Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

• Periklis X. Kolagkis,
• Eirini M. Galathri and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2024, 20, 379–426, doi:10.3762/bjoc.20.36

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

• proposed mechanism, radical species 9, which is generated upon cathodic reduction of active ester 3, is captured by complex 171 (Scheme 34B). The resulting NiIII complex 172 undergoes facile reductive elimination to form cross-coupling product 173 and NiI intermediate 174. Finally, reduction of 174 at the

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

• [90][91]. Due to their wide electrochemical window, imidazolium ILs are commonly used in organic electrochemistry, simultaneously as solvents and supporting electrolytes [92][93][94]. In addition, the cathodic reduction (both in batch [95] and in flow [96]) can be exploited for the generation of N

Beyond n-dopants for organic semiconductors: use of bibenzo[d]imidazoles in UV-promoted dehalogenation reactions of organic halides

• Kan Tang,
• Megan R. Brown,
• Chad Risko,
• Melissa K. Gish,
• Garry Rumbles,
• Phuc H. Pham,
• Oana R. Luca,
• Stephen Barlow and
• Seth R. Marder

Beilstein J. Org. Chem. 2023, 19, 1912–1922, doi:10.3762/bjoc.19.142

• to initiate the coupling of aryl halides and arenes [5]. However, even relatively easily reduced organic halides have sufficiently cathodic reduction potentials (e.g., ca. −1.6 V and −1.8 vs ferrocenium/ferrocene (FeCp2+/0) for diethyl bromomalonate [6] and 4-iodotoluene, see Table 2, respectively

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

• doublet states which are photoexcited to yield super-oxidants or super-reductants while recycling e-PRC involves the turnover of a ‘standard’ (typically closed-shell) photoredox catalyst (PC) by means of anodic oxidation or cathodic reduction [28][29]. Furthermore, a series of new protocols using

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

• oxygen on the cathode. Figure 2 shows a proposed mechanism. Anodic oxidation of cumene on the BDD electrode with a wide potential window preferentially affords the cumyl cation as the reaction intermediate. On the other hand, cathodic reduction of dissolved oxygen produces the superoxide and even the

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

• cathodic reduction producing hydrogen gas. We report electrochemical Friedel–Crafts-type amidomethylation of electron-rich arenes by a novel electrochemical oxidation system using a quasi-divided cell and iPr2NHEtBF4. Results and Discussion We chose 1,3,5-trimethoxybenzene (1) as a model substrate for

• , trifluoroacetic acid (TFA, 1 equiv) as a proton source for the cathodic reduction, and iPr2NEt (1 equiv) as a base for the formation of N-acyliminium ions of DMA at the anode was carried out under constant current conditions (20 mA/cm2) with 3 F/mol of electricity at 0 °C. It was found that 66% of 1 remained

• -acyliminium ions, a proton source for which the conjugate base has no nucleophilicity would be necessary in the cathodic reduction. After several attempts, we finally reached HBF4·OEt2 as a proton source for cathodic reduction and the result is shown in entry 2 of Table 1. Strong increases of conversion of 1

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

• used as organocatalyst in two classical umpolung reactions of cinnamaldehyde: its cyclodimerization and its oxidative esterification. Keywords: Breslow intermediate; cathodic reduction; flow electrochemistry; N-heterocyclic carbene; oxidative esterification; Introduction Ionic liquids (ILs) are well

• can be modified by the presence of a base or by a single electron cathodic reduction of the C–H between nitrogen atoms of the imidazolium ring (Scheme 1), inducing the formation of a N-heterocyclic carbene (NHC) [7][8]. In recent years, NHCs have achieved great success: they have been frequently used

• cathodic reduction in a divided cell using flow electrochemistry technique, and to compare the results with the corresponding batch process. Once established, the flow electrochemistry NHC synthesis would be combined with applications as an organocatalyst in some organic transformations of cinnamaldehyde

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

• Sadanobu Iwase Shinsuke Inagi Toshio Fuchigami Department of Electronic Chemistry, Tokyo Institute of Technology, Yokohama 226-8502, Japan Department of Chemical Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan 10.3762/bjoc.18.88 Abstract The cathodic reduction of

• resulted in much lower product yields. The detailed reaction mechanism was clarified based on the cathodic reduction of 1 in the presence of deuterated acetonitrile, CD3CN. Keywords: bis(phenylthio)difluoromethane; cathodic reduction; deuteration; o-phthalonitrile mediator; (phenylthio)difluoromethylation

• generation of (phenylthio)difluoromethyl reactive species from bromodifluoromethyl phenyl sulfide and their synthetic application as well as mechanistic aspects. Results and Discussion Cathodic reduction of bromodifluoromethyl phenyl sulfide (1) At first, the reduction potential (Epred) of

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

• ]. The key features of this method are the effective cathodic reduction of imines and their rapid use for the subsequent reactions in a microflow system. Successful preliminary results prompted us to perform the electroreductive cyclization of an imine with terminal dihaloalkanes to afford heterocyclic

• amines in a flow microreactor because the reaction involves cathodic reduction of the imine and its rapid use for the subsequent reaction with the terminal dihaloalkanes. In this work, we demonstrate the electroreductive cyclization of an imine with terminal dihaloalkanes in a flow microreactor to

• . Table 2 shows that the yield of 3a increased as the amount of 2a was increased, and reached a maximum at 2 equiv. The yield of 3a began to decrease with the addition of more 2a. This decrease in the yield of 3a can be attributed to the competition of the cathodic reduction of 2a caused by the increase

Electrocatalytic C(sp³)–H/C(sp)–H cross-coupling in continuous flow through TEMPO/copper relay catalysis

• Bin Guo and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2021, 17, 2650–2656, doi:10.3762/bjoc.17.178

• alkyne 27 with the assistance of CF3CH2O−. The added CuII precatalyst is likely reduced at the cathode to produce the requisite CuI. The base CF3CH2O− is produced through cathodic reduction of TFE. The addition of TFE to the reactions helps cathodic H2 evolution and may also stabilize the iminium ion

Regiodivergent synthesis of functionalized pyrimidines and imidazoles through phenacyl azides in deep eutectic solvents

• Paola Vitale,
• Luciana Cicco,
• Ilaria Cellamare,
• Filippo M. Perna,
• Antonio Salomone and
• Vito Capriati

Beilstein J. Org. Chem. 2020, 16, 1915–1923, doi:10.3762/bjoc.16.158

• -azido ketones in iPrOH in the presence of potassium ethylxanthate as a catalyst [28], (b) by exploiting the reaction of arylglyoxals with an excess amount of ammonium acetate in water [29], (c) by the cathodic reduction of 2-azido-1-phenylethanone in a DMF/LiClO4 medium [30], (d) by radical chain

Synthesis of novel multifunctional carbazole-based molecules and their thermal, electrochemical and optical properties

• Nuray Altinolcek,
• Ahmet Battal,
• Mustafa Tavasli,
• William J. Peveler,
• Holly A. Yu and
• Peter J. Skabara

Beilstein J. Org. Chem. 2020, 16, 1066–1074, doi:10.3762/bjoc.16.93

• molecular orbital and the lowest unoccupied molecular orbital energy levels (EHOMO, ELUMO) of compounds 7a and 7b were also calculated from the half-way anodic oxidation and onset cathodic reduction peak potentials, with respect to the energy level of ferrocene (4.8 eV below vacuum level) [38] by using the

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• chloroperoxidase catalyst. H2O2 generated in situ from the cathodic reduction of oxygen was proposed to be responsible for the enzyme-mediated thiol ether oxidation (Scheme 47) [82]. Vitamin B12-dependent enzymes are an exciting representative in the family of chiral inductors for electroorganic chemistry. These

• 1994, Zielinski and Schäfer made a vital contribution in the field of asymmetric electrosynthesis in terms of the diastereoselective cathodic reduction of the carbonyl group of chiral phenylglyoxamides 150 and 152 [89][90]. After initial conversion to its corresponding amides using chiral auxiliaries

• sequential reports, Feroci and Inesi discussed the electrochemical carboxylation of chiral α-bromocarboxylic acid derivatives 165 substituted with Evans-type chiral auxiliaries [96][97]. The cathodic reduction of the C–Br bond in presence of CO2 followed by treatment with diazomethane resulted in the

Oxidative and reductive cyclization in stiff dithienylethenes

• Michael Kleinwächter,
• Ellen Teichmann,
• Lutz Grubert,
• Martin Herder and
• Stefan Hecht

Beilstein J. Org. Chem. 2018, 14, 2812–2821, doi:10.3762/bjoc.14.259

• oxidation wave. Cyclization by cathodic reduction Except for rare examples of methylpyridinium substituted DTEs [27][28] and dithiazolylethenes [29], ring closure under reductive conditions has not been reported for DAEs. For most structures the reduction potential of the open isomer is too negative to be

Electrochemically modified Corey–Fuchs reaction for the synthesis of arylalkynes. The case of 2-(2,2-dibromovinyl)naphthalene

• Fabiana Pandolfi,
• Isabella Chiarotto and
• Marta Feroci

Beilstein J. Org. Chem. 2018, 14, 891–899, doi:10.3762/bjoc.14.76

• alkyne (Et4NBF4) or the bromoalkyne (NaClO4). This study allowed to establish that 2-(bromoethynyl)naphthalene can be converted into 2-ethynylnaphthalene by cathodic reduction. Keywords: arylalkyne; carbon–bromine bond cleavage; cathodic reduction; Corey–Fuchs reaction; 2-(2,2-dibromovinyl)naphthalene

• , temperature, working potential and amount of consumed charge [24]. Our group intensively investigated the electrochemical behavior of 1,1-dibromoalkenes by means of cyclic voltammetry and electrolyses [25] and we reported the selective synthesis of vinyl bromides through the cathodic reduction of 1,1

• decided to carry out our study using 2-(2,2-dibromovinyl)naphthalene (1a) as starting material for the synthesis of 2-ethynylnaphthalene (2a, Scheme 4). Results and Discussion In our previous work [25], we found that the cathodic reduction of 2-(2,2-dibromovinyl)naphthalene (1a), carried out at the

Electrochemical Corey–Winter reaction. Reduction of thiocarbonates in aqueous methanol media and application to the synthesis of a naturally occurring α-pyrone

• Ernesto Emmanuel López-López,
• José Alvano Pérez-Bautista,
• Fernando Sartillo-Piscil and
• Bernardo A. Frontana-Uribe

Beilstein J. Org. Chem. 2018, 14, 547–552, doi:10.3762/bjoc.14.41

• more environmentally friendly than the classical reaction, where a large excess of trialkyl phosphite as reducing agent and high temperatures are required. Thus, cathodic reduction at room temperature of two cyclic thiocarbonates (−1.2 to −1.4 V vs Ag/AgCl) afforded the corresponding alkenes, trans-6

• in mind that the Corey–Winter reaction is in fact a reductive chemical process between the thiocarbonate moiety and the phosphorylated reagent, which oxidize P(III) to P(V), we anticipated that a cathodic reduction process applied to the same cyclic thiocarbonate 4 would provide the desired target

Cathodic hydrodimerization of nitroolefins

• Michael Weßling and
• Hans J. Schäfer

Beilstein J. Org. Chem. 2015, 11, 1163–1174, doi:10.3762/bjoc.11.131

• the group of activated alkenes that can be hydrodimerized by cathodic reduction. There are many olefins with different electron withdrawing groups used for cathodic hydrodimerization, but not much is known about the behaviour of the nitro group. Synthetic applications of this group could profit from

• formation; 1,4-dinitrocompounds; electrosynthesis; nitroalkene; Introduction Olefins being activated by an electron withdrawing group can be hydrodimerized by cathodic reduction [1][2]. Thereby, the cathode serves as cheap, versatile, immobilized and mostly non-polluting reagent providing economical and

• undergoes a nucleophilic addition to a forming a dimer radical anion that is reduced to e that is then protonated to the dimer f. In path (III) the radical coupling of two radical anions b leads to the dianion e, which is protonated to the product. We first checked the cathodic reduction of (E)-2-nitro-1

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

• Huixin Jiang,
• Virginia Mazzanti,
• Christian R. Parker,
• Søren Lindbæk Broman,
• Jens Heide Wallberg,
• Karol Lušpai,
• Adam Brincko,
• Henrik G. Kjaergaard,
• Anders Kadziola,
• Peter Rapta,
• Ole Hammerich and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

• voltammetric studies discussed above, a nearly reversible first cathodic reduction was observed for radiaannulenes 2b and 8. At the low scan rates (2 mV s−1) used in spectroelectrochemistry, the cyclic voltammetric peaks become nearly irreversible indicating much lower stability of the formed radical anions in

• the first EPR signal can be tentatively ascribed to the radical anion 2b•– while the second EPR signal is an unidentified product formed by conversion of this radical anion. Very similar EPR spectra were observed upon cathodic reduction of radiaannulene 8 as shown in Supporting Information File 1

Electrochemical oxidation of cholesterol

• Jacek W. Morzycki and
• Andrzej Sobkowiak

Beilstein J. Org. Chem. 2015, 11, 392–402, doi:10.3762/bjoc.11.45

• biology [18][19][20][21]. In analogy of the oxidation of cholesterol in the human body the Takayama group [22] has employed the process of dioxygen activation by Tl(II), which was electrochemically generated by the cathodic reduction of the Tl(III) hematoporphyrin (HMP) complex. The system produced

• source since no additives were employed. The observed results may be explained by assuming a cathodic reduction of dichloromethane to chloride ions, followed by their diffusion to the anodic compartment, and electrooxidation to chlorine which reacted with cholesterol. An efficient electrochemical

• by the possibility of cathodic dichloromethane reduction yielding chloride ions, which can migrate to the anodic compartment. To prevent the cathodic reduction of dichloromethane a small amount of glacial acetic acid was added to the cathodic compartment, but its leakage to the anodic part of the

Stereoselective cathodic synthesis of 8-substituted (1R,3R,4S)-menthylamines

• Carolin Edinger,
• Jörn Kulisch and
• Siegfried R. Waldvogel

Beilstein J. Org. Chem. 2015, 11, 294–301, doi:10.3762/bjoc.11.34

• additional substituent in position 8 is described. Due to 1,3-diaxial interactions a pronounced diastereoselectivity for the menthylamines is found. Keywords: cathodic reduction; chiral amines; electrosynthesis; menthylamines; oximes; Introduction Optically active amines serve as powerful and versatile

Cathodic reductive coupling of methyl cinnamate on boron-doped diamond electrodes and synthesis of new neolignan-type products

• Taiki Kojima,
• Rika Obata,
• Tsuyoshi Saito,
• Yasuaki Einaga and
• Shigeru Nishiyama

Beilstein J. Org. Chem. 2015, 11, 200–203, doi:10.3762/bjoc.11.21

• -type products were synthesized from the hydrodimer. Keywords: boron-doped diamond (BDD) electrode; cathodic reduction; electrochemistry; electrosynthesis; neolignan; Introduction Numerous lignans and neolignans were found as secondary plant metabolites, and many of them are known to exhibit

• in preparative-scale cathodic reduction of organic compounds [7]. During our investigations of phenolic oxidation reactions using BDD electrodes, we observed the generation of solvent-derived methoxy radicals that conducted an oxidation process of the phenol substrate to the corresponding coupling

• product [8]. In our second investigation on the use of the BDD electrode in organic synthesis, the electrochemical reduction of methyl cinnamate (1a) was investigated to assess the applicability of BDD electrodes under cathodic reduction conditions, and to obtain new neolignan-type bioactive substances

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids

• Roman Matthessen,
• Jan Fransaer,
• Koen Binnemans and
• Dirk E. De Vos

Beilstein J. Org. Chem. 2014, 10, 2484–2500, doi:10.3762/bjoc.10.260

• . However, product formation through cathodic reduction of acetonitrile is ruled out properly, since no cyanoacetic acid was formed when using a cation-exchange membrane. Since most of the product is present in the anolyte, current yields are rather low (24%). Moreover, the electrolyte anion and the

• appeared to be very promising for this purpose, fulfilling both the role of electrolyte and reducing agent. Tetraethylammonium cations have high reduction stability, while still possessing good ion pairing properties. The degree of delocalization of the positive charge is large enough to prevent cathodic

• reduction and small enough to allow a quick and stable interaction with the cathodically formed carboxylate anions. Furthermore, oxalate and formate are easily oxidized at a Pt anode, gradually releasing the tetraethylammonium cations. The combination of both salts in acetonitrile gives near quantitative