Synthesis of polycyclic aromatic quinones by continuous flow electrochemical oxidation: anodic methoxylation of polycyclic aromatic phenols (PAPs)

• Hiwot M. Tiruye,
• Solon Economopoulos and
• Kåre B. Jørgensen

Beilstein J. Org. Chem. 2024, 20, 1746–1757, doi:10.3762/bjoc.20.153

• trap the phenoxonium cation formed in the oxidation as an acetal, that later were hydrolysed to the quinone. Formation of hydrogen gas as the cathode reaction caused challenges in the flow cell and were overcome by recycling the reaction mixture through the cell at increased flow rate several times

• chrysenols nor phenanthrols, suggesting a chemically irreversible reaction of the radical cation intermediate with the ensuing product no longer being electrochemically active within the potential window of the CV scans. However, a reduction peak was observed for compound 1b (see Figure S2 in Supporting

• radical and a naphthyloxy cation leading to the formation of 5. Our CV studies exhibit oxidation peaks, which seem in line with what to expect for an electrochemical oxidation of PAPs. Through the cyclic voltammetry experiments for the investigation of the redox behavior of the PAPs, an estimation of

Regio- and stereochemical stability induced by anomeric and gauche effects in difluorinated pyrrolidines

• Ana Flávia Candida Silva,
• Francisco A. Martins and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2024, 20, 1572–1579, doi:10.3762/bjoc.20.140

• crystallographic data using the 3-fluoropyrrolidinium cation and 3-fluoropyrrolidine. Subsequently, we explored the relative energy of all favored conformations of all different stereoisomers of 2,3-, 2,4-, and 3,4-difluoropyrrolidines at the B3LYP-D3BJ/6-311++G** level. A generalized anomeric effect, arising from

• interactions [4]. Protonation of 3-fluoropyrrolidine generates the 3-fluoropyrrolidinium cation, and this typically results in a highly favored conformation in both the gas phase and solution where the fluorine and nitrogen atoms are cis, mirroring the behavior observed in analagous 4- and 6-membered ring

• -fluoropyrrolidine. To investigate potential changes in the preferred orientation of the fluorine substituent in 3-fluoropyrrolidine and the respective cation, an additional fluorine atom was introduced into the molecule for theoretic studies (Figure 2). The subsequent evaluation focused on the role of anomeric and

Benzylic C(sp³)–H fluorination

• Alexander P. Atkins,
• Alice C. Dean and
• Alastair J. J. Lennox

Beilstein J. Org. Chem. 2024, 20, 1527–1547, doi:10.3762/bjoc.20.137

• functional groups on the aromatic ring and adjacent to the benzylic position. Mechanistic investigations suggested an initial electron transfer to generate a radical cation en route to the intermediate benzylic radical, rather than a HAT process, however, the authors did not distinguish between a stepwise

• a potent HAT reagent capable of generating the benzylic radical, which then performs FAT with Selectfluor to generate the desired benzyl fluoride. Alternatively, the benzylic radical could further be oxidized to the cation, and in the process, regenerating the ground-state catalyst. The benzylic

• cation would then be trapped by the previously liberated fluoride. This reactivity was demonstrated on one primary, one tertiary and eight secondary substrates. When diphenylmethane substrates were subjected to the reaction conditions benzylic ketone products were observed. As highlighted by the examples

Rapid construction of tricyclic tetrahydrocyclopenta[4,5]pyrrolo[2,3-b]pyridine via isocyanide-based multicomponent reaction

• Xiu-Yu Chen,
• Ying Han,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2024, 20, 1436–1443, doi:10.3762/bjoc.20.126

• -deficient alkynes [59][60][61][62][63]. The in situ generated cyclic intermediate C has a resonance hybrid C’. Then, the further nucleophilic addition of the electron-rich enamino unit to 5-(alkylimino)cyclopenta-1,3-diene intermediate C gave intermediate D. At last, the coupling of the iminium cation with

A comparison of structure, bonding and non-covalent interactions of aryl halide and diarylhalonium halogen-bond donors

• Nicole Javaly,
• Theresa M. McCormick and
• David R. Stuart

Beilstein J. Org. Chem. 2024, 20, 1428–1435, doi:10.3762/bjoc.20.125

• (halogen or hypervalent bond) between chloride anion and diarylchloronium cation 9 is non-covalent and likely dominated by electrostatic attraction. A similar switch from non-covalent halogen bond for the lighter (X = Cl and Br) to partially covalent halogen bond for the heavier (X = I and At) was also

• (mesityl)iodonium cation (3) the iodine atom uses 88.54% p-character to bond with the phenyl group. Phenyl iodide (27) has three lone-pairs, whereas the phenyl(mesityl)iodonium cation (3) has two lone-pairs (though it does have another aryl group), and therefore this observation is consistent with Bent’s

Synthesis of cyclic β-1,6-oligosaccharides from glucosamine monomers by electrochemical polyglycosylation

• Md Azadur Rahman,
• Hirofumi Endo,
• Takashi Yamamoto,
• Shoma Okushiba,
• Norihiko Sasaki and
• Toshiki Nokami

Beilstein J. Org. Chem. 2024, 20, 1421–1427, doi:10.3762/bjoc.20.124

• product of monomer 6. The proposed mechanism is shown in Scheme 2. Anodic oxidation of thioglycoside 6 generated radical cation 11, which was converted to glycosyl triflate 12. 1,6-Anhydrosugar 7 was produced via 4C1-to-1C4 conformational change of the pyran ring to generate cation intermediate 13

Challenge N- versus O-six-membered annulation: FeCl₃-catalyzed synthesis of heterocyclic N,O-aminals

• Giacomo Mari,
• Lucia De Crescentini,
• Gianfranco Favi,
• Fabio Mantellini,
• Diego Olivieri and
• Stefania Santeusanio

Beilstein J. Org. Chem. 2024, 20, 1412–1420, doi:10.3762/bjoc.20.123

• -hydrazino form [17][24][25], we conceived the idea of reversing the reactivity of 4a–r in the six-membered cyclization process (N- vs O-annulation) through the generation of an electrophilic oxocarbenium [26][27] cation intermediate from the acetal residue at N-3 of the (thio)hydantoin core. To pursue our

• providing intermediate A. The latter, by loss of a trichloro(alkoxy)ferrate(III) anion, generates a strong electrophile such as the oxocarbenium cation intermediate B. The released trichloro(alkoxy)ferrate(III) splits into FeCl3, which enters the catalytic cycle, and a free alkoxide, which acts as a base

Synthetic applications of the Cannizzaro reaction

• Bhaskar Chatterjee,
• Dhananjoy Mondal and
• Smritilekha Bera

Beilstein J. Org. Chem. 2024, 20, 1376–1395, doi:10.3762/bjoc.20.120

• in the appropriate vicinity for the reaction to take place in appreciably good yields (84%). The barium cation template is the key for the reaction, as is the base concentration for effective hydride transfer (Scheme 14) [29]. They also extended the scope of the intramolecular Cannizzaro reaction to

• proposed strategy where the metal ion acts as the binding cation template for the intramolecular desymmetrization (Scheme 15) [82]. A similar highly efficient intramolecular Cannizzaro reaction of calix[4]arene dialdehydes was observed by Galli et al. where the 1,3-distal cone 35 significantly responded to

Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C–O bonds in organic transformations

• Mithu Roy,
• Bitan Sardar,
• Itu Mallick and
• Dipankar Srimani

Beilstein J. Org. Chem. 2024, 20, 1348–1375, doi:10.3762/bjoc.20.119

• iridium photocatalyst [Ir(dF(CF3)ppy)2(dtbbpy)]PF6 leads to excited-state *[Ir(III)], Ered (*[Ir(III)]/[Ir(II)]) = +1.21 V, possessing sufficient energy to oxidize PPh3, forming the triphenylphosphine radical cation. Subsequently, benzoic acid undergoes deprotonation facilitated by a base, producing

• benzoate. This benzoate then reacts with the triphenylphosphine radical cation, resulting in the formation of the phosphoranyl radical intermediate, which undergoes β-scission, leading to the formation of a benzoyl radical, accompanied by the liberation of a triphenylphosphine oxide molecule. After this

• salicylic acid derivatives and aryl acetylenes. Due to irradiation with blue light, Mes–Acr–Me+ gets excited to Mes–Acr–Me+* and takes up a single electron from Ph2S. The reaction of the diphenyl sulfide radical cation with carboxylate and successive acyloxy C–O bond cleavage forms diphenyl sulfoxide and an

Computation-guided scaffold exploration of 2E,6E-1,10-trans/cis-eunicellanes

• Zining Li,
• Sana Jindani,
• Volga Kojasoy,
• Teresa Ortega,
• Erin M. Marshall,
• Khalil A. Abboud,
• Sandra Loesgen,
• Dean J. Tantillo and
• Jeffrey D. Rudolf

Beilstein J. Org. Chem. 2024, 20, 1320–1326, doi:10.3762/bjoc.20.115

• hyperconjugation via bending the exocyclic methyl group such that the formal p-orbital at C3 no longer aligns with the C2–C7 bond results in the 6/6/6-tricyclic C3 tertiary cation B2+, which is 13.0 kcal mol−1 higher in energy. In principle, either A2+ or B2+ could be deprotonated to form products. A similar

• energy profile is seen for protonation-induced cyclization of 1, although the 6/6/6-tricyclic C3 tertiary cation is 7.1 kcal mol−1 higher in energy than its preceding intermediate (Figure 2C). A lower energy conformer of 1 exists, but we have been unable to find the corresponding cation A1b+, which

Oxidative hydrolysis of aliphatic bromoalkenes: scope study and reactivity insights

• Amol P. Jadhav and
• Claude Y. Legault

Beilstein J. Org. Chem. 2024, 20, 1286–1291, doi:10.3762/bjoc.20.111

• heterocyclic compounds [20][21][22]. Particularly dialkyl bromoketones have been utilized in natural product synthesis [23][24][25], also as a precursor to reactive oxyallyl cation intermediates [26][27][28], and for their photochemical reactions [29]. However, the direct halogenation of unsymmetrical ketones

Synthesis and physical properties of tunable aryl alkyl ionic liquids based on 1-aryl-4,5-dimethylimidazolium cations

• Stefan Fritsch and
• Thomas Strassner

Beilstein J. Org. Chem. 2024, 20, 1278–1285, doi:10.3762/bjoc.20.110

• . With an electrochemical window of up to 6.3 V, which is unprecedented for TAAILs with an NTf2 anion, this new class of TAAILs demonstrates the opportunities that arise from modifications in the backbone of the imidazolium cation. Keywords: conductivity; electrochemical window; ionic liquids; tunable

• use in different fields of chemistry like synthesis [4][5][6][7][8][9], catalysis [10][11][12][13][14] and materials science [15][16][17][18][19][20][21][22][23]. ILs generally consist of an organic cation [24], such as the imidazolium or ammonium ion and an inorganic anion like a halide anion or

• introduced a new class of ionic liquids based on the 1-aryl-3-alkylimidazolium cation in 2009, the tunable aryl alkyl ionic liquids (TAAILs) [29]. This class of ionic liquids allows the modification of physical and chemical properties by variation of the functional groups present at the aryl ring of the

Synthesis of indano[60]fullerene thioketone and its application in organic solar cells

• Yong-Chang Zhai,
• Shimon Oiwa,
• Shinobu Aoyagi,
• Shohei Ohno,
• Tsubasa Mikie,
• Jun-Zhuo Wang,
• Hirofumi Amada,
• Koki Yamanaka,
• Kazuhira Miwa,
• Naoyuki Imai,
• Takeshi Igarashi,
• Itaru Osaka and
• Yutaka Matsuo

Beilstein J. Org. Chem. 2024, 20, 1270–1277, doi:10.3762/bjoc.20.109

• improving their thermal stability, and more specifically, of designing evaporable fullerene derivatives [16][17][18]. Recently, we reported on perovskite solar cells fabricated with indano[60]fullerene ketone (FIDO), which was synthesized through fullerene cation chemistry. These cells demonstrated long

• fullerene cation chemistry as reported by our group [20][21][22][23][24][25][26]. Conversion from ketone to thioketone is usually achieved by using Lawesson's reagent, which tends to form a trimer structure when reacted with indanone without a substituent at the α position [27][28][29]. Introduction of

Domino reactions of chromones with activated carbonyl compounds

• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 1256–1269, doi:10.3762/bjoc.20.108

• observed under these conditions, because the electron-withdrawing character of the additional ester group which destabilizes formation of a cation at the neighboring position. The yields were in most cases moderate (42–54%). Two products were obtained in higher yields (71 and 80%). However, no clear trend

• , because the electron-withdrawing character of the CF3 group which destabilizes the formation of a cation at the neighboring position. In addition, the carbon–sulfur bond was not cleaved, due to the lower leaving group ability of sulfur as compared to oxygen. The yields of the two products were moderate. 3

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• cation was directly observed confirming the previously proposed mechanism of a three-component reaction. Several steps of the photoredox cycle were investigated separately, providing deep insights into the complex mechanism. The triplet-excited Aza-H, which was studied with quantitative LFP, is formed

• as the ionization product resulting from a consecutive two-photon absorption at the selected high laser intensity [69][70], yielding the corresponding long-lived radical cation with second-order decay that is typical for oxidized/reduced species, and a solvated electron as by-product. The latter is

• in equilibrium with the dimeric solvent radical anion in MeCN, it weakly absorbs in our detection window and this species is rather short-lived compared to the triplet as well as the radical cation [71]. The oscillator strengths for the electronic transitions of 3Aza-H (purple) and the radical cation

Stability trends in carbocation intermediates stemming from germacrene A and hedycaryol

• Naziha Tarannam,
• Prashant Kumar Gupta,
• Shani Zev and
• Dan Thomas Major

Beilstein J. Org. Chem. 2024, 20, 1189–1197, doi:10.3762/bjoc.20.101

• insecticidal activities [11], and are bio-fuel alternatives [12][13]. Sesquiterpene synthase can convert FPP to various terpenoids via different initial cyclization processes: 1,6-cyclization to yield the bisabolyl cation, 1,7-cyclization to form the cycloheptanyl cation, 1,10-cyclization lead to the

• germacradienyl cation, and 1,11-cyclization resulting in the humulyl cation [14][15]. Deprotonation of the intermediate germacradienyl cation yields germacrene A, a doorway towards the synthesis of many eudesmane and guaiane sesquiterpene hydrocarbons through its reprotonation-induced transannular reactions

• (Scheme 1) [16]. As an alternative to deprotonation, the germacradienyl cation can be captured by water to yield the sesquiterpene alcohol hedycaryol, which is an important intermediate towards the synthesis of sesquiterpene alcohols [17]. The reprotonation of (R)-(+)-1 germacrene A or hedycaryol at the

Bismuth(III) triflate: an economical and environmentally friendly catalyst for the Nazarov reaction

• Manoel T. Rodrigues Jr.,
• Aline S. B. de Oliveira,
• Ralph C. Gomes,
• Amanda Soares Hirata,
• Lucas A. Zeoly,
• Hugo Santos,
• João Arantes,
• Catarina Sofia Mateus Reis-Silva,
• João Agostinho Machado-Neto,
• Leticia Veras Costa-Lotufo and
• Fernando Coelho

Beilstein J. Org. Chem. 2024, 20, 1167–1178, doi:10.3762/bjoc.20.99

• pentadienyl cation [1][2][3][4][5][6][7][8][9][10][11][12]. Until the past decade, the conditions used for the Nazarov reaction generally involved the use of a stoichiometric amount of a strong Lewis acid (e.g., BF3, TiCl4, SnCl4, AlCl3) in relation to the divinyl ketone derivative [21][22][23]. However

Manganese-catalyzed C–C and C–N bond formation with alcohols via borrowing hydrogen or hydrogen auto-transfer

• Mohd Farhan Ansari,
• Atul Kumar Maurya,
• Abhishek Kumar and
• Saravanakumar Elangovan

Beilstein J. Org. Chem. 2024, 20, 1111–1166, doi:10.3762/bjoc.20.98

• indicates that the cation-coordinative interaction with the catalyst plays a significant role. Moreover, the mechanistic investigation suggested that the observed selectivity is due to the more reactive potassium manganate hydride towards the hydrogenation of imines to amines than the sodium manganate

Light on the sustainable preparation of aryl-cored dibromides

• Fabrizio Roncaglia,
• Alberto Ughetti,
• Nicola Porcelli,
• Biagio Anderlini,
• Andrea Severini and
• Luca Rigamonti

Beilstein J. Org. Chem. 2024, 20, 1076–1087, doi:10.3762/bjoc.20.95

• Ar-SE mechanism, which is reported to proceed through the generation of a mixed molecular halogen [28]. As an alternative to iodine, the trityl cation [29] is reported too. Additional benefits of the method include its ability to work in neutral conditions, and the potential quantitative

Spin and charge interactions between nanographene host and ferrocene

• Akira Suzuki,
• Yuya Miyake,
• Ryoga Shibata and
• Kazuyuki Takai

Beilstein J. Org. Chem. 2024, 20, 1011–1019, doi:10.3762/bjoc.20.89

• diamagnetic molecule (S = 0, no spin magnetism) compared with other metallocenes [17]. However, FeCp2 is easily oxidized to a monovalent cation, the electronic structure of which is magnetic (S = 1/2). Electron spin resonance (ESR) spectroscopy revealed the spin magnetism of cationic FeCp2 accommodated in

• cation spins are less than those for edge-state spins. The apparent reduction in Θ for FeCp2-ACFs-150 is attributed to the contribution of FeCp2+ spins having less exchange interaction in the observed magnetic susceptibility. So, the spin magnetism of the guest molecule is induced by host–guest

Enhancing structural diversity of terpenoids by multisubstrate terpene synthases

• Min Li and
• Hui Tao

Beilstein J. Org. Chem. 2024, 20, 959–972, doi:10.3762/bjoc.20.86

• they often synthesize multiple products from a single substrate through complex cyclization cascades [4][5][6][7][8][9][10]. Based on the mechanism of initial carbocation generation, TSs generally fall into two main classes. Class I TSs generate an allylic cation from a prenyl substrate by

Confirmation of the stereochemistry of spiroviolene

• Yao Kong,
• Yuanning Liu,
• Kaibiao Wang,
• Tao Wang,
• Chen Wang,
• Ben Ai,
• Hongli Jia,
• Guohui Pan,
• Min Yin and
• Zhengren Xu

Beilstein J. Org. Chem. 2024, 20, 852–858, doi:10.3762/bjoc.20.77

• isotope labeling experiments [6], followed by a 2,7-cyclization, afforded C6 cationic intermediate IM-3 with cyclopiane skeleton. Quench of the cation IM-3 with water would give 4, while upon two 1,2-alkyl shifts of IM-3, followed by deprotonation of cation IM-4, would give spiroviolene (1). On the other

• hand, the originally proposed cyclization mechanism (Scheme 1B) involves a 3,6-cyclization of cation IM-1 through a conformation shown as IM-1A to generate cation IM-5, which was proposed to undergo a dyotropic rearrangement, followed by a 1,2-alkyl shift of cation IM-6 to yield the spirocyclic cation

• IM-7. A key 1,3-hydride shift of IM-7 from the β-face, followed by deprotonation of the formed C2-cation IM-8, would deliver the originally proposed structure 1' [6]. However, no related natural products that would be derived from the intermediates of this pathway have been found so far. A third

Skeletal rearrangement of 6,8-dioxabicyclo[3.2.1]octan-4-ols promoted by thionyl chloride or Appel conditions

• Martyn Jevric,
• Julian Klepp,
• Johannes Puschnig,
• Oscar Lamb,
• Christopher J. Sumby and
• Ben W. Greatrex

Beilstein J. Org. Chem. 2024, 20, 823–829, doi:10.3762/bjoc.20.74

• vicinal proton. These results suggested that the formation of the allylic cation occurred readily from alcohols 15 and 18; however, the transition states leading to the rearrangement products were inaccessible and so only chloride addition occurred. The generation of the rearrangement products from the

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• alkene reactivity is essential. Two reactivity scales for alkenes are available in the literature, one considering the reactivity of the alkene itself (Mayr scale) [25] and the other the stability of the corresponding cation after protonation (hydride affinities) [26]. In the polar hydrochlorination

• ). Conveniently, these parameters are freely available on Mayr's database of reactivity parameters [28]. On the other hand, one can assess the stability of the in situ-generated cation. The greater its stability, the easier the protonation of the alkene will be, making it more reactive towards hydrochlorination

• . Thermodynamic and theoretical data provide hydride affinities, which correspond to the negative heat of formation for the combination of a hydride anion with a given cation in the gas phase (Figure 2) [26][29]. It is noteworthy that, in contrast to the hydride affinity scale, the Mayr scale considers energetic

Synthesis and characterization of water-soluble C₆₀–peptide conjugates

• Yue Ma,
• Lorenzo Persi and
• Yoko Yamakoshi

Beilstein J. Org. Chem. 2024, 20, 777–786, doi:10.3762/bjoc.20.71

• ) showed much smaller aggregation (dotted green line, ≈12 nm), providing a transparent solution, while C60–oligo-Arg (5c) remained insoluble over the tested pH value range (4.0–9.2). This was presumably due to the strong cation–π interactions between the cationic Arg moieties and the aromatic C60, which is