Cu-Enabled [3 + 2] Annulation of In Situ Formed Nitrile Ylides with Aryldiazonium Salts: Access to 5-Cyano-1,2,4-Triazoles

Rhodium-Catalyzed [3+2]-Cycloaddition of in-situ Generated Nitrile Ylides with Nitrosoarenes

Herein we report the rhodium-catalyzed one-pot three-component reaction of diazo compounds, nitriles, and nitrosoarenes to construct 2,5-dihydro-1,2,4-oxadiazole derivatives. Mechanistic studies indicate that the transformation may proceed through the formation of nitrile ylides intermediates, which then undergo [3+2]-cycloaddition with nitrosoarenes. The strategy exhibits several synthetic advantages, including operational simplicity, good functional group tolerance, and scalability.

Ag-Catalyzed Annulation of o-Alkynylaryl Aldehydes, Amines, and Diazo Compounds: Construction of Trifluoromethyl- and Cyano-Functionalized Benzo[d]azepines

A Ag-catalyzed three-component annulation protocol, which uses o-alkynylaryl aldehydes, amines, and trifluorodiazoethane or diazoacetonitrile, to forge a new class of trifluoromethyl- and cyano-functionalized benzo[d]azepine is presented in this Letter. The key transformations involved in this reaction are the transient formation of the isoquinolinium intermediate and the subsequent ring-expansive addition of in situ-formed silver trifluorodiazoethylide to this intermediate. The practicality of this protocol is illustrated by realizing access to a wide range of densely functionalized benzo[d]azepines.

Additive-free synthesis of fused tricyclic cyanoisoxazolidines using in situ formed cyanonitrones

Herein, we disclose the first report on the generation of cyanonitrone in situ from diazoacetonitrile and nitrosoarene, and its subsequent [3+2] cycloaddition with oxabicyclic alkenes to access fused tricyclic cyanoisoxazolidines. Further, this methodology could be extended to access fused tricyclic trifluoromethylated and phosphonylated isoxazolidines. Surprisingly, the reductive ring-opening of cyanoisoxazolidines was followed by a spontaneous lactonization to produce fused tricyclic amino lactones. Moreover, the N-O bond of the obtained tricyclic trifluoromethylated isoxazolidines could be cleaved to obtain 1,3-amino alcohols.

Azoarene activation for Schmidt-type reaction and mechanistic insights

The Schmidt rearrangement, a reaction that enables C-C or C-H σ bond cleavage and nitrogen insertion across an aldehyde or ketone substrate, is one of the most important and widely used synthetic tools for the installation of amides and nitriles. However, such a reaction frequently requires volatile, potentially explosive, and highly toxic azide reagents as the nitrogen donor, thus limiting its application to some extent. Here, we show a Schmidt-type reaction where aryldiazonium salts act as the nitrogen precursor and in-situ-generated cyclopenta-1,4-dien-1-yl acetates serve as pronucleophiles from gold-catalyzed Nazarov cyclization of 1,3-enyne acetates. Noteworthy is that cycloketone-derived 1,3-enyne acetates enabled ring-expansion relay to access a series of 2-pyridone-containing fused heterocycles, in which nonsymmetric cycloketone-derived counterparts demonstrated high regioselectivity. Aside from investigating the scope of this Schmidt-type reaction, mechanistic details of this transformation are provided by performing systematic theoretical calculations.

Visible-Light-Induced Imide Synthesis through a Nitrile Ylide Formation/Trapping Cascade

A visible-light-promoted three component reaction of diazo compounds, nitriles, and carboxylic acids is reported. The reaction utilizes acceptor-only diazo compounds as carbene precursors and nitriles as carbene-trapping reagents to form the key nitrile ylides. Under the optimal reaction conditions, a wide range of imide products were obtained in good to excellent yields. The gram-scale synthesis and synthetic application of the imide products to form isoquinoline-1,3(2H,4H)-dione derivatives further proved the value of this method.

Visible Light-Promoted Diazoacetates and Nitriles Generating Nitrilium Ions Trapped by Benzotriazoles and Carboxylic Acids

A visible light-promoted generation of nitrilium ions from diazoacetates and nitriles has been developed. The reaction utilized visible light transformation of diazoacetates to the free carbene that could be trapped by nitriles to generate nitrilium ions, followed by nucleophilic attack on the benzotriazoles and carboxylic acids. This protocol provides an efficient and practical approach to N-imidoylbenzotriazoles and diacylglycine esters in good to excellent yields.

Synthesis of multi-substituted 1,2,4-triazoles utilising the ambiphilic reactivity of hydrazones

The synthesis of N-alkyl-1H-1,2,4-triazoles from N,N-dialkylhydrazones and nitriles via formal [3+2] cycloaddition including the C-chlorination/nucleophilic addition/cyclisation/dealkylation sequence was developed. This sequential reaction utilising the in situ generation of hydrazonoyl chloride based on the ambiphilic reactivity of hydrazones afforded a variety of multi-substituted N-alkyl-triazoles in high yields. The synthetic utility of multi-substituted triazoles was also demonstrated by further transformations.