An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• of a [3 + 2] cycloaddition reactions under UV irradiation with azobis(isobutyronitrile) (AIBN) as the free radical initiator and phenyl disulfide as the catalyst, in which the three-membered rings containing double bonds and substituted olefins were transformed into five-membered-ring structures with

• by the excitation with visible light, the homolytic cleavage of disulfide generates an arylthiyl radical (ArS•), which adds to diphenylacetylene to form a free-radical intermediate 28. Subsequently, this intermediate traps a molecule of singlet oxygen (1O2), and the thiyl radical is regenerated to

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

• and the difficulties associated with the interpretation of the obtained data [53]. During EPR monitoring of the generation and decomposition of iminoxyl radicals, the formation of several free-radical products of a non-iminoxyl type, probably of the general formula R1R2NO•, was observed. It was

• hindered tert-butylmethyliminoxyl and diisopropyliminoxyl radicals, as well as for diaryl and alkylaryliminoxyl radicals, the radical–dimer equilibrium was reached slowly, it was shifted toward the free radical, and a second-order decay kinetics was observed. The first synthesized long-lived iminoxyl

• radical 20 and complex 49 results in the coupling product 48 (Scheme 18). The formation of radical 20 from the oxime 19 under the action of Cu(ClO4)2 in acetonitrile was proved by EPR spectroscopy [46]. Free-radical oxidative C–O coupling of pyrazolones 50 with different classes of N-hydroxy compounds

Synthesis of pyrrolidinedione-fused hexahydropyrrolo[2,1-a]isoquinolines via three-component [3 + 2] cycloaddition followed by one-pot N-allylation and intramolecular Heck reactions

• Xiaoming Ma,
• Suzhi Meng,
• Xiaofeng Zhang,
• Qiang Zhang,
• Shenghu Yan,
• Yue Zhang and
• Wei Zhang

Beilstein J. Org. Chem. 2020, 16, 1225–1233, doi:10.3762/bjoc.16.106

• have immuno modulatory activity [7][8]. Trolline has inhibitory activity against Gram-negative and Gram-positive bacteria [9], also as free radical scavenger in rat brain [10]. Organic chemists have been continuously interested in the development of methods for the synthesis of pyrrolo[2,1-a

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

• strong electrophiles and undergo nucleophilic additions with two-electron donors (Scheme 21a) [93][94]. In contrast, radical anions can act as very strong single-electron nucleophiles and are often subject to fragmentation to give a neutral free radical and a charged species (Scheme 21b) [77][95]. When a

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

• two different types of free radical intermediates, 30 and 31 (Scheme 8). The species 31 was shown to be the primary initiating radical compound. In 2006, Aydin and Arsu employed benzaldehyde (8) as the coinitiator for the photoinitiated free radical polymerization of multifunctional MMA (26) [38

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

In water multicomponent synthesis of low-molecular-mass 4,7-dihydrotetrazolo[1,5-a]pyrimidines

• Irina G. Tkachenko,
• Sergey A. Komykhov,
• Vladimir I. Musatov,
• Svitlana V. Shishkina,
• Viktoriya V. Dyakonenko,
• Vladimir N. Shvets,
• Mikhail V. Diachkov,
• Valentyn A. Chebanov and
• Sergey M. Desenko

Beilstein J. Org. Chem. 2019, 15, 2390–2397, doi:10.3762/bjoc.15.231

• (DPPH) is one of the most common and widespread [30][31][32][33]. The free radical scavenging activity of tetrazolo[1,5-a]pyrimidines 9d,f, 11, and 14 was measured spectrophotometrically as percentage of reducing the free-radical concentration in the presence of a test compound in methanol/dimethyl

• mixture of isomers. Some of the prepared tetrazolopyrimidines showed free-radical scavenging activity towards DPPH. Experimental General. The melting points were determined with a Gallenkamp melting point apparatus. The NMR spectra were recorded at 400 MHz with a Varian MR-400 spectrometer. The EIMS

• Crystallographic Data Centre as supplementary publication numbers CCDC 1942287. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: +44-(0)1223-336033 or by email: deposit@ccdc.cam.ac.uk). Free radical scavenging activity determination. A solution

Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• -BuOOLi (oxenoid), simply generated by deprotonation of t-BuOOH with n-BuLi, led to the copper alkoxide, as anticipated, without the formation of free radical intermediates. As already reported [78], the expected 2,2,3,3-tetrasubstituted cyclopropanols 5 were obtained as single diastereoisomers (Scheme 5

Dirhodium(II)-catalyzed [3 + 2] cycloaddition of N-arylaminocyclopropane with alkyne derivatives

• Wentong Liu,
• Yi Kuang,
• Zhifan Wang,
• Jin Zhu and
• Yuanhua Wang

Beilstein J. Org. Chem. 2019, 15, 542–550, doi:10.3762/bjoc.15.48

•  3, entry 8), indicating the results of this type of reaction are mainly determined by the stability of the free radical intermediate during the reaction. Further investigation revealed cycloaddition preferentially proceeded with the terminal alkene or alkyne. Product 4j was obtained with a 41% yield

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

• a nucleophilic group to obtain the product L (path III). Free radical reactions have flourished and became a powerful tool in organic synthesis [32][33][34][35][36][37][38]. With the significant potential, this strategy has captured the human’s attention and solved considerable problems in the past

• several decades [39][40][41][42]. The free radical reaction was applied in a range of organic transformations because of its unique advantages such as excellent reactivity, mild conditions, functional group tolerance, and atom economy. A series of radicals, such as carbon, Se, CF3, halogen, S and N

• , phenylselenyl radical 26 was produced in the presence of free radical initiator (NH4)2S2O8 [60][61]. Next, the intermediate 26 was added to the C–C double bond of MCPs 23, and then went through a series of ring-opening, intramolecular cyclization, oxidation and dehydrogenation to generate 3

Fabrication of supramolecular cyclodextrin–fullerene nonwovens by electrospinning

• Hiroaki Yoshida,
• Ken Kikuta and
• Toshiyuki Kida

Beilstein J. Org. Chem. 2019, 15, 89–95, doi:10.3762/bjoc.15.10

• abilities for free radical scavengers and solar cell applications [18][19][20]. A serious issue for practical applications of fullerenes is the poor solubility in most solvents. Various methods to improve the solubility have been demonstrated by coating the surface with surfactants or host molecules and

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• species are produced, a wide range of monomers can be polymerized via a free radical or a cationic mechanism (anionic mechanisms are still rare) [8]. A PI can also be used in combination with a photosensitizer (PS) to extend the spectral sensitivity to longer wavelengths. The development of new

• the case of a d5 high spin octahedral complex in Figure 4. As for LMCT, MLCT give intense band in UV spectrum. 1.4 Mechanisms in polymerization reactions Free radical polymerization or/and cationic polymerization can be initiated by photoredox catalysis. Respectively, radicals or/and cations must be

• industrial fields. About 45% of the manufactured plastic material and 40% of synthetic rubber are produced by free radical polymerization worldwide [23]. In both cases, the photoredox catalyst, used as PS, absorbs the light and goes to its excited state. Then, there are two possibilities: the photoredox

Hypervalent iodine compounds for anti-Markovnikov-type iodo-oxyimidation of vinylarenes

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Mikhail A. Syroeshkin,
• Alexander A. Korlyukov,
• Pavel V. Dorovatovskii,
• Yan V. Zubavichus,
• Gennady I. Nikishin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2018, 14, 2146–2155, doi:10.3762/bjoc.14.188

• -containing oxidative systems with the addition of various nucleophiles have been published, all of these processes have common mechanism and the same regioselectivity. The free-radical approach developed in the present work affords the opposite (anti-Markovnikov) regioselectivity of the addition to the

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• . The arylthiols bearing chloro and fluoro substituents gave the expected β-hydroxy sulfides in moderate yields while the much deactivated nitro-thiophenol did not lead to any product formation. The protocol allowed easy scale-up to gram quantities. The results strongly supported a free radical

• 105–109 (Scheme 40) [73]. 3.5 Other synthetic routes to β-hydroxy sulfides Incorporation of amine, silyl and sulfide functional groups into C–C multiple bonds offers an attractive route to appropriately functionalized substrates. Inter- and intramolecular thiol-ene reaction is a highly efficient, free

• -radical mediated “click” process with diverse applications in small molecule and polymer synthesis and has been reviewed [74][75][76]. The importance of the thiol-ene reaction in the synthesis of β-hydroxy sulfides is exemplified by the work of Scanlan and co-workers as shown in Scheme 41 [77][78

On the design principles of peptide–drug conjugates for targeted drug delivery to the malignant tumor site

• Eirinaios I. Vrettos,
• Gábor Mező and
• Andreas G. Tzakos

Beilstein J. Org. Chem. 2018, 14, 930–954, doi:10.3762/bjoc.14.80

• . Furthermore, they stabilize the topoisomerase II DNA complex preventing the transcription. They may also increase quinone type free radical production, however, this plays a role rather in their cytotoxic side effects. Daunorubicin is mainly used in the treatment of leukemia [95] while doxorubicin in the cure

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• radical. Yadav and co-workers presented a metal-free radical thiol–ene approach, using benzophenone as photoredox catalyst (Scheme 13) [43]. No sacrificial oxidant is required for this reaction as benzophenone is regenerated by hydrogen atom transfer to the anti-Markovnikov radical intermediate. Aliphatic

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• in a sealed tube at 110 °C. Mechanistic studies by electron spin resonance were carried out in which both the CF3• and the β-CF3 alkyl radical intermediate were observed by using 2-methyl-2-nitrosopropane as a radical spin trap. A single-electron oxidative free-radical process was clearly ascertained

•  29b) [51]. A single-electron oxidative free-radical process was ascertained for the generation of CF3•. From enynes, the iodination step was realised by I2, which was formed by a multistep redox process from I2O5. The intramolecular carbotrifluoromethylations of alkenes from acrylamides and

• excellent yields. However, to achieve high yields in this trifluoromethylation, one (or more) alkoxy group(s) must be present on the arenes in order to stabilise the free-radical intermediate (see mechanism in Scheme 47). Control experiments such as the trapping of the trifluoromethyl radical with the

Syntheses, structures, and stabilities of aliphatic and aromatic fluorous iodine(I) and iodine(III) compounds: the role of iodine Lewis basicity

• Tathagata Mukherjee,
• Soumik Biswas,
• Andreas Ehnbom,
• Subrata K. Ghosh,
• Ibrahim El-Zoghbi,
• Nattamai Bhuvanesh,
• Hassan S. Bazzi and
• John A. Gladysz

Beilstein J. Org. Chem. 2017, 13, 2486–2501, doi:10.3762/bjoc.13.246

• commercialized [4]. Many research groups have described the syntheses of other types of fluorous alkyl [5][6][7][8] and aryl [9][10][11][12] iodides [13][14][15][16][17]. The former are ubiquitous by virtue of the large number of perfluoroalkyl iodides RfnI that have been shown to undergo free radical additions

• ) dichlorides for free radical chlorinations [25]. In this regard, phenyl iodine(III) dichloride (PhICl2) is an effective free radical chlorinating agent for hydrocarbons [26][27]. Importantly, the mechanism does not involve the liberation of Cl2, followed by the textbook sequence of steps. Rather, hydrogen

• degradation under free radical chlorination conditions. However, no reactions were observed when RfnI were treated with Cl2 or NaOCl/HCl. Nonetheless, perfluoroalkyl iodides RfnI (n = 6–8, 10, 12) can be oxidized using various recipes (e.g., 80% H2O2 in trifluoroacetic acid anhydride) to the iodine(III) bis

Solid-state studies and antioxidant properties of the γ-cyclodextrin·fisetin inclusion compound

• Joana M. Pais,
• Maria João Barroca,
• Maria Paula M. Marques,
• Filipe A. Almeida Paz and
• Susana S. Braga

Beilstein J. Org. Chem. 2017, 13, 2138–2145, doi:10.3762/bjoc.13.212

• activity Developed by Blois in 1958 [40], the DPPH assay determines the antioxidant activity of a test compound by using a commercially available stable free radical, DPPH· (2,2-diphenyl-1-picrylhydrazyl) that has a strong violet color. Upon reaction with an antioxidant, DPPH· is converted into the

• corresponding hydrazine (pale yellow in color), a reaction which can be monitored by UV–vis spectroscopy. As the kinetics of the reaction varies from sample to sample, the stabilization time for a complete reduction of the DPPH· free radical was determined. For all samples studied, the steady-state

• ’), 136.5 (C3), 125.7 (C1’), 120.9 (C6’), 114.7, 112.4 (C6, C10, C2’, C5’), 101.6 (C8). Antioxidant activity by the DPPH method. The radical-scavenging activity of fisetin and the γ-CD·fisetin inclusion compound were determined using the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH·) [45]. A volume of

Transition-metal-free synthesis of 3-sulfenylated chromones via KIO₃-catalyzed radical C(sp²)–H sulfenylation

• Yanhui Guo,
• Shanshan Zhong,
• Li Wei and
• Jie-Ping Wan

Beilstein J. Org. Chem. 2017, 13, 2017–2022, doi:10.3762/bjoc.13.199

• chromones via domino chromone ring construction and C(sp2)–H bond sulfenylation have been achieved under transition-metal-free conditions by using KIO3 as the only catalyst. Keywords: C–H sulfenylation; chromones; domino reaction; free-radical; transition-metal-free; Introduction The C–S bond-forming

• that a free radical intermediate has also occurred in the generation of 6 (reaction 3, Scheme 3). The reactions of 5 with 6 and 2b were both found to yield the sulfenylated chromone 3i in excellent yield, respectively (reactions 4 and 5, Scheme 3). On the other hand, the reaction of 5 and 6 in the

• presence of TEMPO, however, provides only with trace amounts of 3i, supporting that products 3 are yielded via a free radical route (reaction 6, Scheme 3). In addition, the control reaction of 1b and 2b afforded also only trace amounts of product 3i in the presence of 1 equiv TEMPO (reaction 7, Scheme 3

Are boat transition states likely to occur in Cope rearrangements? A DFT study of the biogenesis of germacranes

• José Enrique Barquera-Lozada and
• Gabriel Cuevas

Beilstein J. Org. Chem. 2017, 13, 1969–1976, doi:10.3762/bjoc.13.192

• , a chair conformation due to the higher energy of the boat conformation [2][7][10][11][12][13][14][15][16][17][18][19]. In this mechanism, the electron density of the TS is delocalized into the six carbon atoms [20][21][22]. However, if the diene contains free radical stabilizing groups, this

Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides

• Valentin A. Rassadin,
• Mirko Scholz,
• Anastasiia A. Klochkova,
• Armin de Meijere and
• Victor V. Sokolov

Beilstein J. Org. Chem. 2017, 13, 1932–1939, doi:10.3762/bjoc.13.187

• the nitrooxy derivative 22, presumbaly via the corresponding benzyl-type free radical (Scheme 7). The structure of 22 was proven by single-crystal X-ray diffraction (Figure 2). According to a publication by Metz et al., a N-(4-methoxybenzyl) group can be removed from sultams by treatment with

Block copolymers from ionic liquids for the preparation of thin carbonaceous shells

• Sadaf Hanif,
• Bernd Oschmann,
• Dmitri Spetter,
• Muhammad Nawaz Tahir,
• Wolfgang Tremel and
• Rudolf Zentel

Beilstein J. Org. Chem. 2017, 13, 1693–1701, doi:10.3762/bjoc.13.163

• are applied as catalytic membranes, thermotropic liquid crystals [12], polymer electrolytes, ionic conductive materials, CO2 absorbing materials, microwave absorbing materials and porous materials [4]. Most of these polymers were synthesized by free radical polymerization. There are just few reports

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

• reaction was facilitated at room temperature by N-hydroxyphthalimide (NHPI) and cobalt acetate (Co(OAc)2) as catalysts in acetonitrile (Scheme 20). The reaction followed a free radical mechanism as exemplified by the oxidative dehydrogenation of DHPs. The initial step involved the formation of the

One-pot synthesis of block-copolyrotaxanes through controlled rotaxa-polymerization

• Jessica Hilschmann,
• Gerhard Wenz and
• Gergely Kali

Beilstein J. Org. Chem. 2017, 13, 1310–1315, doi:10.3762/bjoc.13.127

• , free radical copolymerization of a hydrophobic monomer, complexed in a host, with a stopper comonomer [24][25]. This latter has to be large enough to prevent the dissociation of the growing axis and the host, as it happens in the case of aqueous CD assisted homopolymerizations of hydrophobic monomers

• [26][27][28] including dienes [29]. This approach drastically widens the range of suitable hydrophobic polymeric axes, to all monomers being complexed in CD or hydrophilic CD derivatives. Up to now, rotaxa-polymerization was only performed via free radical reaction without control of the polymer chain