Rhodium-Catalyzed Amination and Annulation of Arenes with Anthranils: C-H Activation Assisted by Weakly Coordinating Amides

Advances in transition metal-catalyzed C-H amination strategies using anthranils

Modern times have witnessed an uprise in the synthesis and derivatization of nitrogen-containing fused heterocycles. Amination reactions involving nitrene chemistry have always been the most convenient choice for the incorporation of a nitrogen atom in a molecule. The utilization of an open nitrene species harnesses harsh conditions. Hence, transition metal-catalyzed C-H amination reactions using aminating agents have been an attractive choice. Electrophilic aminating agents for C-H amination reactions are well exploited due to their desirable reaction conditions. Out of all, anthranils have paved the way forward due to their utility in simultaneously forming two new functional groups (amine and carbonyl). Amination using anthranils follows a metal-nitrenoid pathway. Often, the amination has been followed by a Lewis acid or transition metal-mediated intramolecular cyclization to directly produce fused heterocycles. This review broadly demonstrates the utilization of anthranils as an aminating agent for transition metal-catalyzed C-H amination reactions. The focus has been given to the scope, limitations, and mechanistic understanding of using such an electrophilic aminating agent, anthranil, with transition metals.

BF3 ⋅Et2 O-Catalyzed Selective C-4 Alkylation of Isoquinolin-1(2H)-ones Employing p-Quinone Methides

The direct C-4 alkylation of isoquinolin-1(2H)-one moiety is a challenging transformation in organic synthesis. Here we present a practical and efficient synthesis of C-4 alkylated isoquinolin-1(2H)-ones through conjugate addition of isoquinolin-1(2H)-ones to p-quinone methides for the first time. The process is facilitated by Lewis acid catalysis and this operationally straightforward, mild, metal-free and one-pot transformation provides a wide range of C-4 alkylated isoquinolin-1(2H)-ones at ambient temperature in good to excellent yields.

Regio- and chemoselective hydroamination of unactivated alkenes with anthranils via NiH-catalysis

A NiH-catalyzed polarity-reversed hydroamination of β,γ-, γ,δ- and δ,ε-unsaturated alkenes with electrophilic anthranils was developed. This reaction proceeds in a highly regio- and chemoselective manner to afford γ, δ and ε-arylamines bearing a carbonyl or alcohol functionality with 100% atom efficiency. Preliminary mechanistic studies indicate that the chemoselectivity is controlled by the base and the alcohol product is derived from the base-catalyzed hydrosilylation of the CO bond.

TBAI-Catalysed Formal [4+4]-Cycloaddition: Easy Access to Oxa-Bridged Eight-Membered Heterocycles

TBAI-catalysed [4+4]-cyclization reaction of anthranils with hydrazones to deliver oxa-bridged eight-membered heterocycles in accepted yields was developed. Preliminary mechanistic studies indicated that the reaction involved the in situ generation of vinyldiazenes from readily available hydrazones followed by an aza-Michael addition of the anthranil substrates onto the vinyldiazenes and subsequent annulation. This transformation involved the formation of two new C-N bonds and C-O bond in one pot, overcoming the synthetic limitations of anthranils in organic chemistry. This strategy benefits from high efficiency and atomic economy with mild reaction conditions.

Rapid access to polycyclic thiopyrylium compounds from unfunctionalized aromatics by thia-APEX reaction

We developed a sulfur-embedding annulative π-extension (thia-APEX) reaction that could construct a sulfur-embedding cationic hexagonal aromatic ring, thiopyrylium, onto unfunctionalized aromatics in one step. The key of thia-APEX is the use of S-imidated ortho-arenoyl arenethiols, and a variety of π-extended thiopyryliums can easily be synthesized. The synthesized thiopyryliums showed diverse absorption and emission properties over the visible light to NIR region, depending on minor structural differences.

Directing Group Strategies in Rhodium-Catalyzed C-H Amination

Construction of a carbon-nitrogen bond is one of the most prevalent operations in nature and organic synthesis. The resulting amino compounds are privileged structural fragments in natural products, pharmaceutical drugs,...

Cp*Co(III)-catalyzed C-H amination/annulation cascade of sulfoxonium ylides with anthranils for the synthesis of indoloindolones

Cp*Co(iii)-catalyzed [4+1] annulation of sulfoxonium ylides with anthranils has been developed for the synthesis of indole-indolone scaffolds. The dual functionality of anthranils was exploited, wherein the nitrogen has been used for C-H amination and the aldehyde group was utilized in the subsequent intramolecular aldol condensation to furnish the corresponding annulated products.

Highly enantioselective access to chiral chromanes and thiochromanes via Cu-catalyzed hydroamination with anthranils

Highly efficient and atom-economic asymmetric access to 4-arylamino chromanes and thiochromanes bearing a benzylic alcohol functionality were developed by Cu(i)/(R,R)-Ph-BPE-catalyzed enantioselective hydroamination with anthranils.

tert-Butyl Bromide-Promoted Intramolecular Cyclization of 2-Arylamino Phenyl Ketones and Its Combination with Cu-Catalyzed C-N Coupling: Synthesis of Acridines at Room Temperature

Herein, a facile intramolecular cyclization of 2-arylamino phenyl ketones is established to supersede the traditional high-temperature, strongly acidic conditions and achieve 9-substituted acridines, by virtue of the combination of 2,2,2-trifluoroethanol and tert-butyl bromide. This protocol can be merged well with the preceding Cu-catalyzed intermolecular Chan-Evans-Lam cross-coupling reactions, therefore enabling pot-economic modular synthesis of 9-substituted acridines from readily available 2-amino phenyl ketones and aryl boronic acids at room temperature.

Anthranils: versatile building blocks in the construction of C–N bonds and N-heterocycles

This review article provides an overview of the recent progress in the transformations of anthranils, which have emerged as versatile building blocks in the assembly of various C–N bonds and medicinally active heterocyclic systems.

Rhodium-Catalyzed Annulative Coupling of Isothiazoles with Alkynes through N-S Bond Cleavage

A Rh(III)-catalyzed annulative coupling of 3,5-diarylisothiazoles and alkynes is reported. The N-S bond in the isothiazole ring acts as an internal oxidant to regenerate the Rh(III) species in combination with an external Cu(II) oxidant, and the corresponding 1:2 coupling products are obtained. The remarkable difference in the reaction outcome between isothiazoles and the relevant isoxazoles has been investigated by DFT calculations, revealing that the relative stability of the enolate intermediates dictates the product selectivity.

Practical Synthesis of Benzimidazo[1,2-a]quinolines via Rh(III)-Catalyzed C-H Activation Cascade Reaction from Imidamides and Anthranils

We report a novel and practical one-pot Rh(III)-catalyzed strategy to construct benzimidazo[1,2-a]quinolines from readily available imidamides and anthranils. The cascade reaction proceeds via a C-H amination-cyclization-cyclization process in ionic liquid without any additives and possesses simple operation, moderate-to-high yield, and broad substrate scope features, which will provide the reference for the construction of biologically active fused benzimidazoles.

tert-Butyl peroxide (TBHP)/KI-mediated dual C(sp2)-H bond amination of arylamines with α-diazo carbonyls toward 1,2,4-benzotriazines

A new radical-induced dehydrogenative heterocyclization of arylamines with α-diazo carbonyls has been established under metal-free oxidative conditions, enabling two-fold C(sp2)-H bond amination to access a wide range of functionalized 1,2,4-triazine derivatives with generally good yields by combining KI/tert-butyl peroxide (TBHP). The present protocol features wide substrate scope, commercial accessibility, and mild reaction conditions. Mechanistic details of this radical process are rendered by conducting systematic theoretical calculations.

Rh(III)-Catalyzed Sequential C-H Amination/Annulation Cascade Reactions: Synthesis of Multisubstituted Benzimidazoles

An efficient and practical method to construct benzimidazoles via Rh(III)-catalyzed sequential C-H amination and annulation cascade reaction has been developed. The cascade reaction displays high step, atom, and redox economy, is compatible with the air, and has good functional group tolerance and high efficiency. The titled products can be easily further converted into imidazo[4,5-c]acridines, which were observed unique fluorescent properties.

Simple and scalable electrochemical synthesis of 2,1-benzisoxazoles and quinoline N-oxides

At carbon electrodes in a scalable electrosynthetic way to two classes of useful heterocycles.

Site-selective C(sp3)–H amination of thioamide with anthranils under Cp*CoIII catalysis

Synthetically versatile anthranils as a bifunctional amino source have been employed for the first time to enable direct amination on unactivated C(sp³)–H bonds of thioamides under Cp*Co^III catalysis.

Cobalt-Catalyzed Electrophilic Aminations with Anthranils: An Expedient Route to Condensed Quinolines

The reaction of various organozinc pivalates with anthranils provides anilines derivatives, which cyclize under acidic conditions providing condensed quinolines. Using alkenylzinc pivalates, electron-rich arylzinc pivalates or heterocyclic zinc pivalates produces directly the condensed quinolines of which several structures belong to new heterocyclic scaffolds. These N-heterocycles are of particular interest for organic light emitting diodes with their high photoluminescence quantum yields and long exciton lifetimes as well as for hole-transporting materials in methylammonium lead iodide perovskites solar cells due to an optimal band alignment for holes and a large bandgap.