DDQ in mechanochemical C–N coupling reactions

• Shyamal Kanti Bera,
• Rosalin Bhanja and
• Prasenjit Mal

Beilstein J. Org. Chem. 2022, 18, 639–646, doi:10.3762/bjoc.18.64

• practice by applying the strategies like domino, cascade, or tandem [11][12][13]. These environmentally friendly approaches set forth the journey of facilitating sustainable systems by using mechanochemical methods to access small organic compounds [3]. Due to the high reduction potential of the quinone

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

• other hand, the yield of 3a decreased even when the terminal halogen of the dihaloalkane was changed to iodine (Table 7, entry 3). LSV measurements showed that the reduction potential of 1,4-diiodobutane (2c) was almost the same as that of the substrate imine 1 (Supporting Information File 1, Figure S12

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• arenes (Scheme 13). In this transformation, the azide anion is oxidized to its radical, and this process requires a high reduction potential that cannot be achieved by iridium and ruthenium-based catalysts. In contrast, [Cu(dap)2]Cl and [Cu(dap)Cl2] were found suitable for the oxidation. Based on a

Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands

• Sergey V. Norkov,
• Anton V. Cherkasov,
• Andrey S. Shavyrin,
• Maxim V. Arsenyev,
• Viacheslav A. Kuropatov and
• Vladimir K. Cherkasov

Beilstein J. Org. Chem. 2021, 17, 273–282, doi:10.3762/bjoc.17.26

• annulated 1,3-dithiole fragment, an increasing oxidizing ability comparing to that of 3,6-di-tert-butyl-o-benzoquinone (36Q) (Ered(1/2) = −0.50 V) was observed. For o-quinones 6a–d the first reduction potential is shifted by 0.18–0.32 V relative to that of 36Q. Previously reported o-quinone 3b was also

• found to be a stronger oxidant than 36Q [16]. A very similar redox behavior and shifts of reduction potential values were observed for p-quinone derivatives with attached 1,3-dithiole rings [27][49]. UV–vis spectroscopy Sterically hindered o-quinones are deep-colored compounds. Any changes in their

• subsequent one-electron quasi-reversible steps corresponding to the formation of semiquinone and dianion catecholate species, respectively o-Quinones 6b–d bearing an additional redox-active unit in the structure exhibit a more complicated behavior that involve processes on the annulated moiety. The reduction

Controlled decomposition of SF₆ by electrochemical reduction

• Sébastien Bouvet,
• Bruce Pégot,
• Stéphane Sengmany,
• Erwan Le Gall,
• Eric Léonel,
• Anne-Marie Goncalves and
• Emmanuel Magnier

Beilstein J. Org. Chem. 2020, 16, 2948–2953, doi:10.3762/bjoc.16.244

• , CNRS, ICMPE, UMR 7182, 2 rue Henri Dunant, 94320 Thiais, France 10.3762/bjoc.16.244 Abstract The electroreduction of SF6 is shown at ambient temperature in acetonitrile using an array of platinum microelectrodes to improve the electrical detection. Its half reduction potential occurs at −2.17 V vs Fc

• reduction potential of SF6. To allow its electroreduction feasibility in acetonitrile, an electrochemical analytical approach was required [24]. This crucial step was supported by sensors which are based on a micro-disc-array of platinum ultramicroelectrodes (20 µm diameter) acting as multi-probe channels

• controlled decomposition of sulfur hexafluoride was described under electroreduction. The reduction potential was firstly determined and used for preparative studies. The extrapolation on large scale of this methodology is under current development in our laboratory. Experimental Acetonitrile (HPLC grade

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• fluorinated agrochemicals (Figure 2) [7][8]. Fluorine possesses some unique properties, such as the highest atomic electronegativity [9] and, in its molecular form (F2), the most positive standard reduction potential (E0) of +2.87 V [10], as predictable from its position in the periodic table. The C–F bond

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• the design of a photocatalytic cycle based on the SET reduction of the substrate. Furthermore, the relatively low reduction potential of these species (Ered ≈ −1.1 V for N-acetoxyphthalimide) [44] brings them into the operational range of various organic dyes, allowing mild reaction conditions. König

• porphyrin [75] and rhodamine 6G (OD14) [76]. Aryl radicals from aryl halides. Aryl halides are generally more difficult to reduce than aryl diazonium salts (Ered < −1.2 V) [77][78]. However, they are more available and bench-stable. Their reduction potential is dependent on the substitution pattern and on

• [84]. Other sources of aryl radicals. In addition to aryl diazonium salts and aryl halides, arylsulfonyl chlorides can be reduced with common organic dyes due to their relatively low reduction potential [78]. As an example, Gu and co-workers reported the use of eosin Y (OD13) for the SET reduction

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• , respectively (both vs saturated calomel electrode (SCE)). These data indicate that the excited state of TPP is a more efficient electron donor than its ground state. At the same time, the reduction potential value suggests that the excited state of TPP (E1/2(TPP*/TPP−•) = +0.42 V vs SCE) is a more efficient

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• , probably due to their intrinsic reduction potential. Interestingly, the bromide substrate derived from menthol was readily reduced in an excellent 74% isolated yield. The authors conducted some mechanistic studies (including cyclic voltammetry and Stern–Volmer quenching experiments, for instance), and

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• reduction potential of 1QuCN+* was higher than that of benzene (Eox vs SCE = 2.32 V), making the electron transfer from phenol to 1QuCN+* viable. The mechanistic pathway for the C–H hydroxylation of benzene derivatives is shown in Figure 19. On the other hand, Ohkubo et al. reported that substrates like

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

• Eric W. Webb,
• Jonathan P. Moerdyk,
• Kyndra B. Sluiter,
• Benjamin J. Pollock,
• Amy L. Speelman,
• Eugene J. Lynch,
• William F. Polik and
• Jason G. Gillmore

Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240

• as photooxidants, the difference in the reduction potential between LW and SW would need to be increased further, and LW would need to be more reducible to be of use in photooxidation of relevant substrates (e.g., Dewar benzenes, quadricyclanes, or bishomocubanes as quantum amplified isomerization

• carbon insulating the dienone electrophore from the quinoline moiety in the SW form, we expected minimal change in the SW reduction potential relative to the PSHDs, but a significant difference for the completely conjugated LW isomer(s). Previously we reported the detailed synthesis of two novel

• nitrogen are far enough removed from the electrophore to not cause any appreciable change in reduction potential. The other qualitative difference for 3b was the presence of two LW reduction peaks (LW → LW•− → LW2−) on the first scan (Figure 3a, dotted red). However, the observation of the two LW reduction

Friedel–Crafts approach to the one-pot synthesis of methoxy-substituted thioxanthylium salts

• Kenta Tanaka,
• Yuta Tanaka,
• Mami Kishimoto,
• Yujiro Hoshino and
• Kiyoshi Honda

Beilstein J. Org. Chem. 2019, 15, 2105–2112, doi:10.3762/bjoc.15.208

• = 464 nm) showed a large red shift compared to thioxanthylium salt 4b (λmax = 383 nm), which has no methoxy groups (Figure 4 and Figure 5). Finally, we measured the cyclic voltammograms (CV) of thioxanthylium salts 3b and 4b (Figure 6). The CV data analysis implies that the reduction potential of 3b (E

• °’ = −0.79 V vs Fc/Fc+) afforded a negative shift compared to 4b (E°’ = −0.56 V vs Fc/Fc+). It is obviously indicated that the methoxy groups lower the reduction potential by their strong electron-donating effect. Conclusion We have developed the Friedel–Crafts approach as an efficient method to synthesize

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

• DMF. Due to the charge-transfer character in the excited state the absorbances of cNDIs 2 and 6 are shifted into the visible range with a broad band between 500 nm and 650 nm. The reduction potential to form the radical anion of such a cNDI is significantly shifted to a more negative potential of E½(2

• solubilities. The electron-donating diaminoalkyl substituents together with the electron-deficient aromatic core of the naphthalene diimides increase the charge-transfer character of their photoexcited states and thus shift their absorption into the visible light (500–650 nm). The excited state reduction

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

• 7x) also display very high fluorimetric response (up to I/I0 = 690, for 1x–TERRA complex), albeit at the expense of somewhat lower selectivity with respect to ds DNA and ss RNA. It may be suggested that electron-rich heterocyclic substituents (indole and pyrrole) act by lowering the reduction

• 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

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

• absorbance and electrochemical characteristics. Among the synthesized compounds, alkylaminylated N-phenylphenothiazines were identified to be highly suitable for photoredox catalysis. The dialkylamino substituents of these N-phenylphenothiazines shift the estimated excited state reduction potential up to

• dynamics of the radical cation of N-phenylphenothiazine was investigated by Wasielewski et al. This radical cation had a high reduction potential of about +2.1 V (vs SCE) [17] allowing the reduction of poorly oxidizing agents. The combination of both properties in one system is a remarkable feature for

• insufficient reduction potential of the photoredox catalyst, the Markovnikov addition of alcohols through oxidative quenching is yet limited to highly activated, aromatic alkenes. To the best of our knowledge no methods are known today that allow the addition of alcohols to α-methyl-substituted styrenes

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

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

• electronically excited state which significantly changes the distribution of electrons in the molecule. Thus, chemical properties such as reactivity, oxidation potential or reduction potential change drastically. With appropriate donors or acceptors, electron charge transfer is possible via this excited state

• equation: where Eox is the oxidation potential of the electron donor, Ered the reduction potential of the electron acceptor, E* the excited state energy level and C the coulombic term for the initially formed ion pair (if there are ions in solution). For polar solvent, C is neglected. (TMS)3SiH is not

• states [40]. The more the ligand has an electron-donating behavior, the easier is the oxidation of the metal center. For example, adding methyl substituents to the bipyridine ligands of the Ru(bpy)32+ complex, the reduction potential shifts from −1.33 V to −1.45 V [49]. Redox potentials of the complex

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

• reached within the redox window determined by the electrolyte. Thus, a strongly electron-deficient substituent such as pyridinium is necessary to shift the reduction potential to accessible values. However, not every electron-withdrawing group appears to be suited to induce cathodic cyclization [40][42

• ]. In the case of the electron-deficient benzonitrile derivative sDTE66-PhCN the reduction potential could be reached and for the Z-isomer an irreversible two-electron reduction wave at Epc = −2.526 V was detected (Figure 4). Upon re-oxidation, a new peak matching that of the photochemically generated

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

• providing 2 (54–87% yield, not including dppf-based complexes). Interestingly, the best catalyst for the transformation (Cu(tmp)(BINAP)BF4, 99% of 2) was a poor catalyst for a previously reported photoredox reaction [27]. It should be noted that Cu(tmp)(BINAP)+ possesses an excited state reduction potential

• of −1.93 V vs. SCE, much greater than that of Ru(bpy)3+2 (−0.81 V vs SCE), albeit the copper complex has a much shorter excited state lifetime (≈4 ns vs ≈1100 ns for Ru(bpy)3+2). The excited state reduction potential should match favorably with CBr4 (E½ = 0.30 V vs SCE) in DMF [29]. Note that many of

Bi-mediated allylation of aldehydes in [bmim][Br]: a mechanistic investigation

• Mrunesh Koli,
• Sucheta Chatterjee,
• Subrata Chattopadhyay and
• Dibakar Goswami

Beilstein J. Org. Chem. 2018, 14, 2198–2203, doi:10.3762/bjoc.14.193

• [20] etc. are also tedious and not ideal for green chemistry. The use of a second metal with lower reduction potential than the active metals could not reduce the amounts of disposable metallic wastes [21][22]. Since most of the in situ-generated allylmetals are hydrolytically unstable, a large excess

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

• accordance with the anticipated PET mechanism [31][45]. Further, the change in free energy, ∆G, associated with PET was calculated using the Rehm–Weller equation [46]. Therefore, we used a reduction potential of −1.55 V for the 1,3,7,9-tetramethyl-BODIPY core acceptor of 1, 2, and 5 [47] and of −1.81 V for

Investigations of alkynylbenziodoxole derivatives for radical alkynylations in photoredox catalysis

• Yue Pan,
• Kunfang Jia,
• Yali Chen and
• Yiyun Chen

Beilstein J. Org. Chem. 2018, 14, 1215–1221, doi:10.3762/bjoc.14.103

• -donating 3,4-dimethoxy groups. Cyclic voltammetry measurements were also carried out for BI-alkynes 3a–f, in which the reduction potential (Ep re) indicated the electron-accepting capacity of the BI-alkynes. As expected, the reduction potential of 3a was increased with electron-deficient 3,4-difluoro

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

• -benzotropone (11) with dimethyl barbituric acid (62) and subsequent oxidative cyclization reaction using DDQ-Sc(OTf)3 or photoirradiation under aerobic conditions afforded 61+.BF4− (Scheme 12). The pKR+ value and reduction potential of the cation 61 were studied. The relative stability of a carbocation can be

• expressed by the pKR+ value, which is the affinity of the carbocation toward hydroxide ions. The pKR+ value for cation 61 was determined to be 4.7 spectrophotometrically. The reduction potential of the cation 61 was determined as −0.46 and −1.07 V by cyclic voltammetry in acetonitrile. The oxidizing ability

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

• terminated as the current flow stopped very early [30]. When a silver cathode was used, a good yield of desired alkyne 2a was obtained (72%), along with a small amount of hydrogenated alkene 4a (6%). In order to increase the yield of alkyne 2a (and as 2a reduction potential is much more negative, vide infra

• can undergo a rearrangement to yield alkyne 2a. According to the mechanism shown in Scheme 6, the formation of bromoalkyne 3a competes with the formation of 2a in reaction 2 and its rate of formation is comparable to that of 2a. Since its reduction potential is close to that of 1a (see Supporting