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

• majority cases. Moreover, in line with the theme of green chemistry, light is the sole external energy source in EDA complex pathways. Except for the pioneering research on EDA complexes in the 20th century, there was not much progress in the follow-up. Until the past few years, EDA-complex photochemistry

• photochemistry, two kinds of EDA complexes were involved in this approach, explaining the reason why the yield increased significantly when morpholine was employed as an organic base additive, which was exploited in the screening stage of the reaction conditions. In 2019, Xia and colleagues [46] reported that

• yield of this reaction can reach 7.6 g ⋅ h−1 on a gram scale, indicating that the flow step is promising in photochemistry. In 2019, Aggarwal and colleagues [38] employed Katritzky salt 119 as electron acceptor and HE 79 as electron donor to form an EDA complex, providing the corresponding alkyl radical

Mesoionic tetrazolium-5-aminides: Synthesis, molecular and crystal structures, UV–vis spectra, and DFT calculations

• Vladislav A. Budevich,
• Sergei V. Voitekhovich,
• Alexander V. Zuraev,
• Vadim E. Matulis,
• Vitaly E. Matulis,
• Alexander S. Lyakhov,
• Ludmila S. Ivashkevich and
• Oleg A. Ivashkevich

Beilstein J. Org. Chem. 2021, 17, 385–395, doi:10.3762/bjoc.17.34

• tetrazoles [11][12]. The first representatives of tetrazole-5-aminides were reported in the 1950s [13][14], whereas next publications were appeared only five decades later, being devoted to the synthesis and photochemistry of 1,3-diaryltetrazolium-5-aminides [15][16][17][18][19][20][21]. NMR studies of a few

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• . Keywords: aryl phosphates; biarenes; metal-free synthesis; photochemistry; photoextrusion; Introduction It is difficult to overestimate the importance of aromatics in drug development. Indeed, introducing an aromatic or a heteroaromatic ring, most often a (substituted) phenyl ring, into a biologically

• metal-free eco-sustainable conditions we reinvestigated the photochemistry of di- and triaryl phosphates III and IV (Scheme 1e), compounds that can be easily achieved from the corresponding phenols [62][63]. Results and Discussion At the onset of our investigation, we tested a triaryl phosphate such as

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

• . Photochemistry spans a number of reactions. For organic chemistry, 8000 photoreactions have been listed since 1975 [1]. Despite the huge portfolio, there is a lack of industrial applications of photochemistry. Van Gerven et al. listed five industrial applications of photochemistry in commercial wastewater

• has already been proven to be successful [4]. These examples show that photochemistry is a viable alternative to conventional chemistry approaches. In addition to specialty chemicals and wastewater treatment, photochemical pathways can also be used for methanol production [5], N2 fixation [6], and CO2

• sequestration [7]. Still, photochemistry has not been exploited much in industry since the distribution of light inside a photoreactor brings a lot of complexity to the reactor design. Unlike thermochemical reactions, it is not feasible to scale up photoreactions by increasing the dimensions of the reactor due

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

• ; photocatalysis; photochemistry; Introduction Enantioselective catalysis has become a central focus for organic synthetic chemistry, particularly since the Nobel prize was awarded to Sharpless, Knowles, and Noyori for their pioneering work in the field. In the last 15 years, photocatalysis has become a

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• position; ketene; mixed chromophores; Introduction Enones exhibit a rich and diverse photochemistry. The deep-seated photochemical rearrangements found in these systems have attracted numerous mechanistic studies. In this context, the photochemistry of α,β-enones A and β,γ-enones B (Figure 1) has become

• an actively researched area for more than two decades [1][2][3][4][5][6], particularly because of their fascinating photochemical rearrangements. In view of their rich photochemistry, it may be expected that incorporation of both enones into the same molecule C would lead to a variety of more

• interesting reactions. Indeed, this type of mixed enone photochemistry is also an attractive field [7][8] for chemists because the photochemistry of such substrates can feature the intramolecular competition of different photochemical rearrangements. For several years, our laboratory (S. Lahiri et al.) is

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

• catalysis and photochemistry. Where transition metal catalysis provides one strategy for C–H bond activation, transition-metal-free photochemical C–H fluorination can provide a complementary selectivity via a radical mechanism that proceeds under milder conditions than thermal radical activation methods

• unprecedented attention to photochemistry [70][71]. Increasing interest in photochemistry is often attributed to the ability to access radical intermediates that are otherwise difficult or impossible to obtain by classical chemistry but that can achieve unique chemical reactions complementary to two-electron

• processes [72][73][74][75][76][77]. However, the adoption of photochemistry into the toolbox of the synthetic organic chemist has been hindered by three phenomena: i) simple organic-molecule targets typically do not absorb (or have very small extinction coefficients for) visible light, which is among the

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

• has shifted the paradigms of photochemistry, opening new avenues of research with safer and scalable processes that can be readily implemented in academia and industry. Current state-of-the-art photocatalysts are homogeneous transition metal complexes that have favourable photophysical properties

• photon and mass transport. Photocatalysis provides a unique route to carry out complex chemical transformations under mild conditions that are often impossible with “standard” organic synthetic procedures. The earliest report of synthetic photochemistry can be traced back to Trommsdorf in 1834, who

• observed that crystals of santonine would shatter when exposed to sunlight [28]. Credit for the pioneering of photochemistry is usually given to Ciamician, the “grandfather of photochemistry”, who reported many interesting transformations of chemical solutions when irradiated by sunlight [29][30]. His

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• variety of reactions, renders them a class of green, economic, mild, and chemoselective radical catalyst. Apart from this, they are also excellent HAT catalysts in photoredox catalysis systems [2][3]. In various types of organic photochemistry reactions, such as cyclizations, anti-Markovnikov additions

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• derivatives 287–291 [78] (Scheme 52). In 1988, Kanaoka et al. studied the photochemistry of semicyclic and acyclic thioimides 292–294 and 295 with 2,3-dimethylbut-2-ene (215a) afforded the corresponding thietanes 296–299. However, the products were obtained together with pyrrolidinone, thiopyrrolidinone, or

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

• and heteroarenes. The use of flow photochemistry allows the reaction to occur 16 times faster than in batch, while at the same time achieving similar yields. Thanks to the intrinsic properties of microflow systems, especially for the scale-up of photochemical processes, we anticipate this procedure

[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

• systems for the control of photoreactivity. Keywords: [3 + 2] cycloadditions; β-cyclodextrin; inclusion complexes; photochemistry; phthalimides; Introduction Cycloadditions are highly useful reactions in organic synthesis providing complex cyclic structures from easily available precursors [1][2]. Among

• 6420 device. Photochemistry of 2 and 3 under different conditions A solution of 2 (30 mg, 0.11 mmol) in CH3CN (27.5 mL) was prepared and transferred to 7 quartz cuvettes (3.9 mL into each). Then, CH3CN (3.9 mL) or H2O (3.9 mL) was added to each of the cuvettes, followed by the addition of β-CD (200 mg

• values by the WINEQNMR program [51] according to the model for the formation of 1:1 stoichiometry of the inclusion complex 2@β-CD. Irradiation of 1 in the presence of acrylonitrile (AN). Complexation of 2 with β-CD, and formation of a ternary complex AN@2@β-CD. Photochemistry of 2 in the presence of AN

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

• renaissance of photocatalysis. Since the early seminal reports [1][2][3][4], inspired by pioneering works in photochemistry [5][6][7], this field has attracted increasing attention, and organic chemists have developed a wide variety of photocatalytic reactions [8][9][10][11]. One of the reasons for this rapid

• benign photocatalysts is of high importance, and organic dyes represent a powerful platform for pursuing this goal. The ability of organic dyes to absorb light and promote transformations is known since the early stage of photochemistry, and they represent attractive alternatives to the established

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

• -catalyzed cross-coupling reactions [9]. Recently, milder cross-coupling methods using more abundant and affordable metals such as nickel, in combination with photochemistry or electrochemistry, significantly improved accessibility to N-arylated complex amines [10][11][12]. Results and Discussion As we

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

• the last decade, photochemistry has re-emerged as a powerful tool for the scientific community. Although photochemical processes have been discovered over almost two centuries [1], only recently the scientific commuity has improved reactor technologies for the application of these processes on a large

• continuous-flow photochemistry a sustainable alternative approach being applied already by the chemical and pharmaceutical industries. Porphyrinoid is the term given for a class of organic compounds containing four pyrrole rings connected by four methylene bridges, and include porphyrin, chlorin

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

• maxima close to the absorption maximum of each catalyst. Keywords: catalyst concentration; channel height; flow chemistry; photooxidation; Introduction The renaissance of photochemistry that occurred over the last decade has been described as “old light through new windows”, and much of this work

• 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

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

• Maria A. Theodoropoulou Nikolaos F. Nikitas Christoforos G. Kokotos Laboratory of Organic Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Athens 15784, Greece 10.3762/bjoc.16.76 Abstract Photochemistry, the use of light to promote organic transformations, has

• presented. Keywords: aldehyde; green chemistry; photochemistry; photoinitiation; sustainable chemistry; Introduction Photochemistry, and especially photoredox catalysis have altered the way that modern researchers treat radical species [1][2][3][4]. In most cases, a metal-based photocatalyst is employed

• , benzaldehyde (8) has also been studied for the ability to carry out HAT processes. In 1975, Obi and co-worker studied the photochemistry of excited benzaldehyde (9) with the use of electron paramagnetic resonance (EPR) [20]. They detected that the generated radicals from this process were the α-hydroxybenzyl

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

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

• differ. It facilitates their use with modern light sources such LEDs and lasers with emission in the NIR between 800–1100 nm. A purposeful use requires a more detailed understanding of the photochemistry occurring in such compounds. Photophysics and photochemistry General aspects Figure 1 depicts

• photochemistry and photophysics of NIR absorbers from the simplest point of view. Excitation based on one-photon excitation (OP) results in population of higher vibrational levels of the first excited singlet state (S1), which fast relax by vibrational relaxation into the lowest vibrational level of the S1. The

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• radicals are also produced from 2-(1-naphthylmethyl)imidazoline [35], whereas acylaminyl radicals [R(COR)N∙] are formed from the photocleavage of the N–O bond of N,O-diacyl-N-phenylhydroxylamines, along with a carbonyloxyl radical [38]. The photochemistry of O-carbamoyl oximes (or oxime carbamates) is well

• factor of 1.43 [11]. Theoretical calculations Calculations for the photodegradation of carbamates The structures, properties and the basic photochemistry of compounds 11 and 12 was studied using the density functional theory (DFT) method [86][87][88][89] and the functional B3PW91 along with the 6-31 G(d

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

• . While many classes of photoswitches are known [1][2], few of these are easily adaptable to controlling targets, such as proteins [3], while simultaneously exhibiting robust photochemistry in the red or near-infrared (NIR) regions of the spectrum [4][5][6][7]. Azonium ions – protonated forms of

Chemical tuning of photoswitchable azobenzenes: a photopharmacological case study using nicotinic transmission

• Lorenzo Sansalone,
• Jun Zhao,
• Matthew T. Richers and
• Graham C. R. Ellis-Davies

Beilstein J. Org. Chem. 2019, 15, 2812–2821, doi:10.3762/bjoc.15.274

• utilized further in collaboration with Lester [4][5][6], but the power of AB photochemistry for biochemistry and cell physiology was then largely forgotten until 2000, when it was revived by Woolley and co-workers in a seminal paper [7]. Since that time, AB photochromes have been exploited by many research

• a monofluoro-AB (1FAB) [18]. Spectra in HEPES, pH 7.4 at rt. Photochemistry of 4FABTA (2), and thermodynamic stability in physiological buffer. a) Trans–cis photochemical reaction of 2. b) Absorption spectra of all trans-2 (black), cis-2 PSS (from 532 nm laser), and trans-2 PSS (from 405 nm laser

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

• efficiency of these green-emitting “nanolamps”. The agreement of the collected data with the previous published results validates this approach. Keywords: actinometry; diarylethene; lanthanide; photochemistry; upconverting nanoparticle; Introduction The photophysical property of converting low-energy light

• ) imposed by the combination of medium composition (organic compound absorbing mostly in the UV–vis range) and the Beer–Lambert law. Moreover, the NIR excitation wavelengths used are much less damaging when biological applications are in sight [7]. “NIR photochemistry”, based on the upconversion phenomenon

• sources. Since the recent renewal of photochemistry caused by the use of LEDs and microfluidic devices, actinometry has become a convenient tool to parameterize the performances of photoreactors [23][24][25]. Actinometer choice is guided by the operating conditions and by the spectral overlap between the

A toolbox of molecular photoswitches to modulate the CXCR3 chemokine receptor with light

• Xavier Gómez-Santacana,
• Sabrina M. de Munnik,
• Tamara A. M. Mocking,
• Niels J. Hauwert,
• Shanliang Sun,
• Prashanna Vijayachandran,
• Iwan J. P. de Esch,
• Henry F. Vischer,
• Maikel Wijtmans and
• Rob Leurs

Beilstein J. Org. Chem. 2019, 15, 2509–2523, doi:10.3762/bjoc.15.244

• of medicinal chemistry and photochemistry. Classical medicinal chemistry approaches make use of small-molecule ligands binding a target protein, thereby modifying its activity. Photopharmacological approaches use light-sensitive photochromic ligands that provide an advantageous and more precise

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

• photochemistry of two closely related and more reducible quinazolinespirohexadienones (QSHDs), wherein the naphthalene of the PSHD is replaced with a quinoline. In the present work, we report our investigation of the electrochemistry of these asymmetric QSHDs. In addition to the short wavelength and photochromic