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

• subsequent cross-linking. Scheme 1 redrawn from [3]. (A) Structure of typical urushiol in Chinese lacquer, and (B) schematic process of laccase-catalyzed oxidation polymerization of Chinese lacquer and autoxidation reaction on the long aliphatic unsaturated side chain. Scheme 2 redrawn from [9]. A) Primary

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

• radical-chain PINO/NHPI-catalyzed autoxidation proceeds with the selective formation of a benzylic hydroperoxide (Scheme 9), a product that frequently decomposes in the presence of transition metal ions or photoredox catalysts. It was shown that the peroxide is converted to the ketone on the TiO2 surface

New azodyrecins identified by a genome mining-directed reactivity-based screening

• Atina Rizkiya Choirunnisa,
• Kuga Arima,
• Yo Abe,
• Noritaka Kagaya,
• Kei Kudo,
• Hikaru Suenaga,
• Junko Hashimoto,
• Manabu Fujie,
• Noriyuki Satoh,
• Kazuo Shin-ya,
• Kenichi Matsuda and
• Toshiyuki Wakimoto

Beilstein J. Org. Chem. 2022, 18, 1017–1025, doi:10.3762/bjoc.18.102

• nitrogen radical coupling mechanism in the biosynthesis of azoxymycins [12][13], which are aromatic azoxy natural products. A similar mechanism has been envisioned for the autoxidation and spontaneous dimerization of aliphatic hydroxylamines via the azoxy linkage in malleobactin D biosynthesis [14]. A

Synthesis of odorants in flow and their applications in perfumery

• Merlin Kleoff,
• Paul Kiler and
• Philipp Heretsch

Beilstein J. Org. Chem. 2022, 18, 754–768, doi:10.3762/bjoc.18.76

• spectrum wheel ordering different types of odorants from fruity to musky. Classification of odorants as “top note”, “middle note” and “base note” depending on their substantivity. Synthesis of raspberry ketone (5) and raspberry ketone methyl ether (6) in two steps in flow. Autoxidation of (+)-valencene (7

Rapid gas–liquid reaction in flow. Continuous synthesis and production of cyclohexene oxide

• Kyoko Mandai,
• Tetsuya Yamamoto,
• Hiroki Mandai and
• Aiichiro Nagaki

Beilstein J. Org. Chem. 2022, 18, 660–668, doi:10.3762/bjoc.18.67

• 6 was generated via the autoxidation process of aldehyde (reaction 1), which rapidly oxidized coexisting cyclohexene to produce cyclohexene oxide as a major product along with isobutyric acid 4 (reaction 2). Although we did not quantify whether the polymerization of epoxide 3 might proceed when the

• residence time was elongated, leading to a significant decrease in the yield of cyclohexene oxide (Supporting Information File 1, Figure S2) [32]. Overall, we assume that, in our flow system, the highly efficient contact of acyl radical 5 with oxygen during the autoxidation of aldehyde could produce the

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

• reaction mechanisms: free radical autoxidation, cation radical autoxidation, and thermal intersystem crossing (ISC), using 18O2 labeling, spin-trapping, spectroscopic, mass spectrometric, kinetic, and computational techniques. After several experiments, the obtained results have demonstrated that the 2

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Facile synthesis of 7-alkyl-1,2,3,4-tetrahydro-1,8-naphthyridines as arginine mimetics using a Horner–Wadsworth–Emmons-based approach

• Rhys A. Lippa,
• John A. Murphy and
• Tim N. Barrett

Beilstein J. Org. Chem. 2020, 16, 1617–1626, doi:10.3762/bjoc.16.134

• the exact mechanism is not known, it may involve a reactive carbene intermediate formed by α-elimination of the phosphonate as described in previous reports [23]. Alternatively, a base-promoted autoxidation of phosphonate 7 in the presence of trace amounts of oxygen, followed by olefination may be

• taking place (Scheme 8) [24][25][26]. The autoxidation of phosphonates under THF/potassium tert-butoxide has been reported previously [27]. In order to circumvent racemisation of aldehyde 22 during the Horner–Wadsworth–Emmons olefination, alkylation of phosphoramidate 13 was explored using commercially

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

• widely used in industrial processes as promoters of autoxidation in the functionalization of benzylic C–H bonds of aryl alkanes, such as in the synthesis of terephthalic acid from p-xylene [21]. Metal-free oxidants have been used in benzylic C–H to C–O functionalization. Specifically, the use of

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• amount of gold(I) in warm toluene provided us with the oxazoline 40 in an 80% yield. However, this compound turned out to be unstable, either on standing, probably because of an autoxidation, as reported in other instances [27], or in CDCl3, probably because of acid traces. To achieve its isomerization

Volatiles from three genome sequenced fungi from the genus Aspergillus

• Jeroen S. Dickschat,
• Ersin Celik and
• Nelson L. Brock

Beilstein J. Org. Chem. 2018, 14, 900–910, doi:10.3762/bjoc.14.77

• sesquiterpenes arising via cation A with the main product trichodiene was previously reported from Fusarium [34]. The compounds 10 and 11 are directly formed from this cation by deprotonation. A 1,3-hydride shift to B and deprotonation yields 8 and γ-curcumene (C). Instead of the latter compound its autoxidation

• alternative to a previously suggested cyclisation of A to a less stable secondary cation, followed by 1,4-hydride migration to yield the same intermediate F [36]. Again, the dihydrobenzene derivative H is not observed, but instead its autoxidation product 14 is detected. Finally, the main product 15 arises

Is the tungsten(IV) complex (NEt₄)₂[WO(mnt)₂] a functional analogue of acetylene hydratase?

• Matthias Schreyer and
• Lukas Hintermann

Beilstein J. Org. Chem. 2017, 13, 2332–2339, doi:10.3762/bjoc.13.230

• an impurity in the starting alkyne 4, but may also be formed under the reaction conditions if the latter contains autoxidation impurities. Kugelrohr vacuum distillation of 4 reduced the aldehyde level to below 0.3% (Table 1, entries 5–8). Even if technically unsatisfactory, entries 3 and 4 are

• included in Table 1 to illustrate a potential pitfall in the study of catalytic oxyfunctionalization of unsaturated hydrocarbons, where autoxidation products may feign false positive results [35]. The effect is most problematic at low mol % loadings, and it is thus necessary to substantiate a presumed

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

• Baeyer−Villiger oxidation and it is one of the methods for the synthesis of commercially important caprolactone from cyclohexanone with peracetic acid [55][56]. Autoxidation processes with formation of hydroperoxides and their subsequent free-radical transformations with generation of carbon- and oxygen

Iodine-mediated synthesis of 3-acylbenzothiadiazine 1,1-dioxides

• Long-Yi Xi,
• Ruo-Yi Zhang,
• Lei Shi,
• Shan-Yong Chen and
• Xiao-Qi Yu

Beilstein J. Org. Chem. 2016, 12, 1072–1078, doi:10.3762/bjoc.12.101

• condensation of phenylglyoxal with 2-aminobenzenesulfonamide affords intermediate C, followed by intramolecular addition giving intermediate D. Intermediate D undergoes autoxidation leading to the desired product 3a. Conclusion In conclusion, we have developed a novel one-pot protocol for the synthesis of 3

Mycothiol synthesis by an anomerization reaction through endocyclic cleavage

• Shino Manabe and
• Yukishige Ito

Beilstein J. Org. Chem. 2016, 12, 328–333, doi:10.3762/bjoc.12.35

• Gram-negative bacteria. MSH undergoes metal-catalyzed autoxidation more rapidly than glutathione [16]. The biosynthetic pathway of MSH has been well investigated; MSH is synthesized from 1-inositol phosphate and uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) in five steps [15]. It is used by

Photoinduced 1,2,3,4-tetrahydropyridine ring conversions

• Baiba Turovska,
• Henning Lund,
• Viesturs Lūsis,
• Anna Lielpētere,
• Edvards Liepiņš,
• Sergejs Beljakovs,
• Inguna Goba and
• Jānis Stradiņš

Beilstein J. Org. Chem. 2015, 11, 2166–2170, doi:10.3762/bjoc.11.234

• attention has been paid to organic aromatic or heterocyclic hydroperoxides, probably due to their low thermal stability and high reactivity. Stable organic hydroperoxides were isolated in the early 1950s as products of autoxidation as well as catalytic oxygenation of indoles and tetrahydrocarbazoles [3][4

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• reductions and protonations. The ROS generated in these ways oxidize any organic components or pollutants, by well-known oxidation and autoxidation processes, eventually leading to complete mineralization with production of CO2, water and mineral acids. Research in this area has been extensive [17] and as a

Antioxidant potential of curcumin-related compounds studied by chemiluminescence kinetics, chain-breaking efficiencies, scavenging activity (ORAC) and DFT calculations

• Adriana K. Slavova-Kazakova,
• Silvia E. Angelova,
• Timur L. Veprintsev,
• Petko Denev,
• Davide Fabbri,
• Maria Antonietta Dettori,
• Maria Kratchanova,
• Vladimir V. Naumov,
• Aleksei V. Trofimov,
• Rostislav F. Vasil’ev,
• Giovanna Delogu and
• Vessela D. Kancheva

Beilstein J. Org. Chem. 2015, 11, 1398–1411, doi:10.3762/bjoc.11.151

• reactions of the antioxidants with peroxyl radicals; model 2 – lipid autoxidation (lipidAO) used for assessing the chain-breaking antioxidant efficiency and reactivity; model 3 – oxygen radical absorbance capacity (ORAC), which yields the activity against peroxyl radicals generated by an azoinitiator; model

• were applied: model 1 – chemiluminescence of a hydrocarbon substrate used for determination of the rate constants (kA) of the reactions of the antioxidants with peroxyl radicals (RO2•); model 2 – lipid autoxidation used for assessing the chain-breaking antioxidant efficiency and reactivity; model 3

• the side chain that influences the dihedral angle of biphenyl structure. Model 2: Lipid autoxidation Kinetic curves of the lipid autoxidation at concentrations of 1 mM of the studied compounds and of DL-α-tocopherol (11) are presented in Figure 4 and the main kinetic parameters, characterizing the

Electrochemical oxidation of cholesterol

• Jacek W. Morzycki and
• Andrzej Sobkowiak

Beilstein J. Org. Chem. 2015, 11, 392–402, doi:10.3762/bjoc.11.45

• attention started being paid to cholesterol oxidation products [4]. Since then, these compounds have constantly drawn the attention of biochemists and medicinal chemists. Cholesterol that is present in food of animal origin undergoes autoxidation during processing as well as during storage, thus it yields

Streptopyridines, volatile pyridine alkaloids produced by Streptomyces sp. FORM5

• Ulrike Groenhagen,
• Michael Maczka,
• Jeroen S. Dickschat and
• Stefan Schulz

Beilstein J. Org. Chem. 2014, 10, 1421–1432, doi:10.3762/bjoc.10.146

• streptenols A and C (27) [9]. Reduction and transamination leads to the amine 30 that cyclizes to the piperideine 25. Elimination of water leads to the dihydropyridine 31 that is oxidized to the major streptopyridine 12 possibly by spontaneous autoxidation in air. Isomerization of the double bonds during this

Simple two-step synthesis of 2,4-disubstituted pyrroles and 3,5-disubstituted pyrrole-2-carbonitriles from enones

• Murat Kucukdisli,
• Dorota Ferenc,
• Marcel Heinz,
• Christine Wiebe and
• Till Opatz

Beilstein J. Org. Chem. 2014, 10, 466–470, doi:10.3762/bjoc.10.44

• substituent (Table 2, entry 3). As autoxidation and oxidative dealkylation of 2-alkylpyrroles can even be effected by exposure to air [49][50], the lability of 10c towards DDQ oxidation is not very surprising. Conclusion Two simple two-step procedures have been developed to convert enones to 2,4-disubstiuted

3-Pyridinols and 5-pyrimidinols: Tailor-made for use in synergistic radical-trapping co-antioxidant systems

• Luca Valgimigli,
• Daniele Bartolomei,
• Riccardo Amorati,
• Evan Haidasz,
• Jason J. Hanthorn,
• Susheel J. Nara,
• Johan Brinkhorst and
• Derek A. Pratt

Beilstein J. Org. Chem. 2013, 9, 2781–2792, doi:10.3762/bjoc.9.313

• stronger O–H bonds than equivalently substituted phenols, but possess similar reactivities toward autoxidation chain-carrying peroxyl radicals. These attributes suggest that 3-pyridinols and 5-pyrimidinols will be particularly effectiveco-antioxidants when used in combination with more common, but less

• reactive, phenolic antioxidants such as 2,6-di-tert-butyl-4-methylphenol (BHT), which we demonstrate herein. The antioxidants function in a synergistic manner to inhibit autoxidation; taking advantage of the higher reactivity of the 3-pyridinols/5-pyrimidinols to trap peroxyl radicals and using the less

• phenolic antioxidants, but which are equally efficacious as the 3-pyridinol/5-pyrimidinol antioxidants alone at higher loadings. Keywords: antioxidants; autoxidation; free radical; phenols; 3-pyridinols; 5-pyrimidinols; Introduction Radical-trapping (chain-breaking) antioxidants are arguably the most

Damage of polyesters by the atmospheric free radical oxidant NO₃^•: a product study involving model systems

• Catrin Goeschen and
• Uta Wille

Beilstein J. Org. Chem. 2013, 9, 1907–1916, doi:10.3762/bjoc.9.225

• materials, the chemical mechanism of polymer degradation is by far not fully understood. It has generally been assumed that polymer degradation involves a radical-mediated autoxidation mechanism, which propagates through hydrogen abstraction by an intermediate peroxyl radical ROO•. Although this

• autoxidation mechanism was initially proposed only for a limited number of polymers that contain activated allylic hydrogen atoms (for example rubber materials) [1][2][3][4][5], it has been universally adapted as general mechanism for polymer degradation. However, recent comprehensive high-level theoretical

• studies by Coote et al. clearly revealed that polymers possessing only saturated alkyl chains, for example polyesters, will not propagate autoxidation, particularly because the ROO–H bond-dissociation energy (BDE) is usually less than the BDE for unactivated R–H bonds [6]. Polymer surface coatings, which

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• the O2-mediated selective oxidation of organic compounds and looking for environmentally safe alternatives to metal catalysis. Keywords: autoxidation; free-radicals; metal-free; molecular oxygen; N-hydroxyphthalimide; Introduction The development of efficient and cheap catalytic systems for the

• the beneficial impact of selective oxidation on industrial chemistry [2][3][4][5]. Nevertheless, classical autoxidation is usually very slow at low temperatures, and catalysis is required to activate O2. Transition-metal salts are particularly effective for this scope [6], but their use is often

• the role of classical radical initiators obtained by thermal decomposition, we will focus on some intriguing redox systems, including nitric oxides, laccase, quinones and aldehydes, which allow operation under very mild conditions, offering efficient alternative solutions to the classical autoxidation

NHC-catalysed highly selective aerobic oxidation of nonactivated aldehydes

• Lennart Möhlmann,
• Stefan Ludwig and
• Siegfried Blechert

Beilstein J. Org. Chem. 2013, 9, 602–607, doi:10.3762/bjoc.9.65

• led to a higher total conversion. We suppose that this is caused by the oxidation of the NHC, i.e., the consumption of the umpolung catalyst [23]. With this result in hand we focused on the aerobic autoxidation using only D as a precatalyst. An interesting conversion of aromatic aldehydes to acids