Gold-Catalyzed Formal [4 + 2] Cycloaddition of 5-(Ethynylamino)pent-2-yn-1-yl Esters to 1,2,3,5-Tetrahydrobenzo[g]quinolines

Photoredox-Catalyzed Preparation of Sulfones Using Bis-Piperidine Sulfur Dioxide - An Underutilized Reagent for SO2 Transfer

Sulfonyl groups are widely observed in biologically relevant molecules and consequently, SO2 capture is an increasingly attractive method to prepare these sulfonyl-containing compounds given the range of SO2 -surrogates now available as alternatives to using the neat gas. This, along with the advent of photoredox catalysis, has enabled mild radical capture of SO2 to emerge as an effective route to sulfonyl compounds. Here we report a photoredox-catalyzed cross-electrophile sulfonylation of aryl and alkyl bromides making use of a previously under-used amine-SO2 surrogate; bis(piperidine) sulfur dioxide (PIPSO). A broad selection of alkyl and aryl bromides were photocatalytically converted to their corresponding sulfinates and then trapped with various electrophiles in a one-pot multistep procedure to prepare sulfones and sulfonamides.

Recent progress in the homogeneous gold-catalysed cycloisomerisation reactions

This review focuses on recent advancements in the efficacy of gold catalysts for the cycloisomerisation of ynamides, diynes, and 1,n-enynes to build complex molecules, with critical insight into their mechanism and reaction scope.

Rhodium(i)-catalysed cycloisomerisation/6π electrocyclisation of 5-(ethynylamino)pent-2-yn-1-yl esters to 2,3-dihydrobenzo[f]indoles

A rare instance in rhodium catalysis of an in situ formed rhodacycle that undergoes a formal 1,8-acyloxy migration-initiated reductive elimination.

(Z)-γ-Alkylidenebutenolide Synthesis through Au(I)-Catalyzed 1,3-Acyloxy Migration and the Carbonyl-Ene Reaction

A bimetallic protocol has been developed to construct (Z)-γ-alkylidenebutenolide compounds from readily available propargyl α-ketoesters. It involves a gold-catalyzed 1,3-acyloxy migration of propargyl α-ketoesters and a carbonyl-ene cyclization of in situ generated allenyl esters. DFT calculations suggest that the copper salt might play dual roles as both chloride abstractor facilitating the generation of highly active gold catalyst and Lewis acid promoting the stepwise intramolecular carbonyl-ene reaction.

Gold-catalyzed homo- and cross-annulation of alkynyl carboxylic acids: a facile access to substituted 4-hydroxy 2H-pyrones and total synthesis of pseudopyronine A

A Au(i)-catalyzed homo- and cross-annulation reaction of alkynyl carboxylic acids offering 3,6-disubstituted 4-hydroxy 2H-pyrones has been demonstrated. The reaction tolerates various substituted alkynyl carboxylic acids and moderate to good yields of α-pyrone scaffolds have been observed. Later, a gram-scale reaction of the acid and the total synthesis of the natural product pseudopyronine A have been carried out successfully.

Copper-Catalyzed Asymmetric Reaction of Alkenyl Diynes with Styrenes by Formal [3 + 2] Cycloaddition via Cu-Containing All-Carbon 1,3-Dipoles: Access to Chiral Pyrrole-Fused Bridged [2.2.1] Skeletons

The generation of metal-containing 1,3-dipoles from metal carbenes represents a significant advance in 1,3-dipolar cycloaddition reactions. However, these transformations have so far been limited to reactions based on diazo compounds or triazoles as precursors. Herein, we disclose a copper-catalyzed enantioselective reaction of alkenyl N-propargyl ynamides with styrene derivatives by formal [3 + 2] cycloaddition via Cu-containing all-carbon 1,3-dipoles, which constitutes a novel way for the generation of metal-containing 1,3-dipoles via metal carbenes. This protocol allows the practical and atom-economical synthesis of valuable chiral pyrrole-fused bridged [2.2.1] skeletons in moderate to good yields (up to 90% yield) with excellent diastereoselectivities (dr > 50/1) and generally excellent enantioselectivities (up to >99% ee).

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 Homogeneous (Cyclo)Isomerization Reactions

Gold is currently one of the most used metals in organometallic catalysis. The ability of gold to activate unsaturated groups in different modes, together with its tolerance to a wide range of functional groups and reaction conditions, turns gold-based complexes into efficient and highly sought after catalysts. Natural products and relevant compounds with biological and pharmaceutical activity are often characterized by complex molecular structures. (Cyclo)isomerization reactions are often a useful strategy for the generation of this molecular complexity from synthetically accessible reactants. In this review, we collect the most recent contributions in which gold(I)- and/or gold(III)-catalysts mediate intramolecular (cyclo)isomerization transformations of unsaturated species, which commonly feature allene or alkyne motifs, and organize them depending on the substrate and the reaction type.

The mechanism of the gold-catalyzed intramolecular [3 + 2]-cycloaddition of 1,6-diynes: a DFT study

The mechanism and selectivity of the gold-catalyzed intramolecular cycloaddition of 1,6-diynes were unveiled by DFT calculations.

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.

Gold-Catalyzed Formal Dehydro-Diels-Alder Reactions of Ene-Ynamide Derivatives Bearing Terminal Alkyne Chains: Scope and Mechanistic Studies

A new protocol for the synthesis of a variety of N-containing aromatic heterocycles by a formal gold-catalyzed dehydro-Diels-Alder reaction of ynamide derivatives has been developed. Deuterium-labeling experiments and kinetic studies support the involvement of a dual gold catalysis mechanism in which a gold acetylide moiety adds onto an aurated keteneiminium.

Gold(I)-Catalyzed Formal Intramolecular Dehydro-Diels-Alder Reaction of Ynamide-ynes: Synthesis of Functionalized Benzo[ b]carbazoles

A gold-catalyzed cycloisomerization of ynamide-ynes via a formal dehydro-Diels-Alder reaction has been developed, providing an attractive route to diversely substituted benzo[ b]carbazoles. The reaction likely proceeds via regioselective attack of the pendant alkyne moiety to a keteniminium ion intermediate followed by benzannulation. The method offers several advantages such as high efficiency, mild reaction conditions, and wide functional group tolerance and serves as a highly useful complement to the thermal DDA reactions of ynamide-ynes.

Gold-catalyzed cascade cyclization of N-propargyl ynamides: rapid access to functionalized indeno[1,2-c]pyrroles

A new gold-catalyzed cascade cyclization of N-propargyl ynamides involving a presumable vinyl cation intermediate has been developed, allowing the efficient and practical synthesis of various functionalized indeno[1,2-c]pyrroles.

Gold-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes

A gold(i)-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes has been developed, providing facile access to functionalized polycyclic and spiropolycyclic products based on the use of gold(i) catalysts.

Brønsted Acid-Catalysed Allylic Amination of 1-(2-Aminoaryl)prop-2-en-1-ols to 1,2-Dihydroquinolines

A highly efficient synthetic method to prepare 1,2-dihydroquinolines that relies on trifluoromethanesulfonic acid (TfOH)-catalysed allylic amination of 1-(2-aminoaryl)prop-2-en-1-ols is described. Achieved at a catalyst loading of 0.01 mol-% under mild conditions at room temperature, the reaction was found to be robust, with a wide range of substitution patterns tolerated. The corresponding N-heterocyclic adducts were obtained in good to excellent yields of 45–93 %.