Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

• Mohammad A. Alnajjar,
• Jürgen Bartelmeß,
• Robert Hein,
• Pichandi Ashokkumar,
• Mohamed Nilam,
• Werner M. Nau,
• Knut Rurack and
• Andreas Hennig

Beilstein J. Org. Chem. 2018, 14, 1961–1971, doi:10.3762/bjoc.14.171

• motifs for CB7. The unprotonated dyes show low fluorescence due to photoinduced electron transfer (PET), whereas the protonated dyes are highly fluorescent. Encapsulation of the binding motif inside CB7 positions the aniline nitrogen at the carbonyl rim of CB7, which affects the pKa value, and leads to a

• quenching by photoinduced electron transfer (PET), whereas the protonated form was brightly fluorescent [31]. We report herein the synthesis and photophysical characterization of BODIPY derivatives with an aniline substituent in the meso-position to which different anchor groups have been attached, and we

• . This includes indicator displacement assays with favourable absorption and emission wavelengths in the visible spectral region, fluorescence correlation spectroscopy, and noncovalent surface functionalization with fluorophores. Keywords: BODIPY; cucurbituril; fluorescence; pH; photoinduced electron

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

• Siva Sankar Murthy Bandaru,
• Darinka Dzubiel,
• Heiko Ihmels,
• Mohebodin Karbasiyoun,
• Mohamed M. A. Mahmoud and
• Carola Schulzke

Beilstein J. Org. Chem. 2018, 14, 1871–1884, doi:10.3762/bjoc.14.161

• 2b and 2c are very low (Φfl < 0.02). Such low emission intensities have been observed also for donor-substituted 9-arylbenzo[b]quinolizinium derivatives and explained either with a radiationless deactivation of the excited state by torsional relaxation or by a photoinduced electron transfer [33][49

• titration. The fluorescence intensity of the derivatives 2a and 2d is significantly quenched by the addition of DNA, respectively (Figure 8 and Figure 9). This observation usually indicates a photoinduced electron transfer between the excited molecules and the DNA bases [69]. By contrast, the association of

Graphitic carbon nitride prepared from urea as a photocatalyst for visible-light carbon dioxide reduction with the aid of a mononuclear ruthenium(II) complex

• Kazuhiko Maeda,
• Daehyeon An,
• Ryo Kuriki,
• Daling Lu and
• Osamu Ishitani

Beilstein J. Org. Chem. 2018, 14, 1806–1812, doi:10.3762/bjoc.14.153

• in this study. Ag nanoparticles loaded on mpg-C3N4 serves as a promoter of electron transfer from mpg-C3N4 to RuP, as discussed in our previous work [13]. TEM observation indicated that the loaded Ag is in the form of nanoparticles of 5–10 nm in size (Figure 5). Without Ag (i.e., RuP/g-C3N4), formate

• electron transfer, is developed. This is now under investigation in our laboratory. Conclusion Heating urea in air at 773–923 K resulted in the formation of g-C3N4, which exhibited photocatalytic activity for CO2 reduction into formate under visible light with the aid of a molecular Ru(II) cocatalyst

Synthesis and photophysical studies of a multivalent photoreactive Ru^II-calix[4]arene complex bearing RGD-containing cyclopentapeptides

• Sofia Kajouj,
• Lionel Marcelis,
• Alice Mattiuzzi,
• Adrien Grassin,
• Damien Dufour,
• Pierre Van Antwerpen,
• Didier Boturyn,
• Eric Defrancq,
• Mathieu Surin,
• Julien De Winter,
• Pascal Gerbaux,
• Ivan Jabin and
• Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

• upon light irradiation. Two types of photooxidative damages can be induced: (i) by photosensitization of singlet oxygen and subsequent generation of highly reactive oxygen species (ROS) (type I photosensitization) or (ii) by direct oxidative electron transfer to biological molecules such as DNA or

• DNA or the tryptophan (Trp) amino acid residue through a photoinduced electron-transfer (PET) process [16][17][18][19]. Interestingly, the two radical species generated by this PET can recombine to form a covalent photoadduct [20][21][22]. When this photoadduct is formed with the guanine base, the

• ). This quenching of the luminescence of conjugate 9 in the presence of GMP reveals that a photoinduced electron transfer can take place between the excited complex and the guanine moiety, which could give rise to the formation of a photoadduct from the recombination of the monoreduced complex and the

Mild and selective reduction of aldehydes utilising sodium dithionite under flow conditions

• Nicole C. Neyt and
• Darren L. Riley

Beilstein J. Org. Chem. 2018, 14, 1529–1536, doi:10.3762/bjoc.14.129

• piperidines [17], benzil groups [19], nitroarenes and nitroalkanes in the presence of dialkyl viologen electron transfer catalysts [20][21] and immobilized nitroarene’s under phase transfer conditions [22][23]. In this publication we report the efficient reduction of aldehydes under flow conditions utilising

Synthesis of trifluoromethylated 2H-azirines through Togni reagent-mediated trifluoromethylation followed by PhIO-mediated azirination

• Jiyun Sun,
• Xiaohua Zhen,
• Huaibin Ge,
• Guangtao Zhang,
• Xuechan An and
• Yunfei Du

Beilstein J. Org. Chem. 2018, 14, 1452–1458, doi:10.3762/bjoc.14.123

• of a CF3 radical. Then, the reaction of enamine 5a with the CF3 radical affords the carbon-centered radical 11. Next, the reaction of 10 and 11, possibly through an electron-transfer process, along with the conversion of intermediate 10 to 2-iodobenzoic acid enables the conversion of intermediate 11

Atom-economical group-transfer reactions with hypervalent iodine compounds

• Andreas Boelke,
• Peter Finkbeiner and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2018, 14, 1263–1280, doi:10.3762/bjoc.14.108

• moiety in C3 position, affording the trans-isomer 46 exclusively. The reaction mechanism presumably follows a radical pathway, which begins with a single electron transfer (SET) from Fe(II) to 36b generating a Fe(III) species as well as benziodoxolonyl radical A or benzoyloxy radical A’ and an azide

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• single-electron-transfer-based oxidation processes of 162 gave 12 in 60% yield. 3.1.2. Other synthetic approaches: A convenient synthesis of 2,3-benzotropone (12) from α-tetralone (171) by ring expansion was performed by Sato’s group (Scheme 31) [140]. First, 1-ethoxy-3,4-dihydronaphthalene (172) was

Selective carboxylation of reactive benzylic C–H bonds by a hypervalent iodine(III)/inorganic bromide oxidation system

• Toshifumi Dohi,
• Shohei Ueda,
• Kosuke Iwasaki,
• Yusuke Tsunoda,
• Koji Morimoto and
• Yasuyuki Kita

Beilstein J. Org. Chem. 2018, 14, 1087–1094, doi:10.3762/bjoc.14.94

• single-electron-transfer (SET) reactivities [33][34][35][36][37] allow selective activation of the benzylic C(sp3)–H bond for oxidative functionalization and coupling reactions. Initially, the SET oxidation ability of pentavalent iodine reagents, especially o-iodoxybenzoic acid (IBX), in benzylic

Polysubstituted ferrocenes as tunable redox mediators

• Sven D. Waniek,
• Jan Klett,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2018, 14, 1004–1015, doi:10.3762/bjoc.14.86

• are: (i) Both components of the redox couple should be soluble. (ii) Homogeneous and heterogeneous electron-transfer (ET) reactions should be fast. (iii) Both components should be stable under the electrolysis conditions and should not react irreversibly with any component of the supporting

• (homogeneous). The benefit of the presence of a mediator is the switch of the sluggish heterogeneous electron transfer between electrode and substrate to a rapid homogeneous redox reaction between mediator and substrate. Further, the mediator’s redox potential must be below or above of that of the substrate

• (ferrocenylmethyl)ammonium salts acting as catholytes. Ferrocene dicarboxylic acid has been described as mediator for the voltammetric determination of glutathione in hemolized erythrocytes [16]. (Substituted) ferrocenium salts were successfully employed as single-electron transfer (SET) reagents in organic

Anodic oxidation of bisamides from diaminoalkanes by constant current electrolysis

• Tatiana Golub and
• James Y. Becker

Beilstein J. Org. Chem. 2018, 14, 861–868, doi:10.3762/bjoc.14.72

• formation of mono- and dimethoxylated amides is well-documented in the published literature [1][2][3][4][5][6][14][17][23]. It is generally accepted that the initial electron transfer forms an iminium cation radical followed by deprotonation and further oxidation to generate an iminium ion/carbocation that

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• . The species B would then undergo a single-electron transfer (SET) to the alkenyl phosphate 2 to generate a pair of an oxidized cobaltacycle B+ and a radical anion 2•−. This would be followed by the elimination of a phosphate anion and immediate recombination of the cobalt center and the alkenyl

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

• 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

• synthetic organic chemistry to trigger reactions that are otherwise difficult or impossible. In an umpolung reaction, the normal reactivity of the molecules being studied is reversed, e.g., electrophilicity is generated from a nucleophile. The single electron transfer (SET) process has been recognized as

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

• -8588, Japan 10.3762/bjoc.14.51 Abstract Single electron transfer (SET)-triggered radical ion-based reactions have proven to be powerful options in synthetic organic chemistry. Although unique chain processes have been proposed in various photo- and electrochemical radical ion-based transformations

• 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

• Recently, radical ion reactivity has received great attention in the field of synthetic organic chemistry. The single electron transfer (SET) strategy is the key to generating radical ions, which provide powerful intermediates for bond formations. Photo- [1][2][3][4][5][6] and electrochemistry [7][8][9][10

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

• substituents, the anodic fluorination took place to afford the corresponding α-fluorinated products 2 in moderate to reasonable yields along with benzoyl fluoride as byproduct (Table 2). Generally, no fluorination of the phenyl ring was observed. In the case of 1h, electron transfer seems to take place from

• forms the α-fluorinated product 2h selectively. In contrast, the electron transfer of 1i seems to take place mainly from the β-phenyl group as indicated by DFT calculation (Figure 3). As shown in Scheme 1, an electron transfer from the β-phenyl group in 1i followed by deprotonation and an additional

• electron transfer generates the benzylic cationic intermediate A, which affords the benzylic fluorinated product. It is known that benzylic fluorinated compounds are known to be generally prone to lose a fluoride anion [26]. On the other hand, intermediate A may undergo also elimination of a β-proton due

Synthesis and spectroscopic properties of β-meso directly linked porphyrin–corrole hybrid compounds

• Baris Temelli and
• Hilal Kalkan

Beilstein J. Org. Chem. 2018, 14, 187–193, doi:10.3762/bjoc.14.13

• applications [21][22][23]. In order to achieve rapid energy and electron transfer between macrocycles, the short distance between subunits keeps an important place. Therefore, two important factors affect the physical and electronic properties of porphyrin–corrole conjugates: (i) type of linkers and (ii

Progress in copper-catalyzed trifluoromethylation

• Guan-bao Li,
• Chao Zhang,
• Chun Song and
• Yu-dao Ma

Beilstein J. Org. Chem. 2018, 14, 155–181, doi:10.3762/bjoc.14.11

• NMR spectroscopy and ESIMS. It was proposed that [CuCF3] was generated through reduction of S-(trifluoromethyl)diphenylsulfonium triflate by Cu0 through a single-electron transfer (SET) process (Scheme 3). In 2015, the group of Lu and Shen [16] developed a new electrophilic trifluoromethylation

• this conversion. A plausible mechanism is proposed in Scheme 24. First, the CF3 radical, generated from Umemoto’s reagent through copper-mediated single electron transfer (SET), reacts with copper affording CuCF3. Second, Ar–CF3 was formed by the reaction of CuCF3 with the aryl radical derived from the

• , generated through copper-mediated single electron transfer from diazonium salt A, released nitrogen gas affording the aryl radical C. On the other hand, the CF3 radical was generated through the reaction of TBHP with NaSO2CF3 in the presence of Cu(I) species. Then, the CF3 radical reacted with the Cu(I

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

• . Photoredox-active metal complexes or organic dyes are used to initiate photo-induced single-electron transfer (SET) processes upon excitation with visible-light. Such photooxidations or photoreductions yield reactive organic radicals, which can undergo unique bond forming reactions, under very mild

• with white light then triggers a light-induced electron transfer from the anion to the aryl halide, releasing the halide as an anion and resulting in a thiyl radical and an aryl radical. Finally, radical–radical cross-coupling yields the respective diaryl sulfide. Ammonium thiocyanate Formation of

• alternative reductive pathway, where photoexcited [Ru(bpy)3]2+* first oxidizes the sulfur anion by single-electron transfer and is re-oxidized by dioxygen could not be excluded. Lei and co-workers reported an external oxidant-free photocatalyzed procedure for the same reaction, also applying [Ru(bpy)3](PF6)2

The photodecarboxylative addition of carboxylates to phthalimides as a key-step in the synthesis of biologically active 3-arylmethylene-2,3-dihydro-1H-isoindolin-1-ones

• Ommid Anamimoghadam,
• Saira Mumtaz,
• Anke Nietsch,
• Gaetano Saya,
• Cherie A. Motti,
• Jun Wang,
• Peter C. Junk,
• Ashfaq Mahmood Qureshi and
• Michael Oelgemöller

Beilstein J. Org. Chem. 2017, 13, 2833–2841, doi:10.3762/bjoc.13.275

• one of the N-ethyl groups of the side chain. The mechanism of the photodecarboxylation is well established (Scheme 7) and involves triplet sensitization by acetone and electron transfer between the phenylacetate and the excited phthalimide [55][56][57]. Subsequent decarboxylation, radical combination

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

• single-electron transfer (SET) between CF3SO2Cl and the association CuBr/chiral phosphoric acid. In the process, SO2 and HCl were released, but the latter was scavenged by Ag2CO3, minimising its impact on the reaction process by notably avoiding hydroamination side reactions. The trifluoromethyl radical

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

• CF3SO2Na in the presence of copper(I), reacted at the more electron-rich carbon atom of the C=C double bond to give the radical species 5 that was oxidised by copper(II) into the corresponding cationic intermediate 6 via a single electron transfer (SET). Finally, the acetyl cation was eliminated to provide

• -products. The mechanism was similar to previous examples to generate the β-CF3 alkyl radical intermediate 44, which was trapped by halogen atom transfer from the halogenating agent. The nitrogen-centered radical 45 oxidised Mes-Acr* by a single-electron-transfer process to restart the catalytic cycle

• were compatible with the reaction conditions. A series of control experiments that included the inhibition of the reaction in the presence of TEMPO, deuteration and isotope effect experiments were carried out and led the authors to propose the single-electron transfer mechanism presented in Scheme 44

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides

• Irwan Iskandar Roslan,
• Kian-Hong Ng,
• Gaik-Khuan Chuah and
• Stephan Jaenicke

Beilstein J. Org. Chem. 2017, 13, 2739–2750, doi:10.3762/bjoc.13.270

• silylation [72]. In these reactions, the single electron transfer (SET) is initiated by KOt-Bu/DMF [63][67][69][71] or KOt-Bu in combination with additives such as bidentate diamine ligands [61][62][63][64][65], 18-crown-6 [70] or azobisisobutyronitrile (AIBN) [62][66]. Herein, we report the synthesis of

• with 6 (Scheme 4d). After 16 h, 93% of 3a was formed, showing unambiguously that the reaction proceeds via 6 as an intermediate. We propose that KOt-Bu assists in α-bromination of 2a to form the intermediate 6 via single electron transfer (SET). Recent mechanistic work by Murphy and co-workers showed

Palladium-catalyzed Heck-type reaction of secondary trifluoromethylated alkyl bromides

• Tao Fan,
• Wei-Dong Meng and
• Xingang Zhang

Beilstein J. Org. Chem. 2017, 13, 2610–2616, doi:10.3762/bjoc.13.258

• %), Xantphos (7.5 mol %) and KOAc in DCE at 80 °C, the addition of an electron transfer scavenger 1,4-dinitrobenzene [25][26][27] dramatically diminished the yield of 3a (Table 2, entries 2 and 3), and catalytic amount of radical inhibitor hydroquinone totally shut down the reaction (Table 2, entry 4). Thus

Synthesis and application of trifluoroethoxy-substituted phthalocyanines and subphthalocyanines

• Satoru Mori and
• Norio Shibata

Beilstein J. Org. Chem. 2017, 13, 2273–2296, doi:10.3762/bjoc.13.224

• conjugation. The electronic interaction between the covalently connected chromophore unit leads to important changes in the absorption spectra and so these dimers are expected to serve as attractive building blocks for the construction of multicomponent photoinduced electron transfer supramolecular systems

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• radical intermediate 46 governs the formal [4 + 2]-cycloaddition reaction of E-1b with 3,4-di(α-styryl)furan (47, Scheme 15). The photoinduced reaction occurs via an electron-transfer (PET) process and led to the formation of the polycyclic product 48 in a stereospecific manner [52]. Similar products were

• disulfides and diselenides is explained as a redox process through a single-electron transfer (SET) mechanism with E-1a as the oxidizing reagent, which converted into a mixture of diastereoisomeric diethyl dicyanosuccinates 96 [72]. Very likely, an analogous SET mechanism governs also the reaction of E-1

• ). Formation of disulfides through reaction of thiols with E-1a. Formation of CT salts of E-1 with Mn2+ and Cr2+ metallocenes through one-electron transfer. Oxidation of diethyl dicyanofumarate (E-1a) with H2O2 to give oxirane 101. The aziridination of E-1b through nitrene addition. Acknowledgements The