amines are compatible with the current method. The C-C triple bond cleavage of the ynone substrate was observed during the process.

Access to 3-Sulfonamidoquinolines by Gold-Catalyzed Cyclization of 1-(2'-Azidoaryl)propargylsulfonamides through 1,2-N Migration

We describe a gold-catalyzed cyclization of 1-(2'-azidoaryl)propargylsulfonamides for the synthesis of 3-sulfonamidoquinolines, featuring a rare and highly selective 1,2-N migration. The key α-imino gold carbene intermediate is generated through an intramolecular nucleophilic attack of the azide group to the Au-activated triple bonds in a 6-endo-dig manner.

Gold-Catalyzed Oxidative Cyclization Involving Nucleophilic Attack to the Keto Group of α,α'-Dioxo Gold Carbene and 1,2-Alkynyl Migration: Synthesis of Furan-3-carboxylates

A multicomponent strategy for the synthesis of functionalized furan-3-carboxylates based on gold-catalyzed oxidative cyclization of diynones with alcohols or water has been developed. Mechanistic studies revealed that a rare nucleophilic attack to the carbonyl group of the α,α'-dioxo gold carbene instead of the carbene center and 1,2-alkynyl group migration were involved in this transformation. This method offers several advantages such as mild conditions, high regio- and chemoselectivity, and wide functional group compatibility.