Oxidative phenylamination of 5-substituted 1-hydroxynaphthalenes to N-phenyl-1,4-naphthoquinone monoimines by air and light “on water”

• Julio Benites,
• Juan Meléndez,
• Cynthia Estela,
• David Ríos,
• Luis Espinoza,
• Iván Brito and
• Jaime A. Valderrama

Beilstein J. Org. Chem. 2014, 10, 2448–2452, doi:10.3762/bjoc.10.255

• (1) with phenylamines using oxidants such as K3Fe(CN)6, HIO3 and NaIO4 in aqueous alcohol. According to these authors, the oxidative phenylamination mechanism involves a radical cation intermediate generated by an electron transfer process from the phenylamine to the oxidant. Further electrophilic

• substitution at the 4-position of compound 1 followed by oxidation of the aminonaphthol intermediate, yield the N-phenyl-1,4-naphthoquinone-4-imines. A mechanism involving radical cation intermediates is supported by the rather high product yields resulting from the reaction of 1,5-DHN (1) with electron-donor

Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

• Axel G. Griesbeck and
• Melissa Reckenthäler

Beilstein J. Org. Chem. 2014, 10, 1143–1150, doi:10.3762/bjoc.10.114

• two clearly distinguishable reaction protocols were designated as type A and B by Kisch and co-workers [12][13][14][15]. In the type A process, two different products are formed from the initially formed electron–hole pair, one from the substrate radical cation that is formed from electron transfer to

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• ) and qk(N + 1) are the electronic population of atom k in its neutral, radical-cation and radical-anion forms, respectively. In this study, the Fukui function is used to partially rationalize BF3 complexation. In this case, the nucleophilic contribution is the most important parameter. It must be

The Ugi four-component reaction as a concise modular synthetic tool for photo-induced electron transfer donor-anthraquinone dyads

• Sarah Bay,
• Gamall Makhloufi,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 1006–1016, doi:10.3762/bjoc.10.100

• constants of the solvent applied in spectroscopy (εs) and reference solvent used in electrochemistry (εref), and r+ and r− are indicating the effective ionic radii of the donor radical cation and acceptor radical anion, respectively. It is allowed to neglect the forth term, if spectroscopic and

On the mechanism of photocatalytic reactions with eosin Y

• Michal Majek,
• Fabiana Filace and
• Axel Jacobi von Wangelin

Beilstein J. Org. Chem. 2014, 10, 981–989, doi:10.3762/bjoc.10.97

• redox potential can be obtained indirectly via analysis of the thermodynamic cycle involving the energy of the triplet state eosin Y* (T1) (derived from fluorescence measurements) and the energy of the radical cation eosin Y+• (derived from cyclovoltammetric experiments, for more details see Supporting

• product V. Two general pathways of back-electron transfer can be followed: Path A involves one-electron reduction of the radical cation state of the catalyst. Radical chain propagation (B) can occur when the SET occurs with another molecule of the starting material I. Some attempts have been made to

Visible light mediated intermolecular [3 + 2] annulation of cyclopropylanilines with alkynes

• Theresa H. Nguyen,
• Soumitra Maity and
• Nan Zheng

Beilstein J. Org. Chem. 2014, 10, 975–980, doi:10.3762/bjoc.10.96

• % from 21. Mechanistically, the annulation with alkynes probably proceeds through a pathway similar to the one we proposed for the annulation with alkenes (Scheme 2) [29]. The photoexcited Ru(bpz)32+ oxidizes cyclopropylaniline 24 to the corresponding amine radical cation 25, which triggers the

• cyclopropyl ring opening to generate distonic radical cation 26. The primary carbon radical of 26 adds to the terminal carbon of alkyne 27 to afford vinyl radical 28. Intramolecular addition of the vinyl radical to the iminium ion of distonic radical cation 28 closes the five membered ring and furnishes amine

• radical cation 29. Finally, Ru(bpz)31+ reduces amine radical cation 29 to the annulation product 30 while regenerating Ru(bpz)32+. The proposed mechanism accounts for lower reactivity of alkynes towards intermolecular addition of nucleophilic carbon-centered radicals as well as their regiochemistry in the

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

• between the dye and one of the components, for example A in Scheme 3, gives rise to a radical anion (A•−) and the oxidized PS (PS•+). Then, PS•+ can react with the electron donor D (kred) to regenerate the PS ground state (photocyclic reaction), leading to the formation of one radical cation D

Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

• Jacques Lalevée,
• Sofia Telitel,
• Pu Xiao,
• Marc Lepeltier,
• Frédéric Dumur,
• Fabrice Morlet-Savary,
• Didier Gigmes and
• Jean-Pierre Fouassier

Beilstein J. Org. Chem. 2014, 10, 863–876, doi:10.3762/bjoc.10.83

• of the radical → cation step as well as the nature of the cationic centers remains connected with the nature of eA. The key point is to find a radical directly formed through this way and that can be easily oxidized by PIC•+. Another situation is encountered in Scheme 4 where the initially formed

• Schemes, both FRP, CP and FRPCP can be initiated from the free radicals and cations generated. In these three situations, as a function of its structure, the PIC radical cation PIC•+ can behave as an initiating species. Reductible photoinitiator catalysts Scheme 5 shows a situation where the PIC is

• ][48][49][50][51][52]. The nature of the PIC is responsible for the absorption properties. Interestingly, whatever the PIC, the nature of the cation is only dependent of the choice of Add. The three-component system behaves here as an efficient dual radical/cation source. Moreover, as already known [57

Direct and indirect single electron transfer (SET)-photochemical approaches for the preparation of novel phthalimide and naphthalimide-based lariat-type crown ethers

• Dae Won Cho,
• Patrick S. Mariano and
• Ung Chan Yoon

Beilstein J. Org. Chem. 2014, 10, 514–527, doi:10.3762/bjoc.10.47

• . For example, Kubo and coworkers [47] showed that photoreactions of N-methyl-1,2- and 2,3-naphthalimides 8 and 12 with allylsilane 9 in MeCN can produce allylation products [48][49][50][51][52] that arise by a well-known sequence involving intermolecular SET, radical cation desilylation and radical

Efficient carbon-Ferrier rearrangement on glycals mediated by ceric ammonium nitrate: Application to the synthesis of 2-deoxy-2-amino-C-glycoside

• Alafia A. Ansari,
• Y. Suman Reddy and
• Yashwant D. Vankar

Beilstein J. Org. Chem. 2014, 10, 300–306, doi:10.3762/bjoc.10.27

• mechanism The proposed mechanism of the formation of the C-allyl glycosides is shown in Scheme 1. The ring oxygen could donate an electron to the Ce3+ leading to the formation of a radical cation A. Subsequent migration of the double bond and loss of the acetyl radical could result in the formation of the

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