Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• [46], Pb(OAc)4 [44][46][47][48][49][50][51], PbO2 [52], Mn(OAc)3 [46], KMnO4 [46], Ag2O [53], AgO [54], Horseradish peroxidase/H2O2 [55], metal-free oxidants PhI(OAc)2 [46], t-BuOOt-Bu [53] or quinones [56] under UV irradiation. Anodic oxidation was also reported [57]. The establishing of the self

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

• radicals Thiyl (sulfenyl) radicals Thiyl radicals are common, versatile, strong nucleophilic radicals. They are efficient at performing atom abstractions, in particular with H-atoms, adding to π-systems and electrophiles, such as carbonyl compounds [166]. They can be generated from the UV irradiation of

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• that acetone (4) could efficiently initiate photografting under UV irradiation when mixed with water [41] and performed a theoretical study on the matter a few years later [42]. The same research group later studied other aliphatic ketones for their efficiency in initiating photografting [43][44

• of the benzophenone 172 to the triplet state 173 by UV irradiation, followed by HAT from the aldehyde 170 to 173 and the formation of the acyl radical 175. At the same time, the nickel(0) complex 176 performs an oxidative addition reaction to the aryl bromide 171, and the nickel(II) complex 177

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• addition of P–H to unsaturated organic compounds (hydrophosphination) presents an atom economical, efficient and green strategy for the preparation of phosphines. The process can be initiated thermally, chemically or by UV irradiation. Radicals can also be used in hydrophosphination reactions. For example

• , azobisisobutyronitrile (AIBN) can initiate the addition of secondary phosphines to N-vinylpyrroles under heating or UV irradiation resulting in regio- and chemospecific adducts. Using the same approach Trofimov et al. [96] reported on the selective synthesis of tertiary diorganyl pyrrolylphosphines 105 and 106 in high

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

• presence of DNA. Based on our interest in the chemistry and biology of the oxime functionality [54][55][56][57], as well as in their DNA photolytic interaction upon UV irradiation [9][10][11][43] we have decided to investigate the behaviour of carefully designed O-carbamoyl derivatives of p-pyridine

• and subjected to UV irradiation in the presence of plasmid DNA. Not all derivatives were active, nevertheless all amidoxime, ethanone oxime and aldoxime derivatives showed similar effects, indicating the cause of action to be considered on the carbamate moiety rather than the oxime. The affinity of

• , respectively. Photo (A): wells 3–8: DNA + carbamoyl amidoximes (8 or 9, or 10, or 11, or 12, or 13, respectively) + UV irradiation; Photo (B): Mechanistic studies involved by derivative 26 under UV irradiation: well 3: DNA + 26; well 4: DNA + 26 + argon; well 5: DNA + 26 + DMSO (20%); well 6: DNA + 26 + NaN3

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• derivatives using the cumene process or single-step oxygenation suffers from poor yields, high reaction temperatures, and high-energy UV irradiation conditions [155][156]. To overcome this, in 2012, Fukuzumi and co-workers used 3-cyano-1-methylquinolinium perchlorate (8) as a photoredox catalyst for the

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

• Sabrina Müller,
• Jannik Paulus,
• Jochen Mattay,
• Heiko Ihmels,
• Veronica I. Dodero and
• Norbert Sewald

Beilstein J. Org. Chem. 2020, 16, 60–70, doi:10.3762/bjoc.16.8

• and Figure 1C). However, the Z-isomer content could not be increased further by UV irradiation. The Z-isomer could subsequently be switched back to the E-isomer (19% Z-configuration after 30 min) by irradiation at 420 nm (Figure 1D). The thermal conversion to the E-isomer in the dark was slow at room

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos

• Sergii Afonin,
• Oleg Babii,
• Aline Reuter,
• Volker Middel,
• Masanari Takamiya,
• Uwe Strähle,
• Igor V. Komarov and
• Anne S. Ulrich

Beilstein J. Org. Chem. 2020, 16, 39–49, doi:10.3762/bjoc.16.6

• initially handled as ring-open photoforms under ambient (visual, vis) light conditions. Each of the ring-open photoforms was converted into the ring-closed photoforms by UV irradiation in a solution of denaturing agents, reproducing previously documented results [29][30][52]. All studied compounds were

Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

• David Martínez-López,
• Amirhossein Babalhavaeji,
• Diego Sampedro and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2019, 15, 3000–3008, doi:10.3762/bjoc.15.296

• . Photoisomerization UV irradiation was performed by placing a 365 nm LED (897-LZ440U610; LED Engin) operating at 68 mW/cm2 above the sample tube for 1 minute. For blue light irradiation, a 440 nm LED (Luxeon III Star LED Royal Blue Lambertian; Luxeon Star LEDs) operating at 40 mW/cm2 at 700 mA was used in the

Palladium-catalyzed synthesis and nucleotide pyrophosphatase inhibition of benzo[4,5]furo[3,2-b]indoles

• Hoang Huy Do,
• Saif Ullah,
• Alexander Villinger,
• Joanna Lecka,
• Jean Sévigny,
• Peter Ehlers,
• Jamshed Iqbal and
• Peter Langer

Beilstein J. Org. Chem. 2019, 15, 2830–2839, doi:10.3762/bjoc.15.276

• inert atmosphere of argon. Concentrations (c) in the general procedures refer to the limiting reagent and are given in mmol/mL. Thin-layer chromatography (TLC) was carried out on Merck aluminium foil backed sheets precoated with 0.2 mm Kielselgel 60 F254. The spots were visualized by UV irradiation (λ

Photochromic diarylethene ligands featuring 2-(imidazol-2-yl)pyridine coordination site and their iron(II) complexes

• Andrey G. Lvov,
• Max Mörtel,
• Anton V. Yadykov,
• Frank W. Heinemann,
• Valerii Z. Shirinian and
• Marat M. Khusniyarov

Beilstein J. Org. Chem. 2019, 15, 2428–2437, doi:10.3762/bjoc.15.235

• the rigid coordination of the imidazole group to the metal ion, which prevents the rotation of the group needed for cyclization. Families of diarylethene-bases ligands with spatial proximity of coordination site (blue) and photoactive framework (red). Electronic spectra of diarylethene 6 upon UV

• irradiation (313 nm, toluene, c = 3.4 × 10−5 M). Inset: fatigue resistance upon multiple subsequent irradiation with UV (365 nm) and visible light (green LED) in acetonitrile. Molecular structure of complexes 8 (top) and 9 (bottom) at 100 K. The H atoms are omitted for clarity; the thermal ellipsoids are

Reversible switching of arylazopyrazole within a metal–organic cage

• Anton I. Hanopolskyi,
• Soumen De,
• Michał J. Białek,
• Yael Diskin-Posner,
• Liat Avram,
• Moran Feller and
• Rafal Klajn

Beilstein J. Org. Chem. 2019, 15, 2398–2407, doi:10.3762/bjoc.15.232

• photoisomerization of encapsulated E-1. UV irradiation (365 nm light-emitting diode, LED) of the transparent yellow solution of (E-1)22 in water did not result in any pronounced visual changes. However, UV–vis absorption spectroscopy showed (Figure 4) a dramatic decrease in the intensity of E-1’s absorption at 336

• photoisomerization reaction, we investigated it by NMR spectroscopy under in-situ irradiation (with an optical fiber inserted into the NMR spectrometer). Figure 6 shows a series of spectra recorded after increasing UV irradiation times. We found that whereas the position of 2’s H4 signal did not change (9.26 ppm

• with any of the three methyl groups. Furthermore, we note that the resonance due to Hb – very broad in complex (E-1)22 as a consequence of dimer formation – becomes as sharp as those of the other protons after UV irradiation (compare spectra i and ii in Figure S23, Supporting Information File 1). Taken

Mono- and bithiophene-substituted diarylethene photoswitches with emissive open or closed forms

• A. Lennart Schleper,
• Mariano L. Bossi,
• Vladimir N. Belov and
• Stefan W. Hell

Beilstein J. Org. Chem. 2019, 15, 2344–2354, doi:10.3762/bjoc.15.227

• ring-closure reaction was fully reversible by irradiation with longer wavelengths. This offers the possibility of reversible switching a DAE only with visible, avoiding harmful (cytotoxic) UV irradiation. In view of the forthcoming solubilizing strategies applicable to fluorescent DAEs and intended for

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• solutions (λex = 370 nm). (c) The fluorescence quenching of THF 100 vol % (water 0 vol %) solution at 670 nm (broken line) and that of THF/water = 10:90 (v/v) at 585 nm (solid line) upon UV irradiation. (a) Crystals of 1o before UV light irradiation, (b) Green fluorescence of 1o observed under UV light (λ

• = 365 nm) irradiation, (c) Cyclization proceeded to form 1c with suppression of the fluorescence, (d) Fluorescence spectra of 1o in the crystalline state (λex = 370 nm, λmax = 537 nm), (e) The fluorescence quenching of 1o in the crystalline state (λex = 370 nm, λem = 537 nm) upon UV irradiation

Azologization and repurposing of a hetero-stilbene-based kinase inhibitor: towards the design of photoswitchable sirtuin inhibitors

• Christoph W. Grathwol,
• Nathalie Wössner,
• Sören Swyter,
• Adam C. Smith,
• Enrico Tapavicza,
• Robert K. Hofstetter,
• Anja Bodtke,
• Manfred Jung and
• Andreas Link

Beilstein J. Org. Chem. 2019, 15, 2170–2183, doi:10.3762/bjoc.15.214

• unclear. Photochemistry of azastilbenes The photochemical behaviour of stilbenes has been subject to intense investigation in the past. It is reported that unsubstituted stilbene undergoes E→Z photoisomerization [47], as well as photocyclization to dihydrophenanthrene upon UV irradiation, which is

• provided deeper insights and clarified the differential behaviour observed in the UV–vis spectra of 2b and 2f after UV irradiation. As anticipated, UV irradiation lead to E→Z isomerization of the C=C double bond in both compounds. The (Z)-isomers were found to be slightly more polar than the respective (E

• stilbene motive of selected stilbene 2c by a diazeno group, because photoisomerization of azo dyes was anticipated to proceed fast and reversible by application of UV irradiation and visible light, respectively in this analogue. 5-Diazenylnicotinamide 11 was synthetically accessible in two steps through

Reversible end-to-end assembly of selectively functionalized gold nanorods by light-responsive arylazopyrazole–cyclodextrin interaction

• Maximilian Niehues,
• Patricia Tegeder and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2019, 15, 1407–1415, doi:10.3762/bjoc.15.140

• -functionalized with the CD, no assembly could be observed after addition of the divalent azobenzene linker. Moreover, the assemblies could only once be disassembled by the combination of UV irradiation and physical forces by sonication. The light-induced back-isomerization of azobenzenes did not form similar end

• with dAAP during four cycles of irradiation. a) Longitudinal SPR. b) Transversal SPR. TEM-BF images of a) [tCD+tTEG]AuNR. b and c) AuNR end-to-end assemblies by dAAP (15 µM). d) Dissolved AuNR by UV irradiation (λ = 360 nm). Reversible aggregation of [tCD+tTEG]AuNR by addition of dAAP (15 µM) monitored

Remarkable effect of alkynyl substituents on the fluorescence properties of a BN-phenanthrene

• Alberto Abengózar,
• David Sucunza,
• Patricia García-García and
• Juan J. Vaquero

Beilstein J. Org. Chem. 2019, 15, 1257–1261, doi:10.3762/bjoc.15.122

• these compounds are summarized in Table 1, and a picture of their solutions under UV irradiation are shown in Figure 3. The emission maxima were not significantly affected by the presence of substituents, except for 7-amino substituted BN-phenanthrene 1d and 1-alkynyl substituted BN-phenanthrene 5

• BN-phenanthrenes 1 and 5 in cyclohexane (≈0.02 mM). Solutions of 1a–f and 5 (from left to right) under UV irradiation. Synthesis of Cl-substituted BN-phenanthrene 1b. Palladium-catalyzed cross-couplings of Cl-substituted BN-phenanthrene 1b. Pd-catalyzed Sonogashira reactions of Cl-substituted BN

Insertion of [1.1.1]propellane into aromatic disulfides

• Robin M. Bär,
• Gregor Heinrich,
• Martin Nieger,
• Olaf Fuhr and
• Stefan Bräse

Beilstein J. Org. Chem. 2019, 15, 1172–1180, doi:10.3762/bjoc.15.114

• the first to use UV irradiation in this reaction, but did not report detailed conditions [28]. They used diacetyldithiol and 1 to obtain bisacetylthio[n]staffanes. To find feasible conditions for the insertion of 1 into disulfide bonds, a screening with irradiations of different wavelengths and other

• the UV irradiation. In the benzyl group only the aromatic part can absorb the light and a transfer has to take place to promote the homolytic cleavage of the disulfide. In first purification attempts [2]staffane 14 could be identified in a mixture with 13 in traces. From the product mixture we could

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• by a radical process promoted by UV irradiation, with an initial formation of aryl radical 116 from the corresponding aryl iodide 113 (Scheme 33). This radical would cyclize in an intramolecular 5-exo mode to furnish cyclic radical 117 which, in turn, can be caught by intermediate 118, formed by

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• ]-cycloaddition methodology. They used the vertex grinding technique where solid-state grinding and UV irradiation was done simultaneously [111] and verified co-crystal formation of a resorcinol derivative with dipyridylethylene in the solid state. Also, the supramolecular catalysis of [2 + 2] photodimerization

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

• of 1a and 2a under 365 nm UV lamp irradiation without a photocatalyst delivered product 3aa in 75% yield (Table 1, entry 9). This indicates the excitation of xanthate 1a through an n→π* electronic transition of the C=S bond is in operation in the UV irradiation process. The involvement of a radical

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

• Amrita Das,
• Mitasree Maity,
• Simon Malcherek,
• Burkhard König and
• Julia Rehbein

Beilstein J. Org. Chem. 2018, 14, 2520–2528, doi:10.3762/bjoc.14.228

• cleavage has been reported for alkyl and aryl disulfides in an oxidative [44][45][46] and triplet sensitized mechanism [47]. It is also well known in literature that aromatic disulfides are cleaved homolytically under UV irradiation yielding the corresponding radicals [48]. A recent study from Nicewicz

Synthesis of new p-tert-butylcalix[4]arene-based polyammonium triazolyl amphiphiles and their binding with nucleoside phosphates

• Vladimir A. Burilov,
• Guzaliya A. Fatikhova,
• Mariya N. Dokuchaeva,
• Ramil I. Nugmanov,
• Diana A. Mironova,
• Pavel V. Dorovatovskii,
• Victor N. Khrustalev,
• Svetlana E. Solovieva and
• Igor S. Antipin

Beilstein J. Org. Chem. 2018, 14, 1980–1993, doi:10.3762/bjoc.14.173

• film hydration method. To identify an optimal calixarene–AEPCDA ratio a series of PDA vesicles containing 1, 5, 10, 50 mol % of 10b was prepared. Polymerization of AEPCDA–calixarene vesicles was performed under UV irradiation using 254 nm light in quartz cuvettes of 1 cm path length. The absorbance

Visible light-mediated difluoroalkylation of electron-deficient alkenes

• Vyacheslav I. Supranovich,
• Vitalij V. Levin,
• Marina I. Struchkova,
• Jinbo Hu and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2018, 14, 1637–1641, doi:10.3762/bjoc.14.139

• fluorinated alkyl radicals is typically realized either by single-electron reduction or by radical abstraction of iodine [41][42][43]. Furthermore, the carbon–iodine bond is prone to homolytic cleavage under UV irradiation [44]. In this regard, we were inspired by the work of Ryu describing the use of

[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• last possibility of how to influence the cycloaddition between sydnones and alkynes involves photochemical performance of this reaction. Under UV-irradiation sydnones form the corresponding unstable nitrilimines which then undergo [3 + 2]-cycloaddition to give pyrazoles carrying substituents