Gold-Catalyzed CH Annulation of Anthranils with Alkynes: A Facile, Flexible, and Atom-Economical Synthesis of Unprotected 7-Acylindoles

Gold-Catalyzed Formal [3 + 2] Cycloaddition of Ynamides with 4,5-Dihydro-1,2,4-oxadiazoles: Synthesis of Functionalized 4-Aminoimidazoles

A gold-catalyzed formal [3 + 2] cycloaddition of ynamides with 4,5-dihydro-1,2,4-oxadiazoles has been developed. The reaction provides a concise and regioselective access to highly functionalized 4-aminoimidazoles likely via the formation of an α-imino gold carbene intermediate followed by cyclization. 4,5-Dihydro-1,2,4-oxadiazole was found to act as an efficient N-iminonitrene equivalent in these reactions.

Synthesis and structures of gold and copper carbene intermediates in catalytic amination of alkynes

Metal carbenes are often proposed as reactive intermediates in the late transition metal-catalysed transformations of alkynes. Owing to their high reactivity, however, isolation and structural characterization of metal carbene intermediates in these transformations has remained unknown. Herein, we report the isolation of two acyclic gold and copper carbene intermediates in either Au(I)- or Cu(I)-catalysed cyclization of N-alkynyl formamidines through five-exo-dig cyclization. X-ray diffraction, ¹³C NMR spectra data and computational analyses provide evidence for the formation of a gold carbene intermediate with a carbocation-like electronic character. Using the intrinsic bond orbital (IBO) approach, we also evaluate the π-stabilizing effects of organic substituents at the carbene carbon atom in the gold carbene intermediate. Another rare six-membered copper carbene complex is also obtained through 6-endo-dig cyclization. These metal carbenes have proven reactive toward oxidation. The metal-promoted cyclization of N-alkynyl formamidine provides a facile approach to synthesize metal carbene species.

Metal carbenes are typically highly reactive and unstable species, proposed as intermediates in numerous catalytic processes. Here the authors report the isolation and characterization of gold and copper carbene intermediates involved in catalytic cyclization reactions.

Brønsted Acid Catalyzed Oxygenative Bimolecular Friedel-Crafts-type Coupling of Ynamides

A non-metal approach for accessing α-oxo carbene surrogates for a C-C bond-forming bimolecular coupling between ynamides and nucleophilic arenes was developed. This acid-catalyzed coupling features mild temperature, which is critical for the required temporal chemoselectivity among nucleophiles. The scope of nucleophiles includes indoles, pyrroles, anilines, phenols and silyl enolethers. Furthermore, a direct test of S_N 2' mechanism has been provided by employing chiral N,N'-dioxides which also enlightens the nature of the intermediates in related metal-catalyzed processes.

α-Imino Gold Carbenes from 1,2,4-Oxadiazoles: Atom-Economical Access to Fully Substituted 4-Aminoimidazoles

A novel and atom-economical synthesis of fully substituted 4-aminoimidazoles via gold-catalyzed selective [3 + 2] annulation of 1,2,4-oxadiazoles with ynamides is reported. This protocol represents a new strategy to access α-imino gold carbenes, which corresponds to an unprecedented intermolecular transfer of N-acylimino nitrenes to ynamides. Moreover, the reaction proceeds with 100% atom economy, exhibits good functional group tolerance, and can be conducted in gram scale.

Gold-Catalyzed Regiodivergent [2 + 2 + 2]-Cycloadditions of Allenes with Triazines

Gold-catalyzed regiodivergent cycloadditions of functionalized allenes with 1,3,5-triazines, providing diverse N-heterocycles in moderate to excellent yields under mild reaction conditions, are reported. Importantly, different types of allenes exhibit distinct selectivity and reactivity for the reactions. Mechanistic investigations reveal that all of the cycloadditions proceed through a stepwise [2 + 2 + 2]-cycloaddition process.

α,β-Functionalization of saturated ketones with anthranils via Cu-catalyzed sequential dehydrogenation/aza-Michael addition/annulation cascade reactions in one-pot

An efficient method to access functionalized quinolines from the readily available saturated ketones and anthranils have been explored.

Synthesis of 1H-indole-3-sulfonates via palladium-catalyzed tandem reactions of 2-alkynyl arylazides with sulfonic acids

An efficient method for the synthesis of 1H-indole-3-sulfonates via palladium-catalyzed tandem reactions of 2-alkynyl arylazides with sulfonic acids has been developed.

Lewis acid catalyzed diastereoselective [3+4]-annulation of donor–acceptor cyclopropanes with anthranils: synthesis of tetrahydro-1-benzazepine derivatives

The [3+4]-annulation between donor–acceptor cyclopropanes and anthranils has been developed for the diastereoselective synthesis of tetrahydro-1-benzazepine derivatives.

A formal intermolecular [4 + 2] cycloaddition reaction of 1,3-disubstituted indoles and alkylquinones

A formal [4 + 2] cycloaddition reaction of 1,3-disubstituted indoles and alkylquinones was realized to afford polycyclic indolines in good yields.

Pd-PEPPSI-IPentCl: a new highly efficient ligand-free and recyclable catalyst system for the synthesis of 2-substituted indoles via domino copper-free Sonogashira coupling/cyclization

One pot synthesis of 2-substituted indolesviaSonogashira coupling (without a copper catalyst) followed by intermolecular cyclization using Pd-PEPPSI-IPent^Cl.

Rh(iii)-Catalyzed direct C-7 amination of indolines with anthranils

An effective and fascinating method has been developed for direct C-7 amination of indolines under Rh(iii) catalysis with anthranils.

Gold-catalyzed intermolecular cyclocarboamination of ynamides with 1,3,5-triazinanes: en route to tetrahydropyrimidines

1,3,5-Triazinanes serve as surrogates for 1,4-dipoles in gold-catalyzed formal 4+2 cycloadditions.

Tf2NH-catalyzed formal [3 + 2] cycloaddition of oxadiazolones with ynamides: a simple access to aminoimidazoles

We herein develop a formal [3 + 2] approach to access aminoimidazoles through the Tf₂NH-catalyzed cycloaddition of oxadiazolones with ynamides, in which oxadiazolones are first employed as the three-atom building units.

Synthesis of 2-Aza-1,3-butadienes through Gold-Catalyzed Intermolecular Ynamide Amination/C-H Functionalization

A novel gold-catalyzed tandem intermolecular ynamide amination/C-H functionalization has been developed. A variety of highly functionalized 2-aza-1,3-butadienes can be obtained readily by utilizing this strategy. In addition, α-imino gold carbene intermediates are proposed in this amination reaction and with support by DFT (density functional theory) calculations.

Dioxazoles, a new mild nitrene transfer reagent in gold catalysis: highly efficient synthesis of functionalized oxazoles

A gold-catalyzed regioselective [3+2] cycloaddition of ynamides with 1,4,2-dioxazoles was developed and offers a novel approach to obtain highly functionalized oxazoles under mild reaction conditions. 1,4,2-Dioxazole was found to act as an efficient N-acyl nitrene equivalent to trigger a facile generation of α-imino gold-carbene intermediate through the elimination of a ketone.