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

Chlorination of phenylallene derivatives with 1-chloro-1,2-benziodoxol-3-one: synthesis of vicinal-dichlorides and chlorodienes

• Zhensheng Zhao and
• Graham K. Murphy

Beilstein J. Org. Chem. 2018, 14, 796–802, doi:10.3762/bjoc.14.67

• intermediate E, which then abstracted a chlorine atom from a second equivalent of 1b, giving dichlorides 3. Or, in the case of α-alkyl groups, intermediate E was also subject to a competing hydrogen abstraction pathway, resulting in mixtures of 3 and chlorodienes 4. Conclusion In conclusion, we report here an

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

• be increased. To overcome this limitation, anilines were used as redox mediators, which are first oxidized by the photocatalyst and subsequently activate the aliphatic thiol via direct hydrogen abstraction or sequential electron- and proton-transfer steps. With this concept they were now able to

• reduction of tert-butyl hydroperoxide (TBHP) to form a reactive tert-butoxyl radical. After hydrogen abstraction from the sulfinic acid and subsequent radical addition to the alkyne derivative, consecutive steps for rearomatization lead to the cyclic coumarin adduct. The authors used various electron

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• species 7 then underwent an aryl migration/desulfonylation cascade reaction to furnish intermediate 8. In the case of an aryl substituted substrate, this nitrogen radical being stabilised, it directly performed an hydrogen abstraction on acetonitrile to lead to the corresponding α-aryl-β-trifluoromethyl

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

• ) 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

• abstraction is effected by a species other than the chlorine radical Cl·, presumably PhICl· [26][27]. One potential attraction of fluorous iodine(III) dichlorides as chlorinating agents would be the recovery and recycling of the fluorous iodide byproduct. Towards this end, higher fluorophilicities are usually

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

• 4-methoxy-TEMPO radical by oxygen. W gets stabilized by the imine moiety to form the corresponding amine radical X′′. The second hydrogen abstraction between X′′ and 4-methoxy TEMPO/oxygen facilitates the aromatization to afford the desired compounds (Scheme 38). In another example 4-hydroxy-TEMPO

• phthalimide-N-oxyl radical (PINO) via transfer of hydrogen from NHPI to O2. Co2+-assisted this step by associating with oxygen to generate a Co3+–oxygen complex. It then abstracts the hydrogen from NHPI. Next, PINO abstracted a hydrogen from the DHP produced to generate radical X which aromatizes via hydrogen

• abstraction by PINO and/or the Co3+–oxygen complex to provide the pyridine derivatives (Scheme 21). One of the other noteworthy examples is a copper chloride/1,4-diazabicyclo[2.2.2]octane (DABCO) and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-catalyzed aerobic oxidative dehydrogenation approach

Kinetic analysis of mechanoradical formation during the mechanolysis of dextran and glycogen

• Naoki Doi,
• Yasushi Sasai,
• Yukinori Yamauchi,
• Tetsuo Adachi,
• Masayuki Kuzuya and
• Shin-ichi Kondo

Beilstein J. Org. Chem. 2017, 13, 1174–1183, doi:10.3762/bjoc.13.116

• generated by subsequent radical reactions such as hydrogen abstraction and/or recombination after polymer main-chain scission, could be assigned to alkoxylalkyl-type radicals at the C1 and acylalkyl-type radicals at the C2 and/or C3 positions. Therefore, these observed mechanoradicals were mid-chain

• approximately 95% α-D-1,6-linkages, which form a straight chain, and 5% α-1,3-linkages, from which branches begin, as shown in Figure 2 [8][9][10]. The grafting of synthetic polymers onto Dx has generally been carried out using oxygen-based radicals produced via a hydrogen abstraction method (e.g., radical

• would be initially generated by α-1,4- and/or α-1,6-bond cleavage in the course of vibratory milling. Subsequently the mechanoradicals could undergo a following reaction, such as hydrogen abstraction to generate other types of radicals. Thus, the differences in the spectral patterns of amylose, Dx, and

Highly reactive, liquid diacrylamides via synergistic combination of spatially arranged curing moieties

• Maximilian Maier,
• Magnus S. Schmidt,
• Markus Ringwald and
• Christoph P. Fik

Beilstein J. Org. Chem. 2017, 13, 372–383, doi:10.3762/bjoc.13.40

• ]. Yet, acrylamides are particularly affected by the solvent regarding propagation reaction in free radical polymerization, even more so, if water is present [21]. Factors such as hydrogen bonding, hydrogen abstraction and the overall electronic characteristics are crucial in the design of improved

Cyclisation mechanisms in the biosynthesis of ribosomally synthesised and post-translationally modified peptides

• Andrew W. Truman

Beilstein J. Org. Chem. 2016, 12, 1250–1268, doi:10.3762/bjoc.12.120

• to differ slightly as it is unlikely that either carbon initially bonds to this cluster (Figure 10B). Instead, a radical on the lysine β-carbon (generated by 5’-dA• hydrogen abstraction) attacks C-7 on the tryptophan ring. This generates an indolyl radical that can lose an electron to the second [4Fe

Biradical vs singlet oxygen photogeneration in suprofen–cholesterol systems

• Fabrizio Palumbo,
• Francisco Bosca,
• Isabel M. Morera,
• Inmaculada Andreu and
• Miguel A. Miranda

Beilstein J. Org. Chem. 2016, 12, 1196–1202, doi:10.3762/bjoc.12.115

• photoproducts 4 and 5, respectively. By contrast, under the same conditions, 3 did not give rise to any isolable Ch-derived product. These results point to an intramolecular hydrogen abstraction in 1 and 2 from the C7 position of Ch and subsequent C–C coupling of the generated biradicals. Interestingly, 2 was

• singlet oxygen, thus being able to initiate Ch oxidation from their triplet excited states following either of the two competing mechanistic pathways. Keywords: aryl ketones; hydrogen abstraction; lipid peroxidation; photoproducts; triplet excited state; Introduction Among the constituents of cell

• from inflammation to cardiovascular and Alzheimer diseases [1][2]. This type of damage can be induced via free radicals or singlet oxygen (1O2) [3][4]. The former generally involves hydrogen abstraction (HA) of an allylic hydrogen and can be achieved by photosensitizing agents in combination with UVA

From steroids to aqueous supramolecular chemistry: an autobiographical career review

• Bruce C. Gibb

Beilstein J. Org. Chem. 2016, 12, 684–701, doi:10.3762/bjoc.12.69

• -chlorosteroid via internal hydrogen abstraction (Scheme 3). It was not that I was trying to make 9-halogeneated derivatives, or indeed do anything remotely analogous to what Breslow was accomplishing. It was simply that having worked with steroids for a couple of years I appreciated that they really are just a

Solving the puzzling competition of the thermal C²–C⁶ vs Myers–Saito cyclization of enyne-carbodiimides

• Anup Rana,
• Mehmet Emin Cinar,
• Debabrata Samanta and
• Michael Schmittel

Beilstein J. Org. Chem. 2016, 12, 43–49, doi:10.3762/bjoc.12.6

• realistic option for an intramolecular γ-hydrogen abstraction via a six-membered transition state if the diradical is thermally generated. From the computations (vide infra) we conclude that the thermal cyclization of enyne-carbodiimides 7 follows a concerted mechanism along the C2–C6 (Schmittel) channel

• (ΔG‡ = 36.1 kcal mol−1) and the second possibility an intramolecular β–H abstraction via 7c_TSβHT (ΔG‡ = 39.9 kcal mol−1). As a consequence, enyne-carbodiimide 7c preferentially cyclizes via the C2–C6 pathway to 9cDA, because the Myers–Saito route with its rate-limiting γ- or β-hydrogen abstraction

• terminus. For any suitable candidate the intermediate Myers–Saito diradical should undergo intramolecular hydrogen abstraction at a lower barrier than that of the concerted C2–C6 cyclization. In order to realize a facile intramolecular H-abstraction in the Myers–Saito diradical via a 6-membered transition

Pyridine-promoted dediazoniation of aryldiazonium tetrafluoroborates: Application to the synthesis of SF₅-substituted phenylboronic esters and iodobenzenes

• George Iakobson,
• Junyi Du,
• Alexandra M. Z. Slawin and
• Petr Beier

Beilstein J. Org. Chem. 2015, 11, 1494–1502, doi:10.3762/bjoc.11.162

• configuration) and 6i in 16:31:28:25 GC–MS ratio. The presence of these products can be explained only by the formation of the substituted SF5-phenyl radical which undergoes borylation to 2i, hydrogen atom transfer followed by borylation to 2i’, intramolecular cyclization to 5i or hydrogen abstraction to 6i

• from intermolecular competition experiment using 3b and a 1:1 mixture of THF and THF-d8 giving KIE = 5.5 (6:6-D ratio determined by GC–MS) and combined yield of 62%. This means that the hydrogen abstraction is much faster than the deuterium abstraction and suggests the C-H(D) bond formation as the rate

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

Multicomponent versus domino reactions: One-pot free-radical synthesis of β-amino-ethers and β-amino-alcohols

• Bianca Rossi,
• Nadia Pastori,
• Simona Prosperini and
• Carlo Punta

Beilstein J. Org. Chem. 2015, 11, 66–73, doi:10.3762/bjoc.11.10

• the corresponding alkoxy radical (Scheme 4, reaction 4). The latter undergoes hydrogen abstraction from the C–H bond of THF in the α-position of the oxygen (Scheme 4, reaction 5). This promotes the formation of a carbon-centered nucleophilic radical, which in turn quickly adds to the activated carbon

Visible light photoredox-catalyzed deoxygenation of alcohols

• Daniel Rackl,
• Viktor Kais,
• Peter Kreitmeier and
• Oliver Reiser

Beilstein J. Org. Chem. 2014, 10, 2157–2165, doi:10.3762/bjoc.10.223

• reductively quenched photocatalyst followed by mesolysis and subsequent hydrogen abstraction (Scheme 4). Quantum mechanical calculations (B3LYP/6-31G*) for benzhydryl 3,5-bis(trifluoromethyl)benzoate (3) revealed that the electron density of the presumed transient radical anion is mainly located at the phenyl

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

• Christian Ley,
• Julien Christmann,
• Ahmad Ibrahim,
• Luciano H. Di Stefano and
• Xavier Allonas

Beilstein J. Org. Chem. 2014, 10, 936–947, doi:10.3762/bjoc.10.92

• spectral limitation, Type II PIS were developed. They contain the photosensitizer (PS) which absorbs the light and a coinitiator (Co) which reacts with PS excited states through hydrogen abstraction or electron transfer reaction (see Scheme 1). Numerous dyes were reported as PS [9][27][28][29][30][31][32

Visible-light-induced, Ir-catalyzed reactions of N-methyl-N-((trimethylsilyl)methyl)aniline with cyclic α,β-unsaturated carbonyl compounds

• Dominik Lenhart and
• Thorsten Bach

Beilstein J. Org. Chem. 2014, 10, 890–896, doi:10.3762/bjoc.10.86

• reduced iridium complex thus completing the catalytic cycle. However, we have not been able to substantiate the latter hypothesis, e.g., by isolation of a saturated carbonyl compound. Interestingly, we did not find a hint for a radical chain pathway, which would include hydrogen abstraction from the

• starting aniline 5 by intermediate A. The resulting radical would carry a trimethylsilyl group, which would be eventually found in the product. The absence of a trimethylsilyl group in the products indicates that reduction (path a) and cyclization (path b) are more efficient than hydrogen abstraction while

• hydrogen abstraction has been established as a radical chain propagating step in reactions performed with UV light [5][6][8][11][32][34][38][39][40]. Conclusion In summary, it was shown that a photochemical generated aminomethyl radical – produced from N-methyl-N-((trimethylsilyl)methyl)aniline – adds