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

• cage retains its aromatic character, the pyrazole’s aromaticity is lost. As a result, rather than forming o-carborane-fused pyrazoles, the synthesis yielded o-carborane-fused pyrazolines, which are non-aromatic. The limited overlap between the π molecular orbitals (MOs) of the planar heterocycle and

• the n + 1 MOs of the carborane prevents significant electronic delocalization between the two fused components. This contrasts with the fusion of pyrazole and benzene to form indazole, where both rings maintain their 2D aromaticity. Our findings demonstrate that the peripheral σ-aromaticity of

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

• single pentafluorophenyl ring was prepared through the regioselective nucleophilic aromatic substitution reaction of the p-fluorine atoms in 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin with 9-mercapto-m-carborane. The reaction of this porphyrin with sodium azide led to the selective substitution of

• carborane A3B-porphyrin were also synthesized based on the amino-substituted A3B-porphyrin. The structures of the prepared carboranylporphyrins were determined by UV–vis, IR, 1H, 19F, 11B NMR spectroscopic data and MALDI mass spectrometry. Keywords: bioconjugation; carboranes; fluorine; porphyrin; SNAr

• compounds in drug development [34][35][36][37]. Owing to their stability, carboranes also may increase the in vivo stability and bioavailability of pharmaceuticals that might otherwise rapidly metabolize [38]. The functionalization of porphyrins with carborane clusters provides dual-action photo(radio

Synthesis of π-conjugated polycyclic compounds by late-stage extrusion of chalcogen fragments

• Aissam Okba,
• Pablo Simón Marqués,
• Kyohei Matsuo,
• Naoki Aratani,
• Hiroko Yamada,
• Gwénaël Rapenne and
• Claire Kammerer

Beilstein J. Org. Chem. 2024, 20, 287–305, doi:10.3762/bjoc.20.30

• between carboranes and chalcogen-doped π-conjugated heterocycles, Yang and co-workers devised a two-step strategy for the synthesis of carborane-fused thiophene 43 (Scheme 11, bottom) [72]. Double lithiation of carboranyl indole 41 was followed by trapping with disulfur dichloride as chalcogen source to

• afford 1,2-dithiin 42. At room temperature, the latter then spontaneously evolved via a S-extrusion to yield the desired carborane-fused thiophene 43. The same method was further employed to prepare other analogues incorporating a group-16 heteroatom. The strategy involving 6-membered ring contraction by

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• porphyrin subunits and was more efficient in DMSO as compared to chloroform. Also, a clear evidence of a folded conformer was found by electrostatic and CH–π interactions, which was also, confirmed by density functional theory (DFT) calculations. In another report, meso-triazole-bridged porphyrin-carborane

• conjugates 76a,b were synthesized in 80% yield by Ol’shevskaya et al. where a porphyrin unit 74a is covalently linked to 1-azidomethyl-o-carborane 75 [41] (Scheme 15). This boronation of the amide was performed via “click chemistry” in СН2Сl2/Н2О solvent system using Cu(OAc)2·2H2O and sodium ascorbate as the

• catalyst at room temperature. In addition, the free-base porphyrin-carborane conjugate 76b was successfully obtained after the treatment of 76a with trifluoroacetic acid in СН2Сl2. The research group of Ravikanth [42] prepared the triazole-bridged porphyrin-BODIPY conjugates 78 and 80 via CuAAC reaction in

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

• intermediate with an iodine radical, followed by aromatization, generated the desired carbazole. Later in 2015, the group of Che described the synthesis of a zwitterionic copper(I) complex having a phenanthroline ligand (bcp) and a nido-carborane-diphosphine ligand. This complex was used in a benchmark

Application of olefin metathesis in the synthesis of functionalized polyhedral oligomeric silsesquioxanes (POSS) and POSS-containing polymeric materials

• Patrycja Żak and
• Cezary Pietraszuk

Beilstein J. Org. Chem. 2019, 15, 310–332, doi:10.3762/bjoc.15.28

• minor amount of homometathesis. Fortunately, the product of homocoupling could be easily separated from the desired CM products. The presence of the carborane clusters was shown to enhance the thermal stability of the materials. Absorption and emission data of carborane–POSS hybrids indicate a large red

Transition metal-free oxidative and deoxygenative C–H/C–Li cross-couplings of 2H-imidazole 1-oxides with carboranyl lithium as an efficient synthetic approach to azaheterocyclic carboranes

• Lidia A. Smyshliaeva,
• Mikhail V. Varaksin,
• Pavel A. Slepukhin,
• Oleg N. Chupakhin and
• Valery N. Charushin

Beilstein J. Org. Chem. 2018, 14, 2618–2626, doi:10.3762/bjoc.14.240

• of promising heterocyclic carboranes: (i) condensation of decaborane (B10H14) with substituted acetylenes [27][28][29][30], (ii) carboryne-based cycloaddition reactions [31][32][33], and (iii) C–X/C–M cross coupling of halogenated azaheterocycles (X = Br, Cl, F) with carborane organometallic

• ), 11B, 11B{1H} experiments), and mass spectrometry. In the IR spectra of 4a–d and 5a–d, there are absorption bands corresponding to the stretching vibrations of carborane B–B atoms (ν 713–721 cm−1), B–H (ν 2561–2605 cm−1) and C–H (ν 3026–3075 cm−1). In the 1H NMR spectra of 4a–d and 5a–d the resonance

• signals of both carborane and imidazole fragments were observed. Typical 1H NMR spectra of carboranyl-substituted imidazoles and their N-oxides (4d versus 5d) are shown in Figure 1. In these spectra, the characteristic signals of C-substituted carborane are registered as two sets, corresponding to CCarb–H

Cross-metathesis reaction of α- and β-vinyl C-glycosides with alkenes

• Ivan Šnajdr,
• Kamil Parkan,
• Filip Hessler and
• Martin Kotora

Beilstein J. Org. Chem. 2015, 11, 1392–1397, doi:10.3762/bjoc.11.150

• ] saccharides and derivatives thereof because of their interesting properties. Bearing this in mind, we decided to explore the possibility of attaching the carborane moiety by using a cross-metathesis reaction. Cross-metathesis of α-2 with the allylated carborane 3a (Figure 1) was used as a model reaction [20

• boronate α-4g in 66% isolated yield (Table 2, entry 7). Then we turned to reactions of the above mentioned terminal alkenes with β-2. In all cases the corresponding products were obtained in good isolated yields in the range similar to α-2. The metathesis with the allylated carborane 3a provided β-4a in 77

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• : A central azobenzene, a rigid frame composed of oligo(phenylacetylenes), which in turn are anchored to azobenzene through para positions, and wheels based on fullerene C60 (azo-14) or p-carboranes (azo-15). Photoisomerization studies suggest that only the azobenzene system with p-carborane wheels

• [124]. In the case of azo-p-carborane 15, irradiation at λ = 365 nm for 10 min leads to 24% of the cis isomer. The photochemical (λ > 495 nm, 5 min) or thermal (heating to 40 °C, 15 min) reisomerization recovers the initial state. After these preliminary results it remains to be demonstrated whether

Reciprocal polyhedra and the Euler relationship: cage hydrocarbons, C_nH_n and closo-boranes [B_xH_x]²⁻

• Michael J. McGlinchey and
• Henning Hopf

Beilstein J. Org. Chem. 2011, 7, 222–233, doi:10.3762/bjoc.7.30

• , 12) are in accord with Euler's equation. Interestingly, the tetrahedron (4 vertices, 6 edges and 4 faces) is its own reciprocal. Boranes, hydrocarbons and inverse polyhedra Closo-borane anions and their carborane analogues adopt polyhedral structures in which each face is triangular [3]; Figure 3

• and 8 vertices, whereas for closo-boranes it is evident that 2E = 3F, as in [B8H8]2− which has 18 edges and 12 faces. However, one must not assume that bonds are fragile in molecules for which the ratio of valence electrons to interatomic linkages is less than two. For example, the carborane 1,12

Cross-metathesis of allylcarboranes with O-allylcyclodextrins

• Ivan Šnajdr,
• Zbyněk Janoušek,
• Jindřich Jindřich and
• Martin Kotora

Beilstein J. Org. Chem. 2010, 6, 1099–1105, doi:10.3762/bjoc.6.126

• , Czech Republic 10.3762/bjoc.6.126 Abstract Cross-metathesis between allylcarboranes and O-allylcyclodextrins was catalyzed by Hoveyda–Grubbs 2nd generation catalyst in toluene. The corresponding carboranyl-cyclodextrin conjugates were isolated in 15–25% yields. Keywords: carborane; catalysis; cross

• carborane-cyclodextrin conjugates. Herein, we report our preliminary results. Results and Discussion Although studies on the inclusion of carboranes into cyclodextrins have previously been reported [9][10][11][12][13], a synthesis of cyclodextrin-carborane conjugates connected by a linker has not been, to

• ]), consequently, there is considerable interest in the synthesis of water soluble carborane derivatives. One strategy to access such compounds is based on the synthesis of carborane conjugates bearing a water-soluble moiety. With this in mind, we envisioned that this concept could be realized by the synthesis of

Ring-alkyl connecting group effect on mesogenic properties of p-carborane derivatives and their hydrocarbon analogues

• Aleksandra Jankowiak,
• Piotr Kaszynski,
• William R. Tilford,
• Kiminori Ohta,
• Adam Januszko,
• Takashi Nagamine and
• Yasuyuki Endo

Beilstein J. Org. Chem. 2009, 5, No. 83, doi:10.3762/bjoc.5.83

• University, 4-4-1, Komatsushima, Aoba-ku, Sendai 981-8558, Japan 10.3762/bjoc.5.83 Abstract The effect of the phenyl–alkyl connecting group on mesogenic properties of several series of isostructural compounds containing p-carborane (A and B), bicyclo[2.2.2]octane (C), and benzene (D) was investigated using

• B) than for carbocyclic derivatives (C and D). Analysis indicates that this effect may have quadrupolar and conformational origin. Keywords: p-carborane; liquid crystals; structure-property relationship; Introduction During the past decade, we have been investigating mesogenic derivatives of p

• of structurally related series of mesogens containing rings A–D (Figure 2), it became apparent that the benzene ring–alkyl chain connection has a distinctly different impact on phase stability in derivatives of p-carborane (A) than in their isostructural carbocycles. For instance, a larger