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

• a.u. The aromaticity of both indazole and pyrazole molecules is further supported by the computed AICD plots (Figure 5), clearly showing a strong diatropic ring current around the five-membered rings. At difference, such current is interrupted in case of all o-carborane-fused pyrazoles between the

• -pyrazoline (13.0 kcal mol−1 higher in energy). Also in this case, the five-membered rings are clearly confirmed to be non-aromatic (Figure 4). Conclusion In this work, we have quantum chemically analyzed a series of o-carborane-fused pyrazoles that have been recently synthesized, and whose fusion was

Synthesis, structure and π-expansion of tris(4,5-dehydro-2,3:6,7-dibenzotropone)

• Yongming Xiong,
• Xue Lin Ma,
• Shilong Su and
• Qian Miao

Beilstein J. Org. Chem. 2025, 21, 1–7, doi:10.3762/bjoc.21.1

• the arrangement of the carbon atoms and is characterized by a geometric property known as curvature. When five-membered rings of carbon atoms are present, they induce a positive curvature, exemplified by fullerenes. Conversely, seven- or eight-membered rings lead to negative curvature, as seen in

• room temperature yielded partially fused nanographene 3 (20%), with formation of six C–C bonds giving four six-membered rings and two five-membered rings. Performing this reaction at a higher temperature led to a lower yield of compound 3 and the formation of byproducts with lower Rf values on thin

Recent advances in transition-metal-free arylation reactions involving hypervalent iodine salts

• Ritu Mamgain,
• Kokila Sakthivel and
• Fateh V. Singh

Beilstein J. Org. Chem. 2024, 20, 2891–2920, doi:10.3762/bjoc.20.243

Oxidative fluorination with Selectfluor: A convenient procedure for preparing hypervalent iodine(V) fluorides

• Samuel M. G. Dearman,
• Xiang Li,
• Yang Li,
• Kuldip Singh and
• Alison M. Stuart

Beilstein J. Org. Chem. 2024, 20, 1785–1793, doi:10.3762/bjoc.20.157

• difluoro(aryl)-λ5-iodanes were designed originally because of the stabilisation afforded from two five-membered rings (Figure 1). We started our investigation with bicyclic difluoro(aryl)-λ5-iodane 6, building on the hypervalent iodine core skeleton used in fluoroiodane 2, with an additional 5-membered

• 20 (167.2(2)° to 168.6(2)°) and fluoroiodane 2 (166.7(2)°), presumably due to the strain caused by the two five-membered rings. Similar to trifluoroiodane 20, there are two short intermolecular I…F contacts of 2.942(4) Å and 2.999(4) Å in the packing diagram of difluoroiodane 6 (see Figure S1 in

• 7a/b and an sp3-hybridised carbon in 6. This NCC bond angle (111.7°) would certainly increase the angle strain in 7a/b and this, combined with the acute N–I–N bond angle (156.6–156.9°) caused by these two five-membered rings, could be the reason that we could not prepare these compounds. Stability

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

• fluorine gauche effects to evaluate significant conformational biases in all of the possible isomers. Achieving conformational control upon the introduction of a second fluorine atom in fluoropyrrolidine presents challenges. Unlike the chair-like conformation of six-membered rings, five-membered rings lack

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

• ; indanones; Nazarov reaction; Introduction Natural products are the source of inspiration for several research groups that develop new synthetic methodologies. The chemistry of five-membered rings plays an important role in organic chemistry, both because of the wide occurrence in nature [1][2][3][4][5][6

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

• lengths of the bonds (b–f) within the five-membered rings of the cores as well as the exocyclic C=C double bond (a) that is present in compounds 25 and 26 (for bond labels, see Figure 11). A small difference in the exocyclic C=C bond length is observed between 25 and 26, with the bond in 26 being slightly

• (absorption maxima λmax and molar absorptivities ε). Electrochemical data from differential pulse voltammetry of compounds in CH2Cl2 (with 0.1 M Bu4NPF6) if not otherwise stated; potentials in volts vs Fc/Fc+. Bond lengths (Å) within five-membered rings and of exocyclic C=C double bond (for bond assignments

Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

• Robin Klintworth,
• Garreth L. Morgans,
• Stefania M. Scalzullo,
• Charles B. de Koning,
• Willem A. L. van Otterlo and
• Joseph P. Michael

Beilstein J. Org. Chem. 2021, 17, 2543–2552, doi:10.3762/bjoc.17.170

• the six-membered analogues, which readily lose the exocyclic double bond to give the iminium system 27 upon essentially irreversible protonation. Is this perhaps another example of the lower reactivity and greater relative stability of double bonds exo- to five-membered rings when compared with their

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• HgCl2-mediated cyclization reaction of tethered alkynedithioacetals 110 to provide six- and five-membered carbocyclic and heterocyclic derivatives 111 and 112, respectively. They had observed that the formation of five-membered rings (112a–c) was preferred when substitutents were present at the alkyne

Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• chemical and electrochemical means. Through electrochemical methods, only the five-membered rings can be incorporated onto the polymer backbone, and often the polymers produced are insoluble [17]. On the other hand, chemical synthesis provides an avenue to synthesize soluble polymers where azulene can be

• order to construct polyazulenes with the head-to-tail alignment of dipoles, azulene should be functionalized at the 2,6-positions, which are diagonally opposite to each other. This will lead to an alternate arrangement of seven and five-membered rings along the polymer backbone and can facilitate

• . Azulene can be incorporated onto the polymer backbone by involving its five-membered rings via a 1,3-fashion, the seven-membered rings via a 4,7-fashion and, both the rings can be incorporated via 2,6-fashion, and these patterns can influence the properties of the resulting polymer. By and large, the

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• 1,4-naphthoquinone (1a) and 1,4-anthraquinone (1b), which were selected as model dipolarophiles. In addition, an important issue of the work was the examination of the chemoselectivity governing the formation of five-membered rings via competitive cycloaddition of the in-situ-generated 1,3-dipoles

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

• Jan Bartáček,
• Jan Svoboda,
• Martin Kocúrik,
• Jaroslav Pochobradský,
• Alexander Čegan,
• Miloš Sedlák and
• Jiří Váňa

Beilstein J. Org. Chem. 2021, 17, 1048–1085, doi:10.3762/bjoc.17.84

• reactions with seven-membered cyclic enones. However, the effectiveness was decreased in the case of five-membered rings or heterocyclic six-membered rings as the substrates (Table 14) [44]. The unsatisfactory result obtained for substrate B (entry 10, Table 14) was overcome in the next work that focused on

Ring-closing metathesis of prochiral oxaenediynes to racemic 4-alkenyl-2-alkynyl-3,6-dihydro-2H-pyrans

• Viola Kolaříková,
• Markéta Rybáčková,
• Martin Svoboda and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2020, 16, 2757–2768, doi:10.3762/bjoc.16.226

• these conditions a full or nearly complete conversion was observed with the exception of the silylated oxaenediyne 2f as was already reported for analogous published substrates [37]. Quite surprisingly, the necessity of a steric hindrance at the propargylic position in the RCEYM forming five-membered

• rings, as described in reference [23], was not observed in our cases. The absence of ethene resulted in a significant decrease of the yield, which gradually decreased from R = H (2a) to R = Pr (2d). Further, the reaction was not sensitive to the presence of electron-accepting groups (R = COOMe, 2e) at

Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides

• Vladimir P. Rybalkin,
• Sofiya Yu. Zmeeva,
• Lidiya L. Popova,
• Valerii V. Tkachev,
• Andrey N. Utenyshev,
• Olga Yu. Karlutova,
• Alexander D. Dubonosov,
• Vladimir A. Bren,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2020, 16, 1820–1829, doi:10.3762/bjoc.16.149

• persistance to photodegradation. It has been shown that annulation of benzene rings to the five-membered rings of pyrryl, thienyl and furanyl fulgides can promote the additional improvement of these properties [10][18][19][20][21]. In accordance with these data, we have previously synthesized and studied the

One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation

• Ji Ma,
• Yubin Fu,
• Junzhi Liu and
• Xinliang Feng

Beilstein J. Org. Chem. 2020, 16, 791–797, doi:10.3762/bjoc.16.72

• exhibits a narrow energy gap (1.78 eV) and a lower LUMO energy level than the parent peropyrene without the fusion of the five-membered rings. In addition, the effects of the peri-fused pentagons on the aromaticity and molecular orbitals of 1 were evaluated by theoretical calculations. This work presents

• as an efficient route to get access to aromatic hydrocarbons with peri-fused five-membered rings [25][26][27]. For instance, the dicyclopenta-fused pyrene derivatives ii and iii (Scheme 1) were successfully synthesized through palladium-catalyzed carbannulation of brominated pyrene with

• aromatic sextet theory (Figure 2e). Interestingly, the long bond length of a, b, c, and d (1.471–1.504 Å) indicated that the double bonds on the five-membered rings have a small contribution to the overall aromatic delocalization of the carbon framework [26]. In order to evaluate the aromaticity of 1, a

Microwave-assisted synthesis of 2-substituted 4,5,6,7-tetrahydro-1,3-thiazepines from 4-aminobutanol

• María C. Mollo,
• Natalia B. Kilimciler,
• Juan A. Bisceglia and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2020, 16, 32–38, doi:10.3762/bjoc.16.5

• of the corresponding tetrahydro-1,3-oxazepines. This unexpected reaction path is reasonable considering the relative ease of formation of five-membered rings as compared to the isomeric seven-membered heterocycles together with the relatively poor nucleophilicity of the carboxamide oxygen. An

Genome mining in Trichoderma viride J1-030: discovery and identification of novel sesquiterpene synthase and its products

• Xiang Sun,
• You-Sheng Cai,
• Yujie Yuan,
• Guangkai Bian,
• Ziling Ye,
• Zixin Deng and
• Tiangang Liu

Beilstein J. Org. Chem. 2019, 15, 2052–2058, doi:10.3762/bjoc.15.202

• precursor FPP via sesquiterpene synthase have been described. Nearly 75% of these structures have at least one six-membered ring; 69% of these contain five-membered rings, occupying a large portion. Three- and seven-membered ring structures account for just 21% and 24% of these structures, respectively

Synthesis of ([1,2,4]triazolo[4,3-a]pyridin-3-ylmethyl)phosphonates and their benzo derivatives via 5-exo-dig cyclization

• Aleksandr S. Krylov,
• Artem A. Petrosian,
• Julia L. Piterskaya,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2019, 15, 1563–1568, doi:10.3762/bjoc.15.159

• when using C,N-, N,S- and N,N-dinucleophiles. It is characterized by a selective 5-endo-dig cyclization to the corresponding five-membered rings. The obtained new compounds are of special interest due to the practical utility of the formed fused heterocycles, such as indoles [1], thiazolo[2,3-b][1,3,4

Introduction of an isoxazoline unit to the β-position of porphyrin via regioselective 1,3-dipolar cycloaddition reaction

• Xiujun Liu,
• Xiang Ma and
• Yaqing Feng

Beilstein J. Org. Chem. 2019, 15, 1434–1440, doi:10.3762/bjoc.15.143

• [15][16][17][18][19][20][21][22][23][24]. Among them, the 1,3-dipolar cycloaddition reaction [25] is an efficient method to fuse five-membered rings on the periphery of the porphyrin framework. Because the periphery double bonds of the porphyrin macrocycle are nice dipolarophiles, and can trap 1,3

Ring-closing-metathesis-based synthesis of annellated coumarins from 8-allylcoumarins

• Christiane Schultze and
• Bernd Schmidt

Beilstein J. Org. Chem. 2018, 14, 2991–2998, doi:10.3762/bjoc.14.278

• which a heterocycle is annellated to the benzene ring of the coumarin skeleton. In particular the latter group is often further divided into sections according to ring size (five-membered rings: furanocoumarins; six-membered rings: pyranocoumarins) and location of the annellated ring (linear vs angular

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• reaction of a (trimethylsilyl)allene and a suitable cyclic α,β-unsaturated ketone [30][31]. Despite the applicability of the reaction to construct five-membered rings, it has not been extensively examined [32] for the synthesis of complex natural products. As depicted in Scheme 2, the hydrindane core ring

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• oxidant (Scheme 22) [67]. Heterocycles in drugs are not only restricted to five-membered rings. Pyridines, pyrazines, pyrimidines, pyridazines are all common functional groups in biologically active compounds. Liu et al. have published the visible light-catalysed oxidation of dihydropyrimidines (DHPMs

Water-soluble SNS cationic palladium(II) complexes and their Suzuki–Miyaura cross-coupling reactions in aqueous medium

• Alphonse Fiebor,
• Richard Tia,
• Banothile C. E. Makhubela and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1859–1870, doi:10.3762/bjoc.14.160

• of the two protons of the pyridine moiety as a doublet at δH 7.76. Furthermore, the formation of the two fused five-membered rings was confirmed by the appearance of the axial and equatorial protons of the bridging methylene groups as two broad singlets at δH 5.59 and δH 5.16 each integrating for two

Photocatalyzed synthesis of isochromanones and isobenzofuranones under batch and flow conditions

• Manuel Anselmo,
• Lisa Moni,
• Hossny Ismail,
• Davide Comoretto,
• Renata Riva and
• Andrea Basso

Beilstein J. Org. Chem. 2017, 13, 1456–1462, doi:10.3762/bjoc.13.143

• further demonstration that cyclization to isochromanone would be favored with respect to benzofuranone from the reaction of compound 2c with 12a. In this case both substrates bear an ester functionality and in principle both six- and five-membered rings could be obtained. Unexpectedly, upon exposure to

• , selective synthesis of benzo-fused six- or five-membered rings can be achieved. We have demonstrated that the 5-membered ring formation is favored, when the two processes are competitive, and we have also shown that acetonitrile can act as a third component in the cyclization to oxazepinones. By employing