Unraveling aromaticity: the dual worlds of pyrazole, pyrazoline, and 3D carborane

• Zahra Noori,
• Miquel Solà,
• Clara Viñas,
• Francesc Teixidor and
• Jordi Poater

Beilstein J. Org. Chem. 2025, 21, 412–420, doi:10.3762/bjoc.21.29

• Barcelona, Spain 10.3762/bjoc.21.29 Abstract A new series of o-carborane-fused pyrazoles has been recently successfully synthesized. This fusion was expected to create a hybrid 3D/2D aromatic system, combining the 3D aromaticity of o-carborane with the 2D aromaticity of pyrazole. However, while the boron

• therefore non-aromatic. Even when fused with benzene via a C–C bond, pyrazoline remains non-aromatic, which is the case of indazoline. Icosahedral carboranes are globular molecular clusters made of carbon and boron, displaying 3D aromaticity [12][13][14][15]. Their unique properties – such as aromaticity

• , exceptional thermal and chemical stability, and robust synthetic versatility [16][17] – make carborane derivatives essential components in various fields. These include pharmaceuticals [18][19][20][21][22], boron neutron capture therapy (BNCT) [23][24][25][26], organometallic ligands [27], and functional

Red light excitation: illuminating photocatalysis in a new spectrum

• Lucas Fortier,
• Corentin Lefebvre and
• Norbert Hoffmann

Beilstein J. Org. Chem. 2025, 21, 296–326, doi:10.3762/bjoc.21.22

Nickel-catalyzed cross-coupling of 2-fluorobenzofurans with arylboronic acids via aromatic C–F bond activation

• Takeshi Fujita,
• Haruna Yabuki,
• Ryutaro Morioka,
• Kohei Fuchibe and
• Junji Ichikawa

Beilstein J. Org. Chem. 2025, 21, 146–154, doi:10.3762/bjoc.21.8

• -arylbenzofuran 3ab (Table 2, entry 4) compared to that of 1a (X = F, quant.). The strong interaction between fluorine and boron in H likely facilitates β-fluorine elimination and transmetallation. Thus, the considerably different result observed with 1a is attributed to the distinct mechanistic aspects of the

Germanyl triazoles as a platform for CuAAC diversification and chemoselective orthogonal cross-coupling

• John M. Halford-McGuff,
• Thomas M. Richardson,
• Aidan P. McKay,
• Frederik Peschke,
• Glenn A. Burley and
• Allan J. B. Watson

Beilstein J. Org. Chem. 2024, 20, 3198–3204, doi:10.3762/bjoc.20.265

• of borylated functional groups, allowing orthogonal cross-coupling, whilst also offering excellent stability compared to boron-based reagents [57][58][59][60][61][62][63][64][65][66][67]. Based on their utility and stability, germanium units could therefore be useful within CuAAC reactions and offer

• . studentship. G.A.B., F.P., and A.J.B.W. thank the Leverhulme Trust (RPG-2020-380). A.J.B.W. thanks the Leverhulme Trust for a Research Fellowship (RF-2022-014) and the EPSRC Programme Grant ‘‘Boron: Beyond the Reagent’’ (EP/W007517/1) for support.

Hypervalent iodine-mediated intramolecular alkene halocyclisation

• Charu Bansal,
• Oliver Ruggles,
• Albert C. Rowett and
• Alastair J. J. Lennox

Beilstein J. Org. Chem. 2024, 20, 3113–3133, doi:10.3762/bjoc.20.258

• synthesis of various halogenated 1,3-oxazine 50 and 2-oxazoline derivatives 51 using boron trihalides as the halogen source [6][49]. They found that the choice of halogen source influences the reaction outcomes. With the use of BCl3 (Scheme 28), N-cinnamylbenzamides 52 were transformed to give the

N-Glycosides of indigo, indirubin, and isoindigo: blue, red, and yellow sugars and their cancerostatic activity

• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 2840–2869, doi:10.3762/bjoc.20.240

• , albeit, in low yield (Scheme 19) [25]. Cleavage of the benzyl groups using boron tribromide afforded β-31a. In contrast to indirubin-N-rhamnoside 17a, its isomer β-31a proved to be rather unstable. This fact was already earlier observed for indigo-N-rhamnoside 5d and again suggests that compounds

C–C Coupling in sterically demanding porphyrin environments

• Liam Cribbin,
• Brendan Twamley,
• Nicolae Buga,
• John E. O’ Brien,
• Raphael Bühler,
• Roland A. Fischer and
• Mathias O. Senge

Beilstein J. Org. Chem. 2024, 20, 2784–2798, doi:10.3762/bjoc.20.234

• stability than boronic acids and other employed esters as the four methyl groups protect the boron center from attack of water [44][45], preventing protodeboronation from the hydrolysis route. However, protodeboronation can be complex when it comes to pKa considerations, for example, 3,5

Computational design for enantioselective CO₂ capture: asymmetric frustrated Lewis pairs in epoxide transformations

• Maxime Ferrer,
• Iñigo Iribarren,
• Tim Renningholtz,
• Ibon Alkorta and
• Cristina Trujillo

Beilstein J. Org. Chem. 2024, 20, 2668–2681, doi:10.3762/bjoc.20.224

• boron bears CF3 substituents. Thus, an acidic boron atom seems to increase the reactivity of the considered system. Concerning the LB, it appears that, as opposed to the first group of compounds, a phosphorus atom is more active than a nitrogen atom. Asymmetric catalysis After examining the volcano

• excess. Following the volcano plot analysis presented in the previous section, F3_NB_C5_CF3 emerged as one of the top FLP catalysts under study. This catalyst, adhering to mechanism 1, incorporates a CF3 group on the boron atom, serving as a simplified version of the B(p-HC6F4)3. Notably, the nitrogen in

• plot analysis reveals that the best candidate is F3_NB_C5_CF3, which is the catalyst based on the 2-borylbenzenamine scaffold, with a pyrrolidine substituent on the nitrogen atom and CF3 substituents on the boron. Through strategic modification of the Lewis base substituents, a stereoselective catalyst

Transition-metal-free synthesis of arylboronates via thermal generation of aryl radicals from triarylbismuthines in air

• Yuki Yamamoto,
• Yuki Konakazawa,
• Kohsuke Fujiwara and
• Akiya Ogawa

Beilstein J. Org. Chem. 2024, 20, 2577–2584, doi:10.3762/bjoc.20.216

• generating a boron radical (pinB•) by photoirradiation of (Bpin)2 and found that the addition of (PhS)2 was effective in generating the boron radical [30]. We therefore investigated this reaction by adding (PhS)2 as a Lewis base, but the yield of 3a was not improved and (PhS)2 was recovered almost

• control experiments and our previous studies, a proposed reaction pathway is shown in Scheme 5. First, thermal activation of triarylbismuthines in air forms aryl radicals together with the bismuth residues (i.e., metal bismuth and bismuth oxide). Alternatively, oxygen in air and/or boron-centered radicals

• File 138: Investigation of the boron residue in the crude mixture by 11B NMR measurement, characterization data of the compounds, and copies of 1H NMR and 13C{1H} NMR spectra. Acknowledgements We acknowledged Dr. Tran Dat Phuc and Mr. Soichiro Mita (Osaka Prefecture University) for their initial

Anion-dependent ion-pairing assemblies of triazatriangulenium cation that interferes with stacking structures

• Yohei Haketa,
• Takuma Matsuda and
• Hiromitsu Maeda

Beilstein J. Org. Chem. 2024, 20, 2567–2576, doi:10.3762/bjoc.20.215

• 2+-B(C6F5)4−, the distance between the boron of B(C6F5)4− and the central carbon of TATA+ was 7.32 Å, with an offset angle of 47.1° (Figure 3d, Figure 7a, and Figures S14 and S20 in Supporting Information File 1). On the other hand, in 2+-PCCp−, the PCCp− unit (centroid of the five-membered ring

• ) packing structures and (ii) enlarged views for the columnar structures. In (i), cation and anion are represented in cyan and magenta colors, respectively. In (ii), brown, pink, yellow, blue, yellow green, orange, and green (spherical) refer to carbon, hydrogen, boron, nitrogen, fluorine, phosphorus, and

• +-Cl−, (b) 2+-BF4−, and (c) 2+-PF6−. Atom color code: yellow, green, orange, and green (spherical) refer to boron, fluorine, phosphorus, and chlorine, respectively. (i) Single-crystal X-ray structures and (ii) interaction energies for the pairs (a) 2+-Cl−, (b) 2+-BF4−, and (c) 2+-PF6−. In (i), the

A review of recent advances in electrochemical and photoelectrochemical late-stage functionalization classified by anodic oxidation, cathodic reduction, and paired electrolysis

• Nian Li,
• Ruzal Sitdikov,
• Ajit Prabhakar Kale,
• Joost Steverlynck,
• Bo Li and
• Magnus Rueping

Beilstein J. Org. Chem. 2024, 20, 2500–2566, doi:10.3762/bjoc.20.214

• undivided cell using a boron-doped diamond (BDD) anode and a platinum cathode at constant current, resulting in 1,4-dicarbonyls with yields up to 91% and enantiomeric excesses (ee) greater than 99%. This methodology was demonstrated in the LSF of two complex natural product derivatives: a β-ionone

Asymmetric organocatalytic synthesis of chiral homoallylic amines

• Nikolay S. Kondratyev and
• Andrei V. Malkov

Beilstein J. Org. Chem. 2024, 20, 2349–2377, doi:10.3762/bjoc.20.201

• essential to provide a comprehensive overview of this significant topic. Review Asymmetric allylation with boron-based reagents The research on the metal-free, asymmetric organocatalytic allylation of acylimines was pioneered in 2007 by Schaus and co-workers [24]. In their elegant approach, high

• excellent enantioselectivities (89–98% ee) and low to moderate yields (48–72%). The homologation step proceeds via the stereoretentive 1,2-migration of the vinyl group from the tetracoordinated boron to the highly electrophilic carbon of the diazomethane, concerted with the elimination of the nitrogen

• by a nucleophile, is energetically favoured over pathway via 77, in which the imine is activated directly by coordination to the Lewis acidic boron atom of the free imine complex. This supports the mechanism proposed in the original study based on the NMR experiments. In 2021, Jacobsen and co-workers

Efficacy of radical reactions of isocyanides with heteroatom radicals in organic synthesis

• Akiya Ogawa and
• Yuki Yamamoto

Beilstein J. Org. Chem. 2024, 20, 2114–2128, doi:10.3762/bjoc.20.182

• perform. In contrast, tris(trimethylsilyl)silane, (Me3Si)3SiH, has a bond dissociation energy similar to that of n-Bu3SnH (74 kcal/mol) and can be used as an efficient reducing agent/mediator. Radical addition of group 13 compounds to isocyanides Boron, a group 13 typical element, also lacks a non

• -covalent electron pair, making it impossible to generate boron radicals by homolysis via the n–σ* transition. In addition, since boron has an empty orbital, it forms ate complexes when Lewis base compounds coexist. As the result, the boryl groups of the ate complexes are bulky and often cause steric

• groups on boron are 1,2-shifted to the isocyanide carbon, yielding the compounds (H2B-C(=NR)-H or R'2B-C(=NR)-R') with the isocyanide inserted between the B–H or B–alkyl bond [45][46]. The insertion products easily underwent dimerization to afford 2,5-diboradihydropyrazine derivatives 16 (Scheme 10a

Hetero-polycyclic aromatic systems: A data-driven investigation of structure–property relationships

• Sabyasachi Chakraborty,
• Eduardo Mayo Yanes and
• Renana Gershoni-Poranne

Beilstein J. Org. Chem. 2024, 20, 1817–1830, doi:10.3762/bjoc.20.160

• heteroatoms boron, nitrogen, oxygen, and sulfur and ranging in size from four-membered to six-membered rings. Compared to the parent polycyclic aromatic hydrocarbons (PAHs), PASs containing heterocycles offer greater structural diversity as well as a much broader range of optoelectronic properties. Such

• , and contain nitrogen, boron, oxygen, and sulfur atoms. Using these building blocks, we generated a chemical library of cata-condensed hetero-PASs (cc-hPASs) ranging in size from 3- to 10-ring systems, by combining the rings according to the annulation types shown in Figure 1B. The number, type, and

• oxygen raise the HOMO level [41][42], while boron lowers the LUMO level [43]. COMPAS-2 provides, for the first time, the possibility to substantiate these observations in a data-driven manner and, perhaps, to extract quantitative assessments of these effects. In this section, we study the effects of the

Chemo-enzymatic total synthesis: current approaches toward the integration of chemical and enzymatic transformations

• Ryo Tanifuji and
• Hiroki Oguri

Beilstein J. Org. Chem. 2024, 20, 1693–1712, doi:10.3762/bjoc.20.151

• approach, they used a chiral boron catalyst as a Lewis acid and achieved at best an endo/exo selectivity of 1.9:1 in a similar DA reaction. The use of Diels–Alderase in their recent work significantly improved the endo/exo selectivity under mild conditions in water, thereby highlighting the strengths of

Electrophotochemical metal-catalyzed synthesis of alkylnitriles from simple aliphatic carboxylic acids

• Yukang Wang,
• Yan Yao and
• Niankai Fu

Beilstein J. Org. Chem. 2024, 20, 1497–1503, doi:10.3762/bjoc.20.133

• size of the alkyl side chain at the alpha position of arylacetic acids (9–16). These features offer great opportunities for the introduction of a wide range of functional groups, including bromide (9), boron (12), ether (13), nitrile (14), ester (15), and alkene (16) moieties, which are versatile

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

• conventional metal hydrides, such as tin or silicon hydrides. The reaction mechanism is interesting since first, a Lewis acid–base adduct is generated by interaction of Et3N with a boron atom of bis(catecholato)diboron (B2cat2, 19). As a result, one of the catecholate ligands experiences an increase in

Competing electrophilic substitution and oxidative polymerization of arylamines with selenium dioxide

• Vishnu Selladurai and
• Selvakumar Karuthapandi

Beilstein J. Org. Chem. 2024, 20, 1221–1235, doi:10.3762/bjoc.20.105

• derivatives. With this approach, electrophilic substitution can be achieved in ortho and para positions of aniline derivatives by careful selection of the substrates. Kumar et al. used SeO2 and phenylboronic acid to make symmetrical diaryl selenides [34]. In both cases, aryl transfer from the boron to the

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

• boron migration occurred during the hydroboration process of spiroviolene that resulted in the production of a mixture of 1α-hydroxyspiroviolane, 9α- and 9β-hydroxyspiroviolane after oxidation. The assertion of the cis-orientation of the 19- and 20-methyl groups provided further support for the revised

• cyclization mechanism of spiroviolene. Keywords: boron migration; diterpene; spiroviolene; stereochemistry; Introduction Terpenes represent one of the most fascinating families of natural products due to their structural complexity and diversity, as well as their indispensable biological functions that

• intermediate IM-13, or a tertiary 2-organoborane intermediate IM-14. Oxidation of IM-13 with H2O2/NaOH could stereoselectively furnish the normal hydroboration/oxidation product 9. On the other hand, the unstable tertiary 2-organoborane IM-14 would undergo two consecutive thermal 1,2-boron migrations to give

Synthesis of new representatives of A₃B-type carboranylporphyrins based on meso-tetra(pentafluorophenyl)porphyrin transformations

• Victoria M. Alpatova,
• Evgeny G. Rys,
• Elena G. Kononova and
• Valentina A. Ol'shevskaya

Beilstein J. Org. Chem. 2024, 20, 767–776, doi:10.3762/bjoc.20.70

• meso-pentafluorophenyl-substituted porphyrins. Carboranes, due to their unique physical and chemical properties such as high chemical and biological stability [28][29], three-dimensional aromaticity [30][31], low toxicity [28], high hydrophobicity, and enriched boron content [32][33] are perspective

• )sensitizers that are efficient for both PDT and boron neutron capture therapy (BNCT) [27][39]. The preparation of compounds with dual therapeutic efficiency is of great importance since they improve the therapeutic effect of sensitizer by the action on the different cellular sites. Here, we report the

• fluorophenylporphyrin substituents via the boron atom. At the same time the SNAr substitution reaction for the azido-substituted porphyrin 2 with mercaptocarborane 4 also afforded the amino-substituted porphyrin 5 in 32% yield (Scheme 2). During the reaction the reduction of the azide group under the action of

SOMOphilic alkyne vs radical-polar crossover approaches: The full story of the azido-alkynylation of alkenes

• Julien Borrel and
• Jerome Waser

Beilstein J. Org. Chem. 2024, 20, 701–713, doi:10.3762/bjoc.20.64

• increase the yield of different transformations. Using fluoride scavenger such as TMSCl, TFAA or TMS2(O) led to similar or lower yields (Table 7, entries 3–5). We were pleased to see that in the presence of BF3·Et2O, 4a was obtained in 75% yield (Table 7, entry 6). Addition of a less acidic boron Lewis

(E,Z)-1,1,1,4,4,4-Hexafluorobut-2-enes: hydrofluoroolefins halogenation/dehydrohalogenation cascade to reach new fluorinated allene

• Nataliia V. Kirij,
• Andrey A. Filatov,
• Yurii L. Yagupolskii,
• Sheng Peng and
• Lee Sprague

Beilstein J. Org. Chem. 2024, 20, 452–459, doi:10.3762/bjoc.20.40

• compound, but led to the elimination of two fluorine atoms with the formation of 1,1,4,4-tetrafluorobuta-1,3-diene [9]. It was also shown that the reactions of the boron reagent (CAACMe)BH2Li(thf)3 with hydrofluoroolefins, including (Z)-1,1,1,4,4,4-hexafluorobut-2-ene, results in defluoroborylation to form

• the corresponding =CF2 containing products [10]. In addition to complexes of aluminum and boron, several magnesium and lithium silyl reagents were prepared and proved to be good nucleophiles in reactions with (Z)-1,1,1,4,4,4-hexafluorobut-2-ene, as a result of which the corresponding

Chiral phosphoric acid-catalyzed transfer hydrogenation of 3,3-difluoro-3H-indoles

• Yumei Wang,
• Guangzhu Wang,
• Yanping Zhu and
• Kaiwu Dong

Beilstein J. Org. Chem. 2024, 20, 205–211, doi:10.3762/bjoc.20.20

• , synthesized in situ from a chiral boron phosphate complex with water, for asymmetric indole reduction (Scheme 1b) [30]. The mild reaction conditions, low catalyst loading, and high enantioselectivity rendered this transformation an attractive approach to synthesize optically active indolines. However, these

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• ][42][43][44][45][46], azulenes and their homologous compounds [32][47][48][49][50][51][52][53][54][55][56][57][58], boron dipyrromethenes (BODIPYs) [41][59][60][61], porphyrins [62][63][64], chlorophylls [65][66], triazenes [67][68], ynamides [69][70][71], arylynamines [72], indoles [73], and γ

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

• the aldol condensation products. Importantly, the ability to recycle the ionic liquid in subsequent reactions was successfully demonstrated. Keywords: alkyne hydration; boron trifluoride; electrochemical synthesis; ionic liquids; Introduction Alkynes are fundamental starting materials towards more

• -heterocyclic carbenes (NHCs), extensively studied as organocatalysts as well as ligands for transition-metal-promoted synthetic methodologies [97][98][99]. Under anodic oxidation, the electrogeneration of boron trifluoride (BF3) from tetrafluoroborate ILs occurs [100][101]. Moreover, we have recently