Photoinduced in situ generation of DNA-targeting ligands: DNA-binding and DNA-photodamaging properties of benzo[c]quinolizinium ions

• Julika Schlosser,
• Olga Fedorova,
• Yuri Fedorov and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 101–117, doi:10.3762/bjoc.20.11

• radicals 4 and 5, namely by addition of the radical or by hydrogen abstraction at the methylene group of the ethyl substituent (Scheme 4). Subsequently, the intermediate radicals 4 and 5 induce DNA-strand breaks initiated by hydrogen abstraction reactions at the ribose residues [78][87]. Most notably

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

• technique requires radical generation on the polymer backbone. A typical approach involves hydrogen abstraction by organic oxidants such as oxygen radicals from peroxide initiators [114], which is similar to the radical crosslinking process, vide infra. Radicals may also be generated thermally, through

• vinyl groups [132], demonstrating a promising new orientation of radical hydrosilylation. It is noteworthy, that since the 1940s, polysiloxanes were crosslinked via hydrogen abstraction from Si–CH3 and a radical coupling mechanism like polyolefins, vide supra [133]. Irradiation can also lead to the

• , such as organic peroxides, hydrogen peroxide, persulfates undergo homolysis of O–O bonds generating radicals that can break C–H bonds followed by a hydrogen abstraction reaction. Phenolic compounds can be oxidized by molecular oxygen in the presence of laccase, and the resulting phenolic radical reacts

BINOL as a chiral element in mechanically interlocked molecules

• Matthias Krajnc and
• Jochen Niemeyer

Beilstein J. Org. Chem. 2022, 18, 508–523, doi:10.3762/bjoc.18.53

• radical addition of a thiol-based stopper to the α,β-unsaturated carbonyl unit in 12% yield. In this reaction, addition of the thiyl radical to the β-position first gives rise to the corresponding rotaxane radical with the unpaired electron in the α-position, followed by hydrogen abstraction from the next

• thiol. This generates a new stereocenter in the α-position, which takes place under the chiral environment of the BINOL-based macrocycle. However, the hydrogen abstraction takes place with little stereoselectivity, so that both diastereoisomers are formed in almost equal amounts (er = 53:47, see Figure

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

• radical hydrogen abstraction may be possible under similar conditions [31][32]. However, even small amounts of DABCO (Table 1, entry 1) seem to completely shut down this alternative path, probably due to a fast quenching of the excited state photocatalyst, leading to no mechanism competition under the

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

• would give the oxindole scaffold. Hydrogen abstraction would regenerate the reduced iron catalyst and produce the final product. Two years later, Zhou and co-workers expanded the reaction for the synthesis of substituted isoquinoline-1,3(2H,4H)-dione derivatives 64 (Scheme 10) [81]. Both laboratories

• isotope studies revealed the cleavage of the C(sp3)–H bond may be involved in the rate-determining step of this transformation. Mechanistically, prototypical homolysis of the peroxide in the presence of the Fe(II) catalyst will generate the alkyl radical 78 formed via hydrogen abstraction. The

• in the presence of radical scavengers. Both laboratories suggested the mechanism, wherein, after tert-butoxyl radical production, hydrogen abstraction can generate the appropriate radical species. Subsequent radical addition to the π-system followed by a 5-endo-trig radical cyclization would afford

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• the A-ring system were the most reactive sites for hydrogen abstraction, yielding fluorinated steroids 4a and 4b in 32% and 23% yield, respectively. For both products, α-fluorination was dominant over β-fluorination, likely because α-fluorination occurred on the less sterically hindered face

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• (reductive ATR), in which carbon-centered radicals are added to the olefin double bond, followed by a hydrogen abstraction, are a complementary approach to the MHAT methodologies and allow the generation of anti-Markovnikov hydroalkylation products [112][113][114][115][116]. The polar complementarity

• -substituted iodides (Scheme 36B). The radical addition of the electron-poor carbon-centered radical formed to the olefin double bond then leads to another radical intermediate that, after hydrogen abstraction from TBC, affords 92. The ethyl and the α-EWG-substituted radicals formed in the initial steps could

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

• irreversible one-electron oxidation at 0.80 V, in accordance with the involvement of oxygen in the reaction. Remarkably, when the glutarimide was labeled with deuterium in position 3, the deuterium labeling was transferred to the hydrocarbon liberated in the reaction, showing that hydrogen abstraction was

• carried out by the alkyl residue lost from C-4. Based on these observations, a mechanism was proposed, triggered by hydrogen abstraction from C-3 by oxygen (Scheme 5). The stabilized radical generated in this way acts then as a chain carrier, aromatizing by loss of one of the alkyl residues at C-4. In

• turn, this next abstracts hydrogen at C-3, regenerating the carrier and continuing the cycle. The C–H bond at position 3 of Guareschi imides is unusually weak. Hydrogen abstraction by an alkyl radical and formation of a hydrocarbon C–H bond is strongly exothermic (calculated enthalpy change: ≈20 kcal

Heterogeneous photocatalytic cyanomethylarylation of alkenes with acetonitrile: synthesis of diverse nitrogenous heterocyclic compounds

• Guanglong Pan,
• Qian Yang,
• Wentao Wang,
• Yurong Tang and
• Yunfei Cai

Beilstein J. Org. Chem. 2021, 17, 1171–1180, doi:10.3762/bjoc.17.89

• radical A. The subsequent hydrogen abstraction by radical A yields the key alkyl radical B. The addition of radical B or A to the alkene 7a following by an intramolecular cyclization provides the radical intermediates C or E, which are oxidized by the hole of CN-K via SET delivering the product 8a or

Manganese/bipyridine-catalyzed non-directed C(sp³)–H bromination using NBS and TMSN₃

• Kumar Sneh,
• Takeru Torigoe and
• Yoichiro Kuninobu

Beilstein J. Org. Chem. 2021, 17, 885–890, doi:10.3762/bjoc.17.74

• gram scale. The introduced bromine atom can be converted into fluorine and allyl groups. Keywords: bromination; C–H transformation; hydrogen abstraction; manganese; radical; Introduction Organic halides are versatile precursors for various synthetic protocols and are frequently used to introduce a

• homolytic cleavage of the weak Br–N3 bond in bromine azide [54][55]; (3) the bromine radical can also be generated from NBS with the formation of a succinimide radical; (4) alkyl radical intermediate A is then formed via hydrogen abstraction by the succinimidyl radical and/or azidyl radical [56][57]; (5

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• hydrogen abstraction and protodeauration with HOTf. Triflate-mediated abstraction of the hydrogen atom Ha and protodeauration. Synthesis of the enynyl acetate starting material 14. Synthesis and cyclization of enynyl acetate 20. Gold(I)-catalyzed [3,3]-rearrangement/Nazarov reaction of 14.a Supporting

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• catalytic amount of tributylstannane [40] led to a radical cyclization, in which the resultant alkyl radical formed was trapped by AIBN to give a proposed nitrogen-centered radical 70. An 1,4-hydrogen abstraction of the nitrogen-centered radical on 70 produced carbon-centered radical 71, which underwent

Metal-free synthesis of phosphinoylchroman-4-ones via a radical phosphinoylation–cyclization cascade mediated by K₂S₂O₈

• Qiang Liu,
• Weibang Lu,
• Guanqun Xie and
• Xiaoxia Wang

Beilstein J. Org. Chem. 2020, 16, 1974–1982, doi:10.3762/bjoc.16.164

• bond of 1 to generate a new carbon-centered radical II, with sequential attack on the aldehyde group. The oxygen radical III thus formed undergoes a formal 1,2-H shift to generate the benzyl radical IV [45][46]. Finally, hydrogen abstraction by the sulfate radical anion (SO4•−) from the benzyl radical

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• by homolysis of diphenyl disulfide under visible light triggers the HAT-initialized pathway 1. The hydrogen abstraction from the Hantzsch ester 44 by the thiyl radical 43 gives the ester radical 45. Then, the subsequent SET from the Hantzsch ester radical 45 to the acetamide 46 forms the amide

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

• intermediate, 4,5-dihydro-1,2,4-oxadiazole. An example of such intermediate 74 is shown in Scheme 27. Oxidative aromatization of 74 leads to 1,2,4-oxadiazole 72a (Scheme 26). The second pathway, hydrogen abstraction followed by β-scission presumably leads to iminyl radical, which forms the observed

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• one of the residual fragments produced by the N–O homolytic cleavage is a carboxylic or a sulfonic acid, generated upon hydrogen abstraction from the corresponding oxygen centred radicals, carbonyloxyl and sulfonyloxyl, respectively. Some are used in the field of photoresists for semiconductor

Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition

• Yulia V. Khoroshunova,
• Denis A. Morozov,
• Andrey I. Taratayko,
• Polina D. Gladkikh,
• Yuri I. Glazachev and
• Igor A. Kirilyuk

Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200

• signals of carbon atoms in the 1H,13C-HSQC spectra allowed us to assign these signals to an isolated CH2–CH2 system. All these findings unambiguously support the assignment of structure 18 to the isolated alkoxyamine and structure 17 to the corresponding nitroxide. Therefore, 17 is formed due to hydrogen

• abstraction in the spirocyclopentane ring. To the best of our knowledge, similar transformations have never been observed before. Presumably, formation of 17 occurs due to the close proximity of the N+=O group (in the intermediate strained oxoammonium cation) to the hydrogen atom of an adjacent methylene

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• thought to be involved in hydrogen abstraction and oxidation of CuBr to Cu2O. The presence of EW and EDGs on both 2-APs and cinnamaldehyde supported the forward reaction whereas the reaction got failed with aliphatic aldehydes. The reaction mechanism involved the formation of radical intermediates and

• the formation of radical intermediates, as use of TEMPO inhibited intramolecular C(sp3)–H amination of imine species. Aerial oxidation of the Cu(I) species bonded to the N-atom of pyridine and imine 39 resulted in Cu(II) superoxo radical intermediate 40. This was followed by intramolecular hydrogen

• abstraction from the sp3 carbon atom leading to the formation of six-membered Cu(III) species 42. Furthermore, consecutive isomerization/oxidation/reductive elimination leads to the generation of final compound 37 with regeneration of the Cu(I) catalyst (Scheme 14). The presence of EDGs as compared to EWGs on

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

• radical, which forms an OH bond of 88 kcal/mol upon hydrogen abstraction (Figure 7) [63], will preferentially attack the weaker C–H bonds at the benzylic carbon, forming a relatively stable benzylic radical, rather than C–H bonds with stronger bond dissociation enthalpy values. The formed benzylic

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

• AgNO3 and K2S2O8. The radical 98 undergoes a ring-opening to give the alkyl radical 99. Finally, the radical 99 is intercepted by NCS 118 to furnish the chlorinated ketone 119. The generated imidyl radical 120 can also participate in hydrogen abstraction of cyclopropanol 91 to form the radical 98. In

N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

• Fabienne Speck,
• David Rombach and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 52–59, doi:10.3762/bjoc.15.5

• unproductively consumes electrons while oxidizing triethylamine, the hydrogen abstraction pathway generates the reduced phenylethane, which is observed in small concentrations in the reaction mixture. The analysis of the reaction mixture still showed some unreacted starting material. Assuming the first electron

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

• in the literature using the CARET additive for photopolymerization of EPOX. CARET is depicted in Scheme 7. This compound has exactly the same mechanism of reaction than EDB. There is first a hydrogen abstraction on the compound followed by a reaction with the iodonium salt into the photoredox

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• and cleave the Co(III)–C bond of the B12 coenzyme B12 in a homolytic fashion to produce an adenosyl radical [52][53]. In methylmalonyl-CoA mutase (MMCM), the conversion from R-methylmalonyl-CoA to succinyl-CoA (Scheme 1a) starts with hydrogen abstraction by the adenosyl radical. 2-1. Electrochemical

Selective carboxylation of reactive benzylic C–H bonds by a hypervalent iodine(III)/inorganic bromide oxidation system

• Toshifumi Dohi,
• Shohei Ueda,
• Kosuke Iwasaki,
• Yusuke Tsunoda,
• Koji Morimoto and
• Yasuyuki Kita

Beilstein J. Org. Chem. 2018, 14, 1087–1094, doi:10.3762/bjoc.14.94

• reactive than the bromo radical and a large-size effect of the hypervalent iodine species establishes the selectivity over the electronically favored tertiary radical formation. A similar trend in the secondary-preferential hydrogen abstraction at the sp3 carbons was recently reported by Maruoka and co