Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• [3.2.1]oct-6-ene (31) were transformed into bicyclic dioxolane 33. It was suggested that both reactions proceed via the formation of 1,3-radical cation 32 (Scheme 11). Dioxolane 33 was synthesized in the highest yields (91% from 30 and 100% from 31) in acetonitrile with the use of 9,10-dicyanoanthracene

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• are emerging as a powerful tool in amine synthesis. This article reviews synthetic applications of amine radical cations produced by visible light photocatalysis. Keywords: α-amino radical; amine radical cation; catalysis; distonic ion; free radical; iminium ion; photoredox; visible light

• identification of the optimal solvent requires experimentation. Once formed, amine radical cation 2 has been shown to have four modes of reactivity. The first mode is the back electron transfer reaction, which involves amine radical cation 2 giving back one electron to M(n−1). This is a major side reaction

• /or irreversible downstream reactions of 2. The second mode involves hydrogen atom abstraction from 2 to produce iminium ion 4, when a good hydrogen atom acceptor is present in the reaction. The use of amine radical cation 2 as the source of a hydrogen radical has been applied to a number of visible

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

• for the reaction of NO3• with alkylaromatic compounds [22][23]. In the absence of any reactants the resulting radical cation 3•+ undergoes deprotonation to give benzyl radical 7, in analogy to the mechanism of the NO3•-induced oxidation of aromatic amino acids and nucleosides [10][11][12][13]. This

• intermediate radical cation has a lifetime on the nanosecond time scale [23]. It was further demonstrated that deprotonation of arylradical cations is accelerated by nitrate (NO3−) that is present in the reaction system as ‘byproduct’ of the oxidation process and as ligand in CAN, and which acts as a Brønsted

• competitive with NO3•-induced ET in these systems [7][8][24][25]. An initial ET step and formation of an intermediate radical cation 3•+ is further supported by the outcomes of the reaction of 3 with NO3• in the presence of NO2•, which will be outlined below. Formation of nitrate 4 could principally occur via

Anodic coupling of carboxylic acids to electron-rich double bonds: A surprising non-Kolbe pathway to lactones

• Robert J. Perkins,
• Hai-Chao Xu,
• John M. Campbell and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2013, 9, 1630–1636, doi:10.3762/bjoc.9.186

• not appear to be a significant competing pathway. Experimental results indicate that oxidation occurs at the olefin and that the reaction proceeds through a radical cation intermediate. Keywords: carboxylic acid; cyclization; electrolysis; free radical; kolbe; radical cation; Introduction Anodic

• spirocyclic carbocyclic systems [3], cyclic amino acid derivatives [4], cyclic ethers [5][6], and lactones [7][8]. In most of these examples, the reactions can be viewed as arising from an oxidation that forms an olefinic radical cation that is then rapidly trapped by a nucleophile. This triggers a cascade of

• electron-rich olefin was coupled to one of two competing nucleophiles, a sulfonamide and an alcohol (5). When the oxidation was run with 2,6-lutidine as a base (not shown), the reaction led to the formation of a radical cation from the electron-rich olefin followed by trapping by the alcohol nucleophile to

Mechanistic studies on the CAN-mediated intramolecular cyclization of δ-aryl-β-dicarbonyl compounds

• Brian M. Casey,
• Dhandapani V. Sadasivam and
• Robert A. Flowers II

Beilstein J. Org. Chem. 2013, 9, 1472–1479, doi:10.3762/bjoc.9.167

• radical cation, which is deprotonated readily by MeOH to form the radical under the reaction conditions [15][16]. To probe the origin of the effect of substitution on cyclization, the key step of the reaction, namely the cyclization of the β-dicarbonyl radical onto the aromatic ring, was investigated

• intermediate to the aromatic ring. Recently, Houk, MacMillan and co-workers showed that for the organo-SOMO-catalyzed oxidative α-arylation of aldehydes, the preference for the attack of the intermediate enamine radical cation on the substituted aromatic ring leading to ortho/para cyclization depends on the

• oxidation of several β-diketones and their related silyl enol ethers by CAN and the more lipophilic ceric tetra-n-butylammonium nitrate (CTAN) were measured in MeOH, MeCN and CH2Cl2 by using stopped-flow spectrophotometry [16]. In these experiments, initial oxidation of substrates generated radical cation

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• radical cation, such as DES•+, only the α protons experience an appreciable hyperfine coupling, so only these protons can acquire polarizations. In contrast, for an α (heteroatom) substituted ethyl radical, e.g., both the α and the β protons possess large hyperfine coupling constants, which are negative

• through the resulting polarization pattern. The g value of DES•+, regardless of whether it is present as a monomeric radical cation (g = 2.017 [38]) or in its dimeric form (g = 2.011 [25]), is much larger than that of the pyranyl radical TPP• (g = 2.0031 [39]), so Δg must be positive for the sulfide

• radical TPP• (between 2.5 G and 0.4 G [39], as opposed to 18–20 G for Hα in the monomeric [38] and 6.8 G in the dimeric [25] radical cation of the sulfide) in conjunction with its complicated spectral habit, which causes the polarizations to be distributed among many resonances, with concomitant decrease

Synthesis and spectroscopic properties of 4-amino-1,8-naphthalimide derivatives involving the carboxylic group: a new molecular probe for ZnO nanoparticles with unusual fluorescence features

• Laura Bekere,
• David Gachet,
• Vladimir Lokshin,
• Wladimir Marine and
• Vladimir Khodorkovsky

Beilstein J. Org. Chem. 2013, 9, 1311–1318, doi:10.3762/bjoc.9.147

• ) level by using the energies of the corresponding radical cation and anion. Thus, the first electronic transition is predicted at 401 nm (f = 0.30). It is essentially the HOMO → LUMO transition. The next five electronic transitions between 333 and 300 nm are weak (f = 0.001–0.003) and involve mostly the

New core-pyrene π structure organophotocatalysts usable as highly efficient photoinitiators

• Sofia Telitel,
• Frédéric Dumur,
• Thomas Faury,
• Bernadette Graff,
• Mohamad-Ali Tehfe,
• Didier Gigmes,
• Jean-Pierre Fouassier and
• Jacques Lalevée

Beilstein J. Org. Chem. 2013, 9, 877–890, doi:10.3762/bjoc.9.101

• of these Co_Py/Iod (or TH) combinations will be affected by different parameters: (i) their relative light absorption properties, (ii) the quantum yields of radical or radical cation formation in the singlet state (the singlet state is predominant, see above), (iii) the rate constants for reactions

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

• Maurizio Fagnoni,
• Stefano Protti,
• Davide Ravelli and
• Angelo Albini

Beilstein J. Org. Chem. 2013, 9, 800–808, doi:10.3762/bjoc.9.91

• solution) in the presence of tertiary amines allowed the accumulation of the corresponding radical anions, up to quantitative yield for polysubstituted benzenes and partially with naphthalene and anthracene derivatives. The condition for such an accumulation was that the donor radical cation underwent

• OXA due to conformational factors, in particular the steric bulk of the methyl groups. The more efficiently formed radicals scoop away traces of oxygen still present under these conditions. Likewise, in accordance with the role of amine radical cation deprotonation, is the fact that, of the two

• further tertiary amines, iPr3N causes a somewhat slower accumulation (the conformation of the radical cation is known to be less favorable for deprotonation) [48][49][50], and DABCO (for which deprotonation is impossible [51][52]) causes no detectable formation of TCB•−. Indeed, previous laser flash

Electron and hydrogen self-exchange of free radicals of sterically hindered tertiary aliphatic amines investigated by photo-CIDNP

• Martin Goez,
• Isabell Frisch and
• Ingo Sartorius

Beilstein J. Org. Chem. 2013, 9, 437–446, doi:10.3762/bjoc.9.46

• always two-step hydrogen abstractions according to Scheme 1. The source of the polarizations can be either the initially formed radical-ion pair where A•− and DH•+ are the radical anion of the sensitizer A and the radical cation of the amine DH, or a secondary pair of neutral radicals , where AH• and D

• the singlet exit channel (ε = +1). The DABCO signal appearing in absorption (Γ = +1) thus means that the g-value difference and the hyperfine coupling constant must have the same sign. For a radical ion pair, this certainly holds because the reported very high g value of the DABCO radical cation

• (2.0048 [38]) clearly exceeds the g values of all the sensitizer radical anions (between 2.0036 for XA [39] and 2.00443 for AQ [40]) and the proton hyperfine coupling constant in the DABCO radical cation must be positive. For a pair of neutral radicals, the situation is equally predictable although the

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• precursors [112]. A radical cation Cope rearrangement of 1,5-hexadiyne (129) to the 1,2,4,5-hexatetraene radical cation was initiated by oxidizing bipropargyl radiolytically in a Freon matrix at 77 K [113]. The 129→2→130 sequence, and in particular its last step, has also been used several times for the

Efficient electroorganic synthesis of 2,3,6,7,10,11-hexahydroxytriphenylene derivatives

• Carolin Regenbrecht and
• Siegfried R. Waldvogel

Beilstein J. Org. Chem. 2012, 8, 1721–1724, doi:10.3762/bjoc.8.196

• density allows a scale-up of this electroorganic synthesis. Cyclic voltammetry Cyclic voltammetry studies show that triphenylene ketal 2a gets more easily oxidized at lower potentials than subunit 1a (Figure 1). The first reversible process at Eox = 1.22 V corresponds to the oxidation of 2a to a radical

• cation [13]. This SET is followed by the irreversible oxidation at Eox = 1.70 V. According to the Nernst equation, oxidation potentials should be increased due to the insolubility of 2a in PC. Because of the insufficient solubility in this solvent, cyclic voltammograms were measured solely in ACN. The

Thiophene-based donor–acceptor co-oligomers by copper-catalyzed 1,3-dipolar cycloaddition

• Stefanie Potratz,
• Amaresh Mishra and
• Peter Bäuerle

Beilstein J. Org. Chem. 2012, 8, 683–692, doi:10.3762/bjoc.8.76

• the 2-vinylthiophene subunit at 1.15 V and 1.13 V vs Fc/Fc+, respectively. For co-oligomer 11, the oxidation potential was significantly higher (1.23 V) and indicates formation of a radical cation localized on the thiophene subunits. In the negative regime, no reduction wave for the 1,2,3-triazole

A practical microreactor for electrochemistry in flow

• Kevin Watts,
• William Gattrell and
• Thomas Wirth

Beilstein J. Org. Chem. 2011, 7, 1108–1114, doi:10.3762/bjoc.7.127

• place with an iodoarene that is oxidized at the anode. The radical cation then undergoes a reaction with the other arene to form an intermediate, followed by the loss of a second electron [23]. The solvent system consisted of acetonitrile, sulfuric acid (2 M) and acetic anhydride, which was reported to

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan

• Axel G. Griesbeck,
• Jörg Neudörfl and
• Alan de Kiff

Beilstein J. Org. Chem. 2011, 7, 518–524, doi:10.3762/bjoc.7.60

• -radiatively by back electron transfer (BET). In contrast to 10, electron transfer from the electronically excited tyrosine compound 8 is followed by oxidation of the carboxyl anion and subsequent decarboxylation to give N-phthaloyl tyramine (11). If BET from the radical cation state of 10 can be retarded (i.e

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

• Dennis Gerbig,
• David Ley,
• Hans Peter Reisenauer and
• Peter R. Schreiner

Beilstein J. Org. Chem. 2010, 6, 1061–1069, doi:10.3762/bjoc.6.121

• insertions. Attempted generation of 5 and d-5 as well as their corresponding insertion products. Proposed mechanism for the generation of 8 and 9. The [1,2]H-tunneling process apparently cannot compete with C–H-insertion (τ1/2: half-life). Decay of the 2,3-dihydrobenzofuran-3-ol molecular radical cation (8

Redox-active tetrathiafulvalene and dithiolene compounds derived from allylic 1,4-diol rearrangement products of disubstituted 1,3-dithiole derivatives

• Filipe Vilela,
• Peter J. Skabara,
• Christopher R. Mason,
• Thomas D. J. Westgate,
• Asun Luquin,
• Simon J. Coles and
• Michael B. Hursthouse

Beilstein J. Org. Chem. 2010, 6, 1002–1014, doi:10.3762/bjoc.6.113

• the thione causes the oxidation to occur at a higher potential in 3 than in 27. In TTF derivative 25 the two characteristic reversible single electron redox waves, arising from the step-wise formation of the TTF radical cation and dication, are seen at +260 mV and +720 mV, respectively. The formation

Aromatic and heterocyclic perfluoroalkyl sulfides. Methods of preparation

• Vladimir N. Boiko

Beilstein J. Org. Chem. 2010, 6, 880–921, doi:10.3762/bjoc.6.88

• [35]. Another method of catalytic generation of RF• radicals involves electron-transfer from a nucleophile to a perfluoroalkyl halide, in this case using the dimethyl dipyridinium salt (methylviologen, MV2+) as a catalyst. This dication is initially reduced to a radical cation, which then transfers an

• the rate determining step of the process [189] (Scheme 49). This dual influence of sulfur dioxide contributes to the overall efficiency of these reactions. By comparing the possibility of two mediators (SO2 and MV), Koshechko et al., [202] have shown that the radical cation MV+• (Ep = −0.4 V) easily

EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

• Giorgio Bencivenni,
• Riccardo Cesari,
• Daniele Nanni,
• Hassane El Mkami and
• John C. Walton

Beilstein J. Org. Chem. 2010, 6, 713–725, doi:10.3762/bjoc.6.84

• )-cyclohexa-2,5-dienone) and much dark-coloured polymer [31]. The EPR spectrum showed the radical cation of Variamine blue (11b+•) plus broad signals which we attributed to oligomer and/or polymer radical cations (Scheme 2). When anhydrous AlCl3 in DCM – instead of the gallium halide – was added to a solution

• Azides 1, 6 and 7 were chosen to vary the electronic properties and leaving group abilities of 4-substituents. We showed previously that treatment of phenyl azide 1 with GaCl3 gave well-resolved spectra of 4-aminodiphenylamine radical cation (11a+•, the dimer) and of the trimer under different reaction

• those of 11a+• (Table 1, entry for 1 with GaCl3) except that the smaller hfs were not resolved. Minor differences in the magnitudes of the hfs can be attributed to the different counter ions. The trimer radical cation was not observed, but clearly a contribution from this species could be hidden under

Structure and reactivity in neutral organic electron donors derived from 4-dimethylaminopyridine

• Jean Garnier,
• Alan R. Kennedy,
• Leonard E. A. Berlouis,
• Andrew T. Turner and
• John A. Murphy

Beilstein J. Org. Chem. 2010, 6, No. 73, doi:10.3762/bjoc.6.73

• at the 4 and 4′ positions led to only slight changes in the redox potentials. Keywords: dication; 4-DMAP; electron donor; electron transfer; radical cation; redox; reduction; Introduction Neutral organic compounds 1 and 4–10 (Figure 1) have attracted considerable attention as ground-state electron

• ][7][8][9][10][11][12], but is not strong enough to react with alkyl and aryl halides. The driving force for its oxidation is the attainment of some degree of aromaticity in the formation of its radical cation salt 2 on the loss of one electron, and full aromaticity in its dication salt 3 on loss of

• of the second electron, for the conversion of the radical cation to the dication, should be diminished. To see if the same twist occurs with our donor 8, the crystal structure of the disalt 17 was determined [twist (N–C–C–N = 52.5(3) degrees] (Figure 2). The degree of twist is limited by the three

Synthesis and redox behavior of new ferrocene- π-extended- dithiafulvalenes: An approach for anticipated organic conductors

• Abdelwareth A. O. Sarhan,
• Omar F. Mohammed and
• Taeko Izumi

Beilstein J. Org. Chem. 2009, 5, No. 6, doi:10.3762/bjoc.5.6

• of the TTF unit into its radical cation and dication. After organic chemists had discovered organic metal tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) charge transfer complexes, various synthetic approaches to tetrathiafulvalenes gained wide attention, and charge-transfer from TTF to TCNQ

Reduction of arenediazonium salts by tetrakis(dimethylamino)ethylene (TDAE): Efficient formation of products derived from aryl radicals

• Mohan Mahesh,
• John A. Murphy,
• Franck LeStrat and
• Hans Peter Wessel

Beilstein J. Org. Chem. 2009, 5, No. 1, doi:10.3762/bjoc.5.1

• formation of aryl radicals had never been reported using TDAE meant that we were keen to compare its reactions with those of the structurally related TTF (4a). Thus, as shown in Scheme 2, the radical-cation of TTF intercepts intermediates with the formation of C-S bonds in the radical-polar crossover

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• believed to involve single-electron oxidation of the cyclopropanol, fragmentation of a transient radical cation, and diastereoselective radical cyclization. In the enantioselective synthesis, this transformation was more efficiently achieved by treatment of enantioenriched 41b with the AgNO3-ammonium

Generation of pyridyl coordinated organosilicon cation pool by oxidative Si-Si bond dissociation

• Toshiki Nokami,
• Ryoji Soma,
• Yoshimasa Yamamoto,
• Toshiyuki Kamei,
• Kenichiro Itami and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2007, 3, No. 7, doi:10.1186/1860-5397-3-7

• ]. The coordination also stabilizes the thus-generated radical cation and weakens the C-Sn bond. A similar effect of intramolecular coordination was observed in the case of silicon [23]. Another important point is that pyridyl group is rather inactive toward the anodic oxidation. Thus, we chose to use a

• neutral molecules (Supporting Information File 1). Therefore, the significant effect of the 2-pyridyl group on the oxidation potential may be ascribed to effective intramolecular coordination to stabilize the radical cation intermediate. The conformationally less flexible 2-pyridylphenyl group seems to be

• more effective than the 2-pyridylethyl group. The intramolecular coordination in the radical cation is supported by the DFT calculations as shown in Figure 2. It is also important to note that such coordination elongates the Si-Si bond and facilitates its dissociation. Preparative electrochemical