Visible-light-induced radical cascade cyclization: a catalyst-free synthetic approach to trifluoromethylated heterocycles

• Chuan Yang,
• Wei Shi,
• Jian Tian,
• Lin Guo,
• Yating Zhao and
• Wujiong Xia

Beilstein J. Org. Chem. 2024, 20, 118–124, doi:10.3762/bjoc.20.12

• formed radical 7 can be oxidized by 2a or 4 giving a cation 8, which undergoes a deprotonation process and formation of the desired product. Conclusion In conclusion, we have developed a visible-light-promoted protocol for the synthesis of dihydropyrido[1,2-a]indolones bearing a trifluoromethyl group at

Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations

• Laura Abella,
• Gerard Novell-Leruth,
• Josep M. Ricart,
• Josep M. Poblet and
• Antonio Rodríguez-Fortea

Beilstein J. Org. Chem. 2024, 20, 92–100, doi:10.3762/bjoc.20.10

• and reversible process named phase 1. We find that the barriers for the radical cation mechanism are significantly lower than those found for the neutral pathway. The peapod is mainly providing one-dimensional confinement for the reaction to take place in a more efficient way. Car–Parrinello

• the reaction either via singlet excitation or via radical cation formation (Scheme 1). Estimation of the activation barrier for the [2 + 2] cycloaddition when the nanotube acts as a sensitizer is 33.5 ± 6.8 kJ mol−1. This value agrees with computational predictions for the reaction via an excited

• can also be activated through the formation of C60+• radical cation [3][9]. This mechanistic proposal for phase 1, which to our knowledge has not yet been explored in detail inside a carbon nanotube, is analyzed here and compared to the non-activated C60 dimerization. Finally, some intermediates for

Multi-redox indenofluorene chromophores incorporating dithiafulvene donor and ene/enediyne acceptor units

• Christina Schøttler,
• Kasper Lund-Rasmussen,
• Line Broløs,
• Philip Vinterberg,
• Ema Bazikova,
• Viktor B. R. Pedersen and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2024, 20, 59–73, doi:10.3762/bjoc.20.8

• Tetrathiafulvalene (TTF, Figure 1) is a redox-active molecule that has been widely explored in materials chemistry and supramolecular chemistry [1][2][3][4][5][6][7][8]. TTF reversibly undergoes two sequential one-electron oxidations, generating first a radical cation (TTF+•) and subsequently a dication (TTF2

• rate: 0.1 V/s. All potentials are depicted against the Fc/Fc+ redox couple. Radical anion (left), dianion (middle), and radical cation (right) of compound 23; the radical anion has a 14πz-aromatic ring (highlighted in blue; only counting 2π-electrons of each triple bond, here defined as those in πz

• orbitals), the dianion has an additional 6π-aromatic cyclopentadienyl anion (highlighted in green), while the cation has a 6π-aromatic 1,3-dithiolium ring (highlighted in red). ORTEP plots (50% probability) and crystal packing of compounds a) 25, b) 26, and c) 29. The respective crystal packing of each

Using the phospha-Michael reaction for making phosphonium phenolate zwitterions

• Matthias R. Steiner,
• Max Schmallegger,
• Larissa Donner,
• Johann A. Hlina,
• Christoph Marschner,
• Judith Baumgartner and
• Christian Slugovc

Beilstein J. Org. Chem. 2024, 20, 41–51, doi:10.3762/bjoc.20.6

• between P1 and C15 is slightly longer (1.824(2) Å in 2a; 1.828(3) in 2f) when compared to the P–CH2 distance of a tetra-n-butylphosphonium cation [45]. UV–vis spectroscopy All phosphonium phenolate compounds exhibit a bright yellow color in solution (see inset in Figure 3). Investigating the absorption

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

• alkynes was studied in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF4) adding boron trifluoride diethyl etherate (BF3·Et2O) as catalyst. Different ionic liquids were used, varying the cation or the anion, in order to identify the best one, in terms of both efficiency and reduced

• electrogeneration of BF3, the aim of this work was to explore the hydration of alkynes using ILs as reaction medium and BF3 as catalyst. First of all, we investigated the behaviour of diphenylacetylene in BMIm-BF4 containing BF3·Et2O. Then we evaluated the same reaction in different ILs, modifying the cation or the

• ‒ hydrolysis in a 1:1 in volume IL/water solution kept at 45 °C for 24 h) [105]. It should be noted that the same treatment carried out on 1-methyl-3-octylimidazolium tetrafluoroborate (OMIm-BF4) evidenced a much higher extent of BF4‒ hydrolysis. This is probably due to the weaker interaction between cation

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

• the monomeric cation N-DMBI+ (Supporting Information File 1, Figure S15). Thus, the overall reaction is consistent with: Scope of reaction (Y-DMBI)2 with other benzyl, alkyl, and aryl halides Table 2 summarizes the conversions and product yields for the reactions of (N-DMBI)2 or (Cyc-DMBI)2 with

Anion–π catalysis on carbon allotropes

• M. Ángeles Gutiérrez López,
• Mei-Ling Tan,
• Giacomo Renno,
• Augustina Jozeliūnaitė,
• J. Jonathan Nué-Martinez,
• Javier Lopez-Andarias,
• Naomi Sakai and
• Stefan Matile

Beilstein J. Org. Chem. 2023, 19, 1881–1894, doi:10.3762/bjoc.19.140

• ], followed by SWCNTs and MWCNTs two years later [13]. Particularly MWCNTs have the potential to couple anion–π and cation–π catalysis with electric-field-assisted catalysis [14]. While anion–π (and cation–π [15][16]) catalysis, compared to other unorthodox interactions, has been less impactful than expected

• available so far on anion–π catalysis on carbon allotropes. Review Anion–π catalysis on fullerenes The use of fullerenes in catalysis is surprisingly underdeveloped [45][46][47][48][49][50][51]. Anion–π and cation–π interactions on fullerenes attract similarly little attention until today [52][53][54][55

• –16 was as in the amide series from 8 and thus supported entropic contributions to anion–π catalysis. Steric increase of the secondary amide in 17 impeded anion–π catalysis, presumably because the catalytic π surface next to the ammonium cation became inaccessible for anions paired with the tethered

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• a wide range of transformations [7][8]. Moreover, they proposed a plausible mechanism for the aforementioned conversions (Scheme 2). Initially, an NaI/PPh3 complex I was formed through a cation–π interaction. Subsequently, the combination of complex I with N-(cyclohexanecarbonyloxy)phthalimide

Selectivity control towards CO versus H₂ for photo-driven CO₂ reduction with a novel Co(II) catalyst

• Lisa-Lou Gracia,
• Philip Henkel,
• Olaf Fuhr and
• Claudia Bizzarri

Beilstein J. Org. Chem. 2023, 19, 1766–1775, doi:10.3762/bjoc.19.129

• (helping in the deprotonation of the radical cation BIH•+ formed after the reductive quenching of the PS), but also can actively assist the catalysis, by capturing CO2 [50][51][52]. On the other hand, having three hydroxy groups, TEOA is also considered a proton donor and the formation of metal hydrides is

Benzoimidazolium-derived dimeric and hydride n-dopants for organic electron-transport materials: impact of substitution on structures, electrochemistry, and reactivity

• Swagat K. Mohapatra,
• Khaled Al Kurdi,
• Samik Jhulki,
• Georgii Bogdanov,
• John Bacsa,
• Maxwell Conte,
• Tatiana V. Timofeeva,
• Seth R. Marder and
• Stephen Barlow

Beilstein J. Org. Chem. 2023, 19, 1651–1663, doi:10.3762/bjoc.19.121

• and 1,3-dimethyl substituents in pseudo-equatorial positions and the reactive hydridic 2-H-atom pesudo-axial. The cation structures (Figure 5) give some insight into the variety of dopant-ion shapes and sizes that can be afforded by these types of dopants. The angle between the imidazolium ring and

• -membered rather than six-membered aromatic ring, the structure of 1i+PF6− contains a somewhat more planar cation (31.9°). Finally, we note that the new structures reported here mean that the 1b and 1h systems join the 1c (Y = Fc; R = R' = H) system [50] as families for which 1+, 1H, and 12 members are all

• since 4-(dimethylamino)phenyl and metallocenyl groups are π-donors, unlike cyclohexyl, and thus might be expected to be better able to stabilize an adjacent cation. However, aryl and metallocenyl substituents also stabilize adjacent radicals more effectively than alkyl groups and this effect is

Tying a knot between crown ethers and porphyrins

• Maksym Matviyishyn and
• Bartosz Szyszko

Beilstein J. Org. Chem. 2023, 19, 1630–1650, doi:10.3762/bjoc.19.120

• cation and crown ether pocket, dimerisation of the crown porphyrin molecule would occur. The dimerisation led to interesting changes in the visible, NMR, ESR, and emission spectral features. Further developments by Camilleri, Gunter, Boitrel, and Osuka focused on the exploitation of meso-crowned

• -capped calix[4]pyrrole cavitand 4. The heteroditopic receptor had multiple binding sites, proving efficient in encapsulating a CsF ion pair. The calix[4]arene-crown-6-capped pocket was exploited as an excellent binding site for the Cs+ cation, whereas the calix[4]pyrrole was aligned to trap the fluoride

• separation between the cation and anion. Sessler and co-workers introduced a similar ion-pair receptor, in which the calix[4]arene-strapped calix[4]pyrrole 5 demonstrated an additional binding mode of CsF (Figure 5). The binding constant Ka = 1.3·104 M−1 in CHCl3/MeOH 9:1 was reported [101][102]. This

Radical chemistry in polymer science: an overview and recent advances

• Zixiao Wang,
• Feichen Cui,
• Yang Sui and
• Jiajun Yan

Beilstein J. Org. Chem. 2023, 19, 1580–1603, doi:10.3762/bjoc.19.116

• necessary. MF-ROMP, also termed photo-ROMP, is a novel technique to polymerize cyclic olefins. It begins with the reductive quenching of an photoexcited photocatalyst (PC) at an enol ether initiator to produce a radical cation carrier [90]. Then, the carrier undergoes cyclic addition with a cyclic olefin

• monomer to generate a cyclobutene radical cation intermediate. The thermodynamically instable intermediate subsequently forms the propagating radical cation species via a ring-opening process. The reduced PC•− terminates the catalytic loop by reducing the propagating species to provide a polymer chain

Unraveling the role of prenyl side-chain interactions in stabilizing the secondary carbocation in the biosynthesis of variexenol B

• Moe Nakano,
• Rintaro Gemma and
• Hajime Sato

Beilstein J. Org. Chem. 2023, 19, 1503–1510, doi:10.3762/bjoc.19.107

• possibility of through-space interactions with prenyl side chains using DFT calculations. Our calculations show that (i) the unstable secondary carbocation is stabilized by the cation–π interaction from prenyl side chains, thereby lowering the activation energy, (ii) the four-membered ring formation is

• completed through bridging from the exomethylene group, and (iii) the annulation from the exomethylene group proceeds in a barrier-free manner. Keywords: biosynthesis; carbocation; cation–π interaction; DFT; terpene; Introduction Terpene/terpenoids are most abundant natural products in nature, more than

• as the C–H–π interaction between the carbocation intermediate and the Phe residue of terpene cyclase in the biosynthesis of sesterfisherol [21], and the intricated rearrangement reaction mechanism promoted by the equilibrium state of the homoallyl cation and the cyclopropylcarbinyl cation in the

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• sulfur atom to Fe3+ to generate Fe2+ and radical cation I. Subsequent cleavage of the N–S bond led to cation II and radical III. Interaction of III with Fe2+ regenerated the Fe3+ species and IV. At the same time, electrophilic addition of II to alkene 9 yielded intermediate V, which was subjected to the

• (PIDA) and meta-chloroperbenzoic acid (m-CPBA) toward 3-sulfinylated and 3-sulfonylated product, respectively, were performed in this work. A plausible mechanism involves the treatment of 1 with BF3·Et2O toward cation I, which reacted with the C–C triple bond in 12 to give sulfonium intermediate II

• or 14, caused polarization of the S–N bond and produced an electrophilic intermediate I. Through the nucleophilic attack of the alkyne on I, cation II was generated, leaving Al-coordinated phthalimide/succinimide III. Finally, 4-endo-trig spirocyclization of II rendered the unstable intermediate IV

Cyclization of 1-aryl-4,4,4-trichlorobut-2-en-1-ones into 3-trichloromethylindan-1-ones in triflic acid

• Vladislav A. Sokolov,
• Andrei A. Golushko,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2023, 19, 1460–1470, doi:10.3762/bjoc.19.105

• delocalization of the positive charge from the carbonyl group to the aromatic ring. It should be mentioned that cation Bm was generated by two ways in TfOH: either directly by protonation of enone 2m or from hydroxy ketone 1m. The latter was found to undergo fast dehydration into enone 2m in TfOH at room

• analogously to cation Ba. The cyclization of dication Aa into indanone 3a is very favorable (ΔG298 = −101.3 kJ/mol). However, the formation of both enones 2 and indanones 3 from hydroxy ketones 1 is observed in TfOH (Table 1). We assume that, at first, hydroxy ketones 1 undergo dehydration into enones 2

• C1 (0.60 e). This carbon atom gives 14.9% contribution to the LUMO. Contrary to that, the carbon C3 bears no positive charge (−0.13 e) and contributes 12.1% to the LUMO. The intramolecular cyclization of cation Ba takes place between the atom C3 and the ortho-carbons of the phenyl ring. Thus

Functional characterisation of twelve terpene synthases from actinobacteria

• Anuj K. Chhalodia,
• Houchao Xu,
• Georges B. Tabekoueng,
• Binbin Gu,
• Kizerbo A. Taizoumbe,
• Lukas Lauterbach and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2023, 19, 1386–1398, doi:10.3762/bjoc.19.100

• 26 can be well understood from the cyclisation mechanism towards 23 (Scheme 1B). After substrate ionisation to A a 1,10-cyclisation leads to the (E,E)-germacradienyl cation (B) that can either be deprotonated to 24 or captured with water to yield 26. Both compounds are important neutral intermediates

Synthesis of ether lipids: natural compounds and analogues

• Marco Antônio G. B. Gomes,
• Alicia Bauduin,
• Chloé Le Roux,
• Romain Fouinneteau,
• Wilfried Berthe,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2023, 19, 1299–1369, doi:10.3762/bjoc.19.96

• cesium cation with the halogen atom and the activation of the Sn–O bond of the stannylene acetal via a pentacoordinated intermediate with the fluoride anion [110]. The acetylation of the secondary alcohol and the deprotection of the primary alcohol with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• -methylisochroman, 3-methoxyanisole). Mechanism experiments showed that the coupling of aromatic ring radicals with ether oxygen ions produced an intermediate radical cation, which achieves a catalytic cycle through the Cu center. Lee et al. disclosed TBHP as an oxidant and Pd(OAc)2/Cu(OTf)2 as the catalyst to

• ) process, the carbocation intermediate B is generated, which is attacked by a nucleophile to afford the target product. Further, C–H bonds in the ortho-position of a heteroatom are activated through a SET pathway generating a radical cation C, which is easily deprotonated by an oxidant to generate a

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

Exploring the role of halogen bonding in iodonium ylides: insights into unexpected reactivity and reaction control

• Carlee A. Montgomery and
• Graham K. Murphy

Beilstein J. Org. Chem. 2023, 19, 1171–1190, doi:10.3762/bjoc.19.86

• proposed that electron donor–acceptor (EDA) complex 36 was initially formed between 32 and a sacrificial equivalent of 31, and that 36 underwent a SET to give radical anion 37 and radical cation 38 (Figure 8). While one equivalent of the ylide orchestrated a series of proton transfer (PT) and SET events

Selective and scalable oxygenation of heteroatoms using the elements of nature: air, water, and light

• Damiano Diprima,
• Hannes Gemoets,
• Stefano Bonciolini and
• Koen Van Aken

Beilstein J. Org. Chem. 2023, 19, 1146–1154, doi:10.3762/bjoc.19.82

• on the rate than acids and bases and both the anion and cation appear to influence the reaction kinetics. A deliberate choice of salt can either significantly improve the kinetics or quench the reaction. The latter might be exploited e.g., in late-stage functionalization strategies in order to

• originates from water. In this tentative mechanism, the sulfide I forms with water and oxygen a photoactive complex II which is excited at 365 nm towards III. Via single-electron transfer both a radical cation IV and the superoxide V are generated. Subsequently, the sulfide radical cation IV undergoes 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

• radical anion or radical cation. As a semi-stable, higher energy ground-state entity, this can accumulate in sufficient concentration under the reaction conditions to absorb another photon and thereby generate a super-reducing or super-oxidizing excited state (Figure 2 left). In addition to ‘radical ion

• -BF4 as a suitable conPET catalyst. Following the conPET catalytic cycle, the Mes-Acr+ cation is excited and reductively quenched by DIPEA to yield the acridine radical Mes-Acr• (Figure 10C) [54]. Upon excitation to its twisted intramolecular charge-transfer (TICT) state, Mes-Acr• has an excited-state

• oxidizing this radical to the corresponding cation. In the presence of Et3N, [FeIII(btz)3]3+ is reductively quenched after excitation to its 2LMCT excited state to generate [FeII(btz)3]2+ (equivalent to PC•− in the classical conPET mechanism) (Figure 20C). [FeII(btz)3]2+ is excited again to the more

Synthesis of tetrahydrofuro[3,2-c]pyridines via Pictet–Spengler reaction

• Elena Y. Mendogralo and
• Maxim G. Uchuskin

Beilstein J. Org. Chem. 2023, 19, 991–997, doi:10.3762/bjoc.19.74

• rearrangement to a more stable benzhydryl-type cation resulting in the formation of isomeric products. In an alternative group of methods, more accessible 2-substituted furans are used as starting compounds. For example, a construction of tetrahydrofuro[3,2-c]pyridines based on the Pictet–Spengler reaction [17

• ][18] was described (Scheme 1c). The most studied variation of this cyclization is based on the generation of an acyliminium cation from the corresponding alcohols [19][20][21][22][23] or alkenes [24][25][26][27][28][29], subsequent attack of furan ring and the formation of annulated tetrahydrofuro[3,2

• -c]pyridines. Moreover, multistep cascade processes with the simultaneous construction of several cores were described, where the key step is the generation of an acyliminium cation and the Pictet–Spengler cyclization [30][31][32], including solid-phase synthesis [33][34][35]. Another route for the

Aromatic C–H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel–Crafts reaction: a recent update

• Anup Biswas

Beilstein J. Org. Chem. 2023, 19, 956–981, doi:10.3762/bjoc.19.72

• dehydration to generate isoxazolium cation 80 paired with a phosphate anion. This chiral phosphate is engaged in H-bonding with the free NH of the heteroarene ring to ease the stereoselective 1,2-addition to in situ generate the cationic heterocyclic scaffold 81. The reaction proceeded faster with pyrroles

Clauson–Kaas pyrrole synthesis using diverse catalysts: a transition from conventional to greener approach

• Dileep Kumar Singh and
• Rajesh Kumar

Beilstein J. Org. Chem. 2023, 19, 928–955, doi:10.3762/bjoc.19.71

• adjacent strong Lewis acid sites, and the acidity of these Lewis acid sites is due to the inductive effect of sulfate on the metallic cation. Therefore, this nano-sulfated titanium dioxide acts as a new type of Lewis acid catalyst. Intermediate A was first formed by reaction of the catalyst with 2,5-DMTHF