Sustainable Synthesis through Catalyst-Free Photoinduced Cascaded Bond Formation

The beginning of photochemical reactions revolutionized synthetic chemistry through sustainable practices. This review explores cutting-edge developments in leveraging light-induced processes for generating cascaded C-C and C-hetero bonds without catalysts. Significantly, catalyst-free photoinduced methodologies have garnered considerable attention, especially in the creation of varied heterocyclic frameworks for drug design and the synthesis of natural products. The article delves into underlying mechanisms, addresses limitations, and evaluates various methodologies, emphasizing the potential of photocatalyst and transition metal-free photochemical reactions to enhance sustainability. Divided into two sections, it covers recent strides in C-C and C-heteroatom and multiple C-heteroatom bond formation reactions.

BF3·Et2O-assisted synthesis of sulfinylated spiro[5.5]trienones from biaryl ynones

Sulfinyls are valuable structural moieties used for developing synthetically new pharmaceuticals and agrochemicals. Herein, we disclose a straightforward synthesis of sulfinylated spiro[5.5]trienones proceeding via an unprecedented BF3·Et2O-promoted spirocyclization of biaryl ynones. The availability of relatively inexpensive BF3·Et2O to carry out transformations on a bulk scale along with its further application towards the synthesis of dibenzocyclohepten-5-ones delivers a unique opportunity to deploy it in various synthetic directions.

Non-Friedländer Route to Diversely 3-Substituted Quinolines through Au(III)-Catalyzed Annulation Involving Electron-Deficient Alkynes

Gold(III)-catalyzed annulation of electron-deficient alkynes and 2-amino-arylcarbonyls provides general modular one-step access to a broad scope of quinoline products. This highly selective reaction is a useful alternative to the classic Friedländer synthesis, which requires harsh reaction conditions. In contrast, the developed method works under relatively mild PicAuCl2-catalyzed conditions and exhibits a high functional group tolerance (40 examples; yields of ≤96%). Another feature of the developed approach is a versatility toward other electron-deficient alkynes. Alkynylsulfones, alkynylcarbonyls, alkynylphosphonates, propiolonitriles, and trifluoromethylated alkynes can be used as the starting materials for the preparation of quinolines diversely substituted at position 3. On the basis of experimental data, we proposed a reaction mechanism in which gold(III) functions as a strong electrophilic activator of the C≡C bond and the carbonyl group. The synthetic potential of the presented method is additionally illustrated by practical postmodifications of the obtained compounds, including a two-step synthesis of interpirdine, a potent drug candidate.

Facile access to 3-sulfonylquinolines via Knoevenagel condensation/aza-Wittig reaction cascade involving ortho-azidobenzaldehydes and β-ketosulfonamides and sulfones

Quinoline-based sulfonyl derivatives, and especially sulfonamides, are relevant and promising structures for drug design. We have developed a new convenient protocol for the synthesis of 3-sulfonyl-substituted quinolines (sulfonamides and sulfones). The approach is based on a Knoevenagel condensation/aza-Wittig reaction cascade involving o-azidobenzaldehydes and ketosulfonamides or ketosulfones as key building blocks. The protocol is appropriate for both ketosulfonyl reagents and α-sulfonyl-substituted alkyl acetates providing the target quinoline derivatives in good to excellent yields.

Visible light driven multicomponent synthesis of difluoroamidosulfonyl quinoline derivatives

A visible-light-induced photocatalyst-free three-component radical tandem cyclization of N-propargylamine and N-allylbromodifluoroacetamides with the insertion of sulfur dioxide has been developed. Diverse difluoroamidosulfonylated quinolines are obtained in moderate to good yields. This protocol features broad functional group tolerance and high regioselectivity. Moreover, mechanistic studies reveal the involvement of the radical pathway and the formation of an electron donor-acceptor (EDA) complex in this reaction.

3-Arylsulfonylquinolines from N-Propargylamines via Cascaded Oxidative Sulfonylation Using DABSO

We report a cascaded oxidative sulfonylation of N-propargylamine via a three-component coupling reaction using DABCO·(SO₂)₂ (DABSO). 3-Arylsulfonylquinolines were obtained by mixing diazonium tetrafluoroborate, N-propargylamine, and DABSO under argon atmosphere in dichloroethane (DCE) for 1 h. In a radical pathway, DABSO was utilized as the sulfone source and an oxidant in this radical-mediated cascaded reaction.

Photocatalytic Markovnikov-type addition and cyclization of terminal alkynes leading to 4-sulfonyl quinoline-2(1H)-ones

A new and expedient photocatalytic protocol for the construction of quinolin-2(1H)-ones via Markovnikov-type sulfonylation/6-endo-trig cyclization/selective C(O)-CF₃ bond cleavage starting from N-alkyl-N-(2-ethynylphenyl)-2,2,2-trifluoroacetamides and sulfinic acids has been developed. It is as an unprecedented protocol for the preparation of 4-sulfonylquinoline-2(1H)-ones with high efficiency, mild reaction conditions, acceptable yields and a wide range of substrates.

Organic Sulfinic Acids and Salts in Visible Light-Induced Reactions

Sulfinic acids and their salts are a useful source of sulfur-containing structures. Photocatalysis of these compounds with visible light enables to achieve various transformations under mild conditions. This review summarizes visible-light-induced reactions of sulfinic acids and their salts. It is organized by reaction type and brief discussions on plausible reaction mechanisms for typical transformations are presented.

1 Introduction

2 Sulfonylation Reactions

2.1 Sulfonylation of Alkenes

2.2 Sulfonylation of Alkynes

2.3 Sulfonylation of Arenes

2.4 sp3 C–H Functionalization

3 Desulfonylation Reactions

4 Sulfenylation Reactions

4.1 Sulfenylation of Heteroarenes

4.2 Sulfenylation of Carbonyl Chlorides

5 Conclusions

Metal-free regioselective cascade sulfonylation-cyclization of 3-aza-1,5-enynes with sulfur dioxide and aryldiazonium tetrafluoroborates to construct 1,2-dihydropyridines

Radical cascade cyclization of tethered alkynes has emerged as an efficient tool to construct small but complex cyclic compounds. However, it currently relies on aryl or heteroaryl-tethered alkynes to give...

Visible-Light-Induced Multicomponent Cascade Cycloaddition of N-Propargyl Aromatic Amines, Cyclobutanone Oxime Esters, and K2S2O5: Access to Cyanoalkylsulfonylated Quinolines

A visible-light-induced cascade cyanoalkylsulfonylation/cyclization/aromatization of N-propargyl aromatic amines with K₂S₂O₅ and cyclobutanone oxime esters for the construction of cyanoalkylsulfonylated quinolines is developed. This cascade transformation features mild reaction conditions, a broad substrate scope, and excellent functional group compatibility, providing a convenient route toward cyanoalkylsulfonylated quinolines via the formation of a C-C bond and two C-S bonds in one step.

Visible-Light Driven Selective C-N Bond Scission in anti-Bimane-Like Derivatives

In the present study, we report the photochemical transformation of pyrazolo[1,2-a]pyrazolone substrates that reach an excited state upon irradiation with visible light to initiate the homolytic C-N bond cleavage process that yields the corresponding N1-substituted pyrazoles. Moreover, chemoselective heterolytic C-N bond cleavage is possible in the pyrazolo[1,2-a]pyrazole core in the presence of bromomalonate.

Electrochemical synthesis of sulfonated benzothiophenes using 2-alkynylthioanisoles and sodium sulfinates

Electrochemical sulfonylation/cyclization of 2-alkynylthioanisoles with sodium sulfinates was developed under catalyst-, external oxidant- and metal-free conditions. The electrosynthesis provides sustainable and efficient access to 3-sulfonated benzothiophenes with good substrate scope and functional group tolerance. This cascade radical process has been triggered through a sulfonyl radical addition to alkynes using sodium sulfinates under electrochemical conditions.

Visible-light-mediated synthesis of quinolines

Visible light promoted synthetic routes of quinolines using different strategies are hereby documented.

Recent application of visible-light induced radicals in C-S bond formation

The sulphur centered radicals, produced from various organic compounds, in high efficiency by single-electron-transfer (SET) oxidation. These radicals are highly reactive intermediates having various applications in the construction of organosulphur compounds in the field of synthetic organic chemistry. These S-centred radical-mediated organic transformations have been achieved using photoredox catalysts, including organic dyes and transition metal catalysts, as well as in the absence of any catalyst. Compared with previous methods, photoredox catalysis is inexpensive and features the advantages of being environmentally benign, highly efficient and easy to use. This review focuses on recent developments in the photocatalyzed carbon-sulphur bond formation.

Direct Synthesis of Sulfonylated Spiro[indole-3,3'-pyrrolidines] by Silver-Mediated Sulfonylation of Acrylamides Coupled with Indole Dearomatization

A dearomative tandem spiro-cyclization reaction of N-[(1H-indol-3-yl)methyl]methacrylamide derivatives with sulfinate sodium in the presence of AgNO₃ and K₂CO₃ is reported, which produced sulfonylated spiro[indole-3,3'-pyrrolidines] in medium to excellent yields. The characteristics of this transformation contain good functional group tolerance and ease of operation.

p-TsOH-mediated synthesis of substituted 2,4-diaryl-3-sulfonylquinolines from functionalized 2-aminobenzophenones and aromatic β-ketosulfones under microwave irradiation

This study describes an efficient protocol for the preparation of substituted 2,4-diaryl-3-sulfonylquinolines from functionalized 2-aminobenzophenones and aromatic β-ketosulfones by using p-toluenesulfonic acid monohydrate under microwave irradiation. In this atom-economical synthetic route, a series of pharmaceutically active 3-arylsulfonylquinolines with good functional group tolerance are prepared in good to excellent yields. Some structures are confirmed by single-crystal X-ray diffraction analysis.

Synthesis of 3-sulfonylquinolines by visible-light promoted metal-free cascade cycloaddition involving N-propargylanilines and sodium sulfinates

A visible-light promoted radical cascade reaction of N-propargylanilines with sodium sulfinates as sulfonyl radical precursors was developed under metal-free conditions.

Aerobic C(sp3)–H oxidation and oxygenation of quaternarized quinolines and pyridines by visible-light-induced photocatalysis

One stone two birds: two kinds of oxygenation products (>60 new products) including carboxylate inner salts and alcohols have been accessed under mild aerobic photocatalysis.

Recent advances and prospects in the metal-free synthesis of quinolines

Metal-free synthesis of quinolines has recently gained attention, and this review focuses on the recent advances in the metal-free synthesis of quinolines.

Copper-Catalyzed Electrophilic Cyclization of N-Propargylamines with Sodium Sulfinate for the Synthesis of 3-Sulfonated Quinolines

A convenient and effective protocol for the synthesis of 3-sulfonated quinolines via copper-catalyzed electrophilic cyclization of N-propargylamines has been developed, in which cheap and stable sodium sulfinates were utilized as green sulfonylation reagents. This cascade transformation involves radical addition, cyclization and dehydrogenative aromatization processes in a one-pot reaction under mild conditions.

Visible-light-induced decarboxylative sulfonylation of cinnamic acids with sodium sulfinates by using Merrifield resin supported Rose Bengal as a catalyst

A visible-light-induced decarboxylative sulfonylation of cinnamic acids with sodium sulfinates for the synthesis of vinyl sulfones was developed. The reaction proceeded smoothly in the presence of Merrifield resin supported Rose Bengal ammonium salt as a photocatalyst and tert-butyl hydroperoxide (70% in water) as an oxidant in aqueous DMSO solution at room temperature under green LED (530-535 nm) irradiation under an air atmosphere, generating the desired products in good yields. Notably, the supported catalyst can easily be separated from the reaction mixture by filtration and can be recycled at least six times without any significant loss of activity.

Preparation of 2-arylquinolines from β-arylpropionitriles with aryllithiums and NIS through iminyl radical-mediated cyclization

Treatment of β-arylpropionitriles with aryllithiums, followed by the reaction with water and then with NIS under irradiation with a tungsten lamp gave 2-arylquinolines in good to moderate yields.

Visible-light-promoted direct C–H/S–H cross-coupling of quinoxalin-2(1H)-ones with thiols leading to 3-sulfenylated quinoxalin-2(1H)-ones in air

A new and efficient visible-light-mediated strategy has been developed for the synthesis of 3-sulfenylated quinoxalin-2(1H)-ones via rhodamine B catalyzed C–H/S–H cross-coupling of quinoxalin-2(1H)-ones with thiols in air at room temperature.

Visible-light-induced cascade sulfonylation/cyclization of N-propargylindoles with aryldiazonium tetrafluoroborates via the insertion of sulfur dioxide

A simple and efficient visible-light-catalyzed cascade sulfonylation/cyclization of N-propargylindoles with K₂S₂O₅ and aryldiazonium tetrafluoroborates for the construction of 2-sulfonyl-substituted 9H-pyrrolo[1,2-a]indoles is developed.