Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• for product formation and a successful outcome of the reaction. In the same year, the Ritter group [52] reported a Pd-catalyzed fluorination of arylboronic acid derivatives via a Pd(II)/Pd(III) cycle (Scheme 15). A single-electron-transfer (SET) mechanism involving a well-defined Pd(III) intermediate

• group of Van Humbeck [90] reported a selective and mild method for the C–H fluorination of azaheterocycles with Selectfluor at room temperature. In this case, a new radical mechanism was proposed that electron transfer from the heterocyclic substrate to Selectfluor eventually generates a benzylic

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• helped to increase the ability of complexation of 12 with iodide [56]. 2.7. Functional molecular crystal and materials Combining anion–arene interactions and controlling the electron-transfer or charge-transfer process concerning an anionic guest by using a cyclophane is uncommon [57] but can be realized

• . Thus, these complexes could be useful for designing functional molecular crystals and materials which can be applied for the study of photoinduced electron transfer and energy conversion towards application in the field of molecular electronics. 3. Molecular reactors Designing synthetic host systems

• ·TCNQ]2+ complex by pre-reduction to a [TCNQ]−· anion radical in situ, and encapsulation in the host, photochemical excitation of the porphyrin unit in the reactor, photoinduced electron transfer from the excited porphyrin unit to a neutral TCNQ, giving rise to a porphyrin radical cation and a second

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• oxidation potential of 0.38 V vs SCE [59]. Together with the reduction potential of Ered = 0.69 V and E00 = 3.25 eV for NDI 1 (vide infra), this electron transfer is clearly exergonic (ΔG = Eox − Ered − E00 = −2.2 eV). NDI 6 shows a strong and broad fluorescence in CH2Cl2 with a maximum at 640 nm and a

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• for the generation of carbon radicals via single-electron transfer (SET). In 2016, Barriault and co-workers reported a methodology that features the utilization of dimeric gold complex [Au2(dppm)2]Cl2 and ultraviolet A (UV, 365 nm) light to direct arylation of bromide-substituted butenolides or cyclic

Identification of optimal fluorescent probes for G-quadruplex nucleic acids through systematic exploration of mono- and distyryl dye libraries

• Xiao Xie,
• Michela Zuffo,
• Marie-Paule Teulade-Fichou and
• Anton Granzhan

Beilstein J. Org. Chem. 2019, 15, 1872–1889, doi:10.3762/bjoc.15.183

• potential of dyes, rendering the photoinduced electron-transfer reaction with guanine residues in DNA energetically disfavored and resulting in higher fluorescence quantum yields. However, in the absence of redox potential data, this assumption could not be experimentally verified. Finally, we showed that

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• single-electron transfer (SET) with CuI followed by hydride abstraction/intramolecular nucleophilic addition and loss of a proton forming the desired compound 49 (Scheme 19). Cu(I)-catalyzed intramolecular oxidative C–H amidation of N-pyridylenaminones 61 for the synthesis of imidazo[1,2-a]pyridine

• reaction, OMS-2 acted as support and an electron transfer mediator for copper in order to generate a low energy pathway for rapid electron transfer thereby minimizing the catalyst loading (Figure 4). The reaction was supposed to proceed through iodine-catalyzed Ortoleva–King reaction with the assistance of

• not formed. Atmospheric oxygen has oxidized Cu(I) to Cu(II). This Cu(II) acts as an initiator for a single electron transfer (SET) process, to proceed the reaction with benzylamine. A regioselective synthesis of imidazo[1,2-a]pyridines was reported by the group of Kamal and Reddy [123]. They have

2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes

• Li-Li Wang,
• Yi-Kuan Tu,
• Huan Yao and
• Wei Jiang

Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146

• maximum of 1 is located at 350 nm (Figure S22, Supporting Information File 1). It is known that the binding of metal ions could cause fluorescence quenching through photo-induced electron transfer [44]. Indeed, the fluorescence intensity of 1 is quenched gradually upon addition of TBA[AuCl4] (Figure 6a

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• as well-demonstrated fluorescence quenchers acting through a photoinduced electron transfer (PET) mechanism [8][28][29], we hypothesize an electron transfer-induced quenching in the GC5A–Fl complex as underlying mechanism. The binding stoichiometry between GC5A and Fl was determined to be 1:1

• covalent linked calixarene via proton-coupled electron transfer [62]. Kitamura and co-workers reported that the complexation of SC4A could quench the luminescence of tris(2,2'-bipyridine)Ru(II) dichloride (Ru(bpy)3), where SC4A serves as a PET quencher [63]. Shinkai and co-workers reported that the

Extending mechanochemical porphyrin synthesis to bulkier aromatics: tetramesitylporphyrin

• Qiwen Su and
• Tamara D. Hamilton

Beilstein J. Org. Chem. 2019, 15, 1149–1153, doi:10.3762/bjoc.15.111

• out important functions in nature including light harvesting (i.e., chlorophyll), oxygen transport (i.e., heme), biocatalysis, and electron transfer. The ability to synthesize porphyrins bearing a variety of chemical and steric functionalities on the periphery is important in fields as diverse as

Diaminoterephthalate–α-lipoic acid conjugates with fluorinated residues

• Leon Buschbeck,
• Aleksandra Markovic,
• Gunther Wittstock and
• Jens Christoffers

Beilstein J. Org. Chem. 2019, 15, 981–991, doi:10.3762/bjoc.15.96

• the study of electron transfer [26][27] or for building surface molecular devices for different purposes, commonly called integrated molecular systems [19]. These molecular systems are mainly used for pH sensing [28][29][30], inorganic- [31][32][33], organic- and biosensors [34][35]. Self-assembled

A diastereoselective approach to axially chiral biaryls via electrochemically enabled cyclization cascade

• Hong Yan,
• Zhong-Yi Mao,
• Zhong-Wei Hou,
• Jinshuai Song and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2019, 15, 795–800, doi:10.3762/bjoc.15.76

• -centered radicals (NCRs) are attractive reactive intermediates for organic synthesis as they provide opportunities for the efficient construction of C–N bonds [15][16][17][18][19]. Recently, the generation of NCRs through electron transfer-based methods has been attracting attention. Organic

• at the cathode deprotonates 2a to give its conjugate base II. The anionic II is oxidized by radical cation I through single electron transfer (SET) to give radical intermediate III, which undergoes a biscyclization to give V. Further oxidation of V followed by hydrolysis of the cyclic carbamate

Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• usually proceeds through single-electron transfer to dioxygen, leading to either a loss of stereoselectivity, degradation of the organocopper or to the formation of dimer as major products [71]. Therefore, it was clear that a different approach for the oxidation process was needed. Oxenoid, possessing the

Selective benzylic C–H monooxygenation mediated by iodine oxides

• Kelsey B. LaMartina,
• Haley K. Kuck,
• Linda S. Oglesbee,
• Asma Al-Odaini and
• Nicholas C. Boaz

Beilstein J. Org. Chem. 2019, 15, 602–609, doi:10.3762/bjoc.15.55

• proton coupled electron transfer (PCET) type mechanism. Additionally, as shown in Figure 2, 1,2,3,4-tetrahydronaphthalene was functionalized in poor yield (23%) to its acetate 3g if exposed to reaction conditions at lower temperatures (60 °C) than were used for other substrates. At 100 or 150 °C, only

Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions

• Nicholas L. Reed,
• Madeline I. Herman,
• Vladimir P. Miltchev and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30

• photoinduced electron transfer processes. A major theme of research that has emerged from these studies is the application of various cocatalysts to intercept the organoradical intermediates of photoredox reactions and modulate their subsequent reactivity [5][6]. The combination of photoredox catalysis with

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• reaction pathway is outlined in Scheme 13. Initially, the Togni reagent II (30) goes through a single-electron transfer (SET) under the action of Fe2+ to generate the CF3 radical 35. The CF3 radical 35 is trapped by the C–C double bond of substrate 54 to produce the alkyl radical intermediate 57. Then, the

• of azide to Rh2(esp)2 complex (bis[rhodium-(α,α,α’,α’-tetramethyl-1,3-benzenedipropionic acid)]) and extrusion of N2. Then, the Rh-nitrene intermediate 65 goes through an intramolecular single electron transfer (SET) to give the nitrogen-centered radical intermediate 66 [87][88][89][90]. Next, the

Adhesion, forces and the stability of interfaces

• Robin Guttmann,
• Johannes Hoja,
• Christoph Lechner,
• Reinhard J. Maurer and
• Alexander F. Sax

Beilstein J. Org. Chem. 2019, 15, 106–129, doi:10.3762/bjoc.15.12

• conformation; 2) that the neutral molecules do not undergo an electron-transfer interaction to form cation–anion pairs; or 3) that there is no significant change in the electronic structure of the interacting molecules, such as that caused by electronic excitation or covalent bonding. The absence of covalent

• , even today it is more often claimed than actually demonstrated that hydrogen-bonded complexes are predominantly stabilized by electrostatics [6]. If any other interaction but electrostatics is considered, it is “charge-transfer”, which suggests that the dimer stabilization is caused by an electron

• transfer, although this would mean the creation of a cation–anion pair and, thus, a loss of molecular integrity. What is meant, however, is a polarization of the electron density due to a charge shift, which is covered by the basic induction interactions [2]. Although dispersion interaction is a ubiquitous

N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

• Fabienne Speck,
• David Rombach and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 52–59, doi:10.3762/bjoc.15.5

• excited states. Normally, this is the reason why photochemical processes can hardly compete with photophysical decay processes. However, a pre-coordination of the substrate may facilitate electron transfer under non-diffusional controlled conditions. Very recently, the fast (picosecond) excited state

• conditions or heated ion exchange resin [21][22]. These methods are therefore not suitable for the alkoxylation of acid or base-labile substrates. To overcome the current limitations of reduction potentials of single electron transfer processes in photoredox catalysis we present herein a range of new N

• reduction potential interestingly is higher than in the parent compound 1 although there are electron-donating alkyl groups present in the molecular structure. This can be explained by a twist of the arene moieties due to steric bulk causing an interruption of the delocalization. The electron transfer is

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

• rate was observed compared to the optimal reaction conditions (Table 1, entry 9). In principle, visible-light-mediated photocatalysis can serve for electron transfer (for either oxidation or reduction) and/or for energy transfer. We found that the reduction potential Ep/2 of xanthate 1a is −1.78 V vs

• measurement (Figure 2B) can be rationalized using either an energy-transfer or an electron-transfer mechanism. For the same delay times and in the presence of 1a, the ΔOD values in Figure 2D are smaller than those of photocatalyst 8 in the absence of the xanthate (Figure 2A). This is due to the quenching of

• the 3MLCT state of the photocatalyst. If an electron-transfer process occurs from photocatalyst 8 to xanthate 1a, the ΔOD values in the UV region should be noticeably higher due to the TA band contribution from bpy− connected to an Ir metal center of the +4 oxidation state (i.e., absorption due to

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• and redox reactions are possible. This process is called photoinduced electron transfer (PET). In this context, photoredox catalysis was developed. Light is used to excite the photoredox catalyst which allows electron transfer processes with additives. Both oxidation and reduction reactions can be

• already found wide applications such as in water splitting, solar energy storage, proton-coupled electron transfer or photovoltaic for example [18]. 1.3 Electronic transitions involved into photoredox processes For selected photoredox catalysts, light irradiation has enough energy for the excitation of

• species. Most of the transitions observed for this complex are LMCT and MLCT (respectively, described in 1.3.4 and 1.3.5). After electron transfer, the metal complex is promoted to an oxidation or reduction state. With well adapted redox potentials and relatively long-lived excited states, these metal

Photocatalyic Appel reaction enabled by copper-based complexes in continuous flow

• Clémentine Minozzi,
• Jean-Christophe Grenier-Petel,
• Shawn Parisien-Collette and
• Shawn K. Collins

Beilstein J. Org. Chem. 2018, 14, 2730–2736, doi:10.3762/bjoc.14.251

• ]. Specifically, our group has demonstrated that heteroleptic Cu(I) complexes [19][20][21] have significant potential as photocatalysts that can promote a variety of mechanistically distinct photochemical transformations including single electron transfer (SET), energy transfer (ET), and proton-coupled electron

• transfer (PCET) reactions [22][23][24][25][26]. Herein, the evaluation of Cu(I)-complexes for photocatalytic Appel reactions and demonstration in continuous flow is described. Results and Discussion The first step in identifying a heteroleptic diamine/bisphosphine Cu(I)-based photocatalyst for the

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• reductive dehalogenases [88]. The Co(I) species is a key form for electron transfer to a substrate. 4-1. Choice of alternatives to reductases Although anaerobic microbes can be applied to remediation technologies, the dehalogenation abilities of microbes are equal to the intrinsic abilities of nature in

• electrodes and substrates can be achieved without any chemical redox reagents. The use of mediators enables energy savings with mild applied potentials or small amounts of electricity. We constructed electrochemical catalytic systems for dehalogenation of alkyl halides using 1. The electron transfer from

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• importance, since the highly reactive intermediate can be generated by photochemical reaction such as electron transfer and energy transfer [43][44][45]. Among them, light-energy-driven CO2 fixation reactions via C–C bond formation are promising in terms of mimicking photosynthesis. In 2015, Murakami et al

Cobalt-catalyzed peri-selective alkoxylation of 1-naphthylamine derivatives

• Jiao-Na Han,
• Cong Du,
• Xinju Zhu,
• Zheng-Long Wang,
• Yue Zhu,
• Zhao-Yang Chu,
• Jun-Long Niu and
• Mao-Ping Song

Beilstein J. Org. Chem. 2018, 14, 2090–2097, doi:10.3762/bjoc.14.183

• calculations (DFT) [30][31], the C–H activation most possibly proceeded via a single-electron transfer (SET) path compared to a concerted metalation-deprotonation (CMD) path. Followed by an intermolecular SET process, the cation-radical intermediate A was generated, which coordinates with a CoIII species to

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• excited state (S1) or a triplet excited state (T1), by absorption of a photon with energy hν, which then undergoes photoinduced electron transfer (PET). Following this, the photocatalyst is reduced or oxidised accordingly, such that it returns to its ground state and native oxidation state (Figure 1 and

• , there are multiple pathways through which it can decay back to S0. The excited state can decay via non-radiative processes, such as vibrational relaxation. It can also return to S0 via fluorescence or non-radiative emission. While in S1 (or T1) Förster resonance electron transfer (FRET) can occur, a

• comparable to or larger than the Φf and, more importantly, the rate constant for ISC (kISC) must be similar to the rate constant for fluorescence (kf). The lifetime of the T1 state (τT1) is generally orders of magnitude longer than the timescale of electron transfer (ET), meaning that τT1 does not alter the

Functionalization of graphene: does the organic chemistry matter?

• Artur Kasprzak,
• Agnieszka Zuchowska and
• Magdalena Poplawska

Beilstein J. Org. Chem. 2018, 14, 2018–2026, doi:10.3762/bjoc.14.177

• researchers have discussed the reaction pathway [49][50]. Most plausibly, the reaction can be mainly attributed to rapid reactions based on electron-transfer processes. The first step of the diazotization reaction involves the generation of a diazonium salt from the corresponding amino reagent using a nitrite

• species (Figure 7, step a). Then (most likely) the aryl radical is obtained from the diazonium salt via the single electron transfer (SET) process and the inclusion of a graphene sheet (Figure 7, step b). This reaction step results in nitrogen extrusion. The desired functionalization route is most

• . The diazotization approach utilizing amyl nitrites in organic solvent (e.g., o-dichlorobenzene) can therefore (i) enable an efficient electron-transfer process (Figure 7, step b), (ii) facilitate the desired reaction pathway (Figure 7, step c), and (iii) increase the functionalization yield. This