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

• , wide electrochemical redox potentials, and photostability. However, these photocatalysts present serious drawbacks, such as toxicity, limited availability, and the overall cost of rare transition metal elements. This reduces their long-term viability, especially at an industrial scale. Heterogeneous

• , preventing recombination and expanding the redox potentials of the fused material [7]. The history and recent developments of these materials was reviewed by Anusuyadevi, Marre, Yu, and co-workers [7][196]. As briefly mentioned in Section 1.3, upconversion photocatalysis is a developing field of research

4-Hydroxy-3-methyl-2(1H)-quinolone, originally discovered from a Brassicaceae plant, produced by a soil bacterium of the genus Burkholderia sp.: determination of a preferred tautomer and antioxidant activity

• Dandan Li,
• Naoya Oku,
• Yukiko Shinozaki,
• Yoichi Kurokawa and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2020, 16, 1489–1494, doi:10.3762/bjoc.16.124

• immunity [33], among which redox enzymes and antioxidants are the direct countermeasures to neutralize the toxicity of ROS [34]. Limited examples of antioxidants include catecholamine melanin from a fungus Cryptococcus neoformans [35], 1,8-dihydroxynaphthalene melanin from fungi Wangiella dermatitidis and

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

• developed rapidly during the last years, and we believe that this review is essential for the demonstration of a new face of the chemistry of this class of N-oxyl radicals. There are reports on the iminoxyl radical involvement in redox processes occurring in living organisms, for example, in microsomal

Activated carbon as catalyst support: precursors, preparation, modification and characterization

• Melanie Iwanow,
• Tobias Gärtner,
• Volker Sieber and
• Burkhard König

Beilstein J. Org. Chem. 2020, 16, 1188–1202, doi:10.3762/bjoc.16.104

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

• electronically excited species. These reactive intermediates are then used to forge new chemical bonds or to induce structural modifications within the organic substrates. The versatility of these metal complexes is due to their wide operational redox windows, which allows them to interact via their excited

• transition metal-based photocatalysts [14][15][16][17][18]. In addition to their ready availability and low cost, these molecules are often biocompatible, and they can be easily functionalized in order to modulate their spectroscopical and redox features. In the last years, several classes of organic dyes

• each of these steps, the role of A or D is assumed by a redox-active agent, either the substrate, a sacrificial electron donor/acceptor, or a reactive intermediate. This approach, usually named photoredox catalysis, has known a remarkable growth in the last decade and has given access to both neutral

Synthesis and properties of quinazoline-based versatile exciplex-forming compounds

• Rasa Keruckiene,
• Simona Vekteryte,
• Ervinas Urbonas,
• Matas Guzauskas,
• Eigirdas Skuodis,
• Dmytro Volyniuk and
• Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 1142–1153, doi:10.3762/bjoc.16.101

• . The potentials were calibrated against the standard ferrocene/ferrocenium (Fc/Fc+) redox system [24]. The ground-state geometries were optimized by using the B3LYP (Becke three parameters hybrid functional with Lee–Yang–Perdew correlation) [25] functional at the 6-31G (d, p) level of theory in vacuum

Synthesis of novel multifunctional carbazole-based molecules and their thermal, electrochemical and optical properties

• Nuray Altinolcek,
• Ahmet Battal,
• Mustafa Tavasli,
• William J. Peveler,
• Holly A. Yu and
• Peter J. Skabara

Beilstein J. Org. Chem. 2020, 16, 1066–1074, doi:10.3762/bjoc.16.93

• of compounds 7a and 7b are depicted in Figure 1. Thermal properties of compounds 7a and 7b are also summarised in Table 1. Electrochemical properties The redox behaviour of compounds 7a and 7b was investigated by cyclic voltammetry in dichloromethane solution under argon atmosphere using

• tetrabutylammonium hexafluorophosphate as the electrolyte (Figure 2). A platinum disk was used as a working electrode, silver wire as the reference electrode and platinum wire as the counter electrode. The ferrocene-ferrocenium redox couple was used as an internal reference. At positive potentials, compounds 7a and

Synthesis and properties of tetrathiafulvalenes bearing 6-aryl-1,4-dithiafulvenes

• Aya Yoshimura,
• Hitoshi Kimura,
• Kohei Kagawa,
• Mayuka Yoshioka,
• Toshiki Itou,
• Dhananjayan Vasu,
• Takashi Shirahata,
• Hideki Yorimitsu and
• Yohji Misaki

Beilstein J. Org. Chem. 2020, 16, 974–981, doi:10.3762/bjoc.16.86

• Abstract Novel multistage redox tetrathiafulvalenes (TTFs) bearing 6-aryl-1,4-dithiafulvene moieties were synthesized by palladium-catalyzed direct C–H arylation. In the presence of a catalytic amount of Pd(OAc)2, P(t-Bu3)·HBF4, and an excess of Cs2CO3, the C–H arylation of TTF with several aryl bromides

• of 1,3-dithiole rings to aromatic rings appears very appealing since these allow to produce novel multistage redox systems. However, such molecules could formerly not be synthesized by conventional approaches. In 2011, a breakthrough synthesis of arylated TTF derivatives by a palladium-catalyzed

• direct C–H arylation was reported, and the structural and electrochemical properties of the products were clarified [30]. This motivated us to synthesize novel multistage redox-TTFs bearing 1,3-dithiole rings on aromatic rings, 1–3 (Figure 1). In addition, we focused on cross-conjugated systems with 1,3

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

• , planarity and special electronic characteristics to these compounds. As it is well-known, tetrapyrrolic compounds are considered to be the “pigments of life” since they play a key role in essential biological processes, such as photosynthesis (chlorophylls and bacteriochlorophylls), redox reactions for

Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties

• Liliia Moshniaha,
• Marika Żyła-Karwowska,
• Joanna Cybińska,
• Piotr J. Chmielewski,
• Ludovic Favereau and
• Marcin Stępień

Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81

• , and cNMI3H (Table 2 and Table 3, Supporting Information File 1, Tables S2–S4). The redox properties of the new bipyrrole boomerangs were investigated by means of cyclic (CV) and differential pulse (DPV) voltammetry (Supporting Information File 1, Figures S11–S16). All systems showed at least two

Copper catalysis with redox-active ligands

• Agnideep Das,
• Yufeng Ren,
• Cheriehan Hessin and
• Marine Desage-El Murr

Beilstein J. Org. Chem. 2020, 16, 858–870, doi:10.3762/bjoc.16.77

• exploring the possibility of a complementing metal-centered reactivity with electronic participation by the coordination sphere. To achieve this electronic flexibility, redox-active ligands can be used to engage in a fruitful “electronic dialogue” with the metal center, and provide additional venues for

• electron transfer. This review aims to present the latest results in the area of copper-based cooperative catalysis with redox-active ligands. Keywords: bioinspired catalysis; biomimetic copper complexes; cooperative catalysis; redox-active ligands; redox catalysis; Introduction Interaction of earth

• [2][3]. Inspired by the broad chemical repertoire of radical-ligand containing metalloenzymes, chemists have developed redox-active ligands as surrogates for the biologically occurring redox cofactors and this has translated into active developments in homogeneous catalysis [4]. The unique electronic

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

• aliphatic acids and the coupling of the residual chain with various electrophiles. Metal-based catalysts are common in reactions that require a high redox potential for a single electron transfer (SET) procedure to take place. On the other hand, even if organocatalysts have lower redox potentials, they are

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• (III)–P(V) redox cycle, such as in catalytic Wittig-, aza-Wittig-, Staudinger-, Appel- and other reactions [16][17][18][19][20][21]. The ring strain of the four- and five-membered derivatives makes them highly susceptible to deoxygenation, thus they are ideal organocatalysts in P(III)–P(V) redox

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• explored on redox-active alkyl esters derived from N-hydroxyphthalimide (NHPI, 37), in which case the reactions proceeded through a similar radical pathway due to, in part, the alkyl radical surrogate nature of the NHPI esters. The radical generated via decarboxylation of these esters is easily trapped by

Rhodium-catalyzed reductive carbonylation of aryl iodides to arylaldehydes with syngas

• Zhenghui Liu,
• Peng Wang,
• Zhenzhong Yan,
• Suqing Chen,
• Dongkun Yu,
• Xinhui Zhao and
• Tiancheng Mu

Beilstein J. Org. Chem. 2020, 16, 645–656, doi:10.3762/bjoc.16.61

• concentrations of PPh3 both led to decreased yields (Table 4). This indicated that in the active catalytic species the molar ratio of [Rh]:PPh3 was exactly 1:3 (not 1:4 because of the consumption of 1 equiv PPh3 during the redox process), which might be Rh(PPh3)3Cl. The mentioned redox reaction can be explained

• reacted via a redox reaction to form Rh(PPh3)3Cl, which is the active catalytic species able to activate C–I bonds in the aryl iodides for the insertion of CO in the next step. The base Et3N neutralized the proton in the intermediate rhodium hydroiodide (D) complex and regenerated the active Rh species

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

• ) provided a drastic change of paradigm to the community. Indeed, photocatalysis allows carrying out photochemical reactions in the visible region (redox transformation and energy transfer process). This tremendous progress provided a huge gain of selectivity in photochemical transformations. Indeed, as most

• be developed. Among them, the use of first-row transition metals [8][9], particularly copper, is an interesting approach [10][11][12][13]. The high abundance, low price, low toxicity, and intrinsic properties (redox potential, four oxidation states, etc.) of copper are excellent and promising

• suggested a possible mechanism based on the measured and reported redox potential (Scheme 1). Upon irradiation at 530 nm using green light, the Cu(I) catalyst transitions to an excited state. Then, the excited copper complex transfers an electron to the alkyl halide, which can generate an alkyl radical that

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

• electron transfer (ΔGet) and the reorganization energy λ depict additional parameters affecting ket. Knowledge about redox potentials and excitation energy provides information about ΔGet needed for Equation 8 [72]. The dielectric constant ε and refractive index n of the surrounding matrix contribute to

• electrochemically mediated ATRP (eATRP) [122][123][124][125][126][127][128]. In this content, various reducing agents, and electrochemical redox processes, and copper comprising nanoparticles have been accomplished to conduct ATRP by generating the required Cu(I) by the reduction of Cu(II) complexes. A well written

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• , resulting in reactivity different from common two-electron pathways. Photoredox catalysis reactivity is very different from traditional redox reactions, and the same reactivity cannot be achieved by stoichiometric addition of both a reductant and an oxidant to a reaction mixture (as that would lead to a

• rapid redox reaction between the oxidant and the reducing agent instead of converting the substrate). Excitation of the photocatalyst, on the other hand, allows continuous formation of low concentrations of both oxidized and reduced radical forms of the substrate(s), and the excited catalysts (and/or

• their oxidized/reduced forms) can perform both opposed redox events before returning to their original oxidation state for re-excitation. If no substrate is encountered during the lifetime of the excited state the ground state is typically regenerated. Such photogenerated radical intermediates can be

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• ]. In photoredox catalysis, visible light gets absorbed by the photocatalyst (PC), which transitions into a photoexcited state (*PC) that can undergo either energy transfer or redox pathways. As can be seen in Figure 4, the redox pathway consists of reductive and oxidative quenching pathways

• metal catalysis, which include: (i) excellent regioselectivity of the targeted C–H bond formations thanks to favorable dissociation enthalpies and electronic properties as compared to other concurrent C–H bonds; (ii) avoidance of an extra oxidant because the reaction proceeds with overall redox

• neutrality; (iii) the use of household bulbs or LEDs as light sources under operationally simple reaction conditions; (iv) the high redox potential of photocatalysts that can manipulate the oxidation states of transition metal catalysts [54][55]. They have also found applications in novel solar cell

Synthesis and optoelectronic properties of benzoquinone-based donor–acceptor compounds

• Daniel R. Sutherland,
• Nidhi Sharma,
• Georgina M. Rosair,
• Ifor D. W. Samuel,
• Ai-Lan Lee and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2019, 15, 2914–2921, doi:10.3762/bjoc.15.285

• chemistry; physical organic chemistry; spectroscopy; thermally activated delayed fluorescence; Introduction Substituted benzoquinones and derivatives [1] have generated great interest, in particular due to their redox-active nature and their importance in biological mechanisms [2]. Compounds bearing

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• mostly chemically indistinguishable, while many P450s are known to selectively act on specific carbon atom(s). A continuous electron input is required to keep CYPs functional [83]. In general, soluble bacterial CYPs utilize class I redox systems, where the electron from NAD(P)H is delivered to CYPs

• through a ferredoxin reductase (FdR) and ferredoxin (FdX) [85]. Most bacteria have more than one FdR and FdX pair encoded in the genome [86]. It remains challenging to determine a priori which combination can reconstitute an active CYP, especially as the proximity of CYPs to these redox enzymes in the

• ent-kaurenoic acid (27 and 28, respectively, Figure 7b) [41]. Characterization of CYPs is typically achieved by in vitro or in vivo studies. E. coli is the most popular host for obtaining proteins for in vitro studies, and proper selection of a redox system is usually the obstacle to reconstitute CYP

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• between an electrode and an organic substrate, resulting in desired redox transformation of the substrate via the intermediacy of a highly reactive electrogenerated reagent (radical, ion or ionic radical), is generally termed ‘organic electrochemical reactions’. Amidst tremendous effort by synthetic

• potential greener and sustainable alternative to traditional redox protocols [1][2][3][4]. Starting from its inception in 1800, EOC has undergone a series of advances with respect to the design of electrochemical cells; the nature of the electrode materials; the applied current or potential; the available

• redox mediators, electroauxiliaries, supporting electrolyte, types of catalysts; and many other controlling factors [5][6][7]. The complex history of organic electrosynthesis has been revisited in detail in a number of articles [8][9][10][11][12]. The two sequential reviews from Baran’s group and

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• to maximal apparent Stokes shifts of ca. 190–270 nm. As demonstrated previously for other borylated arylisoquinoline dyes [37][38], the emission energy of the LW band is tightly linked with the redox potential of the aryl residue. Having in mind that the borylated naphthyl is present in all four dyes

Formation of alkyne-bridged ferrocenophanes using ring-closing alkyne metathesis on 1,1’-diacetylenic ferrocenes

• Celine Bittner,
• Dirk Bockfeld and
• Matthias Tamm

Beilstein J. Org. Chem. 2019, 15, 2534–2543, doi:10.3762/bjoc.15.246

• . Furthermore, the ability of the new [10]ferrocenophane 2a to bind transition metal cations is outlined, and the redox properties of the new ferrocenophanes are studied by cyclovoltammetry. Results and Discussion The substrates 1a and 1b for the RCAM toward the desired ferrocenophanes 2a and 2b were

• barrier for the chemical oxidation, the cyclovoltammogram of 2a was recorded in DCM (Figure 7). The quasi-reversible redox process assigned to the Fe(II)/Fe(III) couple occurs at a potential of E1/2 = 0.474 V relative to FcH/FcH +. The electron-withdrawing features of the acetylenic diester bridge result

• in the higher potential compared to the standard system FcH/FcH + showing that the ferrocenophane 2a is harder to oxidize than pure ferrocene. As expected, no further oxidation or reduction step could be detected. The redox potential of 0.474 V established for 2a in DCM falls in the range of formal

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

• . Indeed, different redox peaks were observed in the same general LW region for the CV of photolyzed versus electrogenerated LW forms of 3a, consistent with the electrogenerated formation of 5a compared against the known formation of 4a via photolysis. The voltammograms of 3a (Figure 4) did however differ

• ) direction over an 800 mV window roughly centered on the reduction of Fc/Fc+ redox couple at a scan rate of 0.1–0.5 V/s, 10−4 A sensitivity, and 1 mV sample interval. Internal resistance (iR) compensation was manually set to 95–99.5% of the measured resistance so that the peak separation for the reversible

• interval over an appropriate range of potentials and current sensitivity to observe the redox couples of either SW and LW or just LW isomers as desired, without reaching the solvent breakdown limit. Reduction potentials were taken as the half-peak potential of irreversible peaks or the midpoint of