Stepwise radical cation Diels–Alder reaction via multiple pathways

• Ryo Shimizu,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 704–708, doi:10.3762/bjoc.14.59

• -8588, Japan 10.3762/bjoc.14.59 Abstract Herein we disclose the radical cation Diels–Alder reaction of aryl vinyl ethers by electrocatalysis, which is triggered by an oxidative SET process. The reaction clearly proceeds in a stepwise fashion, which is a rare mechanism in this class. We also found that

• two distinctive pathways, including “direct” and “indirect”, are possible to construct the Diels–Alder adduct. Keywords: Diels–Alder reaction; radical cation; rearrangement; single electron transfer; stepwise; Introduction Umpolung, also known as polarity inversion, is a powerful approach in

• produces a radical cation species, which offers electrophilic reactivity for subsequent transformations. Enol ether radical cations are among the simplest members of this class and thus have been widely used in synthetic organic chemistry [13][14][15]. The Diels–Alder reaction is a classic reaction, and

Investigating radical cation chain processes in the electrocatalytic Diels–Alder reaction

• Yasushi Imada,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 642–647, doi:10.3762/bjoc.14.51

• , the turnover number, also referred to as catalytic efficiency, remains unclear in most cases. Herein, we disclose our investigations of radical cation chain processes in the electrocatalytic Diels–Alder reaction, leading to a scalable synthesis. A gram-scale synthesis was achieved with high current

• efficiency of up to 8000%. The reaction monitoring profiles showed sigmoidal curves with induction periods, suggesting the involvement of intermediate(s) in the rate determining step. Keywords: chain process; Diels–Alder reaction; electrocatalytic; radical cation; single electron transfer; Introduction

• ], some of which were achieved with a catalytic amount of electricity. Such electrocatalytic cycloadditions should involve radical cation chain processes, meaning that the reaction is not only triggered by an oxidative SET at the surface of the electrode but also by an intermolecular SET process in bulk

The selective electrochemical fluorination of S-alkyl benzothioate and its derivatives

• Shunsuke Kuribayashi,
• Tomoyuki Kurioka,
• Shinsuke Inagi,
• Ho-Jung Lu,
• Biing-Jiun Uang and
• Toshio Fuchigami

Beilstein J. Org. Chem. 2018, 14, 389–396, doi:10.3762/bjoc.14.27

• organosulfur and amino compounds was generally enhanced by the presence of an α-electron-withdrawing group (EWG) such as a CF3 group. Here, the deprotonation of an anodically generated radical cation intermediate is accelerated by an EWG [7][8]. Based on these facts, we successfully achieved the first anodic

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

• authors propose that the photo-excited state of the organic dye Eosin Y is reductively quenched by the aryl thiol to form the Eosin Y radical anion and the respective aryl thiyl radical cation. Neutral Eosin Y is regenerated through oxidation of the radical anion by dioxygen. The resulting superoxide

• radical anion then deprotonates the thiyl radical cation. Subsequent addition to the alkene yields the anti-Markovnikov radical intermediate. Radical addition to dioxygen leads finally to the β-ketosulfide, which subsequently is oxidized by the in situ generated hydrogen peroxide radical to the respective

• conduction band of TiO2 leads to electron holes in the valence band, which can be reductively quenched by the thiol to form the respective thiyl radical cation. After deprotonation, the thiyl radical undergoes thiol–ene coupling. The scope of the reaction includes the coupling of primary alkyl and aryl

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

• then reacted with the β-nitroalkene to furnish radical intermediate 38, which was reduced by the Eosin Y radical cation to yield the expected product after elimination of NO2. This proposed mechanism can rationalise several limitations of the reaction, such as its incompatibility with aliphatic β

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• simple alkenes, sodium triflinate and diazonium salts. The CF3 radical was produced from CF3SO2Na by oxidation with H2O2 in the presence of silver nitrate. Then, CF3• was added to the terminal position of the alkene to give radical 26 that was trapped by the arenediazonium salt to form the radical cation

• radical from CF3SO2Na with extrusion of SO2. Then, CF3• underwent a radical addition to the alkene to form the radical 29, which was trapped by the aryldiazonium salt to give the radical cation 30. Finally, 30 was reduced by [Ru(bpy)3]2+* to end up with the product 31 (Scheme 13). The

Vinylphosphonium and 2-aminovinylphosphonium salts – preparation and applications in organic synthesis

• Anna Kuźnik,
• Roman Mazurkiewicz and
• Beata Fryczkowska

Beilstein J. Org. Chem. 2017, 13, 2710–2738, doi:10.3762/bjoc.13.269

• cycloalkene is higher than that for triphenylphosphine, the suggested mechanism of formation of the final 1-cycloalkenetriphenylphosphonium salts 19 is analogous to the reactions of the radical cation of triphenylphosphine with other nucleophiles (Scheme 13) [19]. 1.5. Triphenylphosphine addition to a triple

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

• SET mechanism to generate a radical cation B, followed by fragmentation to afford 12 (Scheme 3b). Either of these processes provided the imine moiety, along with o-iodosobenzoic acid (IBA, Scheme 3). In general, IBX-mediated oxidative dehydrogenation is conducted at high temperatures (>50 °C

Transition-metal-catalyzed synthesis of phenols and aryl thiols

• Yajun Liu,
• Shasha Liu and
• Yan Xiao

Beilstein J. Org. Chem. 2017, 13, 589–611, doi:10.3762/bjoc.13.58

• stoichiometric amount of Cu(OAc)2 and H2O in acetonitrile at 130 °C, and the resulting acetate gave phenols in moderate yields through a simple hydrolysis (Scheme 25). A mechanistic investigation revealed that the reaction proceeded via a radical-cation pathway. Notably, their protocol could be also applied in

Identification, synthesis and mass spectrometry of a macrolide from the African reed frog Hyperolius cinnamomeoventris

• Markus Menke,
• Pardha Saradhi Peram,
• Iris Starnberger,
• Walter Hödl,
• Gregory F.M. Jongsma,
• David C. Blackburn,
• Mark-Oliver Rödel,
• Miguel Vences and
• Stefan Schulz

Beilstein J. Org. Chem. 2016, 12, 2731–2738, doi:10.3762/bjoc.12.269

• , leading to the radical cation 18 along pathway a. An additional bond cleavage of a C–O single bond releases a neutral molecule, e.g., methylcyclohexane, giving rise to ion m/z 126 (20). High-resolution mass spectral data support the hypothesis because the ions m/z 126 as well as m/z 182 (25) formed from 2

Copper-catalyzed asymmetric sp³ C–H arylation of tetrahydroisoquinoline mediated by a visible light photoredox catalyst

• Pierre Querard,
• Inna Perepichka,
• Eli Zysman-Colman and
• Chao-Jun Li

Beilstein J. Org. Chem. 2016, 12, 2636–2643, doi:10.3762/bjoc.12.260

• (SET), reducing the iridium complex to Ir(II) III and oxidizing the the nitrogen of THIQ IV to its radical cation V, which then undergoes a hydride abstraction to form the iminium salt form VI, of the THIQ. The pre-formed chiral PhCu–PyBox complex [38], coordinates to the iminium cation VI, followed by

The EIMS fragmentation mechanisms of the sesquiterpenes corvol ethers A and B, epi-cubebol and isodauc-8-en-11-ol

• Patrick Rabe and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 1380–1394, doi:10.3762/bjoc.12.132

• fragment ion m/z = 43 from C3 and C15 (Scheme 4E). As shown by HRMS analysis, this fragment ion contains oxygen (measured: 43.0183, calculated for [C2H3O]+: 43.0179). The radical cation 3a+· can undergo two sequential or consecutive α-fragmentations to K3+·. A subsequent hydrogen rearrangement to L3+· and

• ). Electron impact ionisation at the oxygen lone pairs of 4 results in the radical cation 4a+· that can undergo one of two possible α-cleavages with loss of C12 or C13 to yield A4+. The alternative ionisation of 4 with loss of an electron from the olefinic double bond leads to 4b+· that may react by hydrogen

• radical cation K4+·. Another α-cleavage of the hydroxyisopropyl group results in L4+. Finally, the PMA59 demonstrates formation of this fragment ion from the hydroxyisopropyl group which is possible by a single α-cleavage from 4a+· to M4+ (Scheme 5F). Conclusion Isotopic labelling experiments continue to

Synthesis and fluorosolvatochromism of 3-arylnaphtho[1,2-b]quinolizinium derivatives

• Phil M. Pithan,
• David Decker,
• Manlio Sutero Sardo,
• Giampietro Viola and
• Heiko Ihmels

Beilstein J. Org. Chem. 2016, 12, 854–862, doi:10.3762/bjoc.12.84

• a charge shift (CS) to generate an intermediate excited species, that is a combination of charge neutral radical, i.e., a quinolizinyl radical, and the radical cation of the aromatic substituent (Scheme 3). The proposed photoinduced charge shift in derivatives 6b–e is supported by observations that

• relaxation, the counter anion migrates to the radical cation unit at the aryl substituent. At the same time, this mechanism implies that directly after the "back CS" the bromide anion is still located in the vicinity of the aryl substituent and therefore no longer compensated by a nearby cationic charge

Determination of formation constants and structural characterization of cyclodextrin inclusion complexes with two phenolic isomers: carvacrol and thymol

• Miriana Kfoury,
• David Landy,
• Steven Ruellan,
• Lizette Auezova,
• Hélène Greige-Gerges and
• Sophie Fourmentin

Beilstein J. Org. Chem. 2016, 12, 29–42, doi:10.3762/bjoc.12.5

• most energetically favorable conformation of inclusion complexes. Finally, the effect of encapsulation on the antioxidant properties of 1 and 2 was evaluated using the ABTS radical cation assay. Results and Discussion UV–visible competitive studies Stoichiometries and Kf values of inclusion complexes

• ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS•+) scavenging method was used to determine the radical scavenging potency of free and encapsulated 1 and 2. This method relies on the capacity of an antioxidant to scavenge and reduce ABTS•+ into its colorless reduced

Urethane tetrathiafulvalene derivatives: synthesis, self-assembly and electrochemical properties

• Xiang Sun,
• Guoqiao Lai,
• Zhifang Li,
• Yuwen Ma,
• Xiao Yuan,
• Yongjia Shen and
• Chengyun Wang

Beilstein J. Org. Chem. 2015, 11, 2343–2349, doi:10.3762/bjoc.11.255

• to explore the formation of the charge-transfer complexes. TTF derivates are representative electron donors, while TCNQ is a typical electron acceptor. When one equivalent of TCNQ was added to the solution of T1 in ethyl acetate, TCNQ radical anion species (TCNQ•−) and TTF radical cation species (TTF

• +0.643 V (T2) (vs Ag/AgCl) was in the anodic window. This indicated the successive reversible oxidation of neutral TTF (TTF0) to the radical cation (TTF•+). The second oxidation at = +0.958 V (T1) and +0.973 V (T2) (vs Ag/AgCl) corresponded to the reversible oxidation of the radical cation (TTF•+) to

Photoinduced 1,2,3,4-tetrahydropyridine ring conversions

• Baiba Turovska,
• Henning Lund,
• Viesturs Lūsis,
• Anna Lielpētere,
• Edvards Liepiņš,
• Sergejs Beljakovs,
• Inguna Goba and
• Jānis Stradiņš

Beilstein J. Org. Chem. 2015, 11, 2166–2170, doi:10.3762/bjoc.11.234

• solution. The reaction of dioxygen (3O2) having a triplet ground state with tetrahydropyridine 1 having a singlet ground state is spin forbidden. On the other hand, the electron transfer from the organic compound to 3O2 resulting in the formation of a radical cation of the organic donor and the radical

Supramolecular chemistry: from aromatic foldamers to solution-phase supramolecular organic frameworks

• Zhan-Ting Li

Beilstein J. Org. Chem. 2015, 11, 2057–2071, doi:10.3762/bjoc.11.222

• cavity of cucurbit[8]uril (CB[8]) are highlighted. Keywords: donor–acceptor interaction; foldamer; hydrogen bond; radical cation dimerization; supramolecular organic framework; Review Childhood and growing up I was born on July 23rd, 1966 in the small, remote village of Fang-Liu (a combination of two

• favorite. Many years later at Fudan, I initiated a project to study the potential of its radical cation stacking in controlling the folded conformation of linear molecules and two- and three-dimensional supramolecular polymers and frameworks. My life in the small town of Odense was also memorable. Its calm

• successive intramolecular C–H····F or C–H····Cl hydrogen bonds [70]. Conjugated radical cation dimerization-driven pleated foldamers. The stacking of the radical cations of viologen or TTF were observed in 1964 and 1979 [71][72]. This stacking is typically weak. Several approaches have been developed to

Polythiophene and oligothiophene systems modified by TTF electroactive units for organic electronics

• Alexander L. Kanibolotsky,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2015, 11, 1749–1766, doi:10.3762/bjoc.11.191

• polymer thin film revealed the splitting of the first oxidation wave during the cathodic run, which the authors attributed to a stepwise reduction from the aggregated radical cation to an intermediate mixed valence state, then further reduction to the neutral species. To decrease the difference in the

Star-shaped tetrathiafulvalene oligomers towards the construction of conducting supramolecular assembly

• Masahiko Iyoda and
• Masashi Hasegawa

Beilstein J. Org. Chem. 2015, 11, 1596–1613, doi:10.3762/bjoc.11.175

• self-aggregated in chloroform–dioxane to form a gel. TEM images of the xerogel exhibited helical molecular tapes nanometer wide and micrometer long. A cyclic voltammetry (CV) study on 2b showed the redox properties expected for Pc and TTF, and doping of 2b in CH2Cl2 with I2 produced a radical cation

• of 40, the changes show several isosbestic points, indicating that each TTF unit is oxidized from the neutral to the radical cation (TTF•+) in a stepwise manner (Figure 15b). On the other hand, for 38 and 42, there are no isosbestic points (Figure 15a,c). For 38, a new broad peak around 1850 nm

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• this review we describe how photoactivated SCPCs can either (i) interact with a precursor that donates an electron to the semiconductor thus generating a radical cation; or (ii) interact with an acceptor precursor that picks up an electron with production of a radical anion. The radical cations of

• . Alternatively, *Ru(bpy)32+ acts as an oxidant by accepting an electron from a suitable donor molecule D thus creating the radical cation D+•. Successful protocols have been developed for a variety of preparations including: enantioselective α-alkylations of aldehydes with radicals derived from α-bromocarbonyl

• where the electron can reduce an electron acceptor with a suitable redox potential to a radical anion (A–•) and/or the hole can oxidize an electron donor to the radical cation (D+•, Figure 1). Recombination, whereby the electron drops back down to the VB, occurs in competition with this in the bulk of

Synthesis of racemic and chiral BEDT-TTF derivatives possessing hydroxy groups and their achiral and chiral charge transfer complexes

• Sara J. Krivickas,
• Chiho Hashimoto,
• Junya Yoshida,
• Akira Ueda,
• Kazuyuki Takahashi,
• John D. Wallis and
• Hatsumi Mori

Beilstein J. Org. Chem. 2015, 11, 1561–1569, doi:10.3762/bjoc.11.172

• due to their ability to form radical cation salts with interesting conductive and magnetic properties (Figure 1). The influence of chirality in the TTF molecules on the crystal structure and physical properties has been shown by Avarvari’s (R)-, (S)- and racemic (±)-(ethylenedithio(tetrathiafulvalene

• molecules, and anions in the subsequent radical cation salts [20][21][22]. This may lead to improved order in the crystalline state, which in turn may help the observation of physical properties of the salts. Previously, the synthesis of racemic-2 [21][22], the preliminary synthesis of enantiopure (R,R

• )- and (S,S)-2, and the preparation, and crystal structure of the radical cation salt α’-[(S,S)-2]2ClO4 [22] have been reported. In this article, we report the syntheses of novel racemic-1 and enantiopure (R,R)- and (S,S)-2 possessing one or two hydroxymethyl groups, and the preparations, crystal

Tetrathiafulvalene chemistry

• Peter J. Skabara and
• Marc Sallé

Beilstein J. Org. Chem. 2015, 11, 1528–1529, doi:10.3762/bjoc.11.167

• nineteen seventies [1][2][3] and since then has proved to be exceptionally popular in various fields of chemistry. This success results from the conjunction of intrinsic structural and electronic properties: i) structurally, this sulfur-rich bicyclic compound is essentially planar (at least in the radical

• cation state) and therefore presents, as with most of its substituted derivatives, a good propensity to stack in the solid state. This parameter is favorable for efficient charge delocalization in the solid-state and it is this feature that gave birth to the first conducting and superconducting organic

Tetrathiafulvalene-based azine ligands for anion and metal cation coordination

• Awatef Ayadi,
• Aziz El Alamy,
• Olivier Alévêque,
• Magali Allain,
• Nabil Zouari,
• Mohammed Bouachrine and
• Abdelkrim El-Ghayoury

Beilstein J. Org. Chem. 2015, 11, 1379–1391, doi:10.3762/bjoc.11.149

• prepared electroactive rhenium complex the TTF is neutral and the rhenium cation is hexacoordinated. The electrochemical behavior of the three compounds indicates that they are promising for the construction of crystalline radical cation salts. Keywords: azine ligand; fluoride sensing; rhenium

• ; tetrathiafulvalene; X-ray; Introduction Tetrathiafulvalene (TTF) is known to have excellent electron-donating properties resulting in stable radical cation (TTF•+) and dication (TTF2+) species from two sequential and reversible oxidation processes. The huge interest in the synthesis of TTF and its very numerous

• electrochemical behavior observed for L2 and its corresponding rhenium complex 3 indicate that this compounds are valuable candidates for the electrochemical formation of air-stable radical cation crystalline salts [16]. Conclusion Two multifunctional ligands which associate an electron-donating TTF unit with an

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes

• Luke J. O’Driscoll,
• Sissel S. Andersen,
• Marta V. Solano,
• Dan Bendixen,
• Morten Jensen,
• Troels Duedal,
• Jess Lycoops,
• Cornelia van der Pol,
• Rebecca E. Sørensen,
• Karina R. Larsen,
• Kenneth Myntman,
• Christian Henriksen,
• Stinne W. Hansen and
• Jan O. Jeppesen

Beilstein J. Org. Chem. 2015, 11, 1112–1122, doi:10.3762/bjoc.11.125

• been utilized in the formation of charge-transfer (CT) complexes for more than 40 years [21][22][23]. TTF (1) (Figure 1) is not aromatic according to the Hückel definition as its 14 π-electrons lack cyclic conjugation. Upon oxidation to the radical cation (2) and dication (3) states, a gain in

• materials with applications in supramolecular chemistry, molecular electronics and as sensors. The sequential, reversible oxidation of TTF (1) to its stable radical cation (2) and dication (3) states. Structures and possible substitution positions of MPTTFs (4) and BPTTFs (5). Large-scale synthesis of 6

Regioselective synthesis of chiral dimethyl-bis(ethylenedithio)tetrathiafulvalene sulfones

• Flavia Pop and
• Narcis Avarvari

Beilstein J. Org. Chem. 2015, 11, 1105–1111, doi:10.3762/bjoc.11.124

• conformation. Cyclic voltammetry measurements indicate fully reversible oxidation in radical cation and dication species. Keywords: chirality; crystal structures; molecular materials; sulfones; tetrathiafulvalenes; Introduction Chiral tetrathiafulvalene (TTF) derivatives have been addressed for the first

• -oxaziridines as oxidizing agent [27][28]. However, the inner BEDT-TTF sulfoxide was shown to be of only limited interest as precursor for molecular conductors, since it does not reversibly oxidize into a radical cation. This behavior is due to the moderate kinetic stability of the latter, which releases oxygen

• to transform into BEDT-TTF. Moreover, since the inner sulfur atoms present large orbital coefficients in the HOMO, the introduction of the electron-withdrawing oxygen atom induces a massive increase of the oxidation potential from the neutral to the radical cation states. We have then hypothesized