Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• , wherein the activation of complex 74 takes place through SET under constant current electrolysis [64]. The Glorius and Y. Fu groups have independently proposed the formation of analogous charge-transfer complexes involving NHPI esters, bis(pinacolato)diboron (B2pin2), and Lewis bases (pyridine or

• where NHPI esters have been utilized as radical precursors under electrochemical conditions. Giese-type radical additions, which are usually performed under conditions of photoredox-catalysis (see Scheme 4), can also be achieved under constant-potential electrolysis employing graphite electrodes [110

• ] (Scheme 33A). The mechanism of this redox neutral reaction involves reductive fragmentation of the radical precursor 3 mediated by the cathode under constant-current electrolysis (Scheme 33B). The resulting alkyl radical 9 attacks the protonated quinoline 168, forming radical cation intermediate 169

Additive-controlled chemoselective inter-/intramolecular hydroamination via electrochemical PCET process

• Kazuhiro Okamoto,
• Naoki Shida and
• Mahito Atobe

Beilstein J. Org. Chem. 2024, 20, 264–271, doi:10.3762/bjoc.20.27

• potential than 1 (Figure 2C, grey line); thus, it was subsequently oxidized on the anode to afford the halonium ion (Cl+), which can react with 1 to form unstable N−Cl species (B) in situ (Figure 4). Although we cannot detect the chlorinated intermediate of 1, electrolysis of N-propylcarbamate derivative

Optimizing reaction conditions for the light-driven hydrogen evolution in a loop photoreactor

• Pengcheng Li,
• Daniel Kowalczyk,
• Johannes Liessem,
• Mohamed M. Elnagar,
• Dariusz Mitoraj,
• Radim Beranek and
• Dirk Ziegenbalg

Beilstein J. Org. Chem. 2024, 20, 74–91, doi:10.3762/bjoc.20.9

• emphasis must also be placed on upscaling reactors and catalytic systems to facilitate the transition to cleaner energy sources. There are mainly three categories of solar to hydrogen generation methods based on semiconductors, namely photovoltaic-powered electrolysis (PV-E), photoelectrochemical (PEC

1-Butyl-3-methylimidazolium tetrafluoroborate as suitable solvent for BF₃: the case of alkyne hydration. Chemistry vs electrochemistry

• Marta David,
• Elisa Galli,
• Richard C. D. Brown,
• Marta Feroci,
• Fabrizio Vetica and
• Martina Bortolami

Beilstein J. Org. Chem. 2023, 19, 1966–1981, doi:10.3762/bjoc.19.147

• starting or stopping the electrolysis, 3) the absence of fuming, most probably due to the ability of the IL to stabilize the Lewis acid, 4) reduced sensitivity to moisture, due to the protective action of the IL, and 5) the possibility of recycling the same sample of IL for subsequent reaction cycles. In

• (according to the electrolysis conditions) may have affected the results obtained with these substrates. Further studies will be necessary to clarify the behaviour of alkynes containing a carbonyl group adjacent to the triple bond. After work-up, the electrolysed IL was placed under vacuum to eliminate

• literature for BMIm-F [110]. The only difference between IL 19F NMR spectra before and after electrolysis is a peak at ‒148.7 ppm (referred to BF4− at −150.6 ppm), possibly due to BF3OH− or B2F7− [111][112] (see Supporting Information File 1, Figure S1a vs f and b, c). This last hypothesis is corroborated by

Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

• commercialized. Specifically, the company Twelve are making large advances in the electrolysis of carbon dioxide to carbon monoxide. Their contracts started with materials and have now expanded to fuels [10]. However, industrial electrochemistry either requires a dedicated power source, or plugging into a

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

A new oxidatively stable ligand for the chiral functionalization of amino acids in Ni(II)–Schiff base complexes

• Alena V. Dmitrieva,
• Oleg A. Levitskiy,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2023, 19, 566–574, doi:10.3762/bjoc.19.41

• simple and suitable for gram-scale loadings. Galvanostatic electrolysis of the glycine complex (GlyNi)L7 was performed in a one-compartment electrochemical cell in a methanol solution (CH3OH serves as a reactant and a solvent simultaneously) in the presence of KOH. By this route the (SerNi)L7 complex

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• [74][76][80][86][87][88]. To facilitate the anodic oxidation of N-hydroxyphthalimide, basic pyridine derivatives are used as the N-hydroxyphthalimide proton acceptors [87]. In many cases electrolysis can be performed in the galvanostatic mode in a simple undivided cell, which is convenient for

• multigram-scale syntheses [86]. The selective allylic [86] and benzylic [80] CH-oxidation to the corresponding carbonyl compounds was achieved. Compared to the direct anodic oxidation of organic substrates, the N-oxyl-mediated indirect electrolysis proceeds at lower potentials, demonstrates wider

• -oxyl (ACT) allows for the oxidation of alcohols and aldehydes to carboxylic acids by controlled potential electrolysis, while maintaining the stereocenter configuration in the R-substituent [102] (Scheme 14). The method is also suitable for molecules with chelating pyridine moieties. An outstanding

Molecular and macromolecular electrochemistry: synthesis, mechanism, and redox properties

• Shinsuke Inagi and
• Mahito Atobe

Beilstein J. Org. Chem. 2022, 18, 1505–1506, doi:10.3762/bjoc.18.158

• , polymer electrolyte membrane electrolysis technology, and new methods coupled with photoredox catalysts or transition metal catalysis, resulting in remarkable progress in organic electrosynthetic processes. Theoretical calculations have also led to a better understanding of the electron transfer behavior

Microelectrode arrays, electrosynthesis, and the optimization of signaling on an inert, stable surface

• Kendra Drayton-White,
• Siyue Liu,
• Yu-Chia Chang,
• Sakashi Uppal and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2022, 18, 1488–1498, doi:10.3762/bjoc.18.156

• direct analogy to the experiment shown in Figure 4. The current associated with this redox couple at each of the electrode in the array was again monitored by using the array as an anode and the remote Pt electrode in the electrolysis cell as a cathode. The surface of the array was the arylbromide-based

• on the surface of the electrodes. Supporting Information Supporting Information File 310: Procedures for electrolysis and cyclic voltammetry experiments, characterization of electrolysis products, procedures for synthesis and characterization of electrolysis starting materials. Funding We thank the

A one-pot electrochemical synthesis of 2-aminothiazoles from active methylene ketones and thioureas mediated by NH₄I

• Shang-Feng Yang,
• Pei Li,
• Zi-Lin Fang,
• Sen Liang,
• Hong-Yu Tian,
• Bao-Guo Sun,
• Kun Xu and
• Cheng-Chu Zeng

Beilstein J. Org. Chem. 2022, 18, 1249–1255, doi:10.3762/bjoc.18.130

• , the in situ generated α-iodoketone was proposed to be the key active species. Keywords: 2-aminothiazoles; electrosynthesis; indirect electrolysis; halide ion; Introduction Thiazoles are prevalent structural motifs in a wide range of natural products [1] and synthetic molecules possessing various

• . Organic electrosynthesis has been recognized as a green, modern, and safe technique, since electrons can be used as an alternative for oxidants or reductants [30][31][32][33][34][35][36][37][38]. During our continuous interests in halide-mediated indirect electrolysis [39][40][41][42], we have achieved

• the in situ generation of α-iodocarbonyl ketones from constant current electrolysis (CCE) of ketones in the presence of iodide ions. It is worth noting that we have also reported an electrochemical method for the synthesis of 2-aminothiazoles via the one-pot direct α-C–H functionalization of ketones

Polymer and small molecule mechanochemistry: closer than ever

• José G. Hernández

Beilstein J. Org. Chem. 2022, 18, 1225–1235, doi:10.3762/bjoc.18.128

• of these two different experimental approaches in the development of mechanochemical reactions. For example, Li and co-workers showed that piezoelectric nanoparticles such as BaTiO3 and ZnO could trigger water electrolysis under ultrasonication [53]. Sonication caused deformation of, or strain on the

Reductive opening of a cyclopropane ring in the Ni(II) coordination environment: a route to functionalized dehydroalanine and cysteine derivatives

• Oleg A. Levitskiy,
• Olga I. Aglamazova,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2022, 18, 1166–1176, doi:10.3762/bjoc.18.121

• the chemical step following the first reduction process. Preparative electrolysis Based on the voltammetry results, complexes 3 and 4 were chosen as the models for the preparative study. The electrolysis was performed in a two-compartment electrochemical cell in DMF using a glassy carbon plate as a

• electrolysis of complex 3 can be protonated using acetic acid (pKa in DMSO = 12.3 [53]), in contrast to their counterparts formed from complex 4. In the latter case, a stronger protonating agent is required, e.g., PhNEt2·HCl (pKa in DMSO = 2.45 for PhN+HMe2 [53]). The pKa value of 6 determined in DMSO solution

• bioactivity [54][55]. To increase the yield of the alkene complexes, the addition of an external “H-abstractor” may be helpful, to suppress disproportionation. A possible candidate may be a reduced radical form of azobenzene. Indeed, the preparative electrolysis performed in the presence of the equimolar

Electro-conversion of cumene into acetophenone using boron-doped diamond electrodes

• Mana Kitano,
• Tsuyoshi Saitoh,
• Shigeru Nishiyama,
• Yasuaki Einaga and
• Takashi Yamamoto

Beilstein J. Org. Chem. 2022, 18, 1154–1158, doi:10.3762/bjoc.18.119

• conversion is found to proceed electrochemically. Results and Discussion First, we carried out the electrolysis of cumene (1) in 0.1 M Bu4NBF4/MeCN under constant current conditions in an undivided beaker-type cell (Table 1, entry 1). The main product was acetophenone (3) and α-cumyl alcohol (4) was also

• graphite and Ni are too narrow to oxidize 1 directly, as can be seen in Figure 1b. Overall, the electrochemical measurements indicate the BDD’s wide potential window enables direct oxidation of 1 to produce a key reaction intermediate to afford 3. A series of electrolysis experiments was performed to

• propose a reaction mechanism (Table 2). First, we carried out the electrolysis of 1 in MeCN–MeOH to confirm whether the reaction intermediate is a radical or cationic species (Table 2, entry 1). As a result, methyl cumyl ether, a methoxy adduct to the benzyl position of 1, was obtained as the main product

Synthesis of protected precursors of chitin oligosaccharides by electrochemical polyglycosylation of thioglycosides

• Md Azadur Rahman,
• Kana Kuroda,
• Hirofumi Endo,
• Norihiko Sasaki,
• Tomoaki Hamada,
• Hiraku Sakai and
• Toshiki Nokami

Beilstein J. Org. Chem. 2022, 18, 1133–1139, doi:10.3762/bjoc.18.117

• thioglycosides as monomer is described. Oligosaccharides up to the hexasaccharide were synthesized under optimized reaction conditions. Further, a modified method enabled the synthesis of oligosaccharides up to the octasaccharide by repeating electrolysis with additional monomers. The mechanism of the

• oligosaccharides thus obtained are in progress in our laboratory. Experimental Electrochemical polyglycosylation (see Figure 4, T1 = −60 °C and T2 = −30 °C) was performed using our second-generation automated electrochemical synthesizer equipped with the H-type electrolysis cell. Thioglycoside 1a (0.20 mmol, 109

• mg), Bu4NOTf (1.0 mmol, 393 mg), and dry CH2Cl2 (10 mL) were added to the anodic chamber. Triflic acid (0.2 mmol, 17.6 μL) and CH2Cl2 (10 mL) were added to the cathodic chamber. Electrolysis was performed at −60 °C under constant current conditions until 0.52 F/mol of electricity had been consumed

Electrogenerated base-promoted cyclopropanation using alkyl 2-chloroacetates

• Kouichi Matsumoto,
• Yuta Hayashi,
• Kengo Hamasaki,
• Mizuki Matsuse,
• Hiyono Suzuki,
• Keiji Nishiwaki and
• Norihito Kawashita

Beilstein J. Org. Chem. 2022, 18, 1116–1122, doi:10.3762/bjoc.18.114

• cathodic chamber, 1 (0.5 mmol) was dissolved in 0.3 M Bu4NBr in DMF (4.0 mL) and 0.3 M Bu4NBr in DMF (4.0 mL) was introduced to the anodic chamber. Constant current electrolysis at 12 mA until 1.0 F/mol was consumed in the cathode yielded the corresponding compound 2 in a 46% yield (Table 1, entry 1

• of electricity for the next investigations (Table 3). Finally, the electrolysis using the undivided cell shown in entry 4 of Table 2 yielded 2 in ≪5% yield, indicating that the divided cell is essential for the current reaction. In the undivided cell, the anionic species from the cathode might be

• with the vinyl group did not occur (Table 3, entry 7), but the reaction of compound 15 with the allyl group formed 16 in 34% yield (Table 3, entry 8). Finally, benzyl 2-chloroacetate (17) produced the corresponding compound 18 in 31% yield (Table 3, entry 9). The current electrolysis reaction can be

Electrochemical formal homocoupling of sec-alcohols

• Kosuke Yamamoto,
• Kazuhisa Arita,
• Masashi Shiota,
• Masami Kuriyama and
• Osamu Onomura

Beilstein J. Org. Chem. 2022, 18, 1062–1069, doi:10.3762/bjoc.18.108

• electrolysis; Introduction Carbon–carbon bond formation is one of the most fundamental and important reactions in synthetic organic chemistry. Reductive coupling of carbonyl compounds known as pinacol coupling would be a powerful method to construct vic-1,2-diol scaffolds through C–C bond formation [1][2

• simple and user-friendly undivided cell set-up, consuming the anode material with generating stoichiometric metal waste may be a serious issue in terms of green and sustainable chemistry. Thus, the development of a sacrificial anode-free process such as paired electrolysis would be highly desirable [40

• are summarized in Table 1. The electrolysis was carried out using an undivided cell in the presence of Et4NBr as an electrolyte with a mixed solvent of MeCN and H2O under air atmosphere. When 4 F/mol of electricity was passed through the reaction mixture using two platinum electrodes at 0 ºC, the

Electrochemical hydrogenation of enones using a proton-exchange membrane reactor: selectivity and utility

• Koichi Mitsudo,
• Haruka Inoue,
• Yuta Niki,
• Eisuke Sato and
• Seiji Suga

Beilstein J. Org. Chem. 2022, 18, 1055–1061, doi:10.3762/bjoc.18.107

• , respectively (Figure 2). When a Pd/C catalyst was used, 1a was hydrogenated to 2a selectively, and further reduction to 3a was almost completely suppressed (Figure 2a). In contrast, the use of an Ir/C catalyst afforded both 2a and 3a, and generated 2a was smoothly reduced to 3a by further electrolysis (Figure

Electrochemical Friedel–Crafts-type amidomethylation of arenes by a novel electrochemical oxidation system using a quasi-divided cell and trialkylammonium tetrafluoroborate

• Hisanori Senboku,
• Mizuki Hayama and
• Hidetoshi Matsuno

Beilstein J. Org. Chem. 2022, 18, 1040–1046, doi:10.3762/bjoc.18.105

• , Hokkaido 060-8628, Japan 10.3762/bjoc.18.105 Abstract Electrochemical Friedel–Crafts-type amidomethylation was successfully carried out by a novel electrochemical oxidation system using a quasi-divided cell and trialkylammonium tetrafluoroborates, such as iPr2NHEtBF4. Constant current electrolysis of

• ) [22][23]. We also succeeded in generating N-acyliminium ions from N,N-dimethylformamide (DMF) used as a solvent in the electrochemical carboxylation of benzyl bromides. Electrolysis of benzyl bromides in DMF containing 0.1 M Bu4NBF4 and iPr2NEt (1 equiv) using an undivided cell equipped with a Pt

• good yields [29]. In this reaction system, the use of a quasi-divided cell enabled DMF to be oxidized with high selectivity at the anode even in the presence of carboxylate and bromide ions, which would generally be oxidized more easily than DMF. Accordingly, we tried this electrolysis system using a

Electrochemical vicinal oxyazidation of α-arylvinyl acetates

• Yi-Lun Li,
• Zhaojiang Shi,
• Tao Shen and
• Ke-Yin Ye

Beilstein J. Org. Chem. 2022, 18, 1026–1031, doi:10.3762/bjoc.18.103

• diverse organic frameworks. Herein, we report that the electrochemical oxyfunctionalization strategy could be well applied to the synthesis of α-azidoketone using readily available α-arylvinyl acetates, and azidotrimethylsilane (Scheme 1C). Results and Discussion The constant cell potential electrolysis

First example of organocatalysis by cathodic N-heterocyclic carbene generation and accumulation using a divided electrochemical flow cell

• Daniele Rocco,
• Ana A. Folgueiras-Amador,
• Richard C. D. Brown and
• Marta Feroci

Beilstein J. Org. Chem. 2022, 18, 979–990, doi:10.3762/bjoc.18.98

• NHCs are generated in situ, where they may be used as basic or nucleophilic species. Due to the difficulty isolating highly reactive NHCs, the concentration of the obtained NHC solution can be determined indirectly by addition of elemental sulfur after the electrolysis, which realizes quantitative

• chamber (Figure 1). The requirement for a divided cell (a more complicated device than the undivided configuration) arises from the need to protect electrogenerated NHC from its anodic oxidation in the absence of a consumable anode. To ensure good sealing of the electrolysis cell, the sandwich-type

• membrane, under N2 atmosphere, at room temperature, under galvanostatic conditions (I = 134 mA) with continuous flow rate of 36 mL/min, studying the effect of cathode material, anode solution and number of Faradays per mole of IL supplied (Table 1). At the end of the electrolysis, excess elemental sulfur

Cathodic generation of reactive (phenylthio)difluoromethyl species and its reactions: mechanistic aspects and synthetic applications

• Sadanobu Iwase,
• Shinsuke Inagi and
• Toshio Fuchigami

Beilstein J. Org. Chem. 2022, 18, 872–880, doi:10.3762/bjoc.18.88

• , and dihydrofuran. The results are summarized in Table 1. Regardless of trapping reagents, 1.3–1.4 F/mol of electricity was required to consume the starting material 1. The required electricity was similar to the electrolysis in the absence of the trapping reagent. Only when α-methylstyrene was used as

• electrolysis in the absence of cumene (Table 4, run 1). On the other hand, the yield of product 4 increased in the presence of iPrOH (Table 4, run 3), and the yield further increased to 60% at a higher content of iPrOH of 50% (Table 4, run 4). In the latter case, the required electricity was increased to 2.7 F

• /mol. Reutrakul and Pomakotr et al. also reported that iPrOH is an effective additive for the addition of PhSCF2 radical to olefins [5]. Since the presence of a large amount of a proton source such as iPrOH increased the yield of adduct 4 significantly, the electrolysis of compound 1 in the presence of

Inductive heating and flow chemistry – a perfect synergy of emerging enabling technologies

• Conrad Kuhwald,
• Sibel Türkhan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2022, 18, 688–706, doi:10.3762/bjoc.18.70

• this reaction, CO2 and H2 are converted to CH4 (Scheme 4). This process can be used as a catalytic cycle in combination with electrolysis of water to produce the hydrogen exactly when the demand requires it. The reactions are very powerful and can represent an important access to synthetic fuels. This

• amounts of lignin as a byproduct. The authors compared the fast pyrolysis of poplar wood and switchgrass by RF heating. The highest yield of bio-oil was obtained for switchgrass at a pyrolysis temperature as low as 450 °C. 2.8 Water electrolysis Electrolysis of water as a power-to-hydrogen (PtH) concept

• is not new, but has become one of the most important topics being discussed today. Due to the energy of hydrogen–hydrogen bonding, water electrolysis enables chemical storage of renewable electricity. Chatenet, Carrey and co-workers showed that the electrocatalytic reaction of hydrogen formation from

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• electrolysis (Scheme 10). For this approach, two smooth platinum foil electrodes placed 1 cm apart in the upper aqueous phase were electrolyzed galvanostatically (30 mA/cm2). Additionally, a NaBr solution acidified with H2SO4 was used as electrolyte. The voltage during electrolysis was 2.1 V and when the

Synthesis of piperidine and pyrrolidine derivatives by electroreductive cyclization of imine with terminal dihaloalkanes in a flow microreactor

• Yuki Naito,
• Naoki Shida and
• Mahito Atobe

Beilstein J. Org. Chem. 2022, 18, 350–359, doi:10.3762/bjoc.18.39

• . Furthermore, piperidine and pyrrolidine derivatives could be obtained on preparative scale by continuous electrolysis for approximately 1 hour. Keywords: electrochemical synthesis; electrocyclization; flow microreactor; heterocyclic amines; imine; Introduction Heterocycles are a very important class of

• -current electrolysis in a flow microreactor with fixed channel dimensions, the electricity can be controlled by changing the current density or flow rate. As shown in entries 1 and 2 of Table 4, the yield of 3a increased with the electricity (caused by an increase in the current density) and reached a

• electrolyte, the electrolysis reaction could not be carried out because Et4N∙ClO4 did not dissolve in the THF solution. On the other hand, n-Hex4N∙ClO4 dissolved easily in THF solution and the electrolysis reaction proceeded smoothly. However, the yield of the desired product 3a was slightly lower than that