Synthesis of 4-functionalized pyrazoles via oxidative thio- or selenocyanation mediated by PhICl₂ and NH₄SCN/KSeCN

• Jialiang Wu,
• Haofeng Shi,
• Xuemin Li,
• Jiaxin He,
• Chen Zhang,
• Fengxia Sun and
• Yunfei Du

Beilstein J. Org. Chem. 2024, 20, 1453–1461, doi:10.3762/bjoc.20.128

• presented a method for the C–H thiocyanation of pyrazoles by using a sustainable catalyst of graphite-phase carbon nitride (g-C3N4) under visible light irradiation (Scheme 1c) [2]. Furthermore, Yao harnessed an electrochemical approach to form the electrophilic SCN+ intermediate, which reacted with

Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C–O bonds in organic transformations

• Mithu Roy,
• Bitan Sardar,
• Itu Mallick and
• Dipankar Srimani

Beilstein J. Org. Chem. 2024, 20, 1348–1375, doi:10.3762/bjoc.20.119

• -mediated deoxygenative trifluoromethylation technique worked with both benzylic and unactivated thiocarbonates. The proposed mechanism starts with the homolysis of (bpy)Cu(III)(CF3)3 by blue-light irradiation, which produces CF3 radicals and (bpy)Cu(II)(CF3)2. Subsequently, the interaction between the CF3

• reduction of xanthates. Under blue-light irradiation, xanthates were reacted with B2cat2 (19) in dimethylacetamide (DMAc), providing the borylated product in decent yield. The methodology was metal-free and did not require conventional heating. Nevertheless, the borylation process was limited to secondary

• directly activated via photoredox catalysis. In 2018, Doyle and co-workers [54] documented a catalytic method for the deoxygenation of benzylic alcohols to toluenes, utilizing phosphines and photoredox catalyst under visible-light irradiation (Scheme 18). In this method, they were able to synthesize

Transition-metal-catalyst-free electroreductive alkene hydroarylation with aryl halides under visible-light irradiation

• Kosuke Yamamoto,
• Kazuhisa Arita,
• Masami Kuriyama and
• Osamu Onomura

Beilstein J. Org. Chem. 2024, 20, 1327–1333, doi:10.3762/bjoc.20.116

• conditions. The key to success is the use of 1,3-dicyanobenzene as a redox mediator and visible-light irradiation, which effectively suppresses the formation of simple reduction, i.e., hydrodehalogenation, products to afford the desired products in good to high yields. Mechanistic investigations proposed

• ][53]. Furthermore, odd-numbered [n]cumulenes have proven to be effective redox mediators for electroreductive radical borylation of unactivated aryl chlorides without visible-light irradiation by the group of Milner [54]. Herein, we report transition-metal-catalyst-free electroreductive alkene

• hydroarylation with (hetero)aryl halides using 1,3-dicyanobenzene as a redox mediator under visible-light irradiation. Results and Discussion We began the investigation of the electroreductive hydroarylation using methyl 4-chlorobenzoate (1a) and methyl acrylate (2a) as model substrates (Table 1). After

Light on the sustainable preparation of aryl-cored dibromides

• Fabrizio Roncaglia,
• Alberto Ughetti,
• Nicola Porcelli,
• Biagio Anderlini,
• Andrea Severini and
• Luca Rigamonti

Beilstein J. Org. Chem. 2024, 20, 1076–1087, doi:10.3762/bjoc.20.95

• be employed in two variants modulated by light irradiation. This external switch can be used to selectively trigger side-chain or core halogenation. Keywords: aryl halides; benzyl halides; bromination; sustainability; Introduction Activation through halogens has become a key strategy in achieving

• ] resulting in easier recyclability. Light irradiation often significantly influences the selectivity of halogenation processes. Photolytic cleavage of molecular halogens gives rise to radicals that are known to favour benzylic functionalisation [17]. Conversely, the same molecular halogens exhibit prominent

• incorporation of the halogen into the product (no bromide byproducts are generated). Unfortunately, the safety and selectivity advantages of using NBS are counterbalanced by other issues. Specifically, light irradiation is often ineffective as an initiator for NBS [26][30], introducing the necessity to add a

Synthesis and characterization of water-soluble C₆₀–peptide conjugates

• Yue Ma,
• Lorenzo Persi and
• Yoko Yamakoshi

Beilstein J. Org. Chem. 2024, 20, 777–786, doi:10.3762/bjoc.20.71

• most other solvents. C60–oligo-Lys and C60–oligo-Glu were characterized by 1H and 13C NMR. Photoinduced 1O2 generation was observed in the most soluble C60–oligo-Lys conjugate under visible light irradiation (527 nm) to show the potential of this highly water-soluble molecule in biological systems, for

• the HRESIMS results (Figure S2, Supporting Information File 1), it was confirmed that the highly water-soluble compound 5a was successfully synthesized. 1O2 generation under visible light irradiation To preliminarily evaluate the synthesized C60–oligo-Lys (5a) as a PS, generation of singlet oxygen was

• measured by the ESR spin trapping method under irradiation of visible light (527 nm green LED). 4-Oxo-TEMP was used as a spin trapping reagent to form an adduct with 1O2, i.e., 4-oxo-TEMPO, which was observed by ESR (Figure 7b). As shown in Figure 7a, upon visible light irradiation, three peaks

SOMOphilic alkyne vs radical-polar crossover approaches: The full story of the azido-alkynylation of alkenes

• Julien Borrel and
• Jerome Waser

Beilstein J. Org. Chem. 2024, 20, 701–713, doi:10.3762/bjoc.20.64

• source. Upon light irradiation, it can release an azide radical by homolysis of the I−N3 bond [46]. We were pleased to see that irradiation of a mixture of styrene (1a), Ph-EBX (2) and Ts-ABZ (3) afforded 17% isolated yield of the desired homopropargylic azide 4a (Table 1, entry 1). Heating the reaction

• under blue light irradiation afforded 4a in 17% NMR yield (Table 2, entry 1). The major byproduct formed during the transformation was identified as diazide 6. When a copper photocatalyst is involved, a lot of diazidation can be observed. We assumed it could be caused by the reaction of Ts-ABZ (3) with

• potassium to tetrabutylammonium (7) reduced the yield to 14% (Scheme 2A). When TMS-alkyne 8 was used, no product formation occurred. In this case, we observed that the initial reaction mixture before light irradiation was colorless. This was surprising, as in all the previous experiments a yellow/orange

Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

• Periklis X. Kolagkis,
• Eirini M. Galathri and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2024, 20, 379–426, doi:10.3762/bjoc.20.36

Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• radicals were successfully generated by subjecting NHPI esters to light irradiation in the presence of the photoreductant 1,6-bis(dimethylamino)pyrene (BDMAP). Following their initial discovery, multiple studies have shown their versatility as radical progenitors under thermal, photochemical, and

• readers to recently published review articles for additional discussion [30][31]. Discussion Mechanism under photochemical conditions In this section we provide a summary of the various conditions and activation modes employed in radical reactions of NHPI esters using visible-light irradiation. Upon

• type addition reactions (Scheme 4A). In 1991, Okada and co-workers reported the addition of alkyl radicals to α,β-unsaturated ketones, by subjecting NHPI esters to visible-light irradiation in the presence of the photocatalyst [Ru(bpy)3]Cl2 and the reductant 1-benzyl-1,4-dihydronicotinamide (BNAH) [37

Synthesis of π-conjugated polycyclic compounds by late-stage extrusion of chalcogen fragments

• Aissam Okba,
• Pablo Simón Marqués,
• Kyohei Matsuo,
• Naoki Aratani,
• Hiroko Yamada,
• Gwénaël Rapenne and
• Claire Kammerer

Beilstein J. Org. Chem. 2024, 20, 287–305, doi:10.3762/bjoc.20.30

• concept, a thin-film of the latter sulfoxide precursor, spin-coated onto a glass sample, yielded full conversion to PBI 6a in only 2 min, confirming the potential application of this precursor in electronic devices. Light irradiation was next tested as an alternative activation method, since

Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• compounds [66]. It was shown that despite the prerequisites for the occurrence of the excited-state proton transfer, monoarylated indigos underwent E–Z photoisomerization upon red-light irradiation at 625 nm. Remarkably, the thermal half-life of the Z-isomer of compound 20b was sensitive to the presence of

Visible-light-induced radical cascade cyclization: a catalyst-free synthetic approach to trifluoromethylated heterocycles

• Chuan Yang,
• Wei Shi,
• Jian Tian,
• Lin Guo,
• Yating Zhao and
• Wujiong Xia

Beilstein J. Org. Chem. 2024, 20, 118–124, doi:10.3762/bjoc.20.12

• trifluoromethyl radical source under light irradiation. Umemoto’s reagent, which is capable of releasing a trifluoromethyl radical via a photoinduced single-electron-transfer (SET) process, is usually employed to enable the trifluoromethylation of unsaturated substrates [25][26][27]. Herein, we report a protocol

• that omitting the photocatalyst led to an even higher yield (Table 1, entry 2), but light irradiation was essential to the reaction (Table 1, entries 3 and 4). Initially, some bases were added into the reaction system considering a deprotonation process, but subsequent investigations indicated that

• 450 nm visible light irradiation is optimal (Table 1, entries 9–12). Furthermore, various types of Umemoto’s reagent were also screened (Table 1, entries 13–15). As Umemoto’s reagent 2b was easier to prepare [29] and the use of 2b did not significantly affect the reaction yield, it was chosen as the

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• smoothly delivered an electron donor–acceptor (EDA) complex II via coulombic interactions. Upon 456 nm blue LED light irradiation, the EDA complex II underwent a single electron transfer (SET) process, followed by subsequent decarboxylation to produce the alkyl radical intermediate A, accompanied by

• light irradiation at either 440 nm or 456 nm, and they occurred in acetone at room temperature, without the need for transition metals or organic dyes as photosensitizers. Interestingly, it was discovered that solvation played a vital role in the overall process. These findings shed light on the

• -anion catalysis under visible light irradiation, as depicted in Scheme 9. Subsequent investigations revealed that redox-active esters 3 and Katritzky salts 15 derived from amino acids could be effectively employed in decarboxylative/deaminative cross-coupling reactions [15]. These reactions enabled the

Selectivity control towards CO versus H₂ for photo-driven CO₂ reduction with a novel Co(II) catalyst

• Lisa-Lou Gracia,
• Philip Henkel,
• Olaf Fuhr and
• Claudia Bizzarri

Beilstein J. Org. Chem. 2023, 19, 1766–1775, doi:10.3762/bjoc.19.129

• [20][21][41]. In addition, the benzimidazolidine derivative, BIH (1,3-dimethyl-2-phenyl-benzo[d]imidazolidine) (shown in Figure 1) suited well as a sacrificial electron donor, because of its high reducing power [47]. The photocatalytic experiments were performed under 420 nm light irradiation unless

Visible-light-induced nickel-catalyzed α-hydroxytrifluoroethylation of alkyl carboxylic acids: Access to trifluoromethyl alkyl acyloins

• Feng Chen,
• Xiu-Hua Xu,
• Zeng-Hao Chen,
• Yue Chen and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2023, 19, 1372–1378, doi:10.3762/bjoc.19.98

• ., Zibo 256401, China 10.3762/bjoc.19.98 Abstract A visible-light-induced nickel-catalyzed cross coupling of alkyl carboxylic acids with N-trifluoroethoxyphthalimide is described. Under purple light irradiation, an α-hydroxytrifluoroethyl radical generated from a photoactive electron donor–acceptor

Selective and scalable oxygenation of heteroatoms using the elements of nature: air, water, and light

• Damiano Diprima,
• Hannes Gemoets,
• Stefano Bonciolini and
• Koen Van Aken

Beilstein J. Org. Chem. 2023, 19, 1146–1154, doi:10.3762/bjoc.19.82

• = 365 nm, 96 W) at a distance of 0.5 cm from the reactor wall. In contrary with what has been reported previously for the catalyst-free oxidation under blue light irradiation [28], the reaction occurs also using water as the solvent (Table 1, entry 2). Running the reaction without adding extra water

• increase the concentration from 0.06 M to 0.6 M (Table 1, entry 7) maintaining approximately the same reaction time, while further concentration increase resulted in substantially slower kinetics (see Supporting Information File 1, Table S2). When performing the reaction in the dark or under visible light

• irradiation (e.g., at 405 or 455 nm) no conversion was observed (Table 1, entries 8 and 9). Finally, the effect of the light intensity was investigated irradiating at 365 nm and it turned out to largely effect the kinetic of the reaction (see Supporting Information File 1, Figure S3). In general, the presence

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• in this Review, with a particular emphasis on the challenges and areas for improvement, such as the standardization of reactors capable to conjugate applied potential and light irradiation either in different modules or within the same flow path. 2 conPET in organic synthesis 2.1 Reductive activation

Photoredox catalysis enabling decarboxylative radical cyclization of γ,γ-dimethylallyltryptophan (DMAT) derivatives: formal synthesis of 6,7-secoagroclavine

• Alessio Regni,
• Francesca Bartoccini and
• Giovanni Piersanti

Beilstein J. Org. Chem. 2023, 19, 918–927, doi:10.3762/bjoc.19.70

• of all ergot alkaloids, specifically the decarboxylative cyclization of DMAT, is still a puzzle even though a radical mechanism has been proposed (Figure 1a) [72][73]. Results and Discussion Herein, we propose that visible light irradiation of the cationic iridium photocatalyst Ir[dF(CF3)ppy]2(dtbbpy

• visible-light irradiation of the photoredox catalyst [Ir(dF(CF3)ppy)2(dtbpy)]PF6 to access the excited state *[Ir(dF(CF3)ppy)2(dtbpy)]PF6, which can trigger SET oxidation of 8. Rapid decarboxylation leads to α-amino radical V (and the reduced photocatalyst), which is intercepted by the pendant double bond

Light-responsive rotaxane-based materials: inducing motion in the solid state

• Adrian Saura-Sanmartin

Beilstein J. Org. Chem. 2023, 19, 873–880, doi:10.3762/bjoc.19.64

• counterparts and/or macroscopic motion of the interlocked materials are achieved. Although further development is needed, these materials are envisioned as privileged scaffolds which will be used for different advanced applications in the area of molecular machinery. Keywords: light irradiation; light

• of rotaxanes in crystalline molecular solids has been studied [38][39]. Rotaxane crystals bearing ferrocene motifs experienced elongation and contraction along the axes in a rapid and reversible manner by simply turning on and off a laser light irradiation, thus providing enough free space in order

• , such as bending, jumping and curling, upon light irradiation. Interestingly, the bending of the crystals could proceed in different directions. As an example, crystals of pseudorotaxane 1a (Figure 1b), having hydrogens as substituents R2 and R3 placed at the ferrocenyl motif and macrocycle

Direct C2–H alkylation of indoles driven by the photochemical activity of halogen-bonded complexes

• Martina Mamone,
• Giuseppe Gentile,
• Jacopo Dosso,
• Maurizio Prato and
• Giacomo Filippini

Beilstein J. Org. Chem. 2023, 19, 575–581, doi:10.3762/bjoc.19.42

• charge transfer state which results in a bathochromic shift of the absorption towards the visible range [19][20]. Upon light irradiation, the EDA complex may undergo an intramolecular single-electron-transfer (SET) process to produce a radical ion pair (D•+, A•−). To avoid the occurrence of a back

• ambient temperature and under visible-light irradiation. Interestingly, this method employs 1,4-diazabicyclo[2.2.2]octane (DABCO) as sacrificial donor in the EDA complex formation with 2. To test the feasibility of our design plan, we focused on the reaction between 3-methylindole (1a, 2 equiv) and α

NaI/PPh₃-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides for the efficient synthesis of quaternary oxindoles

• Dan Liu,
• Yue Zhao and
• Frederic W. Patureau

Beilstein J. Org. Chem. 2023, 19, 57–65, doi:10.3762/bjoc.19.5

• is mediated by visible light irradiation. A wide range of substrates bearing different substituents and derived from ubiquitous carboxylic acids, including α-amino acids, were synthesized and examined under this very mild, efficient, and cost effective transition-metal-free synthetic method. These

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• under visible light irradiation. The advantages of this mixed hetero-/homogeneous catalytic system include the easy separation of the products from NHPI and TiO2, recyclability, selectivity control by TiO2/NHPI ratio, and high efficiency at low TiO2 loading due to the radical chain nature of the

• enantioselective hydroxylation of benzylic positions was achieved using a chiral aryl iodide mediator [148] (Scheme 34). At the first stage, under the action of m-CPBA and sodium bromide an active form of the catalyst ArI3-Br is formed, in which the iodine–bromine bond is cleaved homolytically under visible light

• irradiation. The resulting iodoaryl cation radical abstracts the hydrogen atom from the benzylic position to form a benzyl radical, whose bromination gives the racemic benzyl bromide. The second step takes place without the participation of light and leads to only one enantiomer due to the assistance of the

Synthesis of α-(perfluoroalkylsulfonyl)propiophenones: a new set of reagents for the light-mediated perfluoroalkylation of aromatics

• Durbis J. Castillo-Pazos,
• Juan D. Lasso and
• Chao-Jun Li

Beilstein J. Org. Chem. 2022, 18, 788–795, doi:10.3762/bjoc.18.79

• radicals under light irradiation for the diversification of arenes. To verify the generation of perfluoroalkyl radicals from compounds 1, we conducted an experiment with perfluorohexyl analogue 1b and 1,1-diphenylethylene (7) as a radical trapping agent (Scheme 4). Gratifyingly we observed the formation of

Tetraphenylethylene-embedded pillar[5]arene-based orthogonal self-assembly for efficient photocatalysis in water

• Zhihang Bai,
• Krishnasamy Velmurugan,
• Xueqi Tian,
• Minzan Zuo,
• Kaiya Wang and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2022, 18, 429–437, doi:10.3762/bjoc.18.45

• light might be successfully employed to catalyze these reactions. Here, we used white light (20 W) as a solar light simulator for the photocatalytic dehalogenation reactions. Upon light irradiation, the absorbed light energy could be transferred from the m-TPEWP5G donor to the EsY acceptor through the

• FRET process, whilst the m-TPEWP5G-EsY nanorod assembly could act as a nanoreactor providing a suitable environment for the photochemical catalytic reaction in aqueous solution under visible light irradiation. In the presence of 0.5 mol % m-TPEWP5G-EY in aqueous solution, 2-bromo-1-phenylethanone (1a

• ) gave acetophenone (2a) as product in good yield (97%) under white light irradiation for 2 hours (Table 1 and Supporting Information File 1, Figure S6). In comparison, we added an internal standard (1,3,5-trimethoxybenzene) to the final crude reaction mixture and calculated the NMR yield of the product

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• steps whose main difficulties are the separation of pyridine byproducts and inorganic phosphate (Scheme 20). Kulkarni and co-workers reported a method for menadione reduction mediated by 5,6-O-isopropylidene-ʟ-ascorbic acid (70, R = H) under UV light irradiation [120]. Initial studies were carried out

• using lawsone (4) and after optimization of the reaction conditions, it was extended to other quinones, including menadione (10). The best conditions were 1,2-dimethoxyethane (DME) as solvent, temperature 25 °C, under ultraviolet light irradiation (125 W lamp) using a Pyrex filter in an immersion-well