Visible-light-induced bromoetherification of alkenols for the synthesis of β-bromotetrahydrofurans and -tetrahydropyrans

• Run Lin,
• Hongnan Sun,
• Chao Yang,
• Youdong Yang,
• Xinxin Zhao and
• Wujiong Xia

Beilstein J. Org. Chem. 2015, 11, 31–36, doi:10.3762/bjoc.11.5

• alkenol 1a as a model reaction for optimizing the reaction conditions. We were encouraged by the discovery that when 1a, CBr4 and Ru(bpy)3Cl2 were irradiated by blue LEDs in MeCN for 4 hours, trans-β-bromotetrahydrofuran 2a was obtained via 5-endo bromoetherification reaction, although the yield was only

• alkenols To a 10 mL round bottom flask equipped with a magnetic stir bar were added alkenols 1 (0.2 mmol), CBr4 (132 mg, 0.4 mmol), Ru(bpy)3Cl2 (4.6 mg, 0.006 mmol) and dry DMSO (2 mL). The mixture was irradiated with blue LEDs (1 W) at room temperature without being degassed for 4 hours. Then water was

Oxidative phenylamination of 5-substituted 1-hydroxynaphthalenes to N-phenyl-1,4-naphthoquinone monoimines by air and light “on water”

• Julio Benites,
• Juan Meléndez,
• Cynthia Estela,
• David Ríos,
• Luis Espinoza,
• Iván Brito and
• Jaime A. Valderrama

Beilstein J. Org. Chem. 2014, 10, 2448–2452, doi:10.3762/bjoc.10.255

• green route for the preparation of N-phenyl-1,4-naphthoquinone monoimines by on-water oxidative coupling reaction of 1-hydroxynaphthalene derivatives with oxygen-substituted phenylamines under solar light or green LEDs radiation, rose bengal as singlet oxygen sensitizer and aerobic conditions. Results

• (Canchones Experimental Center in Iquique/Chile, latitude 20°26´43.80´´ S, 990 m above sea level) and green LEDs as photochemical sources. Meanwhile, a gently stream of air was bubbled through the solutions. Under these conditions juglone (2) was isolated in 81% (sunlight) and 55% (LEDs) yields. On the other

• )naphthalene-1(4H)-one (6, 98% yield). Under similar conditions, but using green LEDs light radiation, compound 6 was isolated in 80% yield. The structure of 6 was established by means of 1D and 2D NMR and by X-ray crystallographic studies (Figure 2 and Table S1 in Supporting Information File 1). This

Cyclization–endoperoxidation cascade reactions of dienes mediated by a pyrylium photoredox catalyst

• Nathan J. Gesmundo and
• David A. Nicewicz

Beilstein J. Org. Chem. 2014, 10, 1272–1281, doi:10.3762/bjoc.10.128

• frameworks. Results and Discussion Reaction optimization We began our investigation into endoperoxidation conditions with diene 2a as the substrate as it contained both a styene and an aliphatic alkene. Using catalyst 1c in DCM at −41 °C under irradiation with 470 nm LEDs afforded endoperoxide 3a in 40

Visible-light photoredox catalyzed synthesis of pyrroloisoquinolines via organocatalytic oxidation/[3 + 2] cycloaddition/oxidative aromatization reaction cascade with Rose Bengal

• Carlos Vila,
• Jonathan Lau and
• Magnus Rueping

Beilstein J. Org. Chem. 2014, 10, 1233–1238, doi:10.3762/bjoc.10.122

• ] cycloaddition/aromatization cascade catalyzed by Rose Bengal under irradiation with green LEDs. Results and Discussion Initially, we focused on the reaction between methyl dihydroisoquinoline ester 1a and N-methylmaleimide (2a) catalyzed by Rose Bengal. Although the [3 + 2] cycloaddition occurs smoothly in the

Direct C–H trifluoromethylation of di- and trisubstituted alkenes by photoredox catalysis

• Ren Tomita,
• Yusuke Yasu,
• Takashi Koike and
• Munetaka Akita

Beilstein J. Org. Chem. 2014, 10, 1099–1106, doi:10.3762/bjoc.10.108

• examination of photocatalytic trifluoromethylation of 1,1-diphenylethene 2a with 1 equivalent of Umemoto’s reagent 1a in the presence of 5 mol % fac-Ir(ppy)3, a photoredox catalyst, and 2 equivalents of K2HPO4, a base, in [D6]-DMSO under visible light irradiation (blue LEDs: λmax = 425 nm) for 2 h. As a

• –H trifluoromethylation. In fact, the photocatalytic trifluoromethylation of 2a,b and d with 4 equivalents of Umemoto’s reagent 1a in the presence of 5 mol % of [Ru(bpy)3](PF6)2 with irradiation from blue LEDs for 3 h gave geminal bis(trifluoromethyl)ethene (4a,b and d) in 45, 80 and 24% NMR yields

• trifluoromethylation of 2a with 1a with intermittent irradiation by blue LEDs. Representative examples of multisubstituted CF3-alkenes. Catalytic synthesis of CF3-alkenes via trifluoromethylation. Our strategies for synthesis of CF3-alkenes. Synthesis of geminal bis(trifluoromethyl)alkenes. A possible reaction

Allenylphosphine oxides as simple scaffolds for phosphinoylindoles and phosphinoylisocoumarins

• G. Gangadhararao,
• Ramesh Kotikalapudi,
• M. Nagarjuna Reddy and
• K. C. Kumara Swamy

Beilstein J. Org. Chem. 2014, 10, 996–1005, doi:10.3762/bjoc.10.99

• . To achieve this, we treated the functionalized allene precursors 4a–j that are tethered with a methyl ester group, with an excess of trifluoroacetic acid at room temperature for 6 h. Gratifyingly, this readily leds to the phosphinoylisocoumarins 20–29 (Scheme 7) in good yields. In the case of

On the mechanism of photocatalytic reactions with eosin Y

• Michal Majek,
• Fabiana Filace and
• Axel Jacobi von Wangelin

Beilstein J. Org. Chem. 2014, 10, 981–989, doi:10.3762/bjoc.10.97

• reports is the source of irradiation. Several groups including ourselves have used commercial narrow-band LEDs with a maximum intensity at 535 nm (green light) [15][16][17][18][20]. Other reactions were irradiated with white light from broad-band compact fluorescent lamps (CFL) [19][21]. The determination

• -colored LEDs (see Supporting Information File 1 for spectrum). The activation energy of thermal heterolysis of arenediazonium ions is approx. 115 kJ/mol (1.19 eV) [29]. The energy of a photon at the edge of the visible spectrum (400 nm) is 3.1 eV so that such photons carry sufficient energy to heterolyze

Visible light mediated intermolecular [3 + 2] annulation of cyclopropylanilines with alkynes

• Theresa H. Nguyen,
• Soumitra Maity and
• Nan Zheng

Beilstein J. Org. Chem. 2014, 10, 975–980, doi:10.3762/bjoc.10.96

• lamps (CFLs). 13 W CFLs were used as the light source to mediate the annulation with alkenes [29]. White 18 W LEDs were found to be more effective for the annulation with alkynes, resulting in a higher yield (Table 1, entry 6). Control studies showed that both the photocatalyst and light were required

Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

• Jacques Lalevée,
• Sofia Telitel,
• Pu Xiao,
• Marc Lepeltier,
• Frédéric Dumur,
• Fabrice Morlet-Savary,
• Didier Gigmes and
• Jean-Pierre Fouassier

Beilstein J. Org. Chem. 2014, 10, 863–876, doi:10.3762/bjoc.10.83

• -trapping, laser flash photolysis, steady state photolysis, cyclic voltammetry and luminescence experiments. Keywords: LEDs; photoinitiators; photopolymerization; photoredox catalysis; Introduction Photoredox catalysis is now well-known and largely used in organic synthesis, especially in the development

• sources: Several lights were used: 1) polychromatic light from a halogen lamp (Fiber-Lite, DC-950 – incident light intensity: I0 ≈ 12 mW/cm2; in the 370–800 nm range); 2) monochromatic light delivered by a laser diode at 532 nm (I0 ≈ 100 mW/cm2) and 3) LEDs at 514 nm. iii) Free radical photopolymerization

Visible-light photoredox catalysis enabled bromination of phenols and alkenes

• Yating Zhao,
• Zhe Li,
• Chao Yang,
• Run Lin and
• Wujiong Xia

Beilstein J. Org. Chem. 2014, 10, 622–627, doi:10.3762/bjoc.10.53

• liquid bromine. Results and Discussion Our initial investigation was carried out on protected 4-methoxyphenol 1a and CBr4 in dried CH3CN in the presence of Ru(bpy)3Cl2 (5.0 mol %) with visible light irradiation (blue LEDs, λmax = 435 nm) for 6 hours. The corresponding 2-bromo-4-methoxyphenol (2a) was

• photocatalyst or the light source did not afford the desired product 2a. Therefore, the reaction conditions of CBr4 (1 equiv) in dried CH3CN in the presence of Ru(bpy)3Cl2 (5.0 mol %) with visible light irradiation (blue LEDs, λmax = 435 nm) and open to air were utilized to test the scope of the reaction. With

• could be prepared from the same starting materials in two steps (Table 2). We also conducted a control experiment by reacting stilbene with CBr4 (1 equiv) in dry CH3CN in the presence of Ru(bpy)3Cl2 (5.0 mol %) with visible-light irradiation (blue LEDs, λmax = 435 nm) for 72 hours, which led to the anti

Studies on the photodegradation of red, green and blue phosphorescent OLED emitters

• Susanna Schmidbauer,
• Andreas Hohenleutner and
• Burkhard König

Beilstein J. Org. Chem. 2013, 9, 2088–2096, doi:10.3762/bjoc.9.245

• continuous excitation, the samples were irradiated with light of 400 nm high power LEDs (350 mW). This allows for the excitation of the MLCT absorption band and further enables the irradiation through standard chromatography glass vials and glass substrates without having to resort to quartz cuvettes

• made irradiation unit (SIM GmbH). It consists of an aluminum-printed circuit board with thirty 400 nm LEDs (350 mW, Edison Edixeon 3 W Emitter, [LT-1467]), connected to a cooling unit, that ensures a constant temperature of 20 °C of the board during the irradiation. Two 15 sample chromatography trays

Bromination of hydrocarbons with CBr₄, initiated by light-emitting diode irradiation

• Yuta Nishina,
• Bunsho Ohtani and
• Kotaro Kikushima

Beilstein J. Org. Chem. 2013, 9, 1663–1667, doi:10.3762/bjoc.9.190

• without any additives, through radical reactions induced by irradiation with light from commonly used light-emitting diodes (LEDs) [30]. In this reaction, additives, catalysts, heating, and inert reaction conditions are all unnecessary. Results and Discussion First, the bromination of cyclohexane under

New core-pyrene π structure organophotocatalysts usable as highly efficient photoinitiators

• Sofia Telitel,
• Frédéric Dumur,
• Thomas Faury,
• Bernadette Graff,
• Mohamad-Ali Tehfe,
• Didier Gigmes,
• Jean-Pierre Fouassier and
• Jacques Lalevée

Beilstein J. Org. Chem. 2013, 9, 877–890, doi:10.3762/bjoc.9.101

• –10 mW cm−2). Recent works have aimed at working under soft irradiation conditions (near-UV–vis light, low light intensity), which allows the use of Xe lamps, laser diodes, solar radiation, household halogen lamps, fluorescent bulbs and blue, green and white LEDs (see a recent review in [1]). New high

A bisazobenzene crosslinker that isomerizes with visible light

• Subhas Samanta,
• Harris I. Qureshi and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2012, 8, 2184–2190, doi:10.3762/bjoc.8.246

• measuring beam) with LEDs emitting at 407–410 nm (~460 mW, LEDengin LZ1-10UA05) at 4, 10 and 20 °C for 2 min until no further decrease in absorbance was observed, and under this steady-state-irradiation condition the spectra were recorded. Rates of thermal reversion of the irradiated samples were measured

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• moles of photons (einsteins) per hour at a given wavelength (λ) if the total power of emissions at that wavelength is known, is shown in Equation 3. This equation is particularly useful when considering selective narrowband emitters such as a low-pressure mercury lamp or LEDs. For example, a 15 W low

• emission from most common light sources. Even LEDs, which can be considered as planar light sources, often have a beam width wider than the actual channels; however, this issue could easily be addressed by a more directed reactor design. As a result microflow reactors are often inefficient at capturing

• nanoparticles can effectively produce singlet oxygen when irradiated with LEDs in the oxidative degradation of 1,3-diphenylisobenzofuran [40]. Photocatalytic reactions Photocatalytic reactions are an area in which continuous flow can be particularly advantageous due to the large surface-to-volume ratio ensuring

Synthesis and characterization of a novel carboxyl group containing (co)polyimide with sulfur in the polymer backbone

• Miroslav Mrsevic,
• David Düsselberg and
• Claudia Staudt

Beilstein J. Org. Chem. 2012, 8, 776–786, doi:10.3762/bjoc.8.88

• components for high-temperature applications, such as light emitting diodes (LEDs) [34]. UV–vis spectroscopy In order to characterize the optical properties of the (co)polyimides with respect to their color and transparency, UV–vis spectra of free standing films were recorded. The previously described

Sexithiophenes as efficient luminescence quenchers of quantum dots

• Christopher R. Mason,
• Yang Li,
• Paul O’Brien,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2011, 7, 1722–1731, doi:10.3762/bjoc.7.202

• deposition [1]. This has led to the application of oligothiophenes in numerous organic devices including solar cells [2][3][4], light-emitting diodes (LEDs) [5][6], field-effect transistors [7][8][9] and electrochromics [10]. Furthermore, end-capped oligothiophenes are particularly attractive materials for

• LEDs and photovoltaic cells [19][20][21][22][23]. Previously, we reported the synthesis and characterisation of CdS quantum dots in polystyrene beads, in which beads ranging in size from 100 nm to 500 μm were prepared and confocal microscopy showed an even distribution of CdS throughout the polymer

Microphotochemistry: 4,4'-Dimethoxybenzophenone mediated photodecarboxylation reactions involving phthalimides

• Oksana Shvydkiv,
• Kieran Nolan and
• Michael Oelgemöller

Beilstein J. Org. Chem. 2011, 7, 1055–1063, doi:10.3762/bjoc.7.121

• application of LEDs [37]. We have therefore investigated the usage of 4,4’-dimethoxybenzophenone (DMBP) as a photocatalyst that absorbs readily in the UVA region. In this publication we present preliminary results of five DMBP mediated model transformations (Scheme 1). All reactions were previously studied

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• dependent on the substitution pattern and configuration of the enyne and leds to variable product formation. For example, Kozmin and co-workers showed in 2006 that 1,5-enynes can also rearrange to 1,3-cyclohexadienes through a series of 1,2-alkyl shifts (Scheme 15) [112]. In particular, when silyloxy enynes

Novel carbazole–pyridine copolymers by an economical method: synthesis, spectroscopic and thermochemical studies

• Aamer Saeed,
• Madiha Irfan and
• Shahid Ameen Samra

Beilstein J. Org. Chem. 2011, 7, 638–647, doi:10.3762/bjoc.7.75

• for employing organic materials as LEDs [7] and carbazole containing polymers are the most studied group amongst the different polymers intended for OLED applications [8][9][10][11][12][13][14][15]. Carbazole containing polymers exhibit excellent electron-donating properties together with intense

The efficient synthesis of dibenzo[d,d′]benzo[1,2-b:4,3-b′]dithiophene and cyclopenta[1,2-b:4,3-b′]bis(benzo[d]thiophen)-6-one

• Zhihua Wang,
• Sheng Zhu,
• Jianwu Shi and
• Hua Wang

Beilstein J. Org. Chem. 2009, 5, No. 55, doi:10.3762/bjoc.5.55

• fabricate organic field-effect transistors (OFETs) [1][2][3][4][5][6][7], light emitting diodes (LEDs) [8][9], and photovoltaic cells [10]. Various novel π-extended heteroarenes, e.g. dibenzo[d,d′]thieno[3,2-b:4,5-b′]dithiophene [11], pentathienoacene [12], and benzo[1,2-b:4,5-b′]bis[b]benzothiophene [13