NaI/PPh₃-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides for the efficient synthesis of quaternary oxindoles

• Dan Liu,
• Yue Zhao and
• Frederic W. Patureau

Beilstein J. Org. Chem. 2023, 19, 57–65, doi:10.3762/bjoc.19.5

• Discussion Key elements of reaction optimization are summarized in Table 1. With NaI (20 mol %) and PPh3 (20 mol %), acrylamide 1a and redox-active ester 2a were used as model substrates to react for 36 h in acetonitrile (MeCN) under blue LEDs irradiation and N2 atmosphere, delivering the desired oxindole

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• radical (SPyf, Scheme 24) was proposed as a hydrogen atom abstracting agent for unactivated C–H bonds of alkanes and other CH-reagents [123] (Scheme 24). It was generated by the irradiation of the corresponding disulfide with 400 nm LEDs. In the proposed catalytic cycle tetrafluoropyridinyl thiol HSPyf is

Heterogeneous metallaphotoredox catalysis in a continuous-flow packed-bed reactor

• Wei-Hsin Hsu,
• Susanne Reischauer,
• Peter H. Seeberger,
• Bartholomäus Pieber and
• Dario Cambié

Beilstein J. Org. Chem. 2022, 18, 1123–1130, doi:10.3762/bjoc.18.115

• visible-light photocatalysts that enable new reaction pathways that were previously difficult or impossible to realize [2]. Technical advancements, such as the rise of light-emitting diodes (LEDs) and new reactor technologies were similarly important incentives to popularize light-mediated organic

• radiated with 440 nm LEDs at 55 °C. A poor yield (16%) was obtained using a residence time of 3 hours. This result called for a more detailed investigation of crucial reaction parameters to understand if the limitation is of catalytic or technological nature. Steady-state and automated reaction analysis To

Introducing a new 7-ring fused diindenone-dithieno[3,2-b:2',3'-d]thiophene unit as a promising component for organic semiconductor materials

• Valentin H. K. Fell,
• Joseph Cameron,
• Alexander L. Kanibolotsky,
• Eman J. Hussien and
• Peter J. Skabara

Beilstein J. Org. Chem. 2022, 18, 944–955, doi:10.3762/bjoc.18.94

• (the basic unit of processors) [6], solar cells, and LEDs [7]. Inorganic compounds, e.g. III-V type inorganics are widely used, however, in recent years, organic molecules with semiconducting and fluorescent properties have emerged as an alternative with advantages such as solution processing [8][9][10

High-speed C–H chlorination of ethylene carbonate using a new photoflow setup

• Takayoshi Kasakado,
• Takahide Fukuyama,
• Tomohiro Nakagawa,
• Shinji Taguchi and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2022, 18, 152–158, doi:10.3762/bjoc.18.16

• the reaction and the system should be kept dry for continuous production. We are now investigating some other photo gas–liquid flow reactions, which will be reported in due course. Experimental The photoflow setup consisting of a flow photoreactor LX-1 and UV-LEDs were supplied from MiChS Inc., Ltd

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

• Ilya A. P. Jourjine,
• Lukas Zeisel,
• Jürgen Krauß and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2668–2679, doi:10.3762/bjoc.17.181

• electronic and optical properties [16][17][18][19][20][21], utilized in LEDs, semiconducting polymers, and solar cells. Consequently, synthetic approaches to fluorenones have attracted large interest and numerous methodologically diverse approaches have been published in the past decades. Among these are

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• . Under optimized conditions, the substrate scope was examined and determined to include activated olefins, unactivated olefins, and arylalkynes. In parallel, Hu and co-workers [51] reported the photoinduced, copper-catalyzed chlorosulfonylation of alkenes and alkynes under irradiation with blue LEDs

A visible-light-induced, metal-free bis-arylation of 2,5-dichlorobenzoquinone

• Pieterjan Winant and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 2315–2320, doi:10.3762/bjoc.17.149

• through oxidative quenching of the excited substrate. While an excited state of 1 could react in a similar fashion, the absorption maximum of 1 is centered around 280 nm, which is outside the emission spectrum of green LEDs. A recent study by Hashmi et al. [44], however, shed a completely different light

• investigate the transferability of this concept to our system, the light source was changed to blue LEDs. This change seemed to increase reactivity, observed by significantly more vigorous nitrogen release, resulting in shortening of the reaction time to 2 h. The reaction yield on the other hand was slightly

• lower as compared to when green LEDs were used. Based on the report by Hashmi, we hypothesize that the overlap in wavelengths emitted by both green and blue LEDs cause the reaction to work in both instances. The diminished intensity of shorter wavelengths in the green LED causes a slower, more

Photoredox catalysis in nickel-catalyzed C–H functionalization

• Lusina Mantry,
• Rajaram Maayuri,
• Vikash Kumar and
• Parthasarathy Gandeepan

Beilstein J. Org. Chem. 2021, 17, 2209–2259, doi:10.3762/bjoc.17.143

• of aryl chlorides 8 through selective 2-functionalization of 1,3-dioxolane (13) followed by a mild acidic workup (Scheme 9) [61]. Here, the photocatalyst Ir[dF(CF3)ppy]2(dtbbpy)PF6 and nickel catalyst NiCl2·DME with dtbbpy as ligand, along with K3PO4 as base under irradiation with blue LEDs enabled

• efficient HAT photocatalyst to perform the desired C–H abstraction (Scheme 10) [62]. The catalytic reaction required near-ultraviolet light irradiation (Kessil 34 W 390 nm LEDs) and the exclusion of both oxygen and water to the success of the reaction. A variety of cyclic, acyclic, and bicyclic aliphatic

• under irradiation of blue LEDs at ambient temperature afforded the desired α-arylation products 32 from secondary amides 31 and (hetero)aryl bromides 3 (Scheme 18) [72]. The method showed a broad substrate scope for both amides and aryl bromides. The authors also realized the enantioselective variant of

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Heterogeneous photocatalytic cyanomethylarylation of alkenes with acetonitrile: synthesis of diverse nitrogenous heterocyclic compounds

• Guanglong Pan,
• Qian Yang,
• Wentao Wang,
• Yurong Tang and
• Yunfei Cai

Beilstein J. Org. Chem. 2021, 17, 1171–1180, doi:10.3762/bjoc.17.89

• recycling. Reaction conditions: 1a (0.1 mmol, 1 equiv), 2d (0.2 mmol, 2 equiv), CH3CN (6 mL), CN-K (1 mg/mL), 2 × 24 W blue LEDs (460 ± 5 nm) without extra heating (at 40–45 °C). After each reaction, the catalyst was recovered by centrifugation and reused in the next cycle. CN-K-Catalyzed

• cyanomethylarylation of alkenes to access diverse heterocyclic compounds. CN-K-catalyzed cyanomethylarylation of N-arylallylamines for the synthesis of indolines. Reaction conditions: 1 (0.2 mmol, 1 equiv), 2d (0.4 mmol, 2 equiv), CH3CN (8 mL), CN-K (1 mg/mL), 2 × 24 W blue LEDs (460 ± 5 nm) without extra heating (at

• 40–45 °C). aPerformed with 0.017 M of 1. CN-K-catalyzed cyanomethylarylation of N-benzoylallylamines for the synthesis of isoquinolinones. Reaction conditions: 5 (0.2 mmol, 1 equiv), 2d (0.6 mmol, 3 equiv), CH3CN (8 mL), CN-K (1 mg/mL), 2 × 24 W blue LEDs (460 ± 5 nm), 60 °C. CN-K-catalyzed

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• tetramethylethylenediamine (TMEDA) as additive in the EDA complex formation with perfluoroalkyl iodides 42 to afford 2-perfluoroalkylbenzothiazole products 43, employing blue LEDs (25 W) as irradiation source (Scheme 14). Notably, as (2-isocyanophenyl)(methyl)selane was exploited instead of substrate 41, new

• in 158. Significantly, in contrast to most traditional EDA complex approaches that consume the DA pair, the electron-donor catalyst q-OAc in this method could be regenerated. In 2019, Frontera and colleagues [49] obtained target product 162 with blue LEDs irradiation of a solution containing electron

Metal-free visible-light-enabled vicinal trifluoromethyl dithiolation of unactivated alkenes

• Xiaojuan Li,
• Qiang Zhang,
• Weigang Zhang,
• Jinzhu Ma,
• Yi Wang and
• Yi Pan

Beilstein J. Org. Chem. 2021, 17, 551–557, doi:10.3762/bjoc.17.49

• of blue LEDs, allyl boronate 1a (0.1 mmol), disulfide 2a (1.0 equiv) and N-(trifluoromethylthio)phthalimide (Phth-SCF3, 3, 1.5 equiv), the desired trifluoromethylthiolated product 4a was obtained in 71% yield with 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN, 2 mol %) as the

Benzothiazolium salts as reagents for the deoxygenative perfluoroalkylthiolation of alcohols

• Armin Ariamajd,
• Nils J. Gerwien,
• Benjamin Schwabe,
• Stefan Dix and
• Matthew N. Hopkinson

Beilstein J. Org. Chem. 2021, 17, 83–88, doi:10.3762/bjoc.17.8

• the perfluoroisopropyl species BT-SCF(CF3)2. Each reagent was synthesized according to the two-step procedure shown in Scheme 2. Firstly, MBT was reacted with a perfluoroalkyl iodide and NaH in DMF under irradiation with UVA LEDs (λmax = 365 nm). In all cases, efficient S-perfluoroalkylation was

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors

• Emine Kayahan,
• Mathias Jacobs,
• Leen Braeken,
• Leen C.J. Thomassen,
• Simon Kuhn,
• Tom van Gerven and
• M. Enis Leblebici

Beilstein J. Org. Chem. 2020, 16, 2484–2504, doi:10.3762/bjoc.16.202

• same group reported the use of the same reaction in a commercial microchip (Micronit Microfluidics FC_R150.676.2) with an internal volume of 15 µm. This microchip was illuminated by 6 × 75 mW LEDs. The DMBP concentration was 6.7 mM, which resulted in around 95% light transmission through 150 µm channel

• 1.4 min. This reaction could be scaled up using other Corning reactors. For example, if the same conditions could be maintained in a Corning G3 reactor, this reaction would have a productivity of 100 mol/day [45]. The power consumption of the LEDs was not reported in the paper. Therefore, the PSTY

• packed bed reactor so that several microchannels were created among the beads. Glass beads were coated with a TiO2 photocatalyst. The photoreactor was illuminated with 192 LEDs that could provide 100 mW of power each. The distance between the LED board and the reactor was adjusted to give a uniform

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• ; outer diameter 3.2 mm; representing a 15 mL internal volume) and 6 × 20 W 72-LED work light sources (white LEDs, Scheme 30). The reaction mixture (a 12 mL slug) was pumped through. After 4 h, the coil was flushed through with MeCN to collect all of the reaction mixture. In the synthesis of 71, the flow

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

• ) [38][39], and more recently, organic compounds (cyanoarenes, xanthenes, thiazines, pyryliums or acridiniums) [40], emerged. These molecules capable of harvesting visible light from simple household bulbs or easily accessible LEDs, opened the door towards the design of numerous electron or energy

• ]. Targeting more sustainable protocols, a manganese catalyst was selected to trigger the coupling between an aryldiazonium salt and simple (hetero)aryls. A unique reactivity was obtained under irradiation with blue LEDs and a continuous-flow process allowed achieving higher reactivity. Under the optimized

• photoreactor emitting UV light at 254 nm, the same reactivity was also reached under visible-light irradiation (blue LEDs), and in the presence of the photosensitizer, Ir(ppy)3. This transformation hence illustrates clearly the potential of combining metal catalysis and photoinduction to design much milder and

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

• LED light source (TiO2@WLE, Figure 13) [140]. This allowed the efficient irradiation of the TiO2 HPCat from within the reaction mixture and has the benefit of not requiring external LED sources or transparent reactor vessels. The LEDs were powered wirelessly using resonant inductive coupling, and were

• LEDs, which could be problematic when scaling up. Additionally, the attrition of the free floating TiO2@WLE spheres, leading to potential damage or leaching of the TiO2 layer, was not investigated. The excellent chemical and thermal stability of metal alloys makes them ideal supports for applications

Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions

• Shrikant D. Tambe,
• Kwan Hong Min,
• Naeem Iqbal and
• Eun Jin Cho

Beilstein J. Org. Chem. 2020, 16, 1335–1342, doi:10.3762/bjoc.16.114

• under inert conditions. The reaction mixture was stirred at ambient temperature for 2–15 h under visible-light irradiation with blue LEDs (18 W). The progress of the reaction was monitored by using TLC. Upon the completion of the reaction, the crude product was diluted with ethyl acetate and washed with

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

• carried out under the action of a PC-I/TEMPO catalytic system and the irradiation of blue LEDs (Scheme 37) [127]. A variety of electronically rich and electronically poor aryl or heteroaryl groups at the oxime group (R1) are well-tolerated (products 115a–e). Oximes with disubstituted double C=C bond also

Synthesis of esters of diaminotruxillic bis-amino acids by Pd-mediated photocycloaddition of analogs of the Kaede protein chromophore

• Esteban P. Urriolabeitia,
• Pablo Sánchez,
• Alexandra Pop,
• Cristian Silvestru,
• Eduardo Laga,
• Ana I. Jiménez and
• Carlos Cativiela

Beilstein J. Org. Chem. 2020, 16, 1111–1123, doi:10.3762/bjoc.16.98

• spectra were measured on a Thermo Scientific Evolution 600BB spectrophotometer. Cinnamoylglycine (1) was prepared by the Schotten–Baumann method [49]. Irradiation setup for batch synthesis The irradiation setup consisted of a flask (100 mL) irradiated by a printed circuit board (PCB) formed by 24 LEDs of

• 10 mm diameter each LED. The LEDs were serially connected in blocks of 6, with the minimum voltage possible (3 V) and a resistance of 60 Ω (according to Ohm's law). The output power per LED unit (blue, 465 nm) was 250 kmcd; the optical output power of the PCB of LEDs measured with a photometer

• emitting diodes (LEDs) were purchased from Topbright. X-ray crystallography Single crystals of 2c and 4a of suitable quality for X-ray diffraction measurements were grown by slow diffusion of n-pentane into CH2Cl2 solutions of the crude product at –18 °C for several weeks. One selected single crystal was

Accelerating fragment-based library generation by coupling high-performance photoreactors with benchtop analysis

• Quentin Lefebvre,
• Christophe Salomé and
• Thomas C. Fessard

Beilstein J. Org. Chem. 2020, 16, 982–988, doi:10.3762/bjoc.16.87

• conditions compared to a single vial reactor. Active water cooling protects the LEDs from overheating, while additional air cooling with bespoke fans prevents the vessels to heat over 50 °C. Each vessel is placed at equal distance of a 35 W high power blue LED (Figure 1). Reaction monitoring by TLC–MS

A method to determine the correct photocatalyst concentration for photooxidation reactions conducted in continuous flow reactors

• Clemens R. Horn and
• Sylvain Gremetz

Beilstein J. Org. Chem. 2020, 16, 871–879, doi:10.3762/bjoc.16.78

• can be delivered to the catalyst. These limitations are defined by the photoflow setup, specifically the channel height and the emission peak of the light source. This method was tested and shown to work well for three catalysts with different absorption properties through using LEDs with emission

• sources over mercury arcs and other light sources commonly used in industry and classical synthetic organic photochemistry. LEDs typically have much narrower emission spectra when compared to these light sources, all of which have broad emission spectra except for low-pressure sodium vapor lamps [15][16

• emission wavelength, the appropriate wavelength above 365 nm can be selected for every reaction, and the scale-up can be achieved by simply increasing the number of the LEDs applied [19]. The narrower spectra, while providing many benefits and likely reducing the occurrence of side reactions, also

Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts

• David Schönbauer,
• Carlo Sambiagio,
• Timothy Noël and
• Michael Schnürch

Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74

• catalyst loading could be decreased to 2 mol % without negative effects (cf. entries 15 and 16 in Table 1). Further dilution gave no further improvement in the yield (see Supporting Information File 1). Next, increasing the power of the LEDs from 6 to 18 W gave 73% GC yield and a 64% isolated yield of 3

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• organic molecules absorb light in the UV region (UV-A, UV-B, or UV-C), selectivity was a key point to address in photochemistry and photocatalysis using visible light tackled this issue. Moreover, the use of inexpensive and energy-efficient visible light-emitting diodes (LEDs) was an impressive