Visible Light-induced Radical Research Articles

Visible Light-Induced Radical Cascade Functionalization of Quinoxalin-2(1H)-ones: Three-Component 1,2-Di(hetero)arylation Approach with Styrenes and Thianthrenium Salts.

The additive-free visible light-induced three-component 1,2-di(hetero)arylation of styrenes was developed using quinoxalin-2(1H)-ones and thianthrenium salts. The purple visible light excitable quinoxalin-2(1H)-ones were utilized for the single-electron transfer to aryl thianthrenium salts, where the generated aryl radical species underwent the addition cascade to styrenes and quinoxalin-2(1H)-ones. The direct aryl radical addition to quinoxalin-2(1H)-ones also led to the formation of a side product, C3-aryl quinoxalin-2(1H)-ones, capable of a photoredox process to help the formation of 1,2-di(hetero)arylation products.

Recent Advances in Photoinduced Borylation via N-Heterocyclic Carbene Boryl Radicals

AbstractOrganoboron compounds are recognized as essential synthetic intermediates in organic chemistry and have found broad applications in pharmaceutical and materials science. In recent years, the development of novel boronating reagents has opened new avenues for the synthesis of organoboron compounds. Among these, N-heterocyclic carbene boranes (NHC-boranes), with their unique advantages, have garnered sustained interest and have evolved into important precursors for boron-centered radicals, participating in a diverse array of visible-light-induced borylation reactions. This short review primarily focuses on visible-light-induced radical borylation reactions involving NHC-boranes, summarizing the latest advancements in the field and offering inspiration for subsequent research.1 Introduction2 Photoinduced Borylation via NHC-Boryl Radicals2.1 Photoinduced Borylation of Polyfluoroarenes2.2 Photoinduced Borylation of Arenes2.3 Photoinduced Borylation of Alkenes2.4 Photoinduced Borylation of Alkynes2.5 Photoinduced Borylation of Other Substrates3 Conclusion and Future Prospects

Visible Light-Induced Radical Cascade Difluoromethylation/Cyclization of Unactivated Alkenes: Access to CF2H-Substituted Polycyclic Imidazoles.

An efficient and mild protocol for the visible light-induced radical cascade difluoromethylation/cyclization of imidazoles with unactivated alkenes using easily accessible and bench-stable difluoromethyltriphenylphosphonium bromide as the precursor of the -CF2H group has been developed to afford CF2H-substituted polycyclic imidazoles in moderate to good yields. This strategy, along with the construction of Csp3-CF2H/C-C bonds, is distinguished by mild conditions, no requirement of additives, simple operation, and wide substrate scope. In addition, the mechanistic experiments have indicated that the difluoromethyl radical pathway is essential for the methodology.

Synthesis of Acyl Cyclopentaquinolinones through Simultaneous Construction of the Heterocyclic Scaffold and Introduction of the Acyl Group.

Presented herein is an effective and concise synthesis of acyl cyclopentaquinolinone derivatives via the cascade reactions of N-(o-ethynylaryl)acrylamides with α-diazo carbonyl compounds. The formation of product involves a visible light-induced radical formation from α-diazo carbonyl compound followed by its addition onto the acrylamide moiety to trigger double radical annulation, single-electron oxidation, and β-elimination. To our knowledge, this is the first example in which the cyclopentaquinolinone scaffold was constructed along with the introduction of an acyl group under visible light irradiation conditions. Compared with literature methods for similar purpose, this newly developed protocol has advantages such as readily accessible substrates, mild reaction conditions, valuable products, concise synthetic procedure, and high sustainability. With all these merits, this method is expected to find wide applications in the construction of related acyl heterocyclic skeletons.

Photoredox catalyzed reductive trifluoromethylation of imines via a radical umpolung strategy.

Visible light-induced radical umpolung chemistry is utilized to synthesize trifluoromethylated unnatural α-amino acid and amine derivatives. This approach utilizes photoredox catalysis to perform a single-electron-transfer reduction of imines generating a N-centred radical that eventually migrates to the C-centre followed by a radical-radical cross-coupling to deliver reductive trifluoromethylation products.

Visible light-induced radical cyclization of o-alkenyl aromatic isocyanides with thioethers: direct synthesis of 2-thioquinolines

A novel visible-light-induced regioselective radical cyclization reaction of isocyanides with thioethers has been developed. This reaction provides an efficient method for the construction of highly functionalized quinolines in a single step.

Visible light-induced cascade sulfonylation/annulation of ortho-allyloxy chalcones with sodium sulfinates for the synthesis of sulfonated chromane derivatives.

A visible-light-induced radical cascade reaction for the synthesis of structurally diverse sulfonated chromanes is described. The protocol involves the addition of sulfonyl radicals to ortho-allyloxy chalcones and intramolecular Michael addition reactions in the presence of eosin Y as a photocatalyst. Additionally, this protocol shows that it is also an effective method to construct seven-membered oxygen-containing heterocycles. The method features a wide substrate scope, the use of easily accessible materials and excellent functional group tolerance with high to excellent yields. Control experiments and mechanistic studies indicate that a visible light-induced radical cascade process is involved in the transformation.

Synthesis of O-Heterocycle Spiro-Fused Cyclopentaquinolinones and Cyclopentaindenes through Visible Light-Induced Radical Cyclization Reactions.

Presented herein is an effective and sustainable synthesis of O-heterocycle spiro-fused cyclopentaquinolinone and cyclopentaindene derivatives through light-driven cascade reactions of N-(o-ethynylaryl)acrylamides or 2-(2-(phenylethynyl)benzyl)acrylate with various O-heterocycles. Experimental mechanistic studies revealed that these reactions are initiated by visible light-induced radical formation from O-heterocycle and its regioselective addition onto the acrylamide or acrylate moiety followed by 6-exo-dig and 5-endo-trig cascade radical annulation, which is terminated by single electron oxidation and proton elimination. Compared with previously reported synthetic methods for similar purposes, this newly developed protocol has advantages such as a broad substrate scope, extremely mild reaction conditions, excellent atom-economy, high efficiency, and good compatibility with diverse functional groups. With all of these merits, this method is expected to find wide applications in the related research arena.

Porogen Concentration Effect on the Pore Structure and Properties Evolution of Polymer Monolith Based on Oligocarbonate Dimethacrylate OCM-2.

Porous polymer monolith materials of 2-mm thickness were obtained by visible light-induced radical polymerization of oligocarbonate dimethacrylate (OCM-2) in the presence of 1-butanol (10 to 70 wt %) as a porogenic additive. The pore characteristics and morphology of polymers were studied by mercury intrusion porosimetry and scanning electron microscopy. Monolithic polymers with both open and closed pores up to 100 nm in size are formed when the alcohol content in the initial composition is up to 20 wt %. The pore structure in such materials is a system of holes in the bulk of the polymer (hole-type pores). Open interconnected pores with a specific volume up to 2.22 cm3/g and modal pore size up to 10 microns are formed in the volume of the polymer with 1-butanol content of more than 30 wt %. Such porous monoliths are a structure of covalently bonded polymer globules (interparticle-type pores). The free space between the globules represents a system of open interconnected pores. In the transition region of 1-butanol concentrations (from 20 to 30 wt %), areas with both structures and intermediate frameworks, as well as honeycomb structures of polymer globules connected by bridges, are fixed on the polymer surface. It was found that the transition from one type of pore system to another is accompanied by a sharp change in the strength characteristics of the polymer. Approximation of experimental data using the sigmoid function made it possible to determine the concentration of the porogenic agent in the vicinity of which the percolation threshold is observed.

Metal and catalyst-free strategy to access 1,3-thio-heteroaryl BCP derivatives.

The widespread presence of bicyclo[1.1.1]pentane (BCP) and sulfur motifs in pharmaceutical compounds underscores the significance of synthesizing suitably functionalized BCP thioethers. In response, we have developed a metal-free and photocatalyst-free strategy that harnesses visible light-induced radical cascades. This approach culminates in the synthesis of essential thio-BCP derivatives, which serve as crucial precursors for the formation of the corresponding sulfoxides, sulfones, and sulfoximines. Importantly, this methodology exhibits potential for large-scale applications, displaying commendable tolerance towards various functional groups while operating under mild reaction conditions.

Visible light-induced radical cascade acylmethylation/cyclization of 2-(allyloxy)arylaldehydes with α-bromo ketones: access to cyclic 1,5-dicarbonyl-containing chroman-4-one skeletons.

A novel photocatalytic protocol for effective and efficient synthesis of cyclic 1,5-diketones containing chroman-4-one skeletons in moderate to good yields via radical cascade acylmethylation/cyclization of 2-(allyloxy)arylaldehydes with α-bromo ketones has been described. This reaction features a broad substrate scope, good functional group tolerance, and metal- and oxidant-free conditions. An acylmethyl radical-triggered cascade cyclization was involved.

Visible Light-Induced Radical Cyclization for the Construction of 4-Aryl-1,2-dihydronaphthalenes

Visible Light-Induced Radical Cyclization for the Construction of 4-Aryl-1,2-dihydronaphthalenes

Visible light-induced radical polymerization of vinyl acetate mediated by organo-nickel N2O2 Schiff-base complexes

Four nickel(II) complexes with symmetrically substituted N2O2 tetradentate Schiff-base ligands, prepared from the 2:1 condensation of 3-tert-butyl-salicylaldehyde, and ethylenediamine (1), o-phenylenediamine (2), 1,2-cis,trans-cyclohexyldiamine (3), or 1,3-diaminepropane (4), were synthesized. These NiII Schiff-base complexes (1–4) were used as control agents for the polymerization of vinyl acetate (VAc) photoinitiated by diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) according to a photoinduced organometallic-mediated radical polymerization (photo-OMRP) mechanism. All complexes presented good control ability, although the polymerization mediated by 3 showed the best control over molecular weight (Mn matching Mn,th) and dispersity (Ð < 1.50). The livingness of the polymers has been confirmed by LED on and LED off experiments, the polymerization stopped immediately, and no monomer conversion was observed during the light-off period, indicating a negligible concentration of the active radical in the dark. Further, to demonstrate the living nature of this system, block copolymers of poly(vinyl acetate)-b-poly(methyl acrylate) were synthesized using the sequential visible-light-induced process. Kinetic results and computational investigations supported the activation/deactivation equilibrium exerted by complexes 1–4, which occurred on only one face of the complexes via reversible deactivation (RD) mechanism.

Molecular Rubies in Photoredox Catalysis.

The molecular ruby [Cr(tpe) 2 ] 3+ and the tris(bipyridine) chromium(III) complex [Cr(dmcbpy) 3 ] 3+ as well as the tris(bipyrazine)ruthenium(II) complex [Ru(bpz) 3 ] 2+ were employed in the visible light-induced radical cation [4+2] cycloaddition (tpe = 1,1,1-tris(pyrid-2-yl)ethane, dmcbpy = 4,4′-dimethoxycarbonyl-2,2′-bipyridine, bpz = 2,2′-bipyrazine), while [Cr(ddpd) 2 ] 3+ serves as a control system (ddpd = N,N′-dimethyl-N,N′-dipyridin-2-ylpyridine-2,6-diamine). Along with an updated mechanistic proposal for the CrIII driven catalytic cycle based on redox chemistry, Stern-Volmer analyses, UV/Vis/NIR spectroscopic and nanosecond laser flash photolysis studies, we demonstrate that the very weakly absorbing photocatalyst [Cr(tpe) 2 ] 3+ outcompetes [Cr(dmcbpy) 3 ] 3+ and even [Ru(bpz) 3 ] 2+ in particular at low catalyst loadings, which appears contradictory at first sight. The high photostability, the reversible redoxchemistry and the very long excited state lifetime account for the exceptional performance and even reusability of [Cr(tpe) 2 ] 3+ in this photoredox catalytic system.

Visible-light-induced radical cyclization of N-allylbenzamide with [Bis(difluoroacetoxy)iodo]benzene to difluoromethylated dihydroisoquinolinones

A visible light-induced radical difluoromethylation of N-allylbenzamide by [bis(difluoroacetoxy)iodo]benzene to prepare difluoromethylated dihydroisoquinolinones was developed for the first time. To facilitate the oxidative aromatization step, PhI(OAc)2 was employed as oxidant. The inexpensive and readily accessible reagents and the mild reaction conditions render this method an efficient and practical strategy for the synthesis of difluoromethylated dihydroisoquinolinones.

Visible light-induced radical cascade reaction of acryloylbenzamides with N-hydroxyphthalimide esters

An efficient and mild cascade reaction of acryloylbenzamides with N-hydroxyphthalimide (NHPI) esters is disclosed. It goes through radical addition and subsequent cyclization to give 4-alkylated isoquinolinediones in the presence of visible light and photocatalyst Ir[dF(CF3)ppy2](dtbbpy)PF6.

Porous Polymer Scaffolds based on Cross-Linked Poly-EGDMA and PLA: Manufacture, Antibiotics Encapsulation, and In Vitro Study.

Porous polymer materials derived from poly(ethylene glycol dimethacrylate) (poly-EGDMA) and antibiotic containing polylactide (PLA) are obtained for the first time. Porous poly-EGDMA monoliths with a system of open interconnected pores are synthesized by a visible light-induced radical polymerization of EGDMA in the presence of 70wt% of porogenic agent, e.g., 1-butanol, 1-hexanol, 1-octanol, or cyclohexanol. The porosity of the obtained polymers is 75-78%. A modal pore size depends on the nature of the porogen and varies from 0.5µm (cyclohexanol) to 12µm (1-butanol). The polymer matrix made with 1-butanol features the presence of pores ranging from 1 to 100µm. The pore surface of poly-EGDMA matrices is inlayered with poly-D,L-lactide (Mn 23 × 103 Da, PDI1.31). The PLA-modified poly-EGDMA retains a porous structure that is similar to the initial poly-EGDMA but with improved strength characteristics. The presence of antibiotic containing PLA ensures a high and continuous antibacterial activity of the hybrid polymeric material for 7 days. The nontoxicity of all the porous matrices studied makes them promising for clinical tests as osteoplastic materials.

Visible-light induced radical aryldifluoromethylation of N-arylacrylamides by [bis(difluoroacetoxy)iodo]benzene

Visible light-induced radical aryldifluoromethylation of N-arylacrylamides using [bis(difluoroacetoxy)iodo]benzene as a difluoromethylation reagent is reported for the first time. The inexpensive and readily accessible reagents and the mild reaction conditions render this method an alternative and practical strategy for the synthesis of difluoromethyl substituted oxindoles.

Visible Light-Induced Radical Addition/Annulation to Construct Phenylsulfonyl-Functionalized Dihydrobenzofurans Involving an Intramolecular 1,5-Hydrogen Atom Transfer Process.

A visible light-induced radical cascade reaction of 2-alkynylarylethers with sodium sulfinates was established for the synthesis of sulfonyl-functionalized dihydrobenzofurans, and an intramolecular 1,5-hydrogen atom transfer was involved in this transformation. This process provided an efficient and convenient C-C formation protocol for the construction of a dihydrobenzofuran ring. Various substituents on 2-alkynylarylethers and sodium sulfinates were tolerated in the reaction, and the corresponding products were obtained in moderate to good yields.

Visible Light-Induced Transformation of Polymer Networks

Light-responsive polymeric networks have shown diverse applications as spatiotemporally tunable materials. Herein, we present a straightforward and facile strategy to fabricate photoexpandable/transformable-polymer networks (PET-PNs) that can undergo a growth mechanism via visible light-induced radical polymerization. Our PET-PN fabrication and its subsequent photogrowth process is based on using a trithiocarbonate chain transfer agent, dibenzyl trithiocarbonate (DBTTC), that can be activated by either photoredox catalysis or direct photolysis (photoiniferter) mechanisms. We first demonstrated the use of a photoredox catalyst (5,10,15,20-tetraphenyl-21H,23H-porphine zinc (ZnTPP) for initiating the reversible addition–fragmentation chain-transfer (RAFT) polymerization of a cross-linkable system consisting of difunctional monomers (i.e., tetra(ethylene glycol) diacrylate (TEGDA)) alongside with a monofunctional monomer (i.e., oligo(ethylene glycol) methyl ether acrylate) (OEGA)) under red LED light (λ max =...