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

• by chemists. In the radical fluorination, C–F bonds are produced by carbon-based radicals (generated in situ by various methods) with "atomic fluorine" sources, such as XeF2, hypofluorite, or molecular fluorine (Scheme 1c). Notably, transition metals are not biased to one reaction class, and the same

• (Scheme 60). Also, mechanistic studies, a radical clock experiment, revealed the intermediacy of −Cu(CF3)3Me, which undergoes reductive elimination and subsequent oxidation to give the active species Cu(CF3)2. Meanwhile, aliphatic carboxylic acids give the corresponding alkyl radicals via Ag(II)-mediated

• oxidative decarboxylation. Then, Cu(CF3)2 provides a CF3 group to alkyl radicals to obtain the final product. Very recently, MacMillan et al. [120] discovered an efficient approach to the decarboxylative trifluoromethylation of aliphatic carboxylic acids via the combination of photoredox and copper

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• [TCNQ]−· radical anion, dragging the second [TCNQ]− near to the cavity by the help of the electrostatic stabilization supplied by the 1,2,3-triazolium cations, coupling of the two [TCNQ]−· anion radicals in the cavity and rapid formation of the sigma-connected dimer, reduction of the photogenerated

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

• radicals [1]. Introduction of spirocyclic moieties has a smaller effect on the reduction rates of nitroxides than the introduction of linear alkyl substituents does; however, spirocyclic nitroxides may have much longer spin relaxation times at 70–125 K [3] and even at room temperature [4]. The latter

• group of the cyclopentane ring (Scheme 7). The ester groups in 11a–c were easily cleaved in an aqueous–methanol solution of ammonia. Nitroxides 12a–c were isolated as orange compounds moderately soluble in water. Overall yields of these radicals via the acylation–oxidation–deprotection pathway were in

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• for the generation of carbon radicals via single-electron transfer (SET). In 2016, Barriault and co-workers reported a methodology that features the utilization of dimeric gold complex [Au2(dppm)2]Cl2 and ultraviolet A (UV, 365 nm) light to direct arylation of bromide-substituted butenolides or cyclic

Vicinal difunctionalization of alkenes by four-component radical cascade reaction of xanthogenates, alkenes, CO, and sulfonyl oxime ethers

• Shuhei Sumino,
• Takahide Fukuyama,
• Mika Sasano,
• Ilhyong Ryu,
• Antoine Jacquet,
• Frédéric Robert and
• Yannick Landais

Beilstein J. Org. Chem. 2019, 15, 1822–1828, doi:10.3762/bjoc.15.176

• functionalities, have the potential for further elaboration. Keywords: CO; multicomponent reaction; radicals; sulfonyl oxime ethers; xanthogenates; Introduction Multicomponent reactions constitute a powerful and highly efficient tool in organic synthesis to build up intricate compounds from simple molecules in

• /acceptor type C1 synthons [6][7][8][9][10][11][12][13][14][15]. In this context, sulfonyl oxime ethers are powerful acceptors of type C1 synthon [8][16][17], which terminates the multicomponent reaction by a β-scission of RSO2 radicals [18][19][20]. Recently, one of us reported on a three-component radical

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

Insertion of [1.1.1]propellane into aromatic disulfides

• Robin M. Bär,
• Gregor Heinrich,
• Martin Nieger,
• Olaf Fuhr and
• Stefan Bräse

Beilstein J. Org. Chem. 2019, 15, 1172–1180, doi:10.3762/bjoc.15.114

• , which was opened with free radicals in most cases. The reaction with diacetyl and subsequent oxidation leads to the important intermediate bicyclo[1.1.1]pentane-1,3-dicarboxylic acid which provides access to unsymmetrically substituted BCPs (not shown) [13]. It is assumed that the reaction of 1 with

• thiyl radicals is critical to the reaction and most aliphatic disulfides do not absorb UV light at the used wavelength, radical initiators should be taken into account for other disulfides. However, for 12 the reaction was successful without radical initiator and the BCP 13 was obtained as the main

• ]. Presumably, there are two factors contributing to the lowered yield. The bond dissociation energy (BDE) of dialkyldisulfides is higher than the BDE of diaryl disulfides [30]. Therefore lower concentrations of thiyl radicals are present to initiate the reaction. The second reason could be the absorption of

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells

• Ayato Yamada,
• Manabu Abe,
• Yoshinobu Nishimura,
• Shoji Ishizaka,
• Masashi Namba,
• Taku Nakashima,
• Kiyofumi Shimoji and
• Noboru Hattori

Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84

• counterparts (65.8% vs 85.5%). Keywords: caged compound; nitroxide; photolysis; radical; theranostics; two-photon; Introduction Nitroxides (aminoxyl radicals) possess a delocalized unpaired electron and exhibit negligible dimerization reactivity, making them persistent open-shell species [1][2][3][4]. In

• new caged nitroxides (nitroxide donors) 2a and 2b having the TP-responsive NPBF chromophore and the NIR TP-triggered generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical under atmospheric conditions using these species (Scheme 1). Because free radicals are cytotoxic due to their

• strong DNA-damaging activity [65], they play important roles as anticancer therapeutic agents [66]. Among the free radicals, nitroxides including the TEMPO radical have unique properties, where they can act not only as radical scavengers, but also as anticancer agents [67]. Due to the unique properties

A diastereoselective approach to axially chiral biaryls via electrochemically enabled cyclization cascade

• Hong Yan,
• Zhong-Yi Mao,
• Zhong-Wei Hou,
• Jinshuai Song and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2019, 15, 795–800, doi:10.3762/bjoc.15.76

• -centered radicals (NCRs) are attractive reactive intermediates for organic synthesis as they provide opportunities for the efficient construction of C–N bonds [15][16][17][18][19]. Recently, the generation of NCRs through electron transfer-based methods has been attracting attention. Organic

Synthesis of polydicyclopentadiene using the Cp₂TiCl₂/Et₂AlCl catalytic system and thin-layer oxidation of the polymer in air

• Zhargolma B. Bazarova,
• Ludmila S. Soroka,
• Alex A. Lyapkov,
• Мekhman S. Yusubov and
• Francis Verpoort

Beilstein J. Org. Chem. 2019, 15, 733–745, doi:10.3762/bjoc.15.69

• gradually happen during the exposure time of polydicyclopentadiene thin layers in the air as a result of the oxidation of double bonds. A new vibrational band at 1410 cm−1 in the IR spectrum appears which is originating from the primary radicals which are formed alongside the chain initiation. The kinetics

• deformation vibrations and the layer exposure time in air at ambient temperature. The correlation presented in Figure 10 demonstrates that the kinetics of double bond consumption during oxidation occurs in two stages. During the first stage, the chain (formation of primary radicals) initiates, and then the

• chain process of PDCPD oxidation follows. Various mechanisms of chain initiation are possible, e.g., the formation of primary free radicals initiating the chain reaction of polymer oxidation (Equation 1). More often, the chain initiation step is described as a bimolecular interaction between oxygen and

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• % yield) and other compounds evidence the participation of radicals [30]. After the efficient conversion of pyrimidine N-oxide PO14 into pyrimidine PM63 no products of this type were isolated. The regioselectivity is another important feature of the Boekelheide rearrangement if alkyl groups are present at

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

• -iodate system is functioning by a radical-based mechanism where iodine generated in situ captures formed benzylic radicals. The benzylic iodide intermediate then solvolyzes to yield the product ester. Keywords: acetoxylation; benzylic; iodate; NHPI; oxidation; radical; Introduction The ability to

• dyes and transition metal complexes, hypohalous acids, and persulfate anions [12][34][35][36][37][38][39][40]. An important class of catalyzed benzylic C–H to C–O transformations are those catalyzed by N-oxyl radicals. Specifically, N-oxyl radical catalysts based upon the N-hydroxyphthalimide (NHPI

• oxidations occur via a radical pathway mediated in part by chlorine radicals [51]. While the chloride-iodate system was effective in the functionalization of light hydrocarbons and certain model compounds, it exhibited poor functional group tolerance. Oxidation of complex hydrocarbons led to a mixture of

Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions

• Nicholas L. Reed,
• Madeline I. Herman,
• Vladimir P. Miltchev and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30

• combines the photoredox activation of electron-rich alkenes with copper(II)-mediated oxidation of electron-rich radicals as described by Kochi [18][19][20]. These studies resulted in the development of a general new protocol for oxyamination (Figure 1a) and diamination (Figure 1b) of alkenes. The mechanism

• with ground-state dioxygen to afford unstable hydroperoxy radicals that can also decompose unproductively [32][33]. Indeed, in our previous study of photocatalytic alkene difunctionalization, we found that dioxygen and similar commonly used terminal oxidants resulted in unproductive decomposition of

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

• of sufficient interest for the scientific community to further advance the application of oxidative radical strategies in the ring-opening/cyclization of cyclopropane derivatives. Keywords: cyclopropane derivatives; free radicals; ring-opening/cyclization; Introduction Cyclopropane is a cycloalkane

• 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

• -containing radicals, were introduced into the products through oxidative radical ring-opening/cyclization of cyclopropane derivatives. In this review, we conclude recent advance in the oxidative radical ring-opening/cyclization of cyclopropane derivatives (including methylenecyclopropanes, cyclopropyl

Adhesion, forces and the stability of interfaces

• Robin Guttmann,
• Johannes Hoja,
• Christoph Lechner,
• Reinhard J. Maurer and
• Alexander F. Sax

Beilstein J. Org. Chem. 2019, 15, 106–129, doi:10.3762/bjoc.15.12

• 950 kJ/mol (N2), and 3) metallic interactions ranging between 65 kJ/mol (Hg) and 850 kJ/mol (W). Ionic and metallic interactions are the interactions in extended systems, mostly solids, whereas covalent interactions are between molecular subsystems (fragments, radicals) at localized positions, mostly

A convenient and practical synthesis of β-diketones bearing linear perfluorinated alkyl groups and a 2-thienyl moiety

• Ilya V. Taydakov,
• Yuliya M. Kreshchenova and
• Ekaterina P. Dolotova

Beilstein J. Org. Chem. 2018, 14, 3106–3111, doi:10.3762/bjoc.14.290

• , Moscow Region, Russian Federation D. Mendeleev University of Chemical Technology of Russia, Miusskaya sq. 9, 125047 Moscow, Russian Federation 10.3762/bjoc.14.290 Abstract A versatile and robust synthetic protocol for the preparation of β-diketones bearing 2-thienyl and perfluorinated alkyl radicals of

• ]. Diketones bearing perfluorinated radicals are very important for the design of highly effective luminescent materials based on lanthanide coordination compounds. Substitution of aliphatic radicals by perfluorinated ones in the molecules of ligands led to a significant increase in luminescence intensity due

• ). To the best of our knowledge, β-diketones with heavier linear perfluorinated radicals (C4–C8) are unknown. During the ongoing project, we needed to synthesize a family of 2-thienyl diketones with various lengths of a perfluorinated side chain. Here we intend to report a versatile and robust practical

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

• proceeds through a radical chain mechanism, and thus requires an initial formation of carbon radicals A that add onto olefins 2. The subsequent reaction of the resulting alkyl radicals B with xanthates 1 provides xanthate adducts 3 with generation of carbon radicals A that maintain the radical chain

• , giving 3hb in 69% yield (Table 3, entry 7). This method is also suitable for generating α-aminoalkyl radicals from phthalimidomethyl and succinimidomethyl xanthates [64], as well as α-trifluoromethylamino xanthate 1k [65] to afford desired products 3ib–kb in good to moderate yields (Table 3, entries 8–10

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

• with the monomer or a monomer blend. The PI is a component which absorbs light and initiates polymerization alone whereas a photoinitiating system comprises different compounds [8][9][10]. Under irradiation, PI or PIs generate active species: free radicals and/or ions and/or acid. When the active

• catalytic cycles used in organic chemistry, the development of photoredox catalysis for photopolymerization reactions has been proposed. It has emerged as a significant innovation in the field of photoinitiated polymerization. Photoredox catalysis is a new strategy to generate radicals and/or cations upon

• named reduction agent, RA2 in Figure 1) by a redox reaction. In a reductive cycle, the PC* reacts first with a reduction agent (in Figure 1, RA1) which leads to PC●− and RA1●+. Then, PC can be regenerated with an oxidation agent (OA2). Radicals and cations are generated in these cycles [16]. As we can

An overview on recent advances in the synthesis of sulfonated organic materials, sulfonated silica materials, and sulfonated carbon materials and their catalytic applications in chemical processes

• Hashem Sharghi,
• Pezhman Shiri and
• Mahdi Aberi

Beilstein J. Org. Chem. 2018, 14, 2745–2770, doi:10.3762/bjoc.14.253

• carbonyl of acetylacetone 90 to form enamine intermediate II. In the next step, hydroxyl radicals are produced through activation of molecular oxygen in the presence of SSA. Intermediate III is created via the addition of a hydroxyl radical to enamine II. This intermediate loses hydrogen radical to form

• intermediate IV. Finally, this intermediate is split by a nucleophilic attack of hydroxyl radicals to afford byproducts (including acetic acid, acetanilide, and formic acid) and desired product. The proposed mechanism was confirmed by EPR spectrum. The SSA catalyst is an inexpensive and reusable solid acid

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 has an unpaired electron in the axial dz2 orbital. It acts as a high efficient “radical trap” and reacts with alkyl radicals to yield alkylcob(III)alamin (Figure 1b). Four-coordinated cob(I)alamin has a paired electron in the axial dz2 orbital, resulting in high nucleophilicity with a Pearson

• ligand. B12 is reduced to Co(I) species in the active center by reductases in sustainable processes. The partially π-conjugated system of the corrin ring is less easy to be adducted by free radicals than those of porphyrins. B12 is bound to a number of proteins and acts as a module. Different chemical

• (II) species and an alkyl radical intermediate A [54]. The prolonged lifetime of the radical intermediate A could be provided by the channel of MOF, enabling conversion to the acetyl-migrated radical B. The radicals A and B may abstract hydrogen radicals to form the reduced product and the acetyl

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

• Amrita Das,
• Mitasree Maity,
• Simon Malcherek,
• Burkhard König and
• Julia Rehbein

Beilstein J. Org. Chem. 2018, 14, 2520–2528, doi:10.3762/bjoc.14.228

• cleavage has been reported for alkyl and aryl disulfides in an oxidative [44][45][46] and triplet sensitized mechanism [47]. It is also well known in literature that aromatic disulfides are cleaved homolytically under UV irradiation yielding the corresponding radicals [48]. A recent study from Nicewicz

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• have also been obtained (TiCl4/Zn [12][13][14][15][16][17] or TiCl3/Zn-Cu [18][19][20]), often as mixture of diastereomers. The use of samarium diiodide to achieve the pinacol coupling was not advised, since we had observed that intially formed ketyl radicals would add to the alkyne moiety [11], even

Cobalt bis(acetylacetonate)–tert-butyl hydroperoxide–triethylsilane: a general reagent combination for the Markovnikov-selective hydrofunctionalization of alkenes by hydrogen atom transfer

• Xiaoshen Ma and
• Seth B. Herzon

Beilstein J. Org. Chem. 2018, 14, 2259–2265, doi:10.3762/bjoc.14.201

• , and medicinal chemistry [56][57], we investigated the scope of this transformation (Scheme 3). By varying the alkene substitution pattern, we determined that the coupling of tertiary radicals is more efficient than secondary radicals. For example, methallyl p-methoxybenzoate (3a) and prenyl p

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• molecular switch. A first one-electron oxidation [23] converts neutral TTF (1) into the radical-cationic species 1●+ (Figure 1). The TTF radical cation is one of the rare organic radicals that are long-term stable and even isolable. A second oxidation step yields the dication 12+. Both redox-transitions are

• paramagnetic radicals, the resulting dimer has a diamagnetic character due to radical pairing. Although the distance of ≈3.5 Å between the two 1●+ molecules in the dimer is considerably large in comparison to a C–C bond (≈1.5 Å), the interaction can be considered as a type of multi-centered two-electron bond

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

• . It was shown that the iodine atom in the prepared iodo-oxyimides can be substituted by various nucleophiles. Keywords: free radicals; hypervalent iodine; imide-N-oxyl radicals; iodination; N-hydroxyimides; oxidative functionalization; Introduction The presented work opens a new chapter in the

• chemistry of N-hydroxyimides in combination with hypervalent iodine compounds with formation of imide-N-oxyl radicals. These radicals were used as reagents for the addition to a terminal position of the double bond of styrenes with subsequent iodination of the resulting benzylic radical. It is important to

• note, that nitroxyl radicals are widely used in organic and biological chemistry, and in material design [1][2][3]. These radicals are applied in the development of monomolecular magnets [4][5], spintronics [2][6], magneto-LC effect studies [7][8], organic voltaic cells [9], electrodes for