Visible Light-Induced Synthetic Approach for Selenylative Spirocyclization of N -Aryl Alkynamides with Molecular Oxygen as Oxidant

Energy Transfer (EnT)-Mediated Stereoselective Aryl-Heterofunctionalization of Unactivated Alkynes via Radical Rearrangement

In this study, we present a novel catalyst-free energy transfer mediated radical rearrangement strategy for the aryl-heterofunctionalization of unactivated alkynes, leading to the synthesis of polyfunctional olefins with exceptional stereoselectivity. This innovative approach, driven by visible light, exemplifies green chemistry principles by eliminating the reliance on transition metals, external oxidants, and photocatalysts. The broad applicability of our method is demonstrated through the successful synthesis of a diverse array of compounds, including vinyl sulfones, vinyl selenides, and vinyl sulfides. Preliminary mechanistic insights suggest an energy transfer mechanism, highlighting the efficiency and selectivity of this novel strategy.

Halogen Radical-Enabled Dearomatization of N-Arylpropiolamides via Photoinduced Sequential Halogenation/Spirocyclization/Oxidation Process

Here we report a strategy that eliminates the need for photocatalysts and external additives, which provides an operable and mild method for halogen radical-enabled dearomatization of N-arylpropiolamides under an oxygen atmosphere at room temperature. The method is applicable to a wide range of substrates, extending beyond the limited scope of p-methoxyl N-phenylpropynamides. Furthermore, several functional synthetic intermediates and anticancer bioactive molecules were successfully derived from 3-halogenated azaspiro[4.5]trienones.

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.

Recent Progress in Synthetic and Biological Application of Diorganyl Diselenides

Diorganyl diselenides have emerged as privileged structures because they are easy to prepare, have distinct reactivity, and have broad biological activity. They have also been used in the synthesis of natural products as an electrophile in the organoselenylation of aromatic systems and peptides, reductions of alkenes, and nucleophilic substitution. This review summarizes the advancements in methods for the transformations promoted by diorganyl diselenides in the main functions of organic chemistry. Parallel, it will also describe the main findings on pharmacology and toxicology of diorganyl diselenides, emphasizing anti-inflammatory, hypoglycemic, chemotherapeutic, and antimicrobial activities. Therefore, an examination detailing the reactivity and biological characteristics of diorganyl diselenides provides valuable insights for academic researchers and industrial professionals.

Synthesis of Selenium-Containing N-Quinazolinyl Acroleins via a 3,3-Radical Rearrangement Cascade Reaction

An effective approach for the construction of 2-aryl-3-(3-oxo-1-aryl-2-(organoselanyl)prop-1-en-1-yl)quinazolin-4(3H)-ones was developed. Excellent to almost quantitative yields were obtained by the cascade reaction of propargyl quinazoline-4-yl ethers, diselenides, and 70% tert-butyl hydrogen peroxide aqueous solution under metal-free and mild conditions. The synthesized hybrids, with conglomeration of quinazolinone, organoselenium, aldehyde, and fully substituted alkene moieties in one molecule, will have the potential for applications in development of new drugs or drug candidates.

Seleno/Thio-functionalized ipso-Annulation of N-Propiolyl-2-arylbenzimidazole to Construct Azaspiro[5,5]undecatrienones

Till date, the ipso-cyclization of propiolamides is limited to provide azaspiro[4,5]decatrienones. Herein, we present the first example of ipso-carbocyclization, leading to azaspiro[5,5]-undecatrienones from N-propiolyl-2-arylbenzimidazoles, involving both the radical-based and electrophilic reactions. This report establishes an access to a wide range of chalcogenated (SCN/SCF3/SePh) benzimidazo-fused azaspiro[5,5]undecatrienones in good yields.

Photoinduced Copper-Catalyzed 1,2-Difunctionalization of 1,3-Dienes with Aryl Diselenides

Described herein is a photoinduced copper-catalyzed 1,2-difunctionalization of 1,3-dienes. The selenium atom radical was generated by the visible light irradiation of diselenides, triggering radical addition with 1,3-dienes to form allyl radical intermediate. Subsequent rapid Z/E isomerization allowed for thermodynamically favorable intermediate formation and enabled copper catalyzed stereoselective functionalization with various nucleophiles.

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.

Synthesis and Application Dichalcogenides as Radical Reagents with Photochemical Technology

Dichalcogenides (disulfides and diselenides), as reactants for organic transformations, are important and widely used because of their potential to react with nucleophiles, electrophilic reagents, and radical precursors. In recent years, in combination with photochemical technology, the application of dichalcogenides as stable radical reagents has opened up a new route to the synthesis of various sulfur- and selenium-containing compounds. In this paper, synthetic strategies for disulfides and diselenides and their applications with photochemical technology are reviewed: (i) Cyclization of dichalcogenides with alkenes and alkynes; (ii) direct selenylation/sulfuration of C-H/C-C/C-N bonds; (iii) visible-light-enabled seleno- and sulfur-bifunctionalization of alkenes/alkynes; and (iv) Direct construction of the C(sp)-S bond. In addition, the scopes, limitations, and mechanisms of some reactions are also described.

Access to Diverse Seleno-spirocyclohexadienones via Ag(II)-Catalyzed Selenylative ipso-Annulation with Se and Boronic Acids

An efficient and straightforward synthesis of diversified seleno-azaspiro-2,5-cyclohexadienones from N-(4-methoxy aryl)propiolamides using elemental selenium and boronic acids has been demonstrated. The reaction proceeds through silver-catalyzed oxidative dearomatization in the presence of potassium persulfate (K₂S₂O₈) as the oxidant. Further, this approach was extended to N-(4-methoxy aryl)propiolates and biaryl ynones to access the corresponding selenylated oxospiro-2,5-cyclohexadienones and spiro[5,5]trienones, respectively. The present three-component method offers the diverse substitutions on selenium involving two C-Se and one C-C bond formations.

Photomediated Spirocyclization of N-Benzyl Propiolamide with N-Iodosuccinimide for Access to Azaspiro[4.5]deca-6,9-diene-3,8-dione

A metal- and oxidant-free route for affording azaspiro[4.5]deca-6,9-diene-3,8-dione via photomediated iodinated spirocyclization of N-(4-methoxybenzyl) propiolamide has been developed. The reaction underwent a radical addition/ipso-cyclization/dearomatization process at room temperature and successfully constructed C-C and C-I bonds. This green and convenient approach could be generally expanded to produce a range of iodinated spirocyclization products in moderate to good yields.

K2S2O8/I2-Promoted Electrophilic Selenylative Cyclization To Access Seleno-Benzo[b]azepines

A novel and simple organoselenium-involved 7-membered cyclization to access diverse seleno-benzo[b]azepines has been developed. This protocol involves an electrophilic cyclization process and is accomplished under mild conditions. Discussion of the mechanism rationalizes the regioselectivity observed in transformation. The studies of further transformation of seleno-benzo[b]azepines and large-scale experiment reveal the promising utility of this methodology.

Divergent Synthesis of Chalcogenylated Quinolin-2-ones and Spiro[4,5]trienones via Intramolecular Cyclization of N-Aryl­propynamides Mediated by Diselenides/Disulfides and PhICl2

The reaction of N-arylpropynamides with (dichloroiodo)benzene (PhICl2) and diselenides/disulfides resulted in a divergent synthesis of chalcogenylated quinolinones and spiro[4.5]trienes through intramolecular electrophilic cyclization and chalcogenylation. The chalcogenyl functional group was introduced by an electrophilic reactive organosulfenyl chloride or selenenyl chloride species, generated in situ from the reaction of disulfides/diselenides and PhICl2. Notably, the divergent cyclization pathways were determined by the substituent type on the aniline ring in N-arylpropynamide substrates. Substrates bearing a fluoro, methoxy or trifluoromethoxy group at the para-position of the aniline underwent an alternative spiralization pathway to give the 3-chalcogenylated spiro[4,5]trienones.

"Green Is the Color": An Update on Ecofriendly Aspects of Organoselenium Chemistry

Organoselenium compounds have been successfully applied in biological, medicinal and material sciences, as well as a powerful tool for modern organic synthesis, attracting the attention of the scientific community. This great success is mainly due to the breaking of paradigm demonstrated by innumerous works, that the selenium compounds were toxic and would have a potential impact on the environment. In this update review, we highlight the relevance of these compounds in several fields of research as well as the possibility to synthesize them through more environmentally sustainable methodologies, involving catalytic processes, flow chemistry, electrosynthesis, as well as by the use of alternative energy sources, including mechanochemical, photochemistry, sonochemical and microwave irradiation.

Visible-light induced dearomatization reactions

Dearomatization reactions provide rapid access to structurally complex three-dimensional molecules from simple aromatic compounds. Plenty of reports have demonstrated their utilities in the synthesis of natural products, medicinal chemistry, and materials science in the last decades. Recently, visible-light mediated photocatalysis has emerged as a powerful tool to promote many kinds of transformations. The dearomatization reactions induced by visible-light have also made significant progress during the past several years. This review provides an overview of visible-light induced dearomatization reactions classified based on the manner in which aromaticity is disrupted.

Radical selenation of C(sp3)-H bonds to asymmetric selenides and mechanistic study

Selenides are important structural motifs with a broad range of biological activities and versatile transformational abilities. In this study, a novel and mild method was developed for the facile synthesis of asymmetric selenides under metal-free conditions. The key features of this reaction include good functional-group tolerance, the use of readily available reagents and cheap, low-toxicity solvent, and amenability to gram-scale synthesis. The results of preliminary radical-trapping experiments and a kinetic isotope effect study support a radical process.

Selectfluor-mediated construction of 3-arylselenenyl and 3,4-bisarylselenenyl spiro[4.5]trienones via cascade annulation of N-phenylpropiolamides with diselenides

A cascade annulation of N-phenylpropiolamides with diselenides leading to the construction of 3-arylselenenyl spiro[4.5]trienones was realized under mild conditions with Selectfluor as the sole oxidant.

Radical-induced denitration of N-(p-nitrophenyl)propiolamides coupled with dearomatization: access to phosphonylated/trifluoromethylated azaspiro[4.5]-trienones

A robust dearomative denitration of nitroarene derivatives induced by a radical ipso-cyclization process has been developed, delivering valuable phosphonated or trifluoromethylated azaspiro[4.5]trienones with good functional group tolerance. This represents a convenient and powerful approach to activate nitroarenes in a radical manner.

Chalcogenative spirocyclization of N-aryl propiolamides with diselenides/disulfides promoted by Selectfluor

A practical and efficient synthetic route to construct a variety of 3-arylselenenyl/3-arylthio spiro[4.5]trienones was developed using Selectfluor reagent as a mild oxidant. This reaction proceeds via a sequence of electrophilic cation addition, spirocyclization and dearomatization, then offers an approach to introduce Se/S-centered cation into the C–C triple bonds. The utility of this protocol were justified by the excellent compatibility of a wide range of functional groups, good yields and scalability under mild reaction conditions.

Synthesis of Polysubstituted Furans through Electrochemical Selenocyclization of Homopropargylic Alcohols

The current method represents an electrochemically driven synthetic route to access polysubstituted selenofuran derivatives through the diselenide-promoted cyclization of homopropargyl alcohols. The tandem electro-oxidative transformation operates at ambient temperature and in the absence of an external oxidant. This mild and efficient methodology exhibits good functional group compatibility, providing a broad range of substrate scopes up to 84% isolated yield. Further conversion of the seleno-functionality afforded other valuable furan derivatives.

Iron-Catalyzed Dearomatization of Biaryl Ynones with Aldehydes via Double C-H Functionalization in Eco-Benign Solvents: Highly Atom-Economical Synthesis of Acylated Spiro[5.5]trienones

The multiple C-H bonds of biaryl ynones render the 6-exo-trig regioselective C-H activation dearomatization to spiro[5.5]trienones challenging since the competing reactions of C-H bonds on Ar¹ or the ortho-C-H bonds on Ar³ may result in 5-exo-trig cyclization to indenones or 6-exo-trig ortho-dearomatization, respectively. We here report an unprecendented dearomatization of biaryl ynones with aldehydes via double C-H functionalization where a regiospecific remote unactivated para-C-H functionalization of biaryl ynones efficiently furnishes acylated spiro[5.5]trienones. This cascade cyclization features a green catalyst and solvent and high atom- and step-economy.

Highly Diastereoselective Synthesis of Dihydro-benzoimidazo-[1,3]-thiazines via Electro-oxidative Selenocyclization of Thioallyl Benzoimidazoles

The current methodology reveals a green and proficient electro-oxidative tandem selenocyclization of thioallyl benzoimidazoles manufacturing selenylated dihydro-benzoimidazo-thiazine derivatives. Both C-Se and C-N bond formation were achieved via this mild protocol which exhibits good functional group tolerability affording an extensive range of substrate scope up to 96% isolated yields. Complete control over the regioselective formation of the six-membered heterocycle and stereoselective construction of the contiguous stereocenters was established. The practical electrochemical method operates in an undivided cell at ambient temperature without using any metal and external chemical oxidant.

Selenium-promoted electrophilic cyclization of arylpropiolamides: synthesis of 3-organoselenyl spiro[4,5]trienones

This paper describes a selenium-promoted electrophilic cyclization of arylpropiolamides allowing the synthesis of 3-organoselenyl spiro[4,5]trienones via a 5-endo-dig ipso-mode. The 3-organoselenyl-quinolinone derivative formation via 6-endo-dig was avoided using an electrophilic organoselenium species in a metal-free protocol. The use of phenylselenyl bromide (1.3 equiv.), as the electrophilic source, in nitromethane (3 mL) at 90 °C enabled the cyclization of N-(2-methoxyphenyl)-N-methyl-3-phenylpropiolamides, giving 3-organoselenyl[4,5]triene-2,6-dione derivatives. The extension of the standard conditions to the N-(4-methoxyphenyl)-phenylpropiolamides led to the corresponding 3-organoselenyl spiro[4,5]trienones having the carbonyl group at the 8-position. Besides, we demonstrated a general application of our approach by using 3-organoselenyl spiro[4,5]trienones as substrates in Suzuki cross-coupling reactions, which gave the cross-coupled products in good yields.

Radical bromination-induced ipso cyclization-ortho cyclization sequence of N-hydroxylethyl-N-arylpropiolamides

A facile procedure is reported for the synthesis of various 2-bromo-1-phenyl-5,6-dihydro-3H,7aH-benzo[b]pyrrolo[2,1-c][1,4]oxazin-3-ones via a radical bromination-induced ipso cyclization-ortho cyclization sequence of N-arylpropiolamides in the presence of TBAB and oxone. The radical cyclization sequence involves a radical bromo α-addition into the alkyne, ipso-cyclization, and ortho-trapping of the spirocyclic intermediate.

Photocatalytic Radical Ortho-Dearomative Cyclization: Access to Spiro[4.5]deca-1,7,9-trien-6-ones

A highly efficient ortho-dearomative cyclization reaction between alkynes and 2-bromo-2-(2-methoxybenzyl)malonate via visible light-induced photoredox catalysis has been reported. In the presence of 1 mol % fac-Ir(ppy)₃, a variety of spiro[4.5]deca-1,7,9-trien-6-ones were obtained in moderate to excellent yields under mild conditions. Under the optimized reaction conditions, a sample reaction of 3 mmol scale proceeded smoothly to give the desired products in 84% yield with a low catalyst loading of 0.1 mol %.

Light-mediated Seleno-Functionalization of Organic Molecules: Recent Advances

Organoselenium compounds constitute an important class of substances with applications in the biological, medicinal and material sciences as well as in modern organic synthesis, attracting considerable attention from the scientific community. Therefore, the construction of the C-Se bond via facile, efficient and sustainable strategies to access complex scaffolds from simple substrates are an appealing and hot topic. Visible light can be regarded as an alternative source of energy and is associated with environmentally-friendly processes. Recently, the use of visible-light mediated seleno-functionalization has emerged as an ideal and powerful route to obtain high-value selenylated products, with diminished cost and waste. This approach, involving photo-excited substrates/catalyst and single-electron transfer (SET) between substrates in the presence of visible light has been successfully used in the versatile and direct insertion of organoselenium moieties in activated and unactivated C(sp³ )-H, C(sp² )-H, C(sp)-H bonds as well as C-heteroatom bonds. In most cases, ease of operation and accessibility of the light source (LEDs or commercial CFL bulbs) makes this approach more attractive and sustainable than the traditional strategies.

Transition Metal-Free Synthesis of Carbo- and Heterocycles via Reaction of Alkynes with Organylchalcogenides

This manuscript intends to overview the most recent advances in the synthesis of carbo- and heterocycles through reactions of alkynes with organyl chalcogenides (S, Se, Te) under metal-free conditions. Firstly, the use of electrophilic chalcogenyl halides as a selective reagent for alkyne carbon-carbon triple bond activation will be presented. After that, radical cyclization protocols employing electrochemical oxidative conditions, light-induced photoredox catalysis, or mild oxidants with direct chalcogenyl group installation will be discussed accompanied by the proposed mechanisms.

Visible-Light Mediated Diarylselenylative Cyclization of 1,6-Enynes

We herein described a selenylative cyclization reaction of enynes by the utilization of diselenides as radical sources. The visible-light irradiation of the reaction mixture enables the generation of the selenium atom radical to trigger the radical addition/cyclization/selenation sequences. Both terminal alkyne and internal alkyne derived 1,6-enynes were tested and suitable for the current synthetic protocol, delivering various kinds of selenium-containing cycles in good yields.

Strategies and methodologies for the construction of spiro-γ-lactams: an update

This review gives an insight into the most recent synthetic methodologies towards spiro-γ-lactams, a class of compounds that are present in a wide range of synthetic bioactive and naturally occurring molecules.

Visible-light-induced metal-free cascade cyclization of N-arylpropiolamides to 3-phosphorylated, trifluoromethylated and thiocyanated azaspiro[4.5]trienones

Photocatalytic strategies for the preparation of 3-functionalized azaspiro[4.5]trienones via a radical-initiated cascade annulation reaction was developed.

Selenocysteinyl electrophiles efficiently promote the formation of coumarin and quinolinone cores by 6-endo-dig cyclization

Efficient methods have been disclosed for the construction of nitrogen and oxygen containing heterocyclic systems attached to selenocysteine or selenoglutathione.

Copper(i) catalyzed synthesis of selanyl methylene 4-chromanol and aurone derivatives

An efficient copper-catalyzed cyclization cascade approach towards highly functionalized methylene 4-chromanol and aurone derivatives has been developed from reactions of ynols via 6-exo-dig and 5-exo-dig cyclization respectively. The catalysis involves alkyne activation via diorgano-diselenides and also their regioselective incorporation into the methylene 4-chromanol and aurone derivative core and is an open-air transformation.

Electrochemical Synthesis of Spiro[4.5]trienones through Radical-Initiated Dearomative Spirocyclization

A novel and green route has been developed for the electrochemical synthesis of spiro[4.5]trienones through radical-initiated dearomative spirocyclization of alkynes with diselenides. This metal-free and oxidant-free electrosynthesis reaction was performed in an undivided cell under mild conditions. A variety of selenation spiro[4.5]trienones products were prepared in moderate-to-good yields, showing a broad scope and functional group tolerance. Moreover, the developed continuous-flow system combined with electrosynthesis possesses the potential to achieve scaled-up reactions, overcoming the low efficiency of conventional electrochemical scaled-up reactions.

Visible-Light-Promoted Selenylative Spirocyclization of Indolyl-ynones toward the Formation of 3-Selenospiroindolenine Anticancer Agents

A metal-free and efficient visible-light-induced spirocyclization of indolyl-ynones with diselenides at room temperature under air atmosphere to prepare 3-selenospiroindolenines in moderate to good yields has been developed. The resulting products were tested for in vitro anticancer activity by MTT assay, and compounds 3 c and 3 e showed potent cancer cell-growth inhibition activities.

Photo-mediated synthesis of halogenated spiro[4,5]trienones of N-aryl alkynamides with PhI(OCOCF3)2 and KBr/KCl

A novel and convenient photo-mediated halogenated spirocyclization of N-(p-methoxyaryl)propiolamides has been developed. The photolysis of phenyliodine bis(trifluoroacetate) (PIFA) as an iodination reagent led to iodinated ipso-cyclization under the irradiation of a xenon lamp, while brominated ipso-cyclization or chlorinated ipso-cyclization was achieved by irradiating a mixture of PIFA and KBr/KCl under a blue LED. The present protocol simply utilizes light as the safe and clean energy source and doesn't require any external photocatalyst providing various 3-halospiro[4,5]trienones in good to excellent yields (up to 93%).

Fe-catalyzed Decarbonylative Alkylative Spirocyclization of N-Arylcinnamamides: Access to Alkylated 1-Azaspirocyclohexadienones

For the convenient introduction of simple linear/branched alkyl groups into biologically important azaspirocyclohexadienones, a practical Fe-catalyzed decarbonylative cascade spiro-cyclization of N-aryl cinnamamides with aliphatic aldehydes to provide alkylated 1-azaspiro-cyclohexadienones was developed. Aliphatic aldehydes were oxidative decarbonylated into primary, secondary and tertiary alkyl radicals conveniently and allows for the subsequent cascade construction of dual C(sp3)-C(sp3) and C=O bonds via radical addition, spirocyclization and oxidation sequence.

Metal-free spirocyclization of N-arylpropiolamides with glyoxylic acids: access to complex azaspiro-fused tricycles

An efficient K₂S₂O₈-mediated oxidative cascade spirocyclization of N-arylpropiolamides with aryl glyoxylic acids was demonstrated for constructing azaspiro[4,5]-trienones and complex azaspiro-fused architectures.

Visible-light-promoted acyl radical cascade reaction for accessing acylated isoquinoline-1,3(2H,4H)-dione derivatives

A visible-light-promoted radical acylation/cyclization cascade reaction of N-methacryloylbenzamides with α-keto acids was developed to construct acylated isoquinoline-dione derivatives.