Red light excitation: illuminating photocatalysis in a new spectrum

• Lucas Fortier,
• Corentin Lefebvre and
• Norbert Hoffmann

Beilstein J. Org. Chem. 2025, 21, 296–326, doi:10.3762/bjoc.21.22

• the radical cation iPr2NEt•+ (iPr2NEt/iPr2NEt•+ = +0.72 V vs SCE) and the reduction of O2 by the reduced photocatalyst, forming the superoxide radical anion O2•− (O2/O2•− = −0.57 V vs SCE). This latter can then react with arylboronic acids 59 to give, after hydrolysis, phenol derivatives 60. Other

• involving π–π-stacking [75]. The resulting radical anion releases NO also yielding the anion 63. Electron transfer to the radical cation of the photocatalyst regenerates it. In this step, the neutral radical 64 is also formed. Hydrogen abstraction (hydrogen atom transfer, HAT) yields compound 65. NO and the

Oxidation of [3]naphthylenes to cations and dications converts local paratropicity into global diatropicity

• Abel Cárdenas,
• Zexin Jin,
• Yong Ni,
• Jishan Wu,
• Yan Xia,
• Francisco Javier Ramírez and
• Juan Casado

Beilstein J. Org. Chem. 2025, 21, 277–285, doi:10.3762/bjoc.21.20

• oxidized species of compounds 1 and 2 are shown in Figure 3. Initial electrochemical oxidation of 1 resulted in the progressive replacement of its absorption bands by three new features, which were assigned to the 1•+ radical cation, namely at 352/369 nm, a multiplet in the 500–600 nm interval, and a broad

• peak centered at 1173 nm. Further oxidation resulted in a quite silent vis–NIR spectrum characterized by one main peak at 312 nm, which was assigned to the 12+ dication. The spectrum of the first oxidized species of 2, the radical cation 2•+, shows a band at 363 nm, a shoulder at 439 nm, and a broad

• between the bonds of parent molecules. In our case, they will reveal the transformation of the CC bond skeleton upon oxidation. Figure 6 summarizes the set of k[ν(CC)] values calculated for neutral, radical cation, and dication of m-1 and m-2, as well as those obtained at the same level for individual NAP

Recent advances in electrochemical copper catalysis for modern organic synthesis

• Yemin Kim and
• Won Jun Jang

Beilstein J. Org. Chem. 2025, 21, 155–178, doi:10.3762/bjoc.21.9

• cation 30. The [Mes-Acr-Ph]• is regenerated to the ground-state acridinium [Mes-Acr-Ph]+ through a single oxidation step on the anode, and the heteroarene radical cation 30 then reacts with the arylalkene 27 to form a benzylic radical intermediate 31. The benzylic radical intermediate 31 is subsequently

• Figure 11. Initially, the Cu(II) catalyst 50 coordinates with substrate 47 and amine electrophile 48 to generate Cu(II) intermediate 51, which is then oxidized by the iodine radical to form Cu(III) complex 52. Cu(III) complex 52 undergoes electron transfer to produce radical cation intermediate 53

• . Subsequent intramolecular amine transfer to the radical cation intermediate 53, followed by ligand exchange, yields amination product 49 and Cu(I) species 55. Cu(II) catalyst 50 is regenerated by anodic oxidation, thereby completing the catalytic cycle. In 2019, Nicholls et al. reported a Cu-catalyzed

Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts

• Mandeep K. Chahal

Beilstein J. Org. Chem. 2024, 20, 3085–3112, doi:10.3762/bjoc.20.257

• or transform into a long-lived radical cation by substrate reduction, which are the fundamentals of photoredox catalysis (Figure 13a). Monomeric porphyrins and supramolecular porous frameworks composed of porphyrin building blocks, such as metal-organic frameworks (MOF) and covalent organic

Recent advances in transition-metal-free arylation reactions involving hypervalent iodine salts

• Ritu Mamgain,
• Kokila Sakthivel and
• Fateh V. Singh

Beilstein J. Org. Chem. 2024, 20, 2891–2920, doi:10.3762/bjoc.20.243

• group with a less hindered portion is observed. The mechanism revealed the reaction undergoes the homolytic cleavage of the diaryliodonium salt to produce an iodoaryl radical cation, which further reacts with the amine to acquire the corresponding diaryl amines. Moreover, a similar reaction tried with a

Synthesis of spiroindolenines through a one-pot multistep process mediated by visible light

• Francesco Gambuti,
• Jacopo Pizzorno,
• Chiara Lambruschini,
• Renata Riva and
• Lisa Moni

Beilstein J. Org. Chem. 2024, 20, 2722–2731, doi:10.3762/bjoc.20.230

• Scheme 6. Based on the results reported by Zeitler [28], several mechanisms are involved in the oxidation of N-Ph-THIQ. The most probable involves the photoexcitation of the EDA (Electron Donor-Acceptor) complex promoting an electron transfer from N-Ph-THIQ to BrCCl3 to afford the amine radical cation

A review of recent advances in electrochemical and photoelectrochemical late-stage functionalization classified by anodic oxidation, cathodic reduction, and paired electrolysis

• Nian Li,
• Ruzal Sitdikov,
• Ajit Prabhakar Kale,
• Joost Steverlynck,
• Bo Li and
• Magnus Rueping

Beilstein J. Org. Chem. 2024, 20, 2500–2566, doi:10.3762/bjoc.20.214

• cation is formed by oxidation of the substrate at the anode. This radical cation is subsequently deprotonated to produce an allyl radical. The allyl radical is further oxidized to form the allyl cation, which is then attacked by the nucleophilic sulfonamide, leading to the formation of the desired C–N

• , several structurally diverse aromatic acetals have been synthesized. Dehydroabietic and norcholanoic acid derivatives have been effectively modified using the developed protocol. The reaction is reported to involve the oxidation of the benzene core, followed by electron transfer to the radical cation, and

• protocol for the installation of sulfonamide groups using commercially available SO2 and amines (Scheme 12) [20]. This method is highly appealing for industrial applications and LSF. The proposed mechanism begins with the anodic oxidation of the arene substrate. The resulting radical cation intermediate is

Photoredox-catalyzed intramolecular nucleophilic amidation of alkenes with β-lactams

• Valentina Giraldi,
• Giandomenico Magagnano,
• Daria Giacomini,
• Pier Giorgio Cozzi and
• Andrea Gualandi

Beilstein J. Org. Chem. 2024, 20, 2461–2468, doi:10.3762/bjoc.20.210

• reactions limit the utility of this approach. Herein, we report an intramolecular photoredox cyclization of alkenes with β-lactams in the presence of an acridinium photocatalyst. The approach uses an intramolecular nucleophilic addition of the β-lactam nitrogen atom to the radical cation photogenerated in

• functionalization of amides with alkenes under photoredox conditions. Another viable approach for amide functionalization through photoredox catalysis involves the nucleophilic addition, in the presence of base, of an amide to a radical cation obtained by oxidation of an unfunctionalized alkene moiety (Figure 1A

• functionalization of amides with alkenes under oxidative conditions, the oxidation potential of the alkene plays a pivotal role in the oxidation to a radical cation through photoredox catalysis [26]. Alkenes that are less functionalized possess a higher oxidation potential, necessitating the use of potent

Synthesis, electrochemical properties, and antioxidant activity of sterically hindered catechols with 1,3,4-oxadiazole, 1,2,4-triazole, thiazole or pyridine fragments

• Daria A. Burmistrova,
• Andrey Galustyan,
• Nadezhda P. Pomortseva,
• Kristina D. Pashaeva,
• Maxim V. Arsenyev,
• Oleg P. Demidov,
• Mikhail A. Kiskin,
• Andrey I. Poddel’sky,
• Nadezhda T. Berberova and
• Ivan V. Smolyaninov

Beilstein J. Org. Chem. 2024, 20, 2378–2391, doi:10.3762/bjoc.20.202

• in the reaction with a diphenylpicrylhydrazyl (DPPH) radical, ABTS·+ radical cation, CUPRAC test, and inhibition process of superoxide radical anion formation by xanthine oxidase (NBT assay). The presence of a catechol fragment and thioether or thione groups determines the ability to neutralize

• fragment favors the pronounced antiradical activity. The use of ABTS radical cation to assess the antioxidant capacity of compounds is one of the widely used methods which is based on the transfer of an electron from the studied molecules to the acceptor [67]. The obtained IC50 values for synthesized

Harnessing the versatility of hydrazones through electrosynthetic oxidative transformations

• Aurélie Claraz

Beilstein J. Org. Chem. 2024, 20, 1988–2004, doi:10.3762/bjoc.20.175

• formation of dimeric side products. Cyclic voltammetry analysis suggested an initial anodic single electron transfer (SET) to radical cation 5, cyclization and deprotonation. Subsequent SET oxidation in solution by 5 led to cation 7. Final deprotonation furnished aromatic cycle 4. In 2022, Zhang et al

• species to be oxidized, initial SET anodic oxidation of the hydrazone furnishes the highly electrophilic radical cation species D, which undergo nucleophilic addition of the second partner and deprotonation to produce hydrazinyl radical F (route a). Alternatively, if the partner possesses a lower

• + (E1/2(TAC2+/TAC+) = +1.3 V vs SCE). Subsequent SET between highly oxidizing photoexcited species TAC2+* (E1/2(TAC2+*/TAC+) = +3.3 V vs SCE) and 150 generated distonic species 151 by denitrogenation. After Wagner–Merweein shift, the resulting radical cation 152 would undergo SET reduction from an

Development of a flow photochemical process for a π-Lewis acidic metal-catalyzed cyclization/radical addition sequence: in situ-generated 2-benzopyrylium as photoredox catalyst and reactive intermediate

• Masahiro Terada,
• Zen Iwasaki,
• Ryohei Yazaki,
• Shigenobu Umemiya and
• Jun Kikuchi

Beilstein J. Org. Chem. 2024, 20, 1973–1980, doi:10.3762/bjoc.20.173

• , initiating further radical reactions through the formation of radical cations B. Nucleophilic arylmethyl radicals C, which are generated from radical cations B by desilylation, undergo an addition reaction with 2-benzopyrylium intermediates A, giving rise to the corresponding radical cation. Catalytic cycle

• II is completed through a SET from D, a reduced form of the photoredox catalyst 2-benzopyrylium intermediates A, to the generated radical cation, affording 1H-isochromene derivatives 3. The photoredox cycle is also completed with the regeneration of cations A through SET from D. The most distinctive

Novel oxidative routes to N-arylpyridoindazolium salts

• Oleg A. Levitskiy,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2024, 20, 1906–1913, doi:10.3762/bjoc.20.166

• amount (5%) of the N,N’-diaryldihydrophenazine radical cation that is the byproduct corresponding to the intermolecular oxidative C–N coupling of the diarylamine A1 was detected in the reaction mixture. This emphasizes that the both processes are of the same nature and proceed through the same

• intermediate (i.e., the diarylamines’ radical cation) and indicates the dominance of the intramolecular cyclization over the intermolecular C–N coupling process. Oxidation of diarylamines in the presence of an excess of trifluoroacetic acid gave no targeted pyridoindazolium salts, whereas the amount of

• A1, similarly to the chemical oxidation. The radical cation of dihydrophenazine formed was isolated and studied using ESR and HRMS methods. The ESR spectrum (see Supporting Information File 1) was typical for this type of compounds: a characteristic quintet due to hyperfine splitting on two

Electrochemical radical cation aza-Wacker cyclizations

• Sota Adachi and
• Yohei Okada

Beilstein J. Org. Chem. 2024, 20, 1900–1905, doi:10.3762/bjoc.20.165

• cations that offer unique reactivities as intermediates in various bond-formation processes. Such intermediates can potentially take part in both radical and ionic bond formation; however, the mechanisms involved are complicated and not fully understood. Herein, we report electrochemical radical cation

• aza-Wacker cyclizations under acidic conditions, which are expected to proceed via radical cations generated by single-electron oxidation of alkenes. Keywords: alkene; aza-Wacker cyclization; electrochemistry; radical cation; sulfonamide; Introduction Activating bench-stable substrates is the first

• representative radical cation precursors that are widely used to realize the formation of unique bonds. The respective radical cations are trapped by various nucleophiles under radical and/or ion control, where kinetic and/or thermodynamic effects are expected to be dominant. Typical examples that clearly show

Synthesis of polycyclic aromatic quinones by continuous flow electrochemical oxidation: anodic methoxylation of polycyclic aromatic phenols (PAPs)

• Hiwot M. Tiruye,
• Solon Economopoulos and
• Kåre B. Jørgensen

Beilstein J. Org. Chem. 2024, 20, 1746–1757, doi:10.3762/bjoc.20.153

• chrysenols nor phenanthrols, suggesting a chemically irreversible reaction of the radical cation intermediate with the ensuing product no longer being electrochemically active within the potential window of the CV scans. However, a reduction peak was observed for compound 1b (see Figure S2 in Supporting

Benzylic C(sp³)–H fluorination

• Alexander P. Atkins,
• Alice C. Dean and
• Alastair J. J. Lennox

Beilstein J. Org. Chem. 2024, 20, 1527–1547, doi:10.3762/bjoc.20.137

• functional groups on the aromatic ring and adjacent to the benzylic position. Mechanistic investigations suggested an initial electron transfer to generate a radical cation en route to the intermediate benzylic radical, rather than a HAT process, however, the authors did not distinguish between a stepwise

• radical cation II. The acidity of benzylic protons is augmented after oxidation of the adjacent π-system, facilitating rapid proton transfer at this position, resulting in benzylic radical III [13][88]. Single-electron oxidation of the resulting benzylic radical is facile and expected to occur readily

• hypervalent fluoroiodane reagents [92][93]. In 2000, Fuchigami and co-workers demonstrated the effectiveness of these reagents in the oxidative electrochemical fluorination of benzylic positions adjacent to thiocyanate groups (Figure 36) [94]. The authors proposed anodic oxidation to generate a radical cation

Synthesis of cyclic β-1,6-oligosaccharides from glucosamine monomers by electrochemical polyglycosylation

• Md Azadur Rahman,
• Hirofumi Endo,
• Takashi Yamamoto,
• Shoma Okushiba,
• Norihiko Sasaki and
• Toshiki Nokami

Beilstein J. Org. Chem. 2024, 20, 1421–1427, doi:10.3762/bjoc.20.124

• product of monomer 6. The proposed mechanism is shown in Scheme 2. Anodic oxidation of thioglycoside 6 generated radical cation 11, which was converted to glycosyl triflate 12. 1,6-Anhydrosugar 7 was produced via 4C1-to-1C4 conformational change of the pyran ring to generate cation intermediate 13

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

• iridium photocatalyst [Ir(dF(CF3)ppy)2(dtbbpy)]PF6 leads to excited-state *[Ir(III)], Ered (*[Ir(III)]/[Ir(II)]) = +1.21 V, possessing sufficient energy to oxidize PPh3, forming the triphenylphosphine radical cation. Subsequently, benzoic acid undergoes deprotonation facilitated by a base, producing

• benzoate. This benzoate then reacts with the triphenylphosphine radical cation, resulting in the formation of the phosphoranyl radical intermediate, which undergoes β-scission, leading to the formation of a benzoyl radical, accompanied by the liberation of a triphenylphosphine oxide molecule. After this

• salicylic acid derivatives and aryl acetylenes. Due to irradiation with blue light, Mes–Acr–Me+ gets excited to Mes–Acr–Me+* and takes up a single electron from Ph2S. The reaction of the diphenyl sulfide radical cation with carboxylate and successive acyloxy C–O bond cleavage forms diphenyl sulfoxide and an

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• as the ionization product resulting from a consecutive two-photon absorption at the selected high laser intensity [69][70], yielding the corresponding long-lived radical cation with second-order decay that is typical for oxidized/reduced species, and a solvated electron as by-product. The latter is

• in equilibrium with the dimeric solvent radical anion in MeCN, it weakly absorbs in our detection window and this species is rather short-lived compared to the triplet as well as the radical cation [71]. The oscillator strengths for the electronic transitions of 3Aza-H (purple) and the radical cation

• contribution of the radical cation to the TA signal at 640 nm is only minor, which allows us to estimate a triplet lifetime of ≈28 µs at this detection wavelength. Based on our observations, an isolated triplet spectrum can be obtained from the spectral difference between the black and the red spectrum in

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• state thereof, denoted with an asterisk, possessing a reduction potential of 2.0 V versus SCE (saturated calomel electrode). Subsequently, this excited state undergoes quenching through photoinduced electron transfer (PET) with styrene 5. The resulting vinyl radical cation exhibits electrophilicity at

• the homobenzylic position, engaging in an anti-Markovnikov manner with a formal chloride nucleophile. The ultimate step involves hydrogen atom transfer (HAT) with thiol 148, culminating in the formation of the desired product 147. Therefore, the generation of the vinyl radical cation plays a pivotal

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

• . Intramolecular radical addition into the radical cation of the furan ring would then form cation 50 before nucleophilic capture by H2O leads to product 45. In 2020, the Wang group reported the functionalization of enamides employing radicals derived from NHPI esters in combination with indole nucleophiles [57

• hydrogen atom to terminate the radical reaction. The proposed mechanism of the hydroalkylation cascade is depicted in Scheme 13B. Upon excitation of complex 59 with blue light, intra-complex SET takes place from the HE to the NHPI ester, leading to the formation of tert-butyl radical 64 and radical cation

• ). Additionally, Minisci-type additions were carried out in the presence of protonated quinoline radical acceptor 83, affording product 84 (Scheme 16A). Mechanistically, this activation mode involves an intra-complex SET that forms the Ph3P–NaI radical cation species 85 and the corresponding radical anion 86

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• lifetime of 71 ps in toluene. Meanwhile, the absorption at 640 nm, corresponding to the ZnP radical cation, was not observed. The results obtained from Rehm–Weller’s equation [146] suggested that photoinduced electron transfer was thermodynamically permitted in 86. However, ultrafast energy transfer from

• , the emergence of the weak absorption band of the ZnP radical cation at 640 nm was hindered by the overwhelming absorption intensity of the residual porphyrin. The transient absorption spectra of 87 were obtained in benzonitrile solvent, which was expected to stabilize the CS state. Absorption

• corresponding to the ZnP radical cation was clearly observed with a lifetime of 2.3 μs. The occurrence of such a long-living CS state can be rationally associated with the Marcus-inverted-region [143] behavior of the charge-recombination process. For 88, which has no spacer between ZnP and TCBD, as opposed to

Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations

• Laura Abella,
• Gerard Novell-Leruth,
• Josep M. Ricart,
• Josep M. Poblet and
• Antonio Rodríguez-Fortea

Beilstein J. Org. Chem. 2024, 20, 92–100, doi:10.3762/bjoc.20.10

• and reversible process named phase 1. We find that the barriers for the radical cation mechanism are significantly lower than those found for the neutral pathway. The peapod is mainly providing one-dimensional confinement for the reaction to take place in a more efficient way. Car–Parrinello

• the reaction either via singlet excitation or via radical cation formation (Scheme 1). Estimation of the activation barrier for the [2 + 2] cycloaddition when the nanotube acts as a sensitizer is 33.5 ± 6.8 kJ mol−1. This value agrees with computational predictions for the reaction via an excited

• can also be activated through the formation of C60+• radical cation [3][9]. This mechanistic proposal for phase 1, which to our knowledge has not yet been explored in detail inside a carbon nanotube, is analyzed here and compared to the non-activated C60 dimerization. Finally, some intermediates for

Multi-redox indenofluorene chromophores incorporating dithiafulvene donor and ene/enediyne acceptor units

• Christina Schøttler,
• Kasper Lund-Rasmussen,
• Line Broløs,
• Philip Vinterberg,
• Ema Bazikova,
• Viktor B. R. Pedersen and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2024, 20, 59–73, doi:10.3762/bjoc.20.8

• Tetrathiafulvalene (TTF, Figure 1) is a redox-active molecule that has been widely explored in materials chemistry and supramolecular chemistry [1][2][3][4][5][6][7][8]. TTF reversibly undergoes two sequential one-electron oxidations, generating first a radical cation (TTF+•) and subsequently a dication (TTF2

• rate: 0.1 V/s. All potentials are depicted against the Fc/Fc+ redox couple. Radical anion (left), dianion (middle), and radical cation (right) of compound 23; the radical anion has a 14πz-aromatic ring (highlighted in blue; only counting 2π-electrons of each triple bond, here defined as those in πz