Silver-Catalyzed Radical Tandem Cyclization for the Synthesis of 3,4-Disubstituted Dihydroquinolin-2(1H)-ones

Chemoselective Synthesis of 3-Bromomethyloxindoles via Visible-Light-Induced Radical Cascade Bromocyclization of Alkenes

A novel visible-light-induced radical cascade bromocyclization of N-arylacrylamides has been accomplished. This reaction overcomes the overbromination at the benzene rings suffered in traditional electrophilic reactions, thus enabling the first highly chemoselective synthesis of valuable 3-bromomethyloxindoles. The combination of pyridine and anhydrous medium is identified as the key factor for the high chemoselectivity in the current photoreaction system, which might work by suppressing the in situ generation of low-concentration Br2 from N-bromosuccinimide. Moreover, the mild reaction conditions ensure the generation of a wide range of the new desired products with excellent functional group tolerance.

Deconstructive annulation mediated one-pot synthesis of xanthene derivatives

Direct conversion of naphthoxazines to diverse xanthene derivatives was achieved under one-pot operation through deconstructive annulation methodology. Sequential oxidative C(sp3)-O/C(sp3)-N cleavage followed by intramolecular/intermolecular annulation reaction was carried out under aerobic reaction conditions. Mechanistic analyses performed on the substrate revealed that the C(sp3)-O bond cleavage supersedes the C(sp3)-N bond scission. The in situ generated Betti base intermediate through the C(sp3)-O cleavage was successfully isolated. Based on a molecular docking investigation, the intermolecular annulated products demonstrated good α-glucosidase inhibitory properties.

Metal-Catalyst-Free One-Pot Aqueous Synthesis of trans-1,2-Diols from Electron-Deficient α,β-Unsaturated Amides via Epoxidation Using Oxone as a Dual Role Reagent

In organic synthesis, incorporating two functional groups into the carbon-carbon double bond of α,β-unsaturated amides is challenging due to the electron-deficient nature of the olefin moiety. Although a few examples of dihydroxylation of α,β-unsaturated amides have been demonstrated, producing cis-1,2-diols using either highly toxic OsO4 or other specialized metal reagents in organic solvents, they are limited to several specific amides. We describe herein a general and one-pot direct synthesis of trans-1,2-diols from electron-deficient α,β-unsaturated amides through dihydroxylation using oxone as a dual-role reagent in water. This reaction does not require any metal catalyst and produces non-hazardous and nontoxic K2 SO4 as the sole byproduct. Moreover, epoxidation products could also be selectively formed by adjusting the reaction conditions. By the strategy, the intermediates of Mcl-1 inhibitor and antiallergic bioactive molecule can be synthesized in one pot. The gram-scale synthesis of trans-1,2-diol which is isolated and purified by recrystallization further shows the potential applications of this new reaction in organic synthesis.

Visible-Light-Induced Intramolecular Tandem Cyclization of Unactivated Indoloalkynes for the Synthesis of Sulfonylated and Selenylated Indolo[1,2-a]quinolines

A convenient and efficient visible-light-induced method has been developed for the construction of sulfonated and selenylated indolo[1,2-a]quinolines through sulfonyl or selenyl radical-initiated tandem cyclization of unactivated alkynes with sodium sulfinates or diaryl diselenides under mild conditions. This protocol, which simply utilizes visible light as the safe and eco-friendly energy source and an inexpensive and nontoxic organic dye as a photocatalyst without the aid of an external photocatalyst, provides various sulfonyl- and selenyl-containing indolo[1,2-a]quinolines in moderate to good yields.

Visible-Light-Induced Metal- and Photocatalyst-Free Radical Cascade Cyclization of Cinnamamides for Synthesis of Functionalized Dihydroquinolinones

Visible-light-promoted metal- and photocatalyst-free radical cascade cyclization of cinnamamides with α-oxocarboxylic acids is described for sustainable synthesis of diverse pharmaceutically important dihydroquinolinone scaffolds in one pot under mild conditions. The decarboxylative cascade cyclization proceeded efficiently at room temperature without the need for expensive photocatalysts such as Ir or Ru complexes, which indicates the practicability and environmentally benign nature of this protocol. Preliminary mechanistic studies reveal that the blue LED irradiation efficiently cleaves the I-O bond of the hypervalent iodine reagent PhI(O₂CCOAr)₂ formed through ligand exchange between iodobenzene diacetate and arylglyoxylic acid to initiate the cascade reaction. The synthetic value of this operationally simple and energy-efficient method is further demonstrated by late-stage functionalization of drug molecules in excellent yields.

Direct phosphorylation of benzylic C-H bonds under transition metal-free conditions forming sp3C-P bonds

Direct phosphorylation of benzylic C-H bonds was achieved in a biphasic system under transition metal-free conditions. A selective radical/radical sp3C-H/P(O)-H cross coupling was proposed, and various substituted toluenes were applicable. The transformation provided a promising method for constructing sp3C-P bonds.

Recent progress in aryltrifluoromethylation reactions of carbon-carbon multiple bonds

Due to the increasing relevance of fluorine-containing organic molecules in drug design, the synthesis of organofluorine compounds has gained high significance in synthetic organic chemistry. Trifluoromethylative difunctionalizations of carbon-carbon multiple bonds, with the simultaneous incorporation of a CF 3 group and another functional element, have considerable potential. Because of the high importance of carbon-carbon bond-forming reactions in organic synthesis, carbotrifluoromethylations and, in particular, aryltrifluoromethylations or heteroaryltrifluoromethylations are considered to be increasing fields of synthetic organic chemistry. The aim of the current review is to summarize recent developments of aryltrifluoromethylation or heteroaryltrifluoromethylation reactions.

Tandem trifluoromethylthiolation and cyclization of N-aryl-3-butenamides with AgSCF3: divergent access to CF3S-substituted 3,4-dihydroquinolin-2-ones and azaspiro[4,5]dienones

A AgSCF3-mediated tandem trifluoromethylthiolaton and cyclization of N-aryl-3-butenamides was developed. It showed divergent reactivities and enabled the selective syntheses of CF3S-substituted 3,4-dihydroquinolin-2-ones and azaspiro[4,5]dienones. The selectivity was achieved through different...

Radical directed regioselective functionalization of diverse alkene derivatives

Regioselective vicinal difunctionalization of diverse alkene derivatives was successfully carried out using readily available carboxylic acids.

K2S2O8-mediated acylarylation of unactivated alkenes via acyl radical addition/C–H annulation cascade of N-allyl-indoles with silver cocatalysis

A silver-catalyzed, K2S2O8-mediated protocol to access the regioselective acylarylation of unactivated alkenes was reported.

The construction of benzimidazo[2,1-a]isoquinolin-6(5H)-ones from N-methacryloyl-2-phenylbenzoimidazoles through radical strategies

Benzimidazo[2,1-a]isoquinolin-6(5H)-one constitutes a structurally unique class of tetracyclic N-heterocycles that are found throughout a myriad of biologically active natural products, pharmaceutical compounds, and functional materials. Various synthetic routes for the preparation of benzimidazo[2,1-a]isoquinolin-6(5H)-ones have been reported. In particular, the use of N-methacryloyl-2-phenylbenzoimidazoles to construct benzimidazo[2,1-a]isoquinolin-6(5H)-ones through various radical strategies have attracted widespread attention due to the versatility and simple preparation of raw materials, as well as the step-economy and mild reaction conditions. Using representative examples, we highlight significant progress in the synthesis of benzimidazo[2,1-a]isoquinolin-6(5H)-ones, including the selection of the catalytic system, substrate scope, mechanistic understanding, and applications. The contents of this review focus on the development of C-, S-, P-, and Si-centered radical addition-intramolecular cyclization strategies.

K2S2O8-Mediated Synthesis of Highly Functionalized Pyrroles via Oxidative Self-Dimerization of N-Propargylamines

An efficient methodology has been developed for the synthesis of tetra- and pentasubstituted pyrroles via oxidative self-dimerization of N-propargylamines catalyzed by silver benzoate in the presence of K₂S₂O₈ in good yields. The protocol provides a simple route for the synthesis of both tetra- and pentasubstituted pyrroles with two carbonyl groups in the side chain. The methodology can be extended toward the synthesis of pyrrolo[3,4-d]pyridazine.

Manganese-catalyzed Electro-oxidative Azidation-annulation Cascade to Access Oxindoles and Quinolinones

An environmentally benign and proficient electro-oxidative tandem azidation-radical cyclization strategy is reported. Manganese-catalyzed electrochemical reaction in an undivided cell at room temperature and the use of NaN₃ as the cheapest azide source are the key features of this protocol. Using this approach, a series of oxindole and quinolinone derivatives are synthesized in high yields. The synthesized azide functionality was efficiently converted to various valuable derivatives.

Silver-promoted oxidative sulfonylation and ring-expansion of vinylcyclopropanes with sodium sulfinates leading to dihydronaphthalene derivatives

Silver-promoted sulfonylation and ring-expansion of vinylcyclopropanes with sodium sulfinates is established for the construction of 1-sulfonylmethylated 3,4-dihydronaphthalenes. This sulfonylation process involves a radical pathway, including sulfonyl radical formation, radical addition, ring-opening and cyclization. The 1-sulfonylmethylated 3,4-dihydronaphthalenes can be converted into other useful products.

Silver-catalyzed direct C-H oxidative carbamoylation of quinolines with oxamic acids

A silver-catalyzed efficient and direct C-H carbamoylation of quinolines with oxamic acids to access carbamoylated quinolines has been developed through oxidative decarboxylation reaction. The reaction proceeds smoothly over a broad range of substrates with excellent functional group tolerance and excellent yields under mild conditions.

Transition-metal free direct C–H functionalization of quinoxalin-2(1H)-ones with oxamic acids leading to 3-carbamoyl quinoxalin-2(1H)-ones

A practical transition-metal free decarboxylative coupling reaction of oxamic acids with quinoxalin-2(1H)-ones has been developed under mild conditions.

Rhenium-catalyzed alkylarylation of alkenes with PhI(O2CR)2via decarboxylation to access indolinones and dihydroquinolinones

Rhenium-catalyzed alkylarylation of alkenes with hypervalent iodine(iii) reagents (HIRs) via decarboxylation to access various 3,3-disubstituted indolinones and trans-3,4-dihydroquinolinones is described.

Fe-Catalyzed decarbonylative cascade reaction of N-aryl cinnamamides with aliphatic aldehydes to construct 3,4-dihydroquinolin-2(1H)-ones

A practical Fe-catalyzed decarbonylative cascade reaction of N-aryl cinnamamides with aliphatic aldehydes to provide C3 alkylated 3,4-dihydroquinolin-2(1H)-ones is developed. Aliphatic aldehydes were oxidatively decarbonylated into 1°, 2° and 3° alkyl radicals conveniently, allowing for the subsequent cascade construction of C(sp3)-C(sp3) and C(sp3)-C(sp2) bonds via radical addition and HAS-type cyclization. The importance of the amide linkage and the selectivity of the 6-endo-trig over 5-exo-trig cyclization pathway were elucidated by experimental results and DFT calculations.

Metal-Free Visible-Light-Promoted Trifluoromethylation of Vinylcyclopropanes Using Pyrylium Salt as a Photoredox Catalyst

Visible-light-induced metal-free trifluoromethylation of activated, carbocyclic, and unactivated vinylcyclopropanes via a ring-opening reaction using the Langlois reagent (CF₃SO₂Na) is reported to synthesize allylic trifluoromethylated derivatives. Allylic trifluoromethylation was achieved by a photo-oxidative single electron transfer (SET) process at an ambient temperature and under metal-free conditions and visible-light irradiation using pyrylium salt as a photoredox catalyst. The reported methodology has an operational simplicity, broad substrate scope, high functional group tolerance, and scalability.

Silver-catalyzed decarboxylative radical cascade cyclization toward benzimidazo[2,1-a]isoquinolin-6(5H)-ones

A simple and efficient decarboxylative radical addition/cyclization strategy was developed, by which a wide range of benzimidazo[2,1-a]isoquinoline-6(5H)-ones were prepared in one-pot via reaction of functionalized 2-arylbenzoimidazoles and carboxylic acids in the presence of K2S2O8/AgNO3 under mild reaction conditions.

Nickel-catalysed radical tandem cyclisation/arylation: practical synthesis of 4-benzyl-3,3-difluoro-γ-lactams

Enabled by nickel catalysis, a practical access to the synthesis of 4-benzyl-3,3-difluoro-γ-lactams has been developed via radical tandem cyclisation/arylation. This method features a nickel catalyst, high reaction efficiency, and good substrate tolerance and scope. This protocol proceeds through an intramolecular radical addition to form a primary alkyl radical followed by intermolecular Suzuki-type coupling.

Aryltrifluoromethylative cyclization of unactivated alkenes by the use of PhICF3Cl under catalyst-free conditions

A concise and catalyst-free aryltrifluoromethylative cyclization of unactivated alkenes has been developed herein. The use of PhICF3Cl as a powerful trifluoromethylating agent allows easy transformations. A set of trifluoroethylated carbocycles and aza-hereocycles were efficiently synthesized in good yield and selectivity. A broad substrate scope, mild reaction conditions, and easy operation would make this method well-suited for applications.

Catalyst-Free, Direct Electrochemical Tri- and Difluoroalkylation/Cyclization: Access to Functionalized Oxindoles and Quinolinones

The catalyst-free electrochemical di- and trifluoromethylation/cyclization of N-substituted acrylamides was realized under external oxidant-free conditions. The strategy provides expedient access to fluoroalkylated oxindoles and 3,4-dihydroquinolin-2(1 H)-ones with ample scope and broad functional group tolerance by mild, direct electrolysis of sodium sulfinates in an undivided cell. Detailed mechanistic studies provided strong support for a SET-based reaction manifold.

Catalyst-free and selective trifluoromethylative cyclization of acryloanilides using PhICF3Cl

Trifluoromethylative cyclization and biscyclization reactions of acryloanilides efficiently occurred under catalyst-free conditions.

Silver-mediated oxidative C–C bond sulfonylation/arylation of methylenecyclopropanes with sodium sulfinates: facile access to 3-sulfonyl-1,2-dihydronaphthalenes

The novel AgNO₃-mediated sulfonylation/arylation of a C–C σ-bond in MCPs with sodium sulfinates to synthesize 3-sulfonylated 1,2-dihydronaphthalenes is reported.

Transition-metal-free decarboxylative C3-difluoroarylmethylation of quinoxalin-2(1H)-ones with α,α-difluoroarylacetic acids

A facile and efficient transition-metal-free decarboxylative radical coupling reaction of α,α-difluoroarylacetic acids with quinoxalin-2(1H)-ones has been developed under mild conditions.

Molecular Oxygen-Promoted General and Site-Specific Alkylation with Organoboronic Acid

A general alkylating method using organoboronic acid under 1 atm of oxygen is developed. It allows a facile access to a wide range of functionalized molecules with privileged scaffolds in drugs and natural products such as oxindoles, quinolinones, chromones, naphthoquinones, coumarins, and quinolones. In contrast to previous alkylation approaches that generally requiring transition-metal catalysis and a stoichiometric chemical oxidant, the present strategy features metal-free, molecular oxygen as the terminal oxidant and site specificity.

An organocatalytic asymmetric Mannich reaction for the synthesis of 3,3-disubstituted-3,4-dihydro-2-quinolones

The first organocatalytic asymmetric Mannich reaction employing 3,4-dihydro-2-quinolones has been developed for the synthesis of biologically important 3,3-disubstituted-dihydro-2-quinolones. N-Boc imine precursor amidosulfones as well as pre-formed N-Boc imine were used for this purpose. Cyclohexyldiamine derived bifunctional amino-thiourea catalysts were employed to provide the products in high enantio- and good diastereoselectivities.

Photocatalytic acylarylation of unactivated alkenes with diaryliodonium salts toward indanones and related compounds

A photocatalytic acylarylation of unactivated alkenes using diaryliodonium salts is described, giving 2-benzyl indanones and related compounds in promising yields with excellent diastereoselectivity.

Silver-catalyzed decarboxylative cascade radical cyclization of tert-carboxylic acids and o-(allyloxy)arylaldehydes towards chroman-4-one derivatives

A convenient silver-catalyzed decarboxylative cascade radical cyclization of tertiary carboxylic acids and o-(allyloxy)arylaldehydes was developed to synthesize 3-alkyl-substituted chroman-4-one derivatives.

CF3SO2X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF3SO2Na

Sodium trifluoromethanesulfinate, CF3SO2Na, and trifluoromethanesulfonyl chloride, CF3SO2Cl, are two popular reagents that are widely used for the direct trifluoromethylation of a large range of substrates. Further, these two reagents are employed for the direct trifluoromethylsulfenylation and trifluoromethylsulfinylation, the introduction of the SCF3 and the S(O)CF3 group, respectively. In addition to the aforementioned reactions, the versatility of these two reagents is presented in other reactions such as sulfonylation and chlorination. This first part is dedicated to sodium trifluoromethanesulfinate.

Synthesis of Bicyclic Isothiazoles through an Intramolecular Rhodium-Catalyzed Transannulation of Cyanothiadiazoles

An intramolecular rhodium-catalyzed transannulation of readily available cyanothiadiazoles containing an ester, amide, or ether as a linker is described. It provides a wide range of bicyclic isothiazoles in good to excellent yields together with the release of molecular nitrogen. These results indicate that the carbon atom in the α-thiavinyl carbene is nucleophilic and that the sulfur atom is electrophilic.