Radical Cascade Reaction of Aryl Alkynoates at Room Temperature: Synthesis of Fully Substituted α,β-Unsaturated Acids with Chalcogen Functionality

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.

Hierarchical surface-modification of nano-Cu toward one pot H-transfer-coupling-cyclization-CO2 fixation tandem reactions

Fixation of CO2 into dihydroisobenzofuran derivatives has enormous applications in both production of natural products and antidepressant drugs, and reducing the green-house effect. However, the relatively complicated multi-step processes limit the further expansion of such a valuable CO2 conversion strategy. Herein, we hierarchically modify the surface of Cu nanoparticles (NPs) with Ag NPs and the robust metal-organic framework (MOF), ZIF-8, and report the presence of the Cu-Ag yolk-shell nanoalloy based heterogeneous catalysts, Cu@Ag and Cu@Ag@ZIF-8. The latter exhibits a crystalline "raisin bread" structure and specific synergic activity for catalyzing the tandem reactions of intra-molecular H-transfer, C-C and C-O coupling, cyclization, and carboxylation from CO2, leading to the first non-homogeneous preparation of dihydroisobenzofuran derivatives in high yield, selectivity, and recyclability under mild conditions. Theoretical calculations elucidate the tandem reaction pathway synergically catalyzed by Cu@Ag@ZIF-8, which offers insights for designing multiphase catalysts towards both organic synthesis and CO2 fixation through tandem processes in one pot.

Photochemical Radical Bicyclization of 1,5-Enynes: Divergent Synthesis of Fluorenes and Azepinones

A dual nickel- and iridium-photocatalyzed radical cascade bicyclization reaction for the synthesis of highly complex molecular structures in an atom- and step-economic manner has been described. A series of radical precursors are utilized for the divergent synthesis of diversely substituted fluorenes and indenoazepinones bearing quaternary carbons by using cascade cyclization reactions of 1,5-enynes. This reaction is characterized by its mild conditions, broad substrate scope, excellent selectivity, and satisfactory yield including facile scale-up synthesis.

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.

Synthesis of 1,1-Diarylvinylsulfides via Visible-Light-Promoted Cascade Reaction of Alkynoates with Phenyl Disulfides

Without any additives and photocatalysts, the visible-light-promoted radical cascade reaction between alkynoates and phenyl disulfides has been developed at room temperature. Through S-S bond photolysis and homolytic cleavage, addition of a sulfur radical, aryl migration, decarboxylation, and H atom abstraction, the cascade reaction provides an efficient and practical route to trisubstituted 1,1-diarylvinylsulfides with a wide scope of substrates and good to excellent yields.

Mn(OAc)3-Promoted Sulfonation-ipso-Cyclization Cascade via the SO3- Radical: The Synthesis of Spirocyclic Sulfonates

A radical sulfonation-ipso-cyclization cascade promoted by Mn(OAc)3·2H2O using functionalized alkynes or alkenes and potassium metabisulfite (K2S2O5) is reported. A total of 30 spirocyclic sulfonates were synthesized under mild conditions. We also demonstrate a modular synthesis approach in multiple steps for the preparation of various azaspiro[4,5]-trienone-based sulfonamides and sulfonate esters.

Organoselenium Compounds: Chemistry and Applications in Organic Synthesis

Selenium, originally described as a toxin, turns out to be a crucial trace element for life that appears as selenocysteine and its dimer, selenocystine. From the point of view of drug developments, selenium-containing drugs are isosteres of sulfur and oxygen with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. In this article, we have focused on the relevant features of the selenium atom, above all, the corresponding synthetic approaches to access a variety of organoselenium molecules along with the proposed reaction mechanisms. The preparation and biological properties of selenosugars, including selenoglycosides, selenonucleosides, selenopeptides, and other selenium-containing compounds will be treated. We have attempted to condense the most important aspects and interesting examples of the chemistry of selenium into a single article.

Photoinduced radical cascade cyclization of acetylenic acid esters with oxime esters to access cyanalkylated coumarins

A photoinduced radical cascade cyclization of acetylenic acid esters with oxime esters is described, providing cyanalkylated coumarins in superior yields under mild conditions. Radical capture and luminescence quenching experiments showed that this transformation was accomplished via a radical addition/5-exo spirocyclization/1,2-ester migration process.

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.

Aerobic Oxidative Cascade Thiolation and Cyclization to Construct Indole-Fused Isoquinolin-6(5H)-one Derivatives in EtOH

A practical method to construct sulfenylated indole-fused isoquinolin-6(5H)-one derivatives has been developed. Using eco-friendly ethanol as the solvent and air as the oxidant, this reaction could be compatible with sensitive molecular framework. The utility of the product was well illustrated by further transformations. Moreover, the reaction mechanism was investigated by control experiments.

Chlorinative Cyclization of Aryl Alkynoates Using NCS and 9-Mesityl-10-methylacridinium Perchlorate Photocatalyst

In a chlorinative cyclization, Mes-Acr-MeClO₄ acted as a visible-light photocatalyst to obtain 3-chlorocoumarins from aryl alkynoates and N-chlorosuccinimide (NCS). The radical initiated reaction proceeded in a cascading manner via Cl^- addition to alkynoates. Next, 5-exo-trig spirocyclization and subsequent 1,2-ester migration led to the formation of C-C and C-Cl bonds.

Recent Advances in the Tandem Difunctionalization of Alkynes: Mechanism-Based Classification

Recent advances on the tandem difunctionalization of alkynes in the last decade (2010–2020) are summarized into five categories based on the type of mechanism: (1) radical addition and coupling for the synthesis of polysubstituted ketones and alkenes, (2) electrophilic addition of alkynes, (3) reactions mediated by haloalkynes or copper acetylides, (4) the preparation of cyclic compounds via radical processes, palladium-catalyzed reactions or conjugate additions, and (5) cyclic compounds as intermediates in ring openings. Herein, radical, electrophilic and nucleophilic reactions are discussed in detail. We hope this review will help to promote future research in this area.

1 Introduction

2 Radical Addition and Coupling

3 Electrophilic Addition

4 Reactions Mediated by Haloalkynes or Copper Acetylides

5 Cyclization

6 Cyclization and Ring Opening

7 Conclusions

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.

Photocatalyzed formal carbooxygenation of terminal alkynes

An efficient visible-light-induced formal carbooxygenation of N-arylsulfonylamido alkynes with molecular oxygen has been developed.

Metal-free C–S coupling of thiols and disulfides

A literature overview on C–S coupling reactions using thiols or disulfides as sulfur surrogates under metal-free conditions is presented. Reagents for the transformations include polyvalent iodines, peroxides, tert-butyl nitrite (TBN), DDQ, and aerial oxygen, among others.

Atom Transfer Oxidative Radical Cascade of Aryl Alkynoates towards 1,1-Dichalcogenide Olefins

An oxidative trifunctionalization of aryl alkynoates has been devised via the chalcogenide radical triggered intramolecular 1,4-aryl migration/decarboxylation cascade to prepare 1,1-dichalcogenide tetrasubstituted alkenes in high yields (up to 98 %). This operationally simple reaction proceeds under metal-free conditions, can be executed on gram scale, and highlights formal 1,1-difunctionalization of alkynes. Synthetic potential of this protocol was demonstrated through a twofold cascade rearrangement to access highly conjugated tetra-selenylated alkenes along with a cross-dehydrogenative annulation to prepare fluorene derivative.

Diphenyl-Diselenide-Mediated Domino Claisen-Type Rearrangement/Cyclization of Propargylic Aryl Ethers: Synthesis of Naphthofuran-2-carboxaldehyde Derivatives

A diphenyl-diselenide-mediated Claisen-type rearrangement/cyclization of propargylic aryl ethers under metal-free conditions is developed, affording various naphthofuran-2-carboxaldehydes in moderate to excellent yield. The broad substrate scope and excellent functional group compatibility suggest that it can be a straightforward and powerful method to access naphthofuran-2-carboxaldehydes in a highly regioselective manner. Moreover, this reaction can be scaled up to the gram scale.

Copper-catalyzed three-component reaction of N-heteroaryl aldehydes, nitriles, and water

An efficient and straightforward method for the synthesis of N-heteroaroyl imides has been successfully developed involving a copper-catalyzed radical-triggered three-component reaction of N-heteroaryl aldehydes, nitriles, and water. Mechanistic studies indicate that the reaction may undergo a radical-triggered Ritter-type reaction in which water serves as the oxygen source for the formation of the C-O bond. The reaction has advantages such as a broad substrate scope for the N-heteroaryl aldehydes, atom economy, and simple operation.

Metal-free switchable ortho/ipso-cyclization of N-aryl alkynamides: divergent synthesis of 3-selenyl quinolin-2-ones and azaspiro[4,5]trienones

A selenium radical triggered switchable ortho/ipso-cyclization cascade of N-aryl alkynamides has been devised under metal-free conditions to access 3-selenyl quinolin-2-ones and 3-selenospiro[4,5]trienones in high yields (up to 98%).

Copper-catalyzed aminothiolation of terminal alkynes with tunable regioselectivity

A simple, mild, and efficient catalytic aminothiolation of terminal alkynes for the synthesis of both 2- and 3-substituted thiazolo[3,2-a]benzimidazoles is established upon catalysis with copper(i), in which complementary regioselectivities could be achieved by using sterically different phenanthroline-based ligands.

Regio- and stereo-selective decarbonylative alkylative arylation of terminal alkynes with aliphatic aldehydes and arenes via dual C–H bond functionalization

Readily available linear/branched aliphatic aldehydes including sugar derivatives were oxidatively decarbonylated into 1˙, 2˙ and 3˙ alkyl radicals for the alkylative arylation of terminal alkynes via dual C–H bond functionalization.

Synthesis of tri-substituted allyl alcohols via a copper/iron co-catalyzed cascade perfluoroalkylation/rearrangement of aryl propynyl ethers

A copper/iron co-catalyzed fluoroalkylation of aryl propynyl ethers for the synthesis of perfluoroalkylated tri-substituted allyl alcohol derivatives is reported.

Catalyst-free synthesis of α-thioacrylic acids via cascade thiolation and 1,4-aryl migration of aryl alkynoates at room temperature

A simple and facile catalyst-free strategy has been developed for the synthesis of α-thioacrylic acids from readily-available aryl alkynoates and thiols at room temperature under air.