Oxidant-Free Rhodium(I)-Catalyzed Difunctionalization of Acrylamide: An Efficient Approach To Synthesize Oxindoles

N-heterocyclic nitrenium-catalyzed photosynthesis of 3,3-disubstituted oxindoles from α-chloroanilides

The radical cascade reaction of α-halogenated anilides represents an efficient approach for synthesizing 3,3-oxindoles. However, most methods have focused on α-bromoanilides, with limited utilization of the more stable and readily available α-chloroanilides. In addition, the transition-metal-free preparation of 3,3-oxindoles has been far less explored. Here, we present a photoreductive N-heterocyclic nitrenium-catalyzed radical cyclization reaction of α-chloroanilides for the construction of 3,3-oxindoles under transition-metal-free conditions.

Visible-light-promoted difluoroamidated oxindole synthesis via electron donor-acceptor complexes

A method involving a metal-free visible-light-promoted synthesis was developed for the construction of difluoroalkylated oxindoles with N-phenylacrylamides and bromodifluoroacetamides as starting materials in the presence of N,N,N',N'-tetramethylethylenediamine (TMEDA). Twenty-four examples of the photochemical reaction were successfully performed, with good yields (44-99%) and excellent substrate adaptability. Mechanistic studies showed that the visible-light-promoted reaction involved a radical addition to N-phenylacrylamide, intramolecular cyclization, dehydrogenation, and rearomatization. The difluoroacetamide radical was produced as a result of electron transfer to bromodifluoroacetamides from the electron donor TMEDA in their electron-donor-acceptor (EDA) complexes under visible light irradiation. This protocol is a promising photochemical method due to its advantages of mild conditions, simple operation, wide substrate scope and high yields. And the obtained products may have great potential in the field of medicine.

Visible-Light-Mediated Generation of Acyl Radicals from Triazine Esters

Acyl radicals are significant synthetic active species in organic synthesis. However, their generation via green and compatible methods remains challenging. Herein, we report an unprecedented visible-light-mediated approach for generating aryl acyl radicals from readily available triazine esters. This protocol with mild and redox-neutral conditions affords a diverse array of oxindoles attached to alcohol groups in a single operation. The recycling of leaving groups and a range of visible-light-mediated reactions using triazine ester as an acyl radical precursor demonstrate the synthetic potential of this methodology.

Single-carbon atom transfer to α,β-unsaturated amides from N-heterocyclic carbenes

Single-carbon atom transfer reactions are lacking in organic synthesis, partly because of the absence of atomic carbon sources under standard solution-phase conditions. We report here that N-heterocyclic carbenes can serve as atomic carbon donors through the loss of a 1,2-diimine moiety. This strategy is applicable to single-carbon atom transfer to α,β-unsaturated amides, which can be converted into homologated γ-lactams through the formation of four single bonds to one carbon center in one operation.

Synthesis of Benzimidazo[2,1-a]isoquinoline and Indolo[2,1-a]isoquinoline Derivatives via Copper-Catalyzed Silylation/Methylation of 2-Arylindoles and 2-Arylbenzimidazoles

A one-pot method for the synthesis of silylsubstituted/methylsubstituted indolo[2,1-a]isoquinolin-6(5H)-ones and benzimidazo[2,1-a]isoquinoline-6(5H)-ones via copper(II)-initiated silylation/methylation of 2-arylindoles and 2-arylbenzimidazoles was developed. In this procedure, the C-Si bond and C-C bond were constructed by radical addition and cyclization. A series of 2-arylindole and 2-arylbenzimidazole derivatives were facilely transformed to indolo[2,1-a]isoquinolines and benzimidazo[2,1-a]isoquinolines in 39-83% yields.

Synthesis of 3-substituted 2-oxindoles from secondary α-bromo-propionanilides via palladium-catalyzed intramolecular cyclization

In contrast to aromatic halides, coupling reactions involving oxidative addition of alkyl halides, especially secondary or tertiary halides, to transition metals tend to be more challenging. Herein a palladium-catalyzed intramolecular cyclization of α-bromo-propionanilides has been developed, delivering a series of 3-substituted 2-oxindoles in high yields. The method features easy to prepare starting materials, broad substrate scope and excellent functional group tolerance. A detailed mechanistic investigation has been performed.

Visible-light-induced radical cascade reaction to prepare oxindoles via alkyl radical addition to N-arylacryl amides

A photochemical approach towards oxindoles with C3 quaternary centers by the radical cascade reaction of α,β-unsaturated N-arylacryl amides with alkyl bromides or iodides upon visible light irradiation under mild reaction conditions was developed.

Discovery of an Oxidative System for Radical Generation from Csp3-H Bonds: A Synthesis of Functionalized Oxindoles

A facile and versatile method for generating radicals from Csp³-H bonds under metal-free and organic-peroxide-free conditions was developed. By combining safe persulfate and low-toxic quaternary ammonium salt, a wide variety of Csp³-H compounds including ethers, (hetero)aromatic/aliphatic ketones, alkylbenzenes, alkylheterocycles, cycloalkanes, and haloalkanes were selectively activated to generate the corresponding C-centered radicals, which could be further captured by N-arylacrylamides to deliver the valuable functionalized oxindoles. Good functional group tolerance was demonstrated. The useful polycarbonyl compound and esters were also modified with the strategy. Moreover, the combination can also be applied to the practical coupling between simple haloalkanes and N-hydroxyphthalimide (NHPI).

Palladium-catalyzed cascade reactions of alkene-tethered carbamoyl chlorides with N-tosyl hydrazones: synthesis of alkene-functionalized oxindoles

An efficient approach for the construction of alkene-functionalized oxindoles was developed via palladium-catalyzed cascade reactions of alkene-tethered carbamoyl chlorides with N-tosyl hydrazones.

Substrate-switched dual functionalization of alkenes: catalyst-free synthetic route for β-hydroxy and β-keto thioethers

A substrate-controlled dual functionalization of alkenes under catalyst-free and solvent-free conditions to provide β-hydroxy thioethers and β-keto thioethers is described.

Ppm Cu Catalyst Enables tert-Alkylation Followed by C-H Cyclization To Synthesize Substituted Oxindoles

In this paper, we established highly efficient Cu-catalyzed tandem tert-alkylation C-H cyclization of α-bromocarbonyls and methacrylamides to produce substituted oxindoles. The maximum turnover number was up to 48 000 with reasonable yield. Although the catalyst loadings were very low, the reaction was not involving radical chain reaction. The resulting oxindoles were able to transform into aza-multicyclic compound via a reduction.

Transition-Metal-Free Synthesis of N-Hydroxy Oxindoles by an Aza-Nazarov-Type Reaction Involving Azaoxyallyl Cations

A novel transition-metal-free method to construct N-hydroxy oxindoles by an aza-Nazarov-type reaction involving azaoxyallyl cation intermediates is described. A variety of functional groups were tolerated under the weak basic reaction conditions and at room temperature. A one-pot process was also developed to make the reaction even more practical. This method provides alternative access to oxindoles and their biologically active derivatives.

Aerobic thiyl radical addition/cyclization of N-methacryloyl benzamides for the synthesis of isoquinoline-1,3(2H,4H)-dione derivatives

A highly effective dioxygen-triggered oxidative thiyl radical addition/cyclization of N-methacryloylbenzamides was explored. This method provides convenient access to a variety of useful sulfide-containing 4,4-disubstituted isoquinoline-1,3-diones.

Synthesis of oxindole from acetanilide via Ir(iii)-catalyzed C–H carbenoid functionalization

The Ir(iii)-catalyzed intermolecular C–H annulations of acetanilide with diazotized Meldrum's acid furnished the oxindole derivative. Brief synthetic applications of the synthesized oxindole were also demonstrated.

Aroyl chlorides as novel acyl radical precursors via visible-light photoredox catalysis

Abundant and inexpensive aroyl chlorides have been employed for the first time as novel acyl radical precursors in visible-light photocatalysis.

Palladium-catalyzed oxidative arylacetoxylation of alkenes: synthesis of indole and indoline derivatives

A method for the oxidative arylacetoxylation of alkenes has been developed to synthesize indole and indoline derivatives from readily accessible substrates.

Cascade alkylarylation of substituted N-allylbenzamides for the construction of dihydroisoquinolin-1(2H)-ones and isoquinoline-1,3(2H,4H)-diones

An oxidative reaction for the synthesis of 4-alkyl-substituted dihydroisoquinolin-1(2H)-ones with N-allylbenzamide derivatives as starting materials has been developed. The radical alkylarylation reaction proceeds through a sequence of alkylation and intramolecular cyclization. The substituent on the C–C double bond was found to play a key role for the progress of the reaction to give the expected products with good chemical yields. Additionally, N-methacryloylbenzamides were also suitable substrates for the current reaction and provided the alkyl-substituted isoquinoline-1,3(2H,4H)-diones in good yield.

Various difunctionalizations of acrylamide: an efficient approach to synthesize oxindoles

In this review, we summarize the advancement and applications in the difunctionalization of acrylamide to synthesize oxindoles based on the mechanism.

Radical trideuteromethylation with deuterated dimethyl sulfoxide in the synthesis of heterocycles and labelled building blocks

A selective introduction of trideuteromethyl groups for the synthesis of labelled compounds under radical reaction conditions is demonstrated.

Di-tert-butyl peroxide (DTBP) promoted dehydrogenative coupling: an expedient and metal-free synthesis of oxindoles via intramolecular C(sp2)–H and C(sp3)–H bond activation

An efficient di-tert-butyl peroxide (DTBP) promoted synthesis of oxindole has been developed. This methodology involves C(sp³)–H and C(sp²)–H bond activation under metal-free conditions.