When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• interest in g-C3N4 photocatalysts was generated in 2009 by Wang, Domen, and co-workers, who reported the metal-free photolysis of water was possible with the all-organic semiconductor material, a sacrificial electron donor, and visible light irradiation [120]. Prior to this report, poly(p-phenylene) had

[3 + 2] Cycloaddition with photogenerated azomethine ylides in β-cyclodextrin

• Margareta Sohora,
• Leo Mandić and
• Nikola Basarić

Beilstein J. Org. Chem. 2020, 16, 1296–1304, doi:10.3762/bjoc.16.110

• cycloadducts. On the other hand, upon photolysis in the presence of H2O and a base, the photoreaction is about twenty times more efficient, but it delivers simple decarboxylation product 4 only. Attempts to use β-CD to complex both reactants and enhance the efficiency for the cycloaddition failed. In the

• photolysis of 1, β-CD had no effect (Table 1), which may be ascribed to a small size of 1 that cannot fit well in the large cavity of β-CD and form a stable complex. Molecules 2 and 3 are larger, and anticipated to form more stable inclusion complexes with β-CD. Therefore, we performed 1H NMR titrations to

• possible and that photolysis of 2 in such a complex yields 2AMY, which is then readily intercepted with AN in the same complex. Note that cycloadduct 11 was also detected (≈4%), upon irradiation of 3 with AN in the presence of β-CD, suggesting that the photodecarboxylation reaction and subsequent [3 + 2

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

• , arylalkyl, and diaryl oxime radicals was also studied by EPR spectroscopy [53]. Radicals were generated under inert atmosphere directly in the EPR cavity by photolysis of the added di-tert-butyl peroxide (Scheme 1). The authors pointed out the complexity of the processes of iminoxyl radicals’ decomposition

• iminoxyl radical 90. Presumably, the radical 90 underwent cyclization involving the azo group to form indazole 91. During the photolysis of a mixture of di-tert-butyl peroxide with oxime 92 containing an alkenyl fragment at temperatures from −30 to −10 °C, two signals were observed in the EPR spectrum with

• -system. According to EPR data, the authors suggested that iminoxyl radicals 101 generated from oximes 100 by photolysis with the addition of the di-tert-butyl peroxide gave nitroxides 102 [123]. The widespread use of iminoxyl radicals in organic synthesis involving a radical addition to a C=C bond

A simple and easy to perform synthetic route to functionalized thienyl bicyclo[3.2.1]octadienes

• Dragana Vuk,
• Irena Škorić,
• Valentina Milašinović,
• Krešimir Molčanov and
• Željko Marinić

Beilstein J. Org. Chem. 2020, 16, 1092–1099, doi:10.3762/bjoc.16.96

• , which could be accompanied by a photochemical annulation. The photolysis spectra of compound's 3 isomers are shown in Figure 5, as representative examples. Figure 6 presents the UV spectra of products' 3–7 trans-isomers. All the isomers showed an absorption maxima between 300–400 nm. It can be noticed

• bicyclo[3.2.1]octenes/octadienes with cholinesterase inhibitory properties. 1H NMR spectra (CDCl3) for the trans-isomers 3–6. UV spectra in ethanol (95%) of the cis- and trans-isomers of compound 3. Photolysis spectra of cis-3 (a) and trans-3 (b) in ethanol (95%). UV spectra in ethanol (95%) of the trans

• compounds 1, 8, and 9. UV spectra of compounds 1 and 12 in ethanol (95%). Photolysis spectra of compound 12 in ethanol (95%). Synthesis of annulated furobenzobicyclo[3.2.1]octadiene compounds. Synthesis of annulated thiophenebicyclo[3.2.1]octadiene compounds 8-10. Synthesis of compound 11. Synthesis 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

• -butyl ketone (1) yields acetone (4) and propylene (3). Reaction (2) of Scheme 1 refers to a type II intramolecular rearrangement of crotonaldehyde (5) to 3-butenal (7). The triplet state energy donors were quenched by diacetyl and cis-2-butene. In 1970, Cocivera and Trozzollo studied the photolysis of

• the formation of the radical pair mentioned in Scheme 2 or by a triplet state-energy acceptor, such as 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH, 18, Scheme 4). Trying to shed more light on the photolysis of benzaldehyde, Atkins and co-workers studied the photolysis of benzaldehyde (8) with electron spin

• resonance flash photolysis (ESRFP) and CIDNP in various solvents, depending on the efficiency of the solvents as hydrogen donors [19]. More specifically, triplet state benzaldehyde (9) dissolved in an efficient hydrogen donor solvent can lead to an α-hydroxybenzyl radical (11) as the only detectable species

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

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

• photolysis. The mechanism involved in this transformation is shown in Figure 20. Aryl C–H halogenation Aerobic bromination of arenes: In another experiment, Ohkubo et al. reported that for aerobic aryl C–H brominations, HBr can be utilized with photoredox catalyst 2 in the presence of molecular oxygen to

• flash photolysis measurements, and the monobrominated product selectivity was controlled by the difference in electron transfer oxidation reactivity of 127 and 126 of electron transfer state of photocatalyst (Me·+ moiety) and also on the radical cations reactivity with Br−. Recently, König’s group

• bonds in the presence of photoredox catalyst 8, with a similar mechanism as shown in Figure 22, and the photocatalytic mechanism was elucidated by nanosecond laser flash photolysis (Scheme 24) [168]. Fluorine-18 is an important radioisotope used in the radiopharmaceutical industry (e.g., for drug

Synthesis of 3-alkenylindoles through regioselective C–H alkenylation of indoles by a ruthenium nanocatalyst

• Abhijit Paul,
• Debnath Chatterjee,
• Srirupa Banerjee and
• Somnath Yadav

Beilstein J. Org. Chem. 2020, 16, 140–148, doi:10.3762/bjoc.16.16

• photolysis, was characterised by TEM (Figure S1, Supporting Information File 1), which showed polydispersed spherical particles of a size distribution mainly in the range of 10–25 nm, with a mean diameter of 15 nm. The size distribution of the particles from Figure S1, Supporting Information File 1, is

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• cyclohexane. Photolysis experiments The description of the setup is summarized in Figure 2. The sample in a thermostated quartz cuvette was irradiated with a fibered, collimated CW 976 nm-laser beam. The transmitted laser intensity was measured using a calibrated power-meter. This measurement informed us

• the freshly prepared actinometer 1-c and nanoparticles. Practically, the preparation of the 1-o/c solution was achieved using bench-top UV source (TLC lamp), either on the UCNP-1 mixture or before mixing the dye with the UCNPs. Concentrations were standardized prior the photolysis experiments using

• 650 nm under CW 976 nm laser at 4.71 W. Initial slope (red line) was determined on the 2nd order polynomial fit of experimental points (dark curve). Parameters of UCNP used in the photolysis experiment. Obtained results. Supporting Information Supporting Information File 540: Experimental details

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• of 0.2–0.4, reaching in some cases values as high as 0.5–0.6. Laser-flash photolysis provided evidence for the existence of excited triplet states. The dyes form fluoroboronate complexes with fluoride anions, leading to the observation of the quenching of the long-wavelength emission band and

• ratiometric response by the build-up of a hypsochromically shifted emission signal. Keywords: anions; dyes; fluorescence; laser-flash photolysis; organoboron; Introduction Boron-containing tri- and tetra-coordinated chromophores have attracted considerable interest due to their often peculiar and highly

• in some cases very close to the resolution limit of our time-correlated single-photon-counting setup. The LW emission showed considerably longer lifetimes in the 3–6 ns range. The photophysical behavior of the dyes is tentatively summarized in Scheme 4. Laser-flash photolysis The photophysical

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

• Eric W. Webb,
• Jonathan P. Moerdyk,
• Kyndra B. Sluiter,
• Benjamin J. Pollock,
• Amy L. Speelman,
• Eugene J. Lynch,
• William F. Polik and
• Jason G. Gillmore

Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240

• –oxidation peaks was observed upon multiple scans, representing the reduction and oxidation of the electrogenerated long-wavelength form 1b generated in situ. As expected, either photolysis or multiple CV scans led to the same LW reduction and oxidation peaks (within the error bars indicated in Table 1). We

• for spirocyclic ring-opening exist, leading to 4b or 5b. Thus, we postulated that the electrogenerated LW form was in fact 5b. Having found two distinct LW forms depending on generation by photolysis or electrolysis of SW 3b, we turned our attention to whether a similar phenomenon was observed for 3a

• . Indeed, different redox peaks were observed in the same general LW region for the CV of photolyzed versus electrogenerated LW forms of 3a, consistent with the electrogenerated formation of 5a compared against the known formation of 4a via photolysis. The voltammograms of 3a (Figure 4) did however differ

Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex

• Yoichi Kobayashi,
• Yukie Mamiya,
• Katsuya Mutoh,
• Hikaru Sotome,
• Masafumi Koga,
• Hiroshi Miyasaka and
• Jiro Abe

Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229

• emission spectra was measured to separate the fluorescence and phosphorescence. The shutter was controlled by LabVIEW. Nanosecond transient absorption measurements The laser flash photolysis experiments were carried out with a TSP-2000 time resolved spectrophotometer system (Unisoku Co., Ltd.). A 10 Hz Q

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• cycloadduct 5a in excellent enantioselectivity (97% ee), however, with only 9% yield (Table 1, entry 1). Subsequent efforts to improve the activity by enhancing the dissociation efficiency of latent carbocation through heating or photolysis did not lead to any improvement. We next investigated whether the

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells

• Ayato Yamada,
• Manabu Abe,
• Yoshinobu Nishimura,
• Shoji Ishizaka,
• Masashi Namba,
• Taku Nakashima,
• Kiyofumi Shimoji and
• Noboru Hattori

Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84

• for 2b in benzene. The cytocidal effect of compound 2a on lung cancer cells under photolysis conditions was also assessed to test the efficacy as anticancer agents. In a medium containing 100 μg mL−1 of 2a exposed to light, the number of living cells decreased significantly compared to the unexposed

• counterparts (65.8% vs 85.5%). Keywords: caged compound; nitroxide; photolysis; radical; theranostics; two-photon; Introduction Nitroxides (aminoxyl radicals) possess a delocalized unpaired electron and exhibit negligible dimerization reactivity, making them persistent open-shell species [1][2][3][4]. In

• %) for 2a, and 390 (70%) and 890 ps (30%) for 2b (Table 1, entries 1 and 2). For 2a and 2b, intermolecular charge transfer processes induced by the TEMPO moiety may account for the double-exponential decay curves to some extent. OP photolysis of 2a (5 mM) was first conducted in benzene at ≈298 K using

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• methylcobalamin and adenosylcobalamin (coenzyme B12) that serve as organometallic cofactors in B12-dependent enzymes. The photolysis (thermolysis) of alkylcob(III)alamins leads to the formation of the corresponding alkyl radical and cob(II)alamin with homolytic Co(III)–C bond cleavage (Figure 1b). This high

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

• (1,3,5-TMB•+) is formed indeed during the quenching process of the catalyst by 1,3,5-TMB (Scheme 5) ns-time-resolved transient absorption spectroscopy was used [50]. To allow for a decomposition of the multicomponent spectra we conducted laser flash photolysis (LFP) experiments on the single components

Semi-synthesis and insecticidal activity of spinetoram J and its D-forosamine replacement analogues

• Kai Zhang,
• Jiarong Li,
• Honglin Liu,
• Haiyou Wang and
• Lamusi A

Beilstein J. Org. Chem. 2018, 14, 2321–2330, doi:10.3762/bjoc.14.207

• spinosyn molecule interacts with both gamma-aminobutyric acid (GABA) receptor and nicotine acetylcholine (NACh) receptors [9]. Spinosad and spinetoram can be degraded via a combination of photolysis and microbial action, ultimately producing CO2, H2O, and nitrogen oxides [10]. That suggests that along with

Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen – a suitable way to N-hydrazonation of C–H-bonds

• Liudmila L. Rodina,
• Xenia V. Azarova,
• Jury J. Medvedev,
• Dmitrij V. Semenok and
• Valerij A. Nikolaev

Beilstein J. Org. Chem. 2018, 14, 2250–2258, doi:10.3762/bjoc.14.200

• %. Further irradiation of hydrazones derived from furan-fused tricyclic diazocyclopentanediones culminates in the cycloelimination of furans to yield 2-N-(alkyl)hydrazone of cyclopentene-1,2,3-trione. By contrast, the direct photolysis of carbocyclic diazodiketones gives only Wolff rearrangement products

• Michler’s ketone, with different levels of triplet state energy were tested. Furthermore, to clearly demonstrate the difference of light-induced reactions of diazo compounds 1 in the triplet and singlet excited states, the direct photolysis of diazodiketones 1a-c without sensitizers was also examined

• formation of the appropriate hydrazones 2a–d,f and the most effective sensitizer for this reaction was found to be benzophenone. The direct photolysis of diazodiketones 1a–c was carried out by UV light (λ > 210 nm) in THF solution containing a small amount of H2O or MeOH to trap the proposed intermediate α

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

• -triene (78), and triplet 2-naphthylcarbene (79). Formation of allene 83 as an alternative carbene rearrangement product was not detected under the studied photolysis conditions (Scheme 14). Kitahara’s group reported the one-step synthesis of heptafulvalenes and benzoheptafulvalenes from monocyclic

• ], while the allenic rearrangement product 183 for the carbene 75 was not detected in the photolysis of a diazo compound (Scheme 33) [78]. 2,3-Benzotropone (12) was converted to gem-dichloride 187 to achieve diazirine as carbene precursor (Scheme 33) [77][144]. 3.2.2. Ring-expansion reactions via a tropone

Selective carboxylation of reactive benzylic C–H bonds by a hypervalent iodine(III)/inorganic bromide oxidation system

• Toshifumi Dohi,
• Shohei Ueda,
• Kosuke Iwasaki,
• Yusuke Tsunoda,
• Koji Morimoto and
• Yasuyuki Kita

Beilstein J. Org. Chem. 2018, 14, 1087–1094, doi:10.3762/bjoc.14.94

• electrophilic aromatic rings, non-acidic carbonyl groups, and suitable oxygen, nitrogen, and sulfur functionalities. Carbonyloxy radicals derived from typical hypervalent iodine(III) carboxylates by photolysis and other conditions [65][66][67][68] are known to undergo irreversible decarboxylation [69][70

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• alkenylation reaction, affording the product 3aj with an E/Z ratio of 4:1. In our previous study on the C–H alkylation and arylation of pivalophenone N–H imines, we demonstrated that the pivaloyl imine readily undergoes fragmentation into a cyano group via an iminyl radical under peroxide photolysis or copper

• -catalyzed aerobic conditions [29]. Under the same peroxide photolysis conditions (t-BuOOt-Bu with UV (254 nm) irradiation), the ortho-alkenylated imine 3aa underwent a C–N bond-forming cyclization to afford the spirocyclic imine 4 in 81% yield (Scheme 4). The reaction likely involves the initial formation

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• , mutagenous properties were also shown. Freccero et al. examined the photogeneration by laser flash photolysis and reactivity of naphthoquinone methides as well as their activity as purine selective DNA alkylating agents [93]. Farrell et al. studied the mechanism of the cytotoxic action of naphthoquinone

• phenolic Mannich bases bearing functional groups that are suitable for cross-linking DNA; therefore, their antitumor effects could also be confirmed [96]. The formation of o-QMs and their biological properties were also illustrated by kinetic studies. Rokita et al. using laser flash photolysis showed that

Continuous multistep synthesis of 2-(azidomethyl)oxazoles

• Thaís A. Rossa,
• Nícolas S. Suveges,
• Marcus M. Sá,
• David Cantillo and
• C. Oliver Kappe

Beilstein J. Org. Chem. 2018, 14, 506–514, doi:10.3762/bjoc.14.36

• from vinyl azides through an azirine intermediate (Scheme 3). The process starts with the generation of the azirine from the vinyl azide by thermolysis. Formation of azirines from vinyl azides by photolysis and thermolysis in continuous flow has been previously described [38][39]. The azirine

Stimuli-responsive oligonucleotides in prodrug-based approaches for gene silencing

• Françoise Debart,
• Christelle Dupouy and
• Jean-Jacques Vasseur

Beilstein J. Org. Chem. 2018, 14, 436–469, doi:10.3762/bjoc.14.32

• deprotected under photolysis restoring the activity of the native siRNA. As stated previously, the introduction of a photoreactive moiety into the phosphodiester backbone of an ON with diazo compounds is not specific. Xiang et al. developed a more efficient and specific post-synthetic method. It is based on