Cu-Catalyzed Denitrogenative Ring-Opening of 3-Aminoindazoles for the Synthesis of Aromatic Nitrile-Containing (Hetero)Arenes

Copper-catalyzed cross coupling reaction of sulfonyl hydrazides with 3-aminoindazoles

A novel Cu-catalyzed radical-radical cross coupling reaction of 3-aminoindazoles with sulfonyl hydrazides has been disclosed, enabling the production of diverse 1,3-substituted aminoindazoles in good yields. This methodology is distinguished by readily available starting materials, wide substrate scope and operational simplicity. In addition, a gram-scale reaction has been well demonstrated.

Recent advances in 3-aminoindazoles as versatile synthons for the synthesis of nitrogen heterocycles

Nitrogen-based heterocycles are an important class of structural scaffolds distributed in biologically active natural products, medicinal chemistry, and agrochemicals. Hence, there is increasing interest in the development of novel synthetic strategies for the construction of these privileged structural motifs. Recently, 3-aminoindazoles have emerged as versatile synthons participating in a variety of condensation annulation, denitrogenative transannulation and rearrangement ring expansion reactions, which provide efficient synthetic routes for the formation of nitrogen heterocycles. This review systematically highlights for the first time the most recent advances in 3-aminoindazoles to provide a deep understanding of using 3-aminoindazoles as versatile synthons in organic transformations for synthetic and medicinal chemists.

Cu-catalyzed oxidative denitrogenation of 3-aminoindazoles for the synthesis of isoquinolinones

A Cu-catalyzed oxidative dual arylation of active alkenes via the cleavage of two C-N bonds of 3-aminoindazoles is presented for constructing isoquinolinones. Importantly, 3-aminoindazoles are used as efficient arylating agents through a radical process. This method has a good substrate scope and functional group compatibility.

Stereoselective Synthesis of cis-2-Ene-1,4-diones via Aerobic Oxidation of Substituted Furans Catalyzed by ABNO/HNO3

We report a highly efficient and selective catalytic system, ABNO (9-azabicyclo-[3.3.1]nonane N-oxyl)/HNO₃, for the aerobic oxidation of substituted furans to cis-2-ene-1,4-diones under mild reaction conditions using oxygen as the oxidant. The catalyst system is amenable to various substituted (mon-, di-, and tri-) furans and tolerates diverse functional groups, including cyano, nitro, naphthyl, ketone, ester, heterocycle, and even formyl groups. Based on the control and ¹⁸O-labeling experiments, the possible mechanism of the oxidation is proposed.

Visible-Light-Catalyzed in Situ Denitrogenative Sulfonylation of Sulfonylhydrazones

A photocatalyzed in situ denitrogenative sulfonylation of N-arylsulfonyl hydrazones has been developed. This transformation provides a low-carbon strategy to assemble arylalkyl sulfones in a stepwise denitrogenation/sulfonylation manner.

Cu-Catalyzed Oxidative Dual Arylation of Active Alkenes: Preparation of Cyanoarylated Oxindoles through Denitrogenation of 3-Aminoindazoles

A novel and mild Cu-catalyzed oxidative dual arylation of carbon-carbon double bonds in acrylamides with 3-aminoindazoles is proposed for the synthesis of cyanoarylated oxindoles. Notably, 3-aminoindazoles are employed as efficient arylating agents via the cleavage of two C-N bonds. This oxidative dual arylation of active alkenes involves a radical process and undergoes a sequence of 3-aminoindazole oxidation, two-C-N-bond cleavage, cyanoaryl radical addition, and intramolecular cyclization.

A direct synthesis method towards spirocyclic indazole derivatives via Rh(iii)-catalyzed C–H activation and spiroannulation

A rhodium(iii)-catalyzed [4 + 1] spiroannulation of N-aryl phthalazine-diones (pyridazine-diones) with diazo compounds to construct spirocyclic indazole derivatives with diverse structures is described.

Rapid access to 3-aminoindazoles from nitriles with hydrazines: a strategy to overcome the basicity barrier imparted by hydrazines

A practical and efficient base mediated synthesis of free 3-aminoindazoles has been developed from the reaction of nitriles with hydrazines, which successfully overcomes the difficulty of using aromatic hydrazines as substrates and allows for the synthesis of a wide range of N-aryl substituted free 3-aminoindazoles in moderate to excellent yields under mild conditions in one-pot. This finding provides a rapid and useful strategy for the synthesis of various functionalized 3-aminoindazole derivatives.

Studies on the preparation of aminobipyridines and bipyridine sultams via an intramolecular free radical pathway

A variety of aminated bipyridines and bipyridine sultams are prepared by intramolecular radical [1,5]-ipso and [1,6]-ortho substitutions, using a sulfonamide as a linker to connect the pyridyl radical to the pyridine under attack. For the cases studied, different regiochemistries are observed depending on the initial position of the sulfonamide linker.

Results show that intramolecular radical [1,5]-ipso and [1,6]-ortho substitutions offer a method for the preparation of aminobipyridines or bipyridine sultams.

Cu-catalyzed C–N bond cleavage of 3-aminoindazoles for the C–H arylation of enamines

We have presented a novel Cu-catalyzed stereoselective C–H arylation of enamines by using 3-aminoindazoles arylating agents via oxidative cleavage of two C–N bonds.

Cu-Catalyzed Aromatic Metamorphosis of 3-Aminoindazoles

We present a novel Cu-catalyzed aromatic metamorphosis of 3-aminoindazoles via oxidative cleavage of two C-N bonds of 3-aminoindazoles. This unprecedented reactivity of 3-aminoindazoles allows one to forge diverse nitrile-containing triphenylenes in decent yields via generation of the cyano group in situ. The current study reveals that 3-aminoindazoles could be harnessed as radical precursors via oxidative denitrogenation, the reaction mechanism of which was supported by density functional theory calculations.

Facile synthesis of 1,2-thiobenzonitriles via Cu-catalyzed denitrogenative radical coupling reaction

The first example of denitrogenative radical coupling with 3-aminoindazoles is presented. A diverse array of 1,2-thiobenzonitriles were obtained in good yields with wide substrate scope via oxidative C–N cleavage of 3-aminoindazoles.

Oxidant-controlled divergent transformations of 3-aminoindazoles for the synthesis of pyrimido[1,2-b]-indazoles and aromatic nitrile-derived dithioacetals

An oxidant-controlled divergent reactivity of 3-aminoindazoles is presented, which enables the [3 + 3] annulation and C–H arylation of ketene dithioacetals in disparate pathways to assemble pyrimido[1,2-b]-indazoles and aromatic nitrile-derived dithioacetals.