DABCO-promoted photocatalytic C–H functionalization of aldehydes

• Bruno Maia da Silva Santos,
• Mariana dos Santos Dupim,
• Cauê Paula de Souza,
• Thiago Messias Cardozo and
• Fernanda Gadini Finelli

Beilstein J. Org. Chem. 2021, 17, 2959–2967, doi:10.3762/bjoc.17.205

• criterias, expanding the range of catalyst choices. This, in turn, can lead to exciting alternatives in terms of functionalizations, selectivities, and can help to illuminate some of the hazy mechanistic aspects of HAT catalysis with bicyclic amines. Redox potentials of representative nitrogenated HAT

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• thermal conditions or through the Fe redox cycle, can abstract the aldehydic hydrogen to form the acyl radical 71. Subsequent radical addition to the alkene 68 to form 72 followed by cyclization with the nitrile affords the iminyl radical 73 which can abstract a hydrogen atom to form the more stable imine

• variety of electron-donating and electron-withdrawing groups, though bulky silanes 92 afforded the products in reduced yield. The reaction proceeds through the formation of a silicon-centered radical generated via a Fe redox cycle (vide supra). Sequential attack on the alkenyl π-system followed by radical

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• poor chemoselectivity [40]. However, the realization of this redox-neutral aryl–aryl cross-coupling is a formidable challenge. Therefore, the discovery of efficient catalysts and ligands to achieve high stereoselectivity is a fundamental issue in catalytic asymmetric synthesis [14]. In this section, we

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

• ; however, they suffer from relatively poor photostability [14][15][16]. Transition-metal-photoredox catalysts, such as ruthenium and iridium polypyridyl complexes, exhibit high redox potentials, long excited state lifetimes, and strong absorption [17][18][19][20]. However, high cost and their scarcity

• photoredox catalysis of CuI complexes with different ligands were investigated by Reiser’s group [21]. Other studies have since provided more information on the photoredox mechanisms underlying the catalysis of copper complexes [37]. In general, redox-active copper complexes include CuI and CuII complexes

• ). In 2020, Zhang’s group [77] described the photoinduced copper-catalyzed decarboxylative alkynylation of redox-active esters with terminal alkynes. N-Hydroxy-tetrachlorophthalimide (TCNHPI, 36) derived from carboxylic acids was identified as the ideal radical precursor. Under irradiation, the CuI

Synthesis and investigation on optical and electrochemical properties of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridines

• Najeh Tka,
• Mohamed Adnene Hadj Ayed,
• Mourad Ben Braiek,
• Mahjoub Jabli and
• Peter Langer

Beilstein J. Org. Chem. 2021, 17, 2450–2461, doi:10.3762/bjoc.17.162

• reference electrode was calibrated using the ferrocene/ferrocenium (Fc/Fc+) redox system [67], the HOMO and LUMO energies were calculated by using the following equations: Here, VFOC is the potential value of Fc/Fc+ under the same experimental conditions (0.52 V) and 4.8 eV is the HOMO energy value of Fc

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

• developments, which enables a diverse range of previously inaccessible organic transformations in milder reaction conditions [31][32][33][34][35][36][37][38][39][40]. Here, by absorbing visible light, a photocatalyst can function as a single-electron redox mediator through an oxidative or reductive quenching

• cycle (Figure 1), thereby facilitating redox-neutral transformations in the absence of stoichiometric oxidants/reductants. Given the tendency of nickel to mediate the reactions via Ni(0), Ni(I), Ni(II), and Ni(III) intermediates by both giving and accepting a single electron from a photocatalyst or

• . Arylation of α-amino C(sp3)‒H bonds by in situ generated aryl tosylates from phenols. Formylation of aryl chlorides through redox-neutral 2-functionalization of 1,3-dioxolane (13). Photochemical C(sp3)–H arylation via a dual polyoxometalate HAT and nickel catalytic manifold. Photochemical nickel-catalyzed α

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• involving organochromium species generated from alkyl halides [115][116]. Whereas its toxicity has hindered the use of Cr(VI) in organic synthesis, the less toxic Cr(III) and Cr(II) salts have been exploited as plausible catalysts in organic synthesis [117][118]. A good example is a redox-neutral reaction

• manganese is 3d54s2 with a high redox potential due to the high number of available oxidation states (−3 to +7), allowing the formation of compounds with a coordination number of up to 7 [127]. These properties associated with a low toxicity and low cost make manganese a metal with great potential in

• , operating under mild conditions without the need of directing groups, using traceless electrons as sole redox reagents, presenting high scope and chemoselectivity. The robustness of the reaction was proved by the late-stage modification of pharmaceutically relevant compounds by promoting the azidation of a

Natural products in the predatory defence of the filamentous fungal pathogen Aspergillus fumigatus

• Jana M. Boysen,
• Nauman Saeed and
• Falk Hillmann

Beilstein J. Org. Chem. 2021, 17, 1814–1827, doi:10.3762/bjoc.17.124

• the GT concentration at sub-lethal levels via redox cycling and S-methylation of active disulfides in GT, respectively [117][118]. Furthermore, in terms of exogenous factors, not only GT itself but several other biotic and abiotic factors, including neutrophilic granulocytes, media composition, pH

• , temperature and aeration, are known to regulate gliotoxin biosynthesis [115][119][120]. The biological activity of ETP’s like gliotoxin is mediated by the active disulfide bridge that targets vulnerable thiols or catalyses oxidative burst formation via redox cycling [78]. In previous studies, these cytotoxic

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

Recent advances in the application of isoindigo derivatives in materials chemistry

• Andrei V. Bogdanov and
• Vladimir F. Mironov

Beilstein J. Org. Chem. 2021, 17, 1533–1564, doi:10.3762/bjoc.17.111

• trinitrotoluene) in solution was demonstrated (Scheme 30) [110][111]. Miscellaneous applications Taking into account the high thermal, atmospheric, mechanical, and redox stability of isoindigo polymers, various scientific groups focused their studies on the development of new directions for the practical

• , such as staining efficiency (362 cm2⋅C−1 at 1050 nm), fast switching time (0.5 s), high optical contrast (59% at 1500 nm), and redox stability (<8% after 4000 cycles). Poly(isoindigothiophene) 65 containing sulfonate groups in the side chain was used as an anionic photoactive polyelectrolyte in a

• , the first work on combining polyaromatic acceptor and heterocyclic donor fragments in one macromolecule on the isoindigo platform showed the possibility of designing one-component nonfullerene solar cells. The high stability of polymeric isoindigo in air, at elevated temperature, under redox

Icilio Guareschi and his amazing “1897 reaction”

• Gian Cesare Tron,
• Alberto Minassi,
• Giovanni Sorba,
• Mara Fausone and
• Giovanni Appendino

Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93

• ”, formally an internal redox reaction where the heterocyclic system is oxidatively aromatized and one of the substituents at C-4 reductively lost as a hydrocarbon. The reaction involves the treatment of a ketone with a solution of ethylcyanoacetate in ethanolic ammonia [7]. A precipitate of the ammonium salt

• terms of overall redox transformation, the reaction formally “hydrolyses” a ketone into a hydrocarbon and a carboxylic acid, and the mechanism remained a black box for over a century, being eventually clarified only in 2007 by a team of British and Russian chemists [8]. One important starting

Photoinduced post-modification of graphitic carbon nitride-embedded hydrogels: synthesis of 'hydrophobic hydrogels' and pore substructuring

• Cansu Esen and
• Baris Kumru

Beilstein J. Org. Chem. 2021, 17, 1323–1334, doi:10.3762/bjoc.17.92

• novelty. Here, a metal-free semiconductor graphitic carbon nitride (g-CN)-embedded hydrogel as an initial network was synthesized via redox-couple initiation under dark conditions. Post-photomodification of so-formed hydrogel, thanks to the photoactivity of the embedded g-CN nanosheets, was exemplified in

• yellow powder was ultrasonicated in water to obtain a g-CN aqueous colloidal dispersion. The freshly prepared CM/water colloidal dispersion was mixed with water-soluble monomer (N,N-dimethylacrylamide, DMA) and crosslinker (N,N’-methylenebisacrylamide, MBA) followed by the addition of the redox couple

• , ascorbic acid/hydrogen peroxide, respectively. The mixture was immediately placed in a Petri dish to complete the gelation via free radical polymerization under dark conditions. After 3 hours, the resulting hydrogel was purified with water to remove the unreacted species (monomers and redox mediators

Synthesis of 10-O-aryl-substituted berberine derivatives by Chan–Evans–Lam coupling and investigation of their DNA-binding properties

• Peter Jonas Wickhorst,
• Mathilda Blachnik,
• Denisa Lagumdzija and
• Heiko Ihmels

Beilstein J. Org. Chem. 2021, 17, 991–1000, doi:10.3762/bjoc.17.81

• berberrubine (1b), which has been shown to give no products in an Ullmann reaction [31]. Furthermore, the sensitivity of the isoquinolinium unit towards alkaline conditions and redox-active transition metal ions, especially under aerobic conditions, may also cause the low yields [35][36][37]. Unfortunately

Beyond ribose and phosphate: Selected nucleic acid modifications for structure–function investigations and therapeutic applications

• Christopher Liczner,
• Kieran Duke,
• Gabrielle Juneau,
• Martin Egli and
• Christopher J. Wilds

Beilstein J. Org. Chem. 2021, 17, 908–931, doi:10.3762/bjoc.17.76

• and a nuclease resistance that are highly reversible in response to redox changes of the selenium atom [158]. Recent work has also looked at this modification in LNA nucleosides bearing an adenine base [159], but this nucleoside was found to be highly sensitive to heat, making its incorporation into

A chromatography-free and aqueous waste-free process for thioamide preparation with Lawesson’s reagent

• Ke Wu,
• Yichen Ling,
• An Ding,
• Liqun Jin,
• Nan Sun,
• Baoxiang Hu,
• Zhenlu Shen and
• Xinquan Hu

Beilstein J. Org. Chem. 2021, 17, 805–812, doi:10.3762/bjoc.17.69

• incomparable chelating ability towards selected transition metals, and the corresponding complexes were applied in various areas such as chemical-sensor materials, tunable redox-potential complexes, polymer hybrid luminescence materials, building blocks for multinuclear complexes, and as catalysts for cross

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

• 60 and Umemoto reagent 20 as substrates as well as N-methylmorpholine (NMM) as organic base additive at room temperature (Scheme 21). The highly functionalized indole, pyrrole, benzofuran, and electron-rich benzene containing CF3 can be given in good yield. Given the redox potential of NMM and

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• supported metal species (Ru, Ir), due to the ability to activate molecular hydrogen, functioning as redox centres. The mechanisms of the metal-catalysed solvolytic reactions of plastics are all very similar and typical of conventional organic processes: a metal ion acts as Lewis acid centre for the

Amino- and polyaminophthalazin-1(2H)-ones: synthesis, coordination properties, and biological activity

• Zbigniew Malinowski,
• Emilia Fornal,
• Agata Sumara,
• Renata Kontek,
• Karol Bukowski,
• Beata Pasternak,
• Dariusz Sroczyński,
• Joachim Kusz,
• Magdalena Małecka and
• Monika Nowak

Beilstein J. Org. Chem. 2021, 17, 558–568, doi:10.3762/bjoc.17.50

• platinum disc electrode suggested that the [(L3)Cu(II)Cl2]/[(L3)Cu(I)Cl2] redox couple was formed. For more details, see Supporting Information File 2. Bioactivity Cytotoxicity analysis – MTT assay We used the MTT assay to evaluate compounds 5c, 5d, 5f, 5g, 6b, and 6d for their potential activity on

¹⁹F NMR as a tool in chemical biology

• Diana Gimenez,
• Aoife Phelan,
• Cormac D. Murphy and
• Steven L. Cobb

Beilstein J. Org. Chem. 2021, 17, 293–318, doi:10.3762/bjoc.17.28

• species [1]. This reflects its low bioavailability, as it is typically found in insoluble minerals, and its physicochemical properties, in particular its high redox potential and the poor reactivity of the fluoride ion in aqueous solution. Despite its near-absence in biology, it is a particularly

Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands

• Sergey V. Norkov,
• Anton V. Cherkasov,
• Andrey S. Shavyrin,
• Maxim V. Arsenyev,
• Viacheslav A. Kuropatov and
• Vladimir K. Cherkasov

Beilstein J. Org. Chem. 2021, 17, 273–282, doi:10.3762/bjoc.17.26

• State University, 23 Gagarin Ave, 603950, Nizhny Novgorod, Russia 10.3762/bjoc.17.26 Abstract The fused 1,3-dithiole spacer seems to be very suitable for the functionalization of sterically hindered o-quinones with additional groups capable of coordination of metal ions and/or possessing a redox

• ligand; 1,3-dithiole; ditopic ligand; o-quinone; thiete; Introduction There are a number of methods which may be used for the synthesis of new o-quinones in order to vary their redox properties and coordination abilities. The key features of o-quinones are redox activity as well as chelating

• coordination ability. The redox state of o-quinone (semiquinone or catechol) could be changed both as free species or when it is coordinated to a metal ion as a ligand. Thus, the redox isomerism phenomenon was reported for o-quinone complexes with both transition and non-transition metals [1][2][3]. The

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• macrocycle has inherent chromophores that can function as photosensitizers, the efficiency of the energy transfer will be higher and the systems will be simplified. 3) Other kinds of macrocycle-based catalysis need to be explored, such as esterification, polymerization, redox reaction, etc. 4) Hyperbranched

Synthesis of tetrafluorinated piperidines from nitrones via a visible-light-promoted annelation reaction

• Vyacheslav I. Supranovich,
• Igor A. Dmitriev and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2020, 16, 3104–3108, doi:10.3762/bjoc.16.260

• from nitrones and a fluorinated building block is described. The annelation is based on a sequence of visible-light-promoted redox processes and a substitution reaction, and involves the cleavage of the N–O bond. The construction of tetrafluorinated piperidines from nitrones. The scope of the

Controlled decomposition of SF₆ by electrochemical reduction

• Sébastien Bouvet,
• Bruce Pégot,
• Stéphane Sengmany,
• Erwan Le Gall,
• Eric Léonel,
• Anne-Marie Goncalves and
• Emmanuel Magnier

Beilstein J. Org. Chem. 2020, 16, 2948–2953, doi:10.3762/bjoc.16.244

• +/Fc. The exact number of electrons for the full consumption of sulfur hexafluoride was determined and this gas further quantitatively transformed into environmentally benign fluoride anion and sulfur by electrochemical reduction. Keywords: electroreduction; fluoride anion; redox potential; sulfur

• , in accordance with the following relation [26]: To the half limiting current (id/2) can be associated the half wave potential noted E1/2. For reversible electrons exchanged at the interface electrode/electrolyte, the half wave potential can be assimilated to the reversible formal potential redox

• on SF6 concentration. From the voltamogram, the half wave potential of SF6 reduction is deduced and corresponds to −2.17 V vs Fc+/Fc (Figure 1). To the best of our knowledge, this was the first determination of the redox potential of sulfur hexafluoride. Pleasingly, this value was compatible with the

Ultrasound-assisted Strecker synthesis of novel 2-(hetero)aryl-2-(arylamino)acetonitrile derivatives

• Emese Gal,
• Luiza Gaina,
• Hermina Petkes,
• Alexandra Pop,
• Castelia Cristea,
• Gabriel Barta,
• Dan Cristian Vodnar and
• Luminiţa Silaghi-Dumitrescu

Beilstein J. Org. Chem. 2020, 16, 2929–2936, doi:10.3762/bjoc.16.242

• frequencies between 20 and 100 kHz were reported in the literature as optimal to enhance the nucleation and fragmentation rates, but the exact optimal frequency is probably reactor and system specific [8]. The exciting properties of the heterocyclic phenothiazine core displaying tunable chemical, redox

• ferrocene unit displays a remarkably reversible one-electron oxidation behavior offering interesting fields of applications for its derivatives as redox mediators in sensor applications [10]. Medicinal applications of ferrocene derivatives grafted on different pharmacophoric units greatly benefit from the

Synthesis and characterization of S,N-heterotetracenes

• Astrid Vogt,
• Florian Henne,
• Christoph Wetzel,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2020, 16, 2636–2644, doi:10.3762/bjoc.16.214

• precursors and amines [11][12], the series of S,N-heteroacenes has been systematically extended from pentamer SN5 [13][14] up to a stable and still soluble S,N-heterotridecacene SN13 [7][15][16][17]. Correlation of, e.g., absorption or redox potentials vs conjugated chain length led to interesting structure

• are shifted down-field (Hα 7.67, Hß 7.49 ppm) compared to SN4 13. MALDI–HRMS of all synthesized S,N-heteroacenes showed only a single peak for the molecular ions accounting for their purity. Optical and redox properties of S,N-heteroacenes 9, 13, 19, 22, and 33 in comparison to tetrathienoacene (TTA

• planar and conformationally restricted systems [48]. In order to get information about the redox properties and energetics of the frontier orbitals, the S,N-heteroacenes were studied by cyclic voltammetry and all potentials were referenced against the ferrocene/ferricenium couple (Table 1). In the series