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

• -isocyano-1,1'-biaryls 4.1 have been reported, as summarized in Scheme 4. Along with substrate 4.1, a radical source R–X and a photocatalyst (PC), which is activated upon visible-light irradiation, are usually required. Oxidative quenching of the photoexcited PC* by R–X (path a) affords, upon loss of the

• - [55][56] phenanthridines was investigated. On the other hand, Umemoto’s reagent 7.2 was widely employed to introduce a trifluoromethyl group. In one instance, the visible-light irradiation of isocyanides 7.1 in the presence of excess 7.2 (4 equiv) and the Ru(bpy)32+ photoredox catalyst afforded the

• approach, sodium triflinate was adopted as the trifluoromethyl radical source along with diacetyl, that played the dual role of photomediator and reaction medium [60]. The same trifluoromethylated derivatives were obtained from 7.1 in the presence of CF3SO2Cl upon direct UV light irradiation by a Xe arc

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• high regioselectivity [4]. Based on this reaction, Maruoka reported in 2016 that N-tosylvinylaziridines and alkenes could undergo cyclization reactions to generate pyrrolidines, catalyzed by substituted aryl disulfides under ultraviolet-light irradiation (Scheme 1) [5]. In 1997, Jung and co-workers

• of vinylcyclopropanes with olefins [8]. The reaction mechanism of this cycloaddition process was similar to other thiyl radical-catalyzed cycloaddition cascade reactions. The alkylthiyl radical generated by the homolysis of a disulfide-bridged peptide precatalyst under UV-light irradiation triggers

• give the four-membered ring intermediate 29. Finally, the rearrangement of the four-membered intermediate provides the diketone 30 as the product (Scheme 8). In 2017, Wang and co-workers reported an oxidative cleavage of aromatic alkenes at ambient temperature with visible-light irradiation, using

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

• produced the reduced amine product 4a in 67% yield (Scheme 4) [17][18][58][59][60][61]. Based on these observations, a plausible reaction mechanism was proposed for the developed transformation (Scheme 5). Upon visible-light irradiation, the excited photocatalyst [IrIII]* is formed and is reductively

• 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

Photocatalytic trifluoromethoxylation of arenes and heteroarenes in continuous-flow

• Alexander V. Nyuchev,
• Ting Wan,
• Borja Cendón,
• Carlo Sambiagio,
• Job J. C. Struijs,
• Michelle Ho,
• Moisés Gulías,
• Ying Wang and
• Timothy Noël

Beilstein J. Org. Chem. 2020, 16, 1305–1312, doi:10.3762/bjoc.16.111

• Ir photocatalyst was tested under blue light irradiation, but a poor 10% yield was obtained. Experiments in the absence of photocatalyst under violet or blue light gave respectively 17% and 0% yield. The little product obtained with 400 nm light can be explained by the photodecomposition of 1, which

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

• ), in the presence of the sacrificial electron donor DIPEA, can reduce these species under green light irradiation. The ensuing decarboxylation provides a C(sp3) radical, which undergoes a radical conjugate addition with a suitable Michael acceptor 4.2, providing the desired alkylation products 4.3. A

• successfully employed for the generation of C(sp3) radicals via HAT [58]. Interestingly, Wu and co-workers demonstrated that eosin Y (OD13) can also act as a direct HAT catalyst under visible-light irradiation [59]. Organic photoredox catalysis can also drive indirect HAT processes. In these reactions, the

• visible-light irradiation. The key aryl radical was trapped with heteroarenes, such as 11.2, to give the arylation products 11.3. Recently, similar methodologies for aryl radical generations have been developed exploiting flow techniques [74] and different organophotocatalysts, such as a metal-free

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• photocatalysts. Under light irradiation, one electron from the ground state (S0) is promoted to the excited singlet state (S1) which has a short lifetime (10−9 s). Therefore, fast intersystem-crossing of one electron gives the excited triplet state (T1) with a relatively longer lifetime (10−6 s). While the

• platform for dual catalysis due to their ability to promote both metallocatalysis and photocatalysis in a one-pot system [36][37][38][39]. Martin and co-workers carried out the C–O bond cleavage of alcohols using a cobalt porphyrin under visible light irradiation and a carbon monoxide atmosphere (Scheme 11

• highly regioselective photoinduced hydro-defluorination of perfluoroarenes with RhIII(TSPP) [38]. The oxidative addition of the perfluoroarene to the metal complex furnished the active rhodium aryl complex intermediate, which led to the product after visible light irradiation. The hydro-defluorination

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

• seek greener and sustainable processes to advance chemistry, the use of aldehydes in conjunction with light irradiation, even sunlight, will become more popular, providing a vast array of applications. Norrish type I and II dissociations. Proposed radical pair formation after the photolysis of

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• nitride-supported copper nanoparticles was disclosed by Islam and co-workers (Scheme 18) [79][80]. The nanocatalyst 87 was successfully used as a high-performance photoreactor promoting “click” reactions of alkynes with organic azides under light irradiation in the absence of basic condition. In the first

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

• [Cu(I)(dap)2]Cl under green light irradiation (Scheme 5) [21]. Fluorinated sultones are important scaffolds for pharmaceutical syntheses. To illustrate the synthetic utility of the method, a novel benzoxathiin analog was synthesized using this reaction as the key step. The authors suggested a similar

• . To explain the reaction outcome, the authors suggested the involvement of a [Cu(I)] complex as the catalytically active species, even when [Cu(II)(dap)2]Cl2 was used. Indeed, they suggested the formation of the [Cu(I)] species from a homolytic cleavage of the Cu(II)–Cl bond under light irradiation

• [Cu(I)(dpp)2]PF6 complex can be excited under visible light irradiation (530 nm), and the resulting excited [Cu(I)]* complex undergoes an SET to reduce the diaryliodonium species, providing the oxidized [Cu(II)] complex. The reduced diaryliodonium species collapses into an aryl radical and the

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

Design, synthesis and investigation of water-soluble hemi-indigo photoswitches for bioapplications

• Daria V. Berdnikova

Beilstein J. Org. Chem. 2019, 15, 2822–2829, doi:10.3762/bjoc.15.275

• UV light irradiation (254 nm or 366 nm). Column chromatography was performed on Sephadex® columns. 1H NMR and 13C NMR spectra were recorded on a JEOL ECZ 500 spectrometer at 25 °C using 5 mm tubes. Chemical shifts were determined with accuracy of 0.01 ppm and 0.1 ppm for 1H and 13C spectra

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• Photoswitches are molecules that are capable of being reversibly interconverted between (at least) two states by means of light irradiation. The incorporation of photoswitches into multifunctional systems has huge relevance to next-generation materials, with a plethora of applications that range from

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

• Valentina A. Ol’shevskaya,
• Elena G. Kononova and
• Andrei V. Zaitsev

Beilstein J. Org. Chem. 2019, 15, 2704–2709, doi:10.3762/bjoc.15.263

• conjugated to a cystein residue of serum albumin via a Michael addition reaction. At the same time, it is well known that 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin and its chlorin derivatives generate singlet oxygen by the light irradiation under atmospheric oxygen [31]. These tetrapyrrole macrocycles

Plasma membrane imaging with a fluorescent benzothiadiazole derivative

• Pedro H. P. R. Carvalho,
• Jose R. Correa,
• Karen L. R. Paiva,
• Daniel F. S. Machado,
• Jackson D. Scholten and
• Brenno A. D. Neto

Beilstein J. Org. Chem. 2019, 15, 2644–2654, doi:10.3762/bjoc.15.257

• bioimaging experiments and proved to be stable under constant light irradiation for more than 4 hours (see Figure S4 in Supporting Information File 1). Theoretical calculations were then performed for a better comprehension of the photophysical data obtained for BTD-4APTEG by means of the time-dependent

In search of visible-light photoresponsive peptide nucleic acids (PNAs) for reversible control of DNA hybridization

• Lei Zhang,
• Greta Linden and
• Olalla Vázquez

Beilstein J. Org. Chem. 2019, 15, 2500–2508, doi:10.3762/bjoc.15.243

• , artificial probes activated by visible-light irradiation are highly desired in biological applications. Here, we report two novel types of visible-light photoswitchable peptide nucleic acids (PNAs) based on the molecular transducers: hemithioindigo and tetra-ortho-fluoroazobenzene. Our study reveals that the

• tetra-ortho-fluoroazobenzene–PNA conjugates have promising properties (fast reversible isomerization, exceptional thermal stability, high isomer conversions and sensitivity to visible-light irradiation) as reversible modulators to control oligonucleotide hybridization in biological contexts. Furthermore

• first compounds here reported, may find applications in different fields such as chemical biology, nanotechnology and materials science. Keywords: azobenzene; hemithioindigo; peptide nucleic acid (PNA); photoswitch; visible-light irradiation; Introduction Light-driven control of oligonucleotide

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

• isomer and the emergence of a new band in visible upon UV light irradiation (Figure 2) [8]. This color change is due to the reversible photocyclization and formation of a closed-ring isomer (Scheme 2). The results of photochemical studies are listed in Table 1. Absorption maxima of the open-ring ligands

Targeted photoswitchable imaging of intracellular glutathione by a photochromic glycosheet sensor

• Xianzhi Chai,
• Hai-Hao Han,
• Yi Zang,
• Jia Li,
• Xiao-Peng He,
• Junji Zhang and
• He Tian

Beilstein J. Org. Chem. 2019, 15, 2380–2389, doi:10.3762/bjoc.15.230

• ring-closed photoisomer [28]. The absorption band at 550 nm remained unchanged after 3 min of irradiation as the photostationary state (PSS) was reached. The absorption spectra of the ring-opened isomer could be fully recovered upon visible light irradiation (4 min), suggesting a photocycloreversion or

• several times in buffer solution without obvious degradation (Figure 1B), demonstrating the robustness of Glyco-DTE. Figure 1C shows the photoswitching of emission spectra of Glyco-DTE (1 × 10−5 mol/L) in PBS buffer upon alternating UV and visible light irradiation at room temperature. Upon excitation

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

• -type photochromic compounds which reversibly generate an imidazolyl radical and a phenoxyl radical (biradical form) in a molecule upon UV light irradiation [24]. The great advantage of PIC is the tunability of the thermal back reaction from tens of nanoseconds to tens of seconds by simple and rational

• A. PIC generates the biradical species upon UV-light irradiation and shows the broad transient absorption spectrum over the visible- to near infrared-light regions. The half-life of the thermal back reaction of the biradical in benzene is 250 ns (the lifetime is 360 ns) at 298 K. To investigate the

• isomer A accumulated by 8 shots are slightly fluctuated most probably because of the low signal-to-noise ratio, the decay kinetics do not change by repeated irradiation with UV-light pulses. It shows that both isomers generate the same biradical form by UV-light irradiation as shown in Scheme 1

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

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

• . In addition, it shows turn-off type fluorescence switching in an aprotic solvent and in crystals. The fluorescence is quenched as the content of closed-ring isomers increases upon UV light irradiation. Conclusions: A diarylethene containing an ESIPT functional group was prepared. It showed

• fluorescent turn-off behavior during photochromism in aprotic solvents as well as in crystalline state upon UV light irradiation. Furthermore, it showed AIE in THF/water mixtures with blue-shift of the emission. Keywords: AIE; diarylethene; ESIPT fluorescent switching; turn-off fluorescence; Introduction

• ’-methoxyphenyl)imidazo[1,2-a]pyridine 4 [25] followed by ether cleavage according to Figure 1. The photochromic reaction and spectral changes are shown in Figure 2 and Figure 3. The photochromic absorption spectral changes in THF are shown in Figure 3. Upon UV light irradiation of the solution of 1o, the color

Click chemistry towards thermally reversible photochromic 4,5-bisthiazolyl-1,2,3-triazoles

• Chenxia Zhang,
• Kaori Morinaka,
• Mahmut Kose,
• Takashi Ubukata and
• Yasushi Yokoyama

Beilstein J. Org. Chem. 2019, 15, 2161–2169, doi:10.3762/bjoc.15.213

• ethanol (EtOH), acetonitrile (MeCN), ethyl acetate (AcOEt) and toluene, and each solution was irradiated with 313 nm light. The changes in the absorption spectra during UV light irradiation in MeCN are shown in Figure 1 (spectra of the compounds in the other solvents are shown in Figures S1–S9 in

• the thermal back reaction after 313-nm light irradiation to 1o–3o in MeCN at 28 °C. Concentration of compounds are the same as in Figure 1. (a) 1c. (b) 2c. (c) 3c. Reaction mechanisms of Huisgen cyclization catalyzed by Cu(I) and Ru(I). Synthesis and photochromism of bisthiazolyltriazoles. Wavelengths

Friedel–Crafts approach to the one-pot synthesis of methoxy-substituted thioxanthylium salts

• Kenta Tanaka,
• Yuta Tanaka,
• Mami Kishimoto,
• Yujiro Hoshino and
• Kiyoshi Honda

Beilstein J. Org. Chem. 2019, 15, 2105–2112, doi:10.3762/bjoc.15.208

• green light irradiation [24][25]. In the course of this study, we found that these thioxanthylium photocatalysts efficiently oxidized styrene derivatives such as trans-anethole, and promoted radical cation Diels–Alder reactions. Based on the background mentioned above, in order to expand the utility of

An azobenzene container showing a definite folding – synthesis and structural investigation

• Abdulselam Adam,
• Saber Mehrparvar and
• Gebhard Haberhauer

Beilstein J. Org. Chem. 2019, 15, 1534–1544, doi:10.3762/bjoc.15.156

• chemistry. Here, we present the synthesis of a foldable container consisting of two different types of Lissoclinum macrocyclic peptides which are connected via two azobenzene units. The container is controllable by light: irradiation with UV light causes a switching process to the compact cis,cis-isomer

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

• reversibility of the switching behavior. The dispersion of AuNR assemblies after visible light irradiation can also be verified by TEM bright field images (Figure 4d) showing that the disassembly is possible without the combination of irradiation and sonication. This can be attributed to the favorable

• photostationary states of the AAP moiety in comparison to azobenzenes used in previous studies. Furthermore, dynamic light scattering was conducted to analyze the assembly in solution (Figure 5). The mean diameter increases upon dAAP addition from ca. 100 nm to ca. 230 nm. Upon UV-light irradiation, the mean

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

• , at wavelengths of 710–760 nm and power of 700 mW. ESR spectra acquired during the photolysis of 2a (5 mM) in benzene using 365 nm light. Irradiation time-dependent decline in viability of LLC cells with compound 2a. Detection of intracellular ROS only in irradiated LLC cells with 2a-containing medium