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