[1, 2]-Migration Reactions Catalyzed by Gold Complexes and their Applications in Total Synthesis

Gold-catalyzed endo-selective cyclization of alkynylcyclobutanecarboxamides: synthesis of cyclobutane-fused dihydropyridones

Cyclobutane-fused dihydropyridones can be efficiently synthesized by a completely endo-selective gold-catalyzed cyclization of alkynylcyclobutanes bearing an appended amide, which proceeds under mild conditions. The observed selectivity, which is reversed from that previously observed for the cyclization of related alcohols and acids, is supported by DFT calculations.

Efficient Synthesis of Orphaned Cyclopropanes Using Sulfones as Carbene Equivalents

Small molecules containing 1,1-dimethylcyclopropanes are prevalent throughout nature but are difficult to synthesize using state-of-the-art metal-catalyzed carbene transfer methods without competing 1,2-hydride shifts. Herein, we introduce a mechanistically distinct platform to transfer 1,1-dialkylcarbene units to olefins using carbometalation reactions of dialkyl sulfonyl anions. In the presence of NaNH₂ or n-BuLi in ethereal solvents, dialkyl sulfones react with styrenes and arylbutadienes between 23 and 70 °C to produce the corresponding 1,1-dialkylcyclopropanes. We report 40 examples of this reactivity including 16 different styrenes (up to 89% isolated yield), 9 arylbutadienes (51-88% yield), and 13 different sulfones (46-80% yield). In addition, we report an example of a sequential cyclopropanation reaction using this method. Preliminary mechanistic studies suggest a stepwise anionic process that is initiated by the direct addition of sulfonyl anions to a carbon-carbon double bond.

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.

Exo-Cyclization: Intermolecular Methylene Transfer Sequence in Au-Catalyzed Reactions of O-Homopropargylic Oximes

The Au-catalyzed reactions of O-homopropaylic oximes afforded the 3-alkenylated isoxazolines in good to high yields. The mechanistic studies suggest that the reaction proceeds through an exo-cyclization followed by intermolecular methylene group transfer. In addition, oligomeric species of the starting material were observed in the reaction mixture by mass spectra, supporting our proposed mechanism, which proceeds through a repeated intermolecular C-C bond forming process.

Gold-Catalyzed Synthesis of Small Rings

Three- and four-membered rings, widespread motifs in nature and medicinal chemistry, have fascinated chemists ever since their discovery. However, due to energetic considerations, small rings are often difficult to assemble. In this regard, homogeneous gold catalysis has emerged as a powerful tool to construct these highly strained carbocycles. This review aims to provide a comprehensive summary of all the major advances and discoveries made in the gold-catalyzed synthesis of cyclopropanes, cyclopropenes, cyclobutanes, cyclobutenes, and their corresponding heterocyclic or heterosubstituted analogs.

Gold Catalysed 1,4-Enyne Acetate Strategy for the Synthesis of 1H-Indenes and Partially Hydrogenated Methanonaphtho[1,2-c]furan-1,3(4H)-diones

A synthetic method to prepare 1H-indenes and partially hydrogenated methanonaphtho[1,2-c]furan-1,3(4H)-diones from gold(i)-catalysed 1,4-enyne acetate cycloisomerisation and oxidation or Diels–Alder reaction with maleic anhydride is described. The proposed mechanism involves Rautenstrauch rearrangement of the 1,4-enyne motif to give an insitu formed 1,3-cyclopentadiene intermediate. This is followed by 6-endo-dig cyclisation of the cyclic adduct and oxidation to give the aromatic carbocycle or Diels–Alder reaction with maleic anhydride to afford the bridged furan product.

Gold-Catalyzed Silyl-Migrative Cyclization of Homopropargylic Alcohols Enabled by Bifunctional Biphenyl-2-ylphosphine and DFT Studies

The development of novel ligands specifically tailored for homogeneous gold catalysis permits the development of new gold catalysis. In this work, we report that a remotely functionalized biphenyl-2-ylphosphine ligand enables gold-catalyzed cyclization of homopropargylic alcohols accompanied by an unusual silyl migration, which provides efficient access to 3-silyl-4,5-dihydrofurans. DFT studies of the mechanism of this novel transformation suggest the synergy between the steric bulk of the ligand and its properly positioned remote tertiary amino group in facilitating a concerted silyl migration and cyclative C-O bond formation step.

Gold-catalyzed cyclization of 1-(2′-azidoaryl) propynols: synthesis of polysubstituted 4-quinolones

α-Imino gold carbene intermediate is produced from 1-(2′-azidoaryl) propynols, which triggers a 1,2-carbon migration and is converted to 2,3-disubstituted 4-quinolones. The reaction works under mild conditions and tolerates various functional groups.

Gold-Catalysed Oxidative Cycloisomerisation of 1,6-Diyne Acetates to 1-Naphthyl Ketones

A synthetic method to prepare 1-naphthyl ketones from gold(i)-catalysed oxidative cycloisomerisation of 1,6-diyne acetates is described. The proposed mechanism involves cyclopropenation–cycloreversion of the 1,6-diyne motif initiated by a 1,2-acyloxy migration. This is followed by nucleophilic attack of the ensuing gold carbenoid species by a molecule of water and autoxidation to give the aromatic product.