Synthesis of 2-Amino-3-hydroxy-3H-indoles via Palladium-Catalyzed One-Pot Reaction of Isonitriles, Oxygen, and N-Tosylhydrazones Derived from 2-Acylanilines

The Carbene Chemistry of N-Sulfonyl Hydrazones: The Past, Present, and Future

N-Sulfonyl hydrazones have been extensively used as operationally safe carbene precursors in modern organic synthesis due to their ready availability, facile functionalization, and environmental benignity. Over the past two decades, there has been tremendous progress in the carbene chemistry of N-sulfonyl hydrazones in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Many carbene transfer reactions of N-sulfonyl hydrazones are unique and cannot be achieved by any alternative methods. The discovery of novel N-sulfonyl hydrazones and the development of highly enantioselective new reactions and skeletal editing reactions represent the notable recent achievements in the carbene chemistry of N-sulfonyl hydrazones. This review describes the overall progress made in the carbene chemistry of N-sulfonyl hydrazones, organized based on reaction types, spotlighting the current state-of-the-art and remaining challenges to be addressed in the future. Special emphasis is devoted to identifying, describing, and comparing the scope and limitations of current methodologies, key mechanistic scenarios, and potential applications in the synthesis of complex molecules.

Blue Light-Promoted Cross-Coupling of α-Diazo Esters with Isocyanides: Synthesis of Ester-Functionalized Ketenimines

A metal-free scalable synthesis of functionalized ketenimines from alkyl α-(aryl/heteroaryl)-α-diazoacetates and alkyl isocyanides induced by blue light irradiation has been developed. The reaction proceeds at room temperature without any photocatalyst and provides ketenimines in moderate to good yields. Density functional theory (DFT) calculations and the experimental study showed that aryl(alkoxycarbonyl)carbenes in both singlet and triplet states can react with isocyanides but only the reaction of the former leads to the smooth formation of ketenimines. The obtained ketenimines were used for the synthesis of functionalized amidines under mild metal-free conditions.

Mn(iii)-Catalyzed cascade cyclization reaction of o-acyl aromatic isocyanides with boronic acids

A Mn(iii)-catalyzed cascade cyclization of o-acyl aromatic isocyanides with boronic acids was examined to give a series of 3-hydroxyindolenines in single-step. This cascade process involved a transmetalation/nucleophilic addition/intramolecular cyclization sequence.

Specific Synthesis of 3H-Indole Derivatives via Rh(III)-Catalyzed Cascade Annulation between N-Phenylbenzimidamides and Pyridotriazoles

An efficient synthetic method to construct 3H-indole derivatives has been successfully developed involving rhodium-catalyzed highly selective C-H bond activation of N-phenylbenzimidamides and subsequent couplings with pyridotriazoles. This cascade approach features excellent chemoselectivity and unique of products containing quaternary carbon center with the pyridyl moiety.

Rhodium-Catalyzed Formal C-O Insertion in Carbene/Alkyne Metathesis Reactions: Synthesis of 3-Substituted 3 H-Indol-3-ols

An efficient and novel rhodium-catalyzed formal C-O insertion reaction of alkyne-tethered diazo compounds for the synthesis of 3 H-indol-3-ols is described. A type of donor/donor rhodium carbene generated in situ via a carbene/alkyne metathesis (CAM) process is the key intermediate and terminates in a unique transformation different from donor/acceptor carbenoids. In addition, ¹⁸O-labeling experiments indicate that intramolecular oxygen-atom transfer from the amide group to the carbon-carbon triple bond occurs during this transformation.