Skeletal Editing of Isatins for Heterocycle Molecular Diversity

Isatins have been widely used in the preparation of a variety of heterocyclic compounds, where the skeletal editing of isatins has shown significant advantages for the construction of diverse heterocycles. This review highlights the progress made in the last decade (2013-2023) in the skeletal editing of the isatin scaffold. A series of ring expansion reactions for the construction of quinoline skeleton, quinolone skeleton, polycyclic quinazoline skeleton, medium-sized ring skeleton, as well as a series of ring opening reactions for the generation of 2-(azoly)aniline skeleton by the cleavage of C-C bond and C-N bond are highlighted. It is hoped that this review will provide some understanding of the chemical transformations of isatins and contribute to the further realization of its molecular diversity.

NBS-Promoted Synthesis of Thiocyanated Aminomaleimides and Site-Selective Intramolecular Cyclization Access to 1,4-Benzothiazepines via S-CN Bond Cleavage

A transition metal-free concise and efficient protocol for the synthesis of thiocyanated aminomaleimides and benzo[e][1,4]thiazepine derivatives has been developed. The method involves an initial α-C-H thiocyanation of aminomaleimides with KSCN and TEMPO-mediated tandem S-CN bond cleavage/intramolecular cyclization substitution processes, which enables the formation of seven-membered S/N-heterocycles. This synthetic strategy provides a reliable method for the synthesis of biologically interesting benzo[e][1,4]thiazepine derivatives by using KSCN as sulfur sources as well as expands the application of enaminones thiocyanation reactions in heterocycles synthesis.

Three-Component Reaction for the Synthesis of Spiro-Heterocycles from Isatins, Substituted Ureas, and Cyclic Ketones

We reported an efficient three-component reaction to access new spiro heterocycles through the annulation reactions of isatins, substituted ureas, and cyclic ketones under normal laboratory conditions, which is another example of isatins being used to build spiro compounds by the ring-opening and recyclization processes. The wide range of substrates, simple operation, normal experimental conditions, and high yields make the approach of high practical value.

Palladium-Catalyzed Chemoselective Oxygenation of C(sp2)-H and C(sp3)-H Bonds in Isatins

The palladium-catalyzed chemoselective C(sp²)-H and C(sp³)-H bond oxygenation of substituted isatin derivatives is reported. This mild protocol exhibits the C5 C(sp²)-H oxygenation of isatins through electrophilic intermolecular C-H palladation in concentrated solutions using PhI(OAc)₂ or Selectfluor as an oxidant, whereas it exhibits-N-CH₃ C(sp³)-H oxygenation in dilute solutions via carbonyl-assisted intramolecular palladation in the presence of K₂S₂O₈. This oxygenation reaction provides a direct and unified approach for synthesizing diverse oxygenated isatins with sensitive functionalities, including biorelevant compounds.

Switchable C2/C3 positional selectivity of thioisatins in a three-component domino reaction: combined computational and experimental studies

The nucleophile-induced domino reaction is a featured reactivity mode of thioisatin, but the C2/C3 positional selectivity towards a nucleophile has not been understood in-depth. In this work, a domino reaction of thioisatin with bromoacetophenone and tryptamine hydrochloride to produce a benzothiophene-fused eight-membered N-heterocycle was described, showing that the Brønsted acid-base form of the amine partner was crucial for the selectivity, because using tryptamine instead of tryptamine hydrochloride gave a different product. Control experiments and density functional calculations revealed that the domino reaction using tryptamine or tryptamine hydrochloride was triggered by a condensation reaction at the C2 or C3 position of thioisatin, respectively. A delicate balance between local electrophilicity and polarization effect may be responsible for the observed selectivity.

Visible-Light-Promoted Phosphorylation/Cyclization of 1-Acryloyl-2-cyanoindoles in Green Solvent

A visible-light-induced persulfate-promoted cascade phosphorylation/cyclization reaction to access various phosphorylated pyrrolo[1,2-a]indolediones under mild conditions was developed. Notably, the transformation was carried out with diethyl carbonate/H₂O as a green medium at room temperature. More impressively, traditional metal catalysts and photocatalysts could be effectively avoided. The reactions are simple to operate, easy to scale up, and have good functional group tolerance.

Sustainable access to benzothiophene derivatives bearing a trifluoromethyl group via a three-component domino reaction in water

A catalyst-free three-component domino reaction was developed for the synthesis of benzothiophene fused pyrrolidones bearing a CF3 group for the first time. The notable advantages of this strategy over the existing methods include the use of water as a solvent at room temperature, transition metal-free conditions, a broad substrate scope, and easy scale-up synthesis. More importantly, the benzothiophene derivatives have been found to show potent anticancer activities using the Cell Counting Kit-8 (CCK-8) assay.

Copper(i)-catalyzed synthesis of natural alkaloid tryptanthrin and its derivatives

A facile one-pot synthesis of natural alkaloid tryptanthrin and its derivatives from isatins catalyzed by CuI in the presence of KHCO3 has been developed.

Cooperative Palladium-Catalyzed and P(NEt2)3-Mediated (4+1) Annulation of Isatins with 2-Hydroxymethylallylcarbonates

P(NR2)3-promoted transformations of isatins with electron-withdrawing alkenes have received consistently attention over the last decades. However, no example involving chemical transformations of nonactivated or weakly activated alkenes is discovered in...

Isothiourea-catalysed enantioselective annulation of 2-aminobenzothiophenes with α,β-unsaturated anhydrides

An isothiourea-catalysed asymmetric Michael/lactamization cascade reaction of 2-aminobenzothiophenes and α,β-unsaturated anhydrides for the enantioselective synthesis of benzothienopiperidones with high stereoselectivities was developed.