An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• by the excitation with visible light, the homolytic cleavage of disulfide generates an arylthiyl radical (ArS•), which adds to diphenylacetylene to form a free-radical intermediate 28. Subsequently, this intermediate traps a molecule of singlet oxygen (1O2), and the thiyl radical is regenerated to

• the photoexcited disulfide–enol complex 35 from the disulfide–enol complex 34 under irradiation. Then, the photoexcited complex 35 reacts with triplet oxygen (3O2) to yield the reactive 1O2. The subsequent reaction of singlet oxygen with the disulfide–enol complex 34 furnishes the desired

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• converted the aryl and alkyl α-keto acids 17.1 to the 3-acylindoles 17.3 using rose bengal (OD15) as a photocatalyst under aerobic conditions. Mechanistic studies suggest that rose bengal (OD15) acts as an energy transfer sensitizer generating singlet oxygen. The authors proposed that the latter would be

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• semicontinuous process was reported for the synthesis of racemic fluorinated phenylalanine·HCl starting from benzylamines 47a–c. Thus, a singlet oxygen-driven photooxidative cyanation of amines 47a–c using tetraphenylporphyrin (Tpp), followed by an acid-mediated hydrolysis of the intermediate fluorinated α-amino

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• catalysts in both oxidative and reductive quenching. The use of porphyrins as a photosensitizer for singlet oxygen generation is presented in the second topic, which was subdivided into two sections: pericyclic reactions and heteroatom oxidations. The first section describes the use of singlet oxygen in

• pericyclic reactions with olefins and dienes, and the second deals with heteroatom oxidations carried out by singlet oxygen. Review Porphyrins as photoredox catalysts Porphyrins and metalloporphyrins have been extensively studied as photosensitizers in singlet oxygen generation, but underexploited as

• photoredox catalysts up to now [10][22]. Remarkably the same system can be applied for both pathways, oxidative and reductive processes, beyond singlet oxygen generation [9][10][23]. Only a few photocatalysts can be applied in both photoredox processes (oxidative and reductive quenching), for example, [Ru

Regioselectively α- and β-alkynylated BODIPY dyes via gold(I)-catalyzed direct C–H functionalization and their photophysical properties

• Takahide Shimada,
• Shigeki Mori,
• Masatoshi Ishida and
• Hiroyuki Furuta

Beilstein J. Org. Chem. 2020, 16, 587–595, doi:10.3762/bjoc.16.53

• triplet state can be another pathway to understand the lower emission quantum yield of the BODIPYs. However, reactive singlet oxygen species (1O2) was not observed under the aerobic conditions probed by the near-infrared photoluminescence at 1270 nm. The above spectral features were likewise shown with

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• these into the triplet state and brings benefits known from UV systems to NIR systems either. This can be the generation of singlet oxygen and would enable the use of NIR absorbers in photodynamic therapy. Another benefit can be seen to increase the efficiency of photoinduced electron transfer needed in

• of the diaryl iodonium salt, Scheme 6. This occurred from the singlet state while no indication has been available regarding the involvement of triplet states [89]. Sometimes singlet oxygen was believed to play a major role to explain the bleaching of cyanines [90][91]. This report does not consist

• with our findings where no formation of singlet oxygen was confirmed [89]. Other pathways request attention which could be formation of the O2-• radical to propose an alternative [90]. Such intermediates exhibit high reactivity resulting in similar photoproducts as disclosed for photoinduced electron

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• radical to escape from the cage. However, performing the same experiment for the rest of the amidoxime derivatives 8–11 (20% DMSO, data not shown), we did not observe any enhancement of the photocleavage above the statistical error. Counting for the singlet oxygen it is not very clear whether it is

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

• Valentina A. Ol’shevskaya,
• Elena G. Kononova and
• Andrei V. Zaitsev

Beilstein J. Org. Chem. 2019, 15, 2704–2709, doi:10.3762/bjoc.15.263

• widely used to generate singlet oxygen for PDT applications [9][23]. We intend here to combine within one molecule the structural specificity of a meso-fuorinated porphyrin/chlorin macrocycle and maleimide units to develop novel multifunctional compounds with improved properties for various applications

• conjugated to a cystein residue of serum albumin via a Michael addition reaction. At the same time, it is well known that 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin and its chlorin derivatives generate singlet oxygen by the light irradiation under atmospheric oxygen [31]. These tetrapyrrole macrocycles

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• ). This dendrimer retains some fluorescence as well as very high TPA cross-sections in a broad range of the NIR (near infra-red) biological spectral window. Furthermore, it displays significant singlet oxygen production, thus this dendrimer combines unique properties for bioimaging and anticancer therapy

• . Indeed, photodynamic therapy is used in oncology for the treatment of certain types of tumors. It is based on the activation by light of photosensitizers, able to generate singlet oxygen and/or other reactive oxygen species (ROS), to induce the destruction of the targeted tissues [66]. The dendrimer

α-Photooxygenation of chiral aldehydes with singlet oxygen

• Dominika J. Walaszek,
• Magdalena Jawiczuk,
• Jakub Durka,
• Olga Drapała and
• Dorota Gryko

Beilstein J. Org. Chem. 2019, 15, 2076–2084, doi:10.3762/bjoc.15.205

• University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland 10.3762/bjoc.15.205 Abstract Organocatalytic α-oxygenation of chiral aldehydes with photochemically generated singlet oxygen allows synthesizing chiral 3-substituted 1,2-diols. Stereochemical results indicate that the reaction in the presence

• dichroism (ECD) and TD-DFT methods. Keywords: 1,2-diols; ECD; enamines; organocatalysis; porphyrins; silyl ethers of diarylprolinols; singlet oxygen; Introduction Carbonyl compounds are one of the most important building blocks in organic synthesis. As a consequence, there is a constant need for new

• ], TEMPO [4], or benzoyl peroxide [5][6][7][8]. Therefore, the use of environmentally friendly reagents instead is highly desirable. Along this line, singlet oxygen by being easily photochemically generated from triplet oxygen in the presence of organic dyes seems promising. Despite its high reactivity and

Synthesis of a water-soluble 2,2′-biphen[4]arene and its efficient complexation and sensitive fluorescence enhancement towards palmatine and berberine

• Xiayang Huang,
• Xinghua Zhang,
• Tianxin Qian,
• Junwei Ma,
• Lei Cui and
• Chunju Li

Beilstein J. Org. Chem. 2018, 14, 2236–2241, doi:10.3762/bjoc.14.198

• of isoquinoline alkaloids‘ family, P and B can produce singlet oxygen (1O2) and oxide biological substrates under light, and thereby have applications in photodynamic therapy (PDT) [48][49][50]. However, their low quantum yields limit such applications, which could be potentially improved or restored

Synthesis and photophysical studies of a multivalent photoreactive Ru^II-calix[4]arene complex bearing RGD-containing cyclopentapeptides

• Sofia Kajouj,
• Lionel Marcelis,
• Alice Mattiuzzi,
• Adrien Grassin,
• Damien Dufour,
• Pierre Van Antwerpen,
• Didier Boturyn,
• Eric Defrancq,
• Mathieu Surin,
• Julien De Winter,
• Pascal Gerbaux,
• Ivan Jabin and
• Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

• upon light irradiation. Two types of photooxidative damages can be induced: (i) by photosensitization of singlet oxygen and subsequent generation of highly reactive oxygen species (ROS) (type I photosensitization) or (ii) by direct oxidative electron transfer to biological molecules such as DNA or

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• acid to afford 241 in almost quantitative yield. Bicyclic endoperoxides generated from the cycloaddition of singlet oxygen to 1,3-dienes serve as excellent synthetic precursors and have led to developments in tropone chemistry [170][171][172]. Taking advantage of the endoperoxide transformation, the

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• after the radical thiol–ene cross-coupling of the thiol with the alkene, the respective sulfide-adduct is oxidized by in situ generated singlet oxygen instead of the superoxide radical anion. Their method was compatible with a similar scope of thiols and alkenes like the one of Wei and Wang. A very

• is accomplished by in situ generated singlet oxygen, which is generated by energy-transfer of the excited state of Eosin Y and only possible under aerobic conditions. The authors also found that zinc acetate is beneficial for the selective oxidation. A series of electron-rich and electron-poor

Preparation and isolation of isobenzofuran

• Morten K. Peters and
• Rainer Herges

Beilstein J. Org. Chem. 2017, 13, 2659–2662, doi:10.3762/bjoc.13.263

• + 8] and [4 + 6] additions [7][8][9][10]. Highly strained alkenes and alkynes have been trapped with isobenzofurans. 1,3-Diphenylisobenzofuran is the preferred trapping reagent for singlet oxygen and is used to quantify the generation of 1O2 in photodynamic therapy [4][11]. The most important

Synthesis and application of trifluoroethoxy-substituted phthalocyanines and subphthalocyanines

• Satoru Mori and
• Norio Shibata

Beilstein J. Org. Chem. 2017, 13, 2273–2296, doi:10.3762/bjoc.13.224

• laser only to the target tumor cells. The features of ideal PDT agents include, among others: i) strong absorption in the red wavelength region; ii) non-aggregation property; iii) high biocompatibility; iv) good selectivity to cancer cells; v) high quantum yield of singlet oxygen [96]. Since the PDT

Superstructures with cyclodextrins: Chemistry and applications IV

• Gerhard Wenz

Beilstein J. Org. Chem. 2017, 13, 2157–2159, doi:10.3762/bjoc.13.215

• , buckminsterfullerene C60 was covalently linked to two γ-CD rings [14]. This conjugate is highly soluble in water because it forms a sandwich-like self-complex, which makes it particularly useful as a sensitizer for singlet oxygen 1O2 generation [14]. Amphiphilic CD derivatives with oligoethylene oxide side chains form

Detection of therapeutic radiation in three-dimensions

• John A. Adamovics

Beilstein J. Org. Chem. 2017, 13, 1325–1331, doi:10.3762/bjoc.13.129

• the methine carbon provide the greatest color stability. In contrast the para-substituent DTBs have demonstrated the most facile color fading [39]. A combination of singlet oxygen and light is thought to be the cause of bleaching of DTBs [54] even though for these dosimeters the effect is minimal [55

Energy down converting organic fluorophore functionalized mesoporous silica hybrids for monolith-coated light emitting diodes

• Markus Börgardts and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2017, 13, 768–778, doi:10.3762/bjoc.13.76

• aggregation induced self-quenching and singlet oxygen dependent dye degradation can be efficiently prevented [14][15]. By the rigid silica host framework bimolecular photochemical reactions are also suppressed [16]. Additionally, mesoporous materials possess the crucial advantage that they can be synthesized

Exploring endoperoxides as a new entry for the synthesis of branched azasugars

• Svenja Domeyer,
• Mark Bjerregaard,
• Henrik Johansson and
• Daniel Sejer Pedersen

Beilstein J. Org. Chem. 2017, 13, 644–647, doi:10.3762/bjoc.13.63

• + 2]-cycloaddition between a diene and singlet oxygen. The endoperoxides were dihydroxylated and protected to provide a series of endoperoxide building blocks for organic synthesis, with potential use as precursors for the synthesis of branched azasugars. Preliminary exploration of the chemistry of

• . Results and Discussion We set out to synthesise two diene substrates for a photochemical [4 + 2]-cycloaddition with singlet oxygen to provide two different endoperoxides (Scheme 1, n = 1–2). Based on literature precedent Boc-protection was utilised for the amino group (Scheme 2) [13][14]. Moreover, the

• sufficient material of dienes 14–16 was available to proceed to the critical cycloaddition and dihydroxylation steps and thus no further optimisation was performed. The cycloaddition reaction of dienes 14–16 with singlet oxygen was performed in a modified photochemical reactor that had been fitted with a gas

Novel β-cyclodextrin–eosin conjugates

• Gábor Benkovics,
• Damien Afonso,
• András Darcsi,
• Szabolcs Béni,
• Sabrina Conoci,
• Éva Fenyvesi,
• Lajos Szente,
• Milo Malanga and
• Salvatore Sortino

Beilstein J. Org. Chem. 2017, 13, 543–551, doi:10.3762/bjoc.13.52

• -cyclodextrin–EoY conjugate retains both the fluorescence properties and the capability to photogenerate singlet oxygen of the unbound chromophore. In contrast, the corresponding β-cyclodextrin–EoB conjugate did not show either relevant emission or photosensitizing activity probably due to aggregation in

• aqueous medium, which precludes any response to light excitation. Keywords: β-cyclodextrins; fluorescence; photodynamic therapy; photosensitizers; singlet oxygen; xanthene; Introduction Cyclodextrins (CDs) are cyclic oligosaccharides able to form host–guest inclusion complexes with drugs and this

• being excited with visible light, the PS – while reverting to the ground state – transfers the energy of its lowest excited triplet state to nearby molecular oxygen. This leads to an in situ generation of singlet oxygen (1O2), which is the main responsible species for cytotoxic reactions in cells [6

A self-assembled cyclodextrin nanocarrier for photoreactive squaraine

• Ulrike Kauscher and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2016, 12, 2535–2542, doi:10.3762/bjoc.12.248

• interference of the PS with the triplet ground state of oxygen, leading to the production of singlet oxygen. In both mechanisms, the PS harvests the energy of incident light to form reactive oxygen species or singlet oxygen, which are highly cytotoxic [6][7]. Most clinically used PSs are based on porphyrins

• cytotoxicity. Santos et al. postulated the production of singlet oxygen as a result of interaction between the squaraines and the ground state of oxygen [19][20]. A few years later, Salice et al. showed that squaraines are not efficient singlet oxygen producing agents, but can be applied successfully as

• singlet oxygen quenchers [23]. The authors discussed that this behaviour is based on charge-transfer processes between stacked squaraines as well as oxygen squaraine complexes. Within the same year, Rapozzi et al. described the photooxidation process of benzothiazol squaraines [24]. They showed that the

A flow reactor setup for photochemistry of biphasic gas/liquid reactions

• Josef Schachtner,
• Patrick Bayer and
• Axel Jacobi von Wangelin

Beilstein J. Org. Chem. 2016, 12, 1798–1811, doi:10.3762/bjoc.12.170

• to oxidation chemistry of utmost sustainability. Under irradiation in the presence of a sensitizer, singlet oxygen can easily be generated from the triplet ground state. Several applications of such photooxidations to chemical synthesis have been reported [71][72][73], in recent years most

• effectively under microflow conditions [41][42][50][51][74][75]. We applied the home-made photo-flow reactor (Figure 7) to the visible light mediated oxygenation of a cyclohexene derivative (i.e., Schenck ene reaction with singlet oxygen) [72][73] and evaluated the critical reaction and reactor parameters

• singlet oxygen. Photooxygenation of N-methyl-1,2,3,6-tetrahydrophthalimide and reductive work-up to alcohol 3a. Oxidation of N-methyl-1,2,3,6-tetrahydro-3-acetamidophthalimide and reductive work-up to alcohol 3b. Molar attenuation coefficients of common photosensitizersa (bpy = 2,2‘-bipyridine

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

• model of the in vivo oxidation of cholesterol (219) by singlet oxygen produces cholesterol-5α-OOH 220, which is subjected to a Hock reaction to form the aldolization product 221 and keto aldehyde (atheronal A, 222) (Scheme 64) [67]. Keto aldehyde (atheronal A, 222) exhibits proatherogenic activity and

• of luciferin yields the peroxy compound 1,2-dioxetane. This four-membered peroxide cycle is unstable and spontaneously decays to carbon dioxide and excited ketones, which release excess energy through light emission (bioluminescence) [62][63][64][65]. The in vivo oxidation of cholesterol by singlet

• oxygen produces the hydroperoxide cholesterol-5α-OOH, which undergoes a Hock oxidation to form atheronal A. The latter possesses proatherogenic effects and triggers the development of cardiovascular diseases [66][67][68][69][70][71]. The development of the chemistry of organic peroxides is closely

Biradical vs singlet oxygen photogeneration in suprofen–cholesterol systems

• Fabrizio Palumbo,
• Francisco Bosca,
• Isabel M. Morera,
• Inmaculada Andreu and
• Miguel A. Miranda

Beilstein J. Org. Chem. 2016, 12, 1196–1202, doi:10.3762/bjoc.12.115

• i Politècnic La Fe, Avenida de Fernando Abril Martorell 106, 46026 Valencia, Spain 10.3762/bjoc.12.115 Abstract Cholesterol (Ch) is an important lipidic building block and a target for oxidative degradation, which can be induced via free radicals or singlet oxygen (1O2). Suprofen (SP) is a

• singlet oxygen was assessed by time-resolved near infrared emission studies in dichloromethane using perinaphthenone as standard. The quantum yields (ΦΔ) were 0.52 for 1 and 2 and 0.56 for 3. In conclusion, SP-α-Ch dyads are unique in the sense that they can be used to photogenerate both biradicals and

• singlet oxygen, thus being able to initiate Ch oxidation from their triplet excited states following either of the two competing mechanistic pathways. Keywords: aryl ketones; hydrogen abstraction; lipid peroxidation; photoproducts; triplet excited state; Introduction Among the constituents of cell