Visible-light-mediated flow protocol for Achmatowicz rearrangement

• Joachyutharayalu Oja,
• Sanjeev Kumar and
• Srihari Pabbaraja

Beilstein J. Org. Chem. 2024, 20, 2493–2499, doi:10.3762/bjoc.20.213

• light and biomass-derived furfuryl alcohols as starting material making it more environmental benign. Results and Discussion A batch process Achmatowicz rearrangement mediated by less expensive rose bengal as photocatalyst (PC) was first reported by Vassilikogiannakis et al. [24] and was further

Synthesis and characterization of water-soluble C₆₀–peptide conjugates

• Yue Ma,
• Lorenzo Persi and
• Yoko Yamakoshi

Beilstein J. Org. Chem. 2024, 20, 777–786, doi:10.3762/bjoc.20.71

• corresponding to 4-oxo-TEMPO were observed in the solution of C60–oligo-Lys (5a), similar to the results with rose bengal, a standard compound for 1O2 generation. By taking into account that the absorption intensity of 5a at 527 nm used for the photoirradiation was ≈10 times smaller than that of rose bengal, it

• crude sample of 5b, with the penta-Glu impurity being soluble in pyridine-d5 (Figures S13–S17, Supporting Information File 1). a) X-band ESR spectra of the 4-oxo-TEMP adduct with 1O2 generated by C60–oligo-Lys (5a) and rose bengal (RB), respectively, in aqueous solutions under irradiation with a green

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• heterocyclic aromatics with α-C–H bonds of ethers was achieved under the irradiation of a 34 W blue LED using rose bengal (RB) as the organic photoredox catalyst, TBHP as oxidizing agent, and DABCO as the base (Scheme 43c) [125]. The wide scope of substrates, aerobic conditions, and gram-scale suitability are

Combining the best of both worlds: radical-based divergent total synthesis

• Kyriaki Gennaiou,
• Antonios Kelesidis,
• Maria Kourgiantaki and
• Alexandros L. Zografos

Beilstein J. Org. Chem. 2023, 19, 1–26, doi:10.3762/bjoc.19.1

• substantial decrease of the product yield. FGI, followed by methylenation provided the common scaffold 88. Further elaboration of 88 to natural products 90 and 89 was accomplished by UV irradiation at 365 nm in MeOH and by utilizing singlet oxygen (using rose Bengal) in MeCN/pyridine, 40:1, respectively

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

• Alessandra Del Tito,
• Havall Othman Abdulla,
• Davide Ravelli,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

• exploited for the construction of phenanthridine 6-carboxylates (Scheme 12). Notably, the process occurred in water under metal-free conditions in the presence of rose bengal (5 mol %) and made use of molecular oxygen as the terminal oxidant. Thus, N-biarylglycine esters 12.1a–d promoted the reductive

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

• . Other organic dyes, including several acridinium salts, have been successfully applied in organophotocatalytic decarboxylation protocols. For example, rhodamine 6G (OD14, E(PC+*/PC) ≈ 1.2 V) [42] was used for the photocatalytic decarboxylative azidation of cyclic amino acids and rose bengal (OD15) [43

• similar strategy for radical generations was applied by Glorius and co-workers. They exploited a combination of organophotoredox and copper catalysis to achieve the conversion of carboxylic acids into alkenes using N,N-diaryldihydrophenazine as an organic photocatalyst [46]. Rose bengal (OD15) was also

• 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

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

• shows the values measured for the extinction coefficient, the LED peak, and the absorption maximum based on the measured values and the predicted concentration for the catalyst using the channel height of 0.04 cm. Figures 4–6 serve to illustrate three possible examples. For rose bengal (D, Figure 4

• made for TPP catalyst (H) concentrations. Rose bengal (D) gave similar results: increasing the amount of the catalyst by 50% provided a slightly higher conversion for high flow rates, and the change of the solvent from ethanol to acetonitrile had the same impact (Figure 10). This can be attributed to

• at 0.5 mm pathlength. cCatalyst concentration: 0.1 mol %. Measured transmission spectrum of a 5 mmol/L (1 mol %) solution of TPP (H) in dichloromethane with 0.5 N citronellol and the emission spectrum of the LED with an emission maximum at 624 nm. Transmission spectra of rose bengal (D) and the

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• luminescent dyes. Fluorescein, eosin Y, rose bengal, tetraphenylporphine sulfonate and sulfonated aluminum phthalocyanine were employed as classical aggregation-induced quenching dyes. 2-(p-Toluidinyl)naphthalene-6-sulfonic acid and 1-anilinonaphthalene-8-sulfonic acid were selected as representatives of

• (EY), rose bengal (RB), tetraphenylporphine sulfonate (TPPS), sulfonated aluminum phthalocyanine (AlPcS4), 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS), 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS), phosphated tetraphenylethylene (P-TPE), sulfonated acedan (TPS), and a ruthenium(II) complex

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

• charge transfer using Cs2CO3 as base [41]. Two recent reports showed the synthesis of C-3 sulfenylated indoles and 3-sulfenylimidazopyridine via C–H functionalization using Rose Bengal as photocatalyst [42][43]. In general, the arylation reactions use the reductive cycle of the photocatalyst and for this

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• an organophotocatalytic version of the Ugi reaction. These procedures were undertaken in a flow chemistry set-up, using irradiation by green LEDs and Rose Bengal as the photocatalyst (Scheme 13) [56]. The scope of the reaction is fairly broad, especially considering the method was developed in a flow

• performing a visible light-driven oxidative cyclisation of arylamidines using Rose Bengal as the photocatalyst, in the presence of base and CBr4 as the oxidant (Scheme 25) [69]. The scope of the reaction is restricted to mono-substituted benzenes and lacks any carbonyl derivatives as ligands. The reaction

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

• and aromatic thiols react under these conditions with aliphatic alkenes and styrenes. The direct C-3 sulfenylation of indoles with aryl thiols was reported by Guo, Chen and Fan, using Rose Bengal as organic photoredox catalyst and aerobic oxygen as oxidative species (Scheme 14) [44]. They propose that

• 1O2 is generated by photoexcited Rose Bengal via energy transfer and abstracts a hydrogen atom from the aryl thiol. Radical addition on the indole derivative, oxidation and rearomatization via deprotonation yields the corresponding sulfenylated indole derivative. Very recently, Wei, Wang and co

• -workers and the working groups of Fraile and Aleman independently reported of visible-light photocatalyzed procedures for the preparation of sulfoxides from the respective sulfides and alkenes by radical thiol–ene reactions (Scheme 15) [45][46]. Wei and Wang applied Rose Bengal as organic photocatalyst

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

• the reaction was performed with the sensitizer rose bengal the diene was observed to quickly disappear from the system and only a low yield of endoperoxide 17 was obtained. Due to the many problems encountered with the Boc-protection strategy it was abandoned at this stage and we turned our attention

• to the phthalimide-protected dienes 15,16. When the same reaction was performed with rose bengal on diene 16 a very low yield of endoperoxide 19 was obtained and most starting material was recovered (78%) even after prolonged reaction time (40 h). However, the reaction outcome was greatly improved by

• exchanging the sensitizer with tetraphenylporphyrin (TPP) to give a good yield of the desired endoperoxide 19. Likewise, diene 15 was converted to the corresponding endoperoxide 18 in good yield using TPP, whereas no product was obtained using rose bengal. With endoperoxides 18 and 19 in hand the stage was

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

Eosin Y-catalyzed visible-light-mediated aerobic oxidative cyclization of N,N-dimethylanilines with maleimides

• Zhongwei Liang,
• Song Xu,
• Wenyan Tian and
• Ronghua Zhang

Beilstein J. Org. Chem. 2015, 11, 425–430, doi:10.3762/bjoc.11.48

• and not sustainable. Similar to the redox properties of these organometallic complexes, some metal-free organic dyes such as Eosin Y, Rose Bengal, Fluorescein, and Methylene Blue, have shown superiority of their applications as photocatalysts, which are easy to handle, environmentally friendly

• 1), Rose Bengal gave a slightly lower yield (Table 1, entry 2), whereas Methylene Blue and Fluorescein gave poor yields (Table 1, entries 3 and 4). Under an O2 atmosphere, the yield of tetrahydroquinoline product 3a was decreased to 77% (Table 1, entry 5). When the molar proportion of 1a and 2a 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

• by on-water oxidative phenylamination of 1,5-dihydroxynaphthalene (1) and 5-acetylamino-1-hydroxynaphthalene (5) with oxygen-substituted phenylamines under aerobic conditions and either solar or green LED radiation, in the presence of rose bengal as singlet oxygen sensitizer. As compared to the

• conventional oxidative phenylamination procedures, this novel synthetic method offers the advantage of aerobic conditions “on water” instead of hazardous oxidant reagents currently employed in aqueous alcoholic media. Keywords: 1,4-naphthoquinone monoimines; on water; oxidative coupling; rose bengal; solar

• 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

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

• , to exclude the intervention of a singlet oxygen mechanism, we conducted the reaction in the presence of Rose Bengal. Under these conditions, we observed only 1O2 ene reactivity with the isoprenyl group (65% yield of hydroperoxide), underscoring the unique reactivity garnered by this catalyst system

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

• /oxidative aromatization cascade using Rose Bengal as an organo-photocatalyst. A variety of pyrroloisoquinolines have been obtained in good yields under mild and metal-free reaction conditions. Keywords: alkaloids; [3 + 2] cycloaddition; organocatalysis; oxidation; photochemistry; photoredox catalysis; Rose

• ] 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

• presence of Rose Bengal (5 mol %) in acetonitrile under irradiation with visible light, the reaction was not selective affording the dihydropyrrolo[2,1-a]isoquinoline 3aa in 35% yield and the hexahydropyrrolo[2,1-a]isoquinoline 4aa in 26% yield, after column chromatography (Scheme 1). In order to improve

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

• Christian Ley,
• Julien Christmann,
• Ahmad Ibrahim,
• Luciano H. Di Stefano and
• Xavier Allonas

Beilstein J. Org. Chem. 2014, 10, 936–947, doi:10.3762/bjoc.10.92

• , an electron acceptor and an electron donor leading to energy conversion through electron transfer, was the basis of the so called three-component systems. In this paper, an experimental work combining Rose bengal dye with a triazine derivative as electron acceptor and ethyl 4-(dimethylamino)benzoate

• on the Rose Bengal as dye, and a triazine derivative (TA) as an acceptor (coinitiator). In addition, an amine (ethyl 4-(dimethylamino)benzoate, EDB) was chosen as redox (electron donor) additive for the PCIS (see Scheme 1). Type II photoinitiating system In Scheme 2, the typical reaction mechanism of

• under argon bubbling at room temperature. The quenching rate constants kq of the excited states were obtained according to the Stern–Volmer analysis where the reciprocal lifetime is plotted as a function of quencher concentration: [57]. Chemicals: Rose Bengal extra (RB) and ethyl 4-(dimethylamino

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• . The authors proposed a mechanism similar to that proposed by Stephenson and coworkers for the aza-Henry reaction catalyzed by the Ir complex (Scheme 3). The Tan group simultaneously reported that another organic dye, Rose Bengal (RB), can be used in place of Eosin Y to catalyze the aza-Henry reaction

• dark after 4 h irradiation. This observation supports the formation of hydroperoxide intermediate 21. Tan and coworkers employed a cocatalyst system composed of the organic dye Rose Bengal and graphite oxide (GO) for α-cyanation of N-aryltetrahydroisoquinolines (Scheme 7) [70]. The use of GO as

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

• have been employed in the Rose Bengal-sensitised oxygenation of cyclopentadiene 19 (Scheme 7) [30][31]. Although this method allowed good temperature control and the immediate quenching of the potentially explosive peroxide intermediate 20 as it formed, the process was low yielding (20%), and whilst

• 0.95 g of product 21 was produced the lack of reported details make it difficult to say how scaleable this is likely to be. Rose Bengal has also been employed as a sensitiser in a microchip reactor equipped with a 20 W tungsten lamp for the addition of singlet oxygen to α-terpinene to yield the

• rose oxide 27. It was shown that Rose Bengal was approximately twice as effective a sensitiser as Ru(t-bpy)3Cl2 when a 450 W Xe lamp was employed. Through the use of an LED light source in the microreactor, the authors reported that the microflow system was slightly superior to the batch-type Schlenk