Radical chemistry in polymer science: an overview and recent advances

• Zixiao Wang,
• Feichen Cui,
• Yang Sui and
• Jiajun Yan

Beilstein J. Org. Chem. 2023, 19, 1580–1603, doi:10.3762/bjoc.19.116

• based on the radical polymerization of catechol derivatives. Catechols are known as easily oxidizable compounds and are prone to undergo oxidation by losing one or two electrons [3]. This way, either semiquinone radicals or o-quinones are formed by single or double-electron oxidation, respectively [4

• –substrate interface. The mfp's contain up to 27 mol % of DOPA (ʟ-3,4-dihydroxyphenylalanine), which plays a crucial role on mussel adhesion [11]. Although the crucial role of DOPA in mussel adhesion is not fully understood, a prevailing view suggests that DOPA can be oxidized to o-quinones at an acidic pH

• and the quinones react with unoxidized catechols to form o-semiquinone radicals afterwards [12]. The semiquinone radicals can help DOPA adhere onto organic surfaces. At a basic pH, the system is cured and mechanically stabilized through the formation of DOPA-metal coordination bonds. The cohesion of

Synthesis of 5-arylidenerhodanines in L-proline-based deep eutectic solvent

• Stéphanie Hesse

Beilstein J. Org. Chem. 2023, 19, 1537–1544, doi:10.3762/bjoc.19.110

• same protocol as described by Molnar et al. [43] where DPPH and the synthesized compounds were tested in a solution at 0.2 mM concentration in DMSO as solvent. Because phenolic compounds can be easily oxidized to quinones, it is well known that most hydroxylated compounds have antioxidant properties

Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

• solvent polarity [24][25]. Hence, it is important when considering new reagents and catalysts to only compare potentials measured in conditions as close to the photocatalytic conditions as possible. For instance, quinones have 2 one-electron reductions in aprotic media and one two-electron reduction at a

• photosynthesis. It is also noteworthy that the reduced pyridinium compounds resemble Hantzsch esters which are organic reductants commonly used in organic synthesis. Quinones and hydroquinones have also been used in RFBs. Notably, 1,4-hydroquinone and 1,4-benzoquinone were used to create membrane-less RFBs with

• decoupled water-splitting studies are re-reduced using protons from water in acidic conditions, and are used to transport hydrogen equivalents across membranes and between reactors. Some examples have been used as recyclable reductants [58]. These particular quinones have low enough oxidation potentials for

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• /peroxide, quinones, and iodine(I/III) compounds are the most developed catalyst types which are covered here. Keywords: CH-functionalization; free radicals; hypervalent iodine; N-oxyl radicals; redox-active molecules; Introduction Organocatalysis can be defined as catalysis by small organic molecules

• classified according to the catalytically active species or key intermediates: N-oxyl radicals, oxoammonium cations, amine cation radicals, thiyl radicals, quinones, dioxiranes and oxaziridines, hypervalent iodine compounds, etc. However, some examples of organocatalyzed oxidative processes, in which an

• transfer between the C-centered radical and (SPyf)2, whereas for Me-, CF3-, Ph-, and C6F5-derived thiols and disulfides HAT is more favorable than thiyl group transfer [123]. Quinone catalysis Quinones are well known as redox-active cofactors in biochemical processes and have found wide synthetic

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• , Brazil 10.3762/bjoc.18.43 Abstract Naphthoquinones are important natural or synthetic compounds belonging to the general class of quinones. Many compounds in this class have become drugs that are on the pharmaceutical market for the treatment of various diseases. A special naphthoquinone derivative is

• ; quinone; synthetic platform; vitamin K; Introduction Naphthoquinones belong to the chemical family of quinones and are widely present in synthetic and natural products (Figure 1). In nature, quinones are biosynthesized as secondary metabolites by various organisms, from simple single-celled

• microorganisms to more complex beings, such as higher plants and animals [1]. Actually, quinones play important roles in several physiological processes in these organisms, such as photosynthesis [2] and oxidative phosphorylation [3][4], as well as many other metabolic processes [5][6][7]. Quinones also received

1,2-Naphthoquinone-4-sulfonic acid salts in organic synthesis

• Ruan Carlos B. Ribeiro,
• Patricia G. Ferreira,
• Amanda de A. Borges,
• Luana da S. M. Forezi,
• Fernando de Carvalho da Silva and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 53–69, doi:10.3762/bjoc.18.5

• synthesis; Introduction The general class of quinones is very important because their compounds show biological activities against several pathogens related to important diseases and are used for the production of special materials [1][2][3][4]. These compounds are biosynthesized by oxidative processes of

• catecholamines and other compounds, but they can also be ingested as exogenous products of air and water. The most common quinones, such as benzoquinone, naphthoquinone, anthraquinone, and phenanthrenequinone, can be formed by incomplete combustion or photooxidation of their respective polycyclic aromatic

• new fragments in the general structure or modifying functional groups. In Figure 1, eight low molecular weight naphthoquinones are highlighted, which are the most commonly used in organic synthesis. Among them, quinones 1–5 are naturally occurring, are simple to prepare and are commercially available

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

• ) (Scheme 2). The electronic properties of the substituents on the 2-naphthylamine showed remarkable effects on the chemical yield but had negligible impact on the enantioselectivity [42]. The direct arylation reaction of quinones 6 and 2-naphthols 7 was described by Tan and co-workers in 2015. The

• 2019, Li and co-workers developed a synthetic strategy for the atroposelective construction of phenylindole 20 by the chiral phosphoric acid-catalyzed cross-coupling of quinones 18 and indoles 19. In this reaction, the chiral phosphoric acid (R)-CPA 6 acts as a bifunctional catalyst to activate indoles

• and quinones through a dual H-bond activation mode to form the intermediate I-3, and aromatization with central-to-axial chirality transfer occurs to afford the axially chiral phenylindoles in good yield (76–92%) with good to excellent enantioselectivity (88–96% ee, Scheme 8a). The position and

A visible-light-induced, metal-free bis-arylation of 2,5-dichlorobenzoquinone

• Pieterjan Winant and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 2315–2320, doi:10.3762/bjoc.17.149

• salts; Green Chemistry; Meerwein arylation; photoredox; Introduction Quinones or quinoid-based structures are ubiquitous in nature [1][2][3]. These versatile structures have shown promising antimalarial [4][5], antibacterial [6], and chemotherapeutic [6][7][8] properties. Their inherent oxidative

• nature makes them crucial players in both the regulation of reactive oxygen species and biological stress levels in human tissue [9], as well as in the photosynthesis of plants and bacteria [10]. Aside from their use in therapeutics, quinones possess unique photophysical and electronic properties

• , resulting in a multitude of applications in dyes [11], molecular electronics [12], and oxidants or ligands in organic chemistry [13][14]. This wide range of applications has long fueled an interest in exploring innovative ways of functionalizing quinones. However, arylation of (benzo)quinones has proven to

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• agents. Although the synthesis of 7,7’-bis-indolyl ether was known prior to Chai’s report [114]. In 1989, Black found the 7,7’-dimerised product 179 of the indole derivative 178 as a hindered biphenyl analog via its prompt oxidation in the presence of quinones. The bis(indol-7-yl) ether 180 was found in

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• substituents on the benzaldeydes 169 [72]. Cycloaddition reactions In 2014, Gao, Li, and their co-workers published a facile strategy to synthesize polysubstituted aromatic compounds from the reaction of quinones or maleimides with β-enamino esters (Scheme 39) [73]. They synthesized anthraquinone derivatives

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• -8057 Zurich, Switzerland Department of Physical Chemistry, Faculty of Chemistry, University of Lodz, Pomorska 163/165, 90236 Łódź, Poland 10.3762/bjoc.17.108 Abstract In-situ-generated N-aryl nitrile imines derived from trifluoroacetonitrile efficiently react with polycyclic 1,4-quinones, yielding

• naphthoquinone-derived products and low-intensity bands in the visible region (≈400 nm) for the anthraquinone series. Keywords: [3 + 2]-cycloadditions; fluorinated compounds; fused pyrazoles; N-heterocycles; nitrile imines; 1,4-quinones; Introduction The 1,4-quinone scaffold belongs to the most important

• structural motifs present in naturally occurring compounds as well as synthetic drugs and other functionalized organic molecules of great practical importance, e.g., in materials chemistry (Figure 1) [1][2][3][4]. Selective functionalization of 1,4-quinones is a challenging task in current organic synthesis

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

• activity. An effective method for the synthesis of sterically hindered o-quinones containing 1,3-diketonate, dinitrile and p-quinone-methide functional groups at the periphery of the ligand has been developed. The novel compounds have rigid and conjugated structures and exhibit properties typical of o

• -quinones. A study of their monoreduced semiquinone derivatives reveal that the spin density is delocalized across the whole molecule, including peripheral fragments. The first stable o-quinone derivative bearing an annulated thiete heterocycle has been isolated and characterized. Keywords: dioxolene

Construction of pillar[4]arene[1]quinone–1,10-dibromodecane pseudorotaxanes in solution and in the solid state

• Xinru Sheng,
• Errui Li and
• Feihe Huang

Beilstein J. Org. Chem. 2020, 16, 2954–2959, doi:10.3762/bjoc.16.245

• the further capping of the pseudorotaxanes to construct rotaxanes. Keywords: host–guest chemistry; pillar[4]arene[1]quinones; pillararenes; pseudorotaxanes; supramolecular chemistry; Introduction Relying on the research of basic science, supramolecular chemistry has become an important mean for

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• pyrazine-fused trichalcogenasumanenes have been assembled via the transformation of 1,2-dibutoxybenzene unit into the corresponding ortho-quinones by means of FeCl3 in CH2Cl2/MeCN at room temperature (Scheme 44) [79][80][81]. Interestingly, it was observed that 1,2-dibutoxy groups could be selectively

• transformed to the ortho-quinones in the presence of FeCl3. From the experimentations, they noticed that heteroatoms also play a significant role in this reaction for instance with sulfur and selenium-doped systems, ortho-quinones 166 and 167 were obtained (Scheme 44). In sharp contrast, the tellurium-doped

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

• iminoxyl radicals: generation, structure, stability, and spectral data Iminoxyl radicals were first discovered in 1964 by EPR spectroscopy as short-living intermediates formed from the oximes of both aromatic and aliphatic ketones and aldehydes, as well as from the oximes of quinones under the action of a

• [46], Pb(OAc)4 [44][46][47][48][49][50][51], PbO2 [52], Mn(OAc)3 [46], KMnO4 [46], Ag2O [53], AgO [54], Horseradish peroxidase/H2O2 [55], metal-free oxidants PhI(OAc)2 [46], t-BuOOt-Bu [53] or quinones [56] under UV irradiation. Anodic oxidation was also reported [57]. The establishing of the self

Towards triptycene functionalization and triptycene-linked porphyrin arrays

• Gemma M. Locke,
• Keith J. Flanagan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2020, 16, 763–777, doi:10.3762/bjoc.16.70

• [43], there is a high degree of interdigitation between the aromatic rings of the triptycene unit (Figure 2b) akin to some triptycene-quinones [44]. This is due to two of the triptycene aromatic rings i [C8A to C8, centroid···centroid distance of 3.845(3) Å and shift distance of 1.507(5) Å] and ii

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

• heteroarenes with the CF3 radical through a Cu(I/II) catalytic cycle. In 2013, the Szabó [143] and Wang group [144] described the copper-mediated C–H trifluoromethylation of quinones with Togni’s reagent. Szabó utilized a stoichiometric amount of CuCN combined with catalytic bis(pinacolato)diboron, whereas

Mechanochemical Friedel–Crafts acylations

• Mateja Đud,
• Anamarija Briš,
• Iva Jušinski,
• Davor Gracin and
• Davor Margetić

Beilstein J. Org. Chem. 2019, 15, 1313–1320, doi:10.3762/bjoc.15.130

• demonstrate that quinones could be prepared by simple one-pot FC protocols in the case of reactive aromatics. In situ Raman spectroscopy [60] was applied to study mechanistic aspects of the solid state reaction of phthalic anhydride with p-xylene. Raman spectra were simulated and positions of signals for

Heck- and Suzuki-coupling approaches to novel hydroquinone inhibitors of calcium ATPase

• Robert J. Kempton,
• Taylor A. Kidd-Kautz,
• Soizic Laurenceau and
• Stefan Paula

Beilstein J. Org. Chem. 2019, 15, 971–975, doi:10.3762/bjoc.15.94

• with CAN to the corresponding quinones 11 and 13, respectively. Numerous unsuccessful attempts were made to convert the dimethoxy compound [12] or one of its precursors into a hydroquinone (e.g., 14), either in one step (BBr3·S(CH3)2 [18] or (CH3)3SiCl/NaI [19]), or sequentially (CAN followed by

Selective benzylic C–H monooxygenation mediated by iodine oxides

• Kelsey B. LaMartina,
• Haley K. Kuck,
• Linda S. Oglesbee,
• Asma Al-Odaini and
• Nicholas C. Boaz

Beilstein J. Org. Chem. 2019, 15, 602–609, doi:10.3762/bjoc.15.55

• hypervalent iodine oxidants to mediate benzylic C–H oxidation is one area experiencing a surge of interest [22][23][24][25][26][27][28][29][30][31][32][33]. Nonmetal-based benzylic oxidations have also been mediated by species including, but not limited to, electron deficient quinones, photoexcited organic

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• and vinyl azides 92 for the synthesis of azaheterocyles 93 (Scheme 20) [98]. This strategy could also be applied to the synthesis of the quaternary indole alkaloid and melinonine-E. Quinones play an important role in organic chemistry because of their unique structure. In 2013, Malayappasamy and co

• -workers reported an efficient and convenient method for the synthesis of γ-carbonyl quinones 95 via ring-opening and functionalization of cyclopropanols 91 with quinones 94 (Scheme 21) [99]. In this transformation, both AgNO3 and FeSO4 were all efficient catalysts for the ring-opening and

• functionalization reaction. However, AgNO3 was superior than FeSO4 according to the reaction yields and time. Interestingly, aromatic cyclopropanols delivered higher yields than aliphatic ones. The mechanism for the Ag(I)-catalyzed oxidative ring-opening and functionalization of cyclopropanols with quinones is

Preparation and X-ray structure of 2-iodoxybenzenesulfonic acid (IBS) – a powerful hypervalent iodine(V) oxidant

• Irina A. Mironova,
• Pavel S. Postnikov,
• Rosa Y. Yusubova,
• Akira Yoshimura,
• Thomas Wirth,
• Viktor V. Zhdankin,
• Victor N. Nemykin and
• Mekhman S. Yusubov

Beilstein J. Org. Chem. 2018, 14, 1854–1858, doi:10.3762/bjoc.14.159

• of phenols to 1,2-quinones [15], the cyclization and cross-coupling reactions [16], and the site-selective hydroxylative dearomatization of 2-substituted phenols to either 1,2-benzoquinols or their cyclodimers [17]. The first preparation and isolation of IBS (1) was attempted in 2006 using two

First thia-Diels–Alder reactions of thiochalcones with 1,4-quinones

• Grzegorz Mlostoń,
• Katarzyna Urbaniak,
• Paweł Urbaniak,
• Anna Marko,
• Anthony Linden and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2018, 14, 1834–1839, doi:10.3762/bjoc.14.156

• Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland 10.3762/bjoc.14.156 Abstract Aryl and hetaryl thiochalcones react smoothly with 1,4-quinones in THF solution at 60 °C yielding the corresponding fused 4H-thiopyrans after spontaneous dehydrogenation of the

• cycloadduct was isolated in 37% yield. Keywords: hetero-Diels–Alder reactions; quinone dyes; quinones; sulfur heterocycles; thiochalcones; Introduction Hetero-Diels–Alder reactions are considered to be a powerful methodology widely explored for the synthesis of six-membered heterocycles [1][2] with numerous

• regioselective manner [16][20]. In cycloaddition chemistry, 1,4-quinones are applied widely both as dipolarophiles and dienophiles. In the case of [3 + 2] cycloadditions, reactions can occur chemoselectively with either the C=O or the C=C unit [21][22][23]. On the other hand, reactions with diverse 1,3-dienes

Oxidative dehydrogenation of C–C and C–N bonds: A convenient approach to access diverse (dihydro)heteroaromatic compounds

• Santanu Hati,
• Ulrike Holzgrabe and
• Subhabrata Sen

Beilstein J. Org. Chem. 2017, 13, 1670–1692, doi:10.3762/bjoc.13.162

• et al. utilized a modular catalytic system comprised of C-quinones for the oxidative dehydrogenation of tetrahydroquinolines 104 to an (2,1-c)quinoline 105. This was further transformed to 106, an antiprotozoal agent, and 107, a topoisomerase inhibitor, presently in the phase II clinical trial

Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study

• Nikolay O. Chalkov,
• Vladimir K. Cherkasov,
• Gleb A. Abakumov,
• Andrey G. Starikov and
• Viacheslav A. Kuropatov

Beilstein J. Org. Chem. 2016, 12, 2450–2456, doi:10.3762/bjoc.12.238

• dissolves in solutions of o-quinones [9][10][11]. This process is greatly accelerated by the presence of auxiliary ligands, such as phosphines or pyridines. But the oxidation of copper metal with a reduced protonated quinone, which is (1)H2 in fact, was observed for the first time. This process leads to the