Surprising acidity for the methylene of 1,3-indenocorannulenes?

• Shi Liu,
• Märt Lõkov,
• Sofja Tshepelevitsh,
• Ivo Leito,
• Kim K. Baldridge and
• Jay S. Siegel

Beilstein J. Org. Chem. 2024, 20, 3144–3150, doi:10.3762/bjoc.20.260

• of the first acidity constant (pKa) for BFC (27.6 in CH3CN) and FIC (27.8 in CH3CN) shows the methylene protons to be significantly more acidic than those in related cyclopentadiene (32 in CH3CN), indene (34 in CH3CN), or fluorene (37 in CH3CN) and comparable to the methine of 9

• ; Loschmidt group element; molecular graph; Introduction A classic textbook tetrad linking hydrocarbon acidity to aromatic stabilization energy comprises cyclopentadiene (CpH), indene (InH), fluorene (FlH), and diphenylmethane (DPMH) [1][2], with pKa values in DMSO equal to 18 [3], 20.1 [3], 22.6 [3], and

• is more nuanced [10][11]. Subsequently, literature and computational examples reveal a leitmotif for CpH-PAH-based redox-active carbon-rich materials. Results and Discussion From competitive titrations against 9-C6F5-fluorene (pKa = 28.14 in CH3CN) [12][13] and (4-Me-C6F4)(C6H5)CHCN (pKa = 26.98 in

Advances in radical peroxidation with hydroperoxides

• Oleg V. Bityukov,
• Pavel Yu. Serdyuchenko,
• Andrey S. Kirillov,
• Gennady I. Nikishin,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2024, 20, 2959–3006, doi:10.3762/bjoc.20.249

• fluorenes 51 peroxidation (Scheme 19) [50][62]. Initially, the complex A of 2,2′-bipyridine with manganese(III) acetate is formed. Further oxidation of A by TBHP leads to complex B and tert-butoxy radical C. The later one abstracts an hydrogen atom from fluorene 51 to form C-centered radical F. The reaction

Novel truxene-based dipyrromethanes (DPMs): synthesis, spectroscopic characterization and photophysical properties

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2024, 20, 2163–2170, doi:10.3762/bjoc.20.186

• for diverse applications in future studies. Keywords: condensation; co-timerization; dipyrromethane; Friedel–Crafts acylation; heterocycles; pyrrole; truxene; Introduction The scaffold of truxene (10,15‐dihydro‐5H‐diindeno[1,2‐a;1′,2′‐c]fluorene) and its congeners comprises three fluorene subunits

• , that is the isotruxene scaffold [30] – having differences in clipping of fluorene moieties, chemists began to synthesize the heteroatom-doped truxenes as well as isotruxene molecules, so-called “hetero-truxenes/isotruxenes” [31][32][33]. As can be inspected from the scientific literature, to date a

• TMS. UV–vis data were recorded on a PerkinElmer (Lambda 365) UV–vis spectrophotometer in HPLC grade CHCl3. Synthesis of 10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene (9): The truxene scaffold 9 was prepared according to a literature report procedure [38]. l-Indanone (8, 6.8 g, 51.4 mmol) was added

Cofactor-independent C–C bond cleavage reactions catalyzed by the AlpJ family of oxygenases in atypical angucycline biosynthesis

• Jinmin Gao,
• Liyuan Li,
• Shijie Shen,
• Guomin Ai,
• Bin Wang,
• Fang Guo,
• Tongjian Yang,
• Hui Han,
• Zhengren Xu,
• Guohui Pan and
• Keqiang Fan

Beilstein J. Org. Chem. 2024, 20, 1198–1206, doi:10.3762/bjoc.20.102

• intermediate with a benzo[b]fluorene skeleton undergoes further conversion into fluostatins with a benzo[a]fluorene skeleton remains to be elucidated [27][28]. Inhibition of cofactor-independent catalytic activities of AlpJ-family oxygenases by superoxide dismutase There are many reported cofactor-independent

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

Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

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

• indenofluorene (IF) or fluorene cores and containing various dithiafulvene (DTF) donor units that gain aromaticity upon oxidation and a variety of acceptor units, such as vinylic diesters, enediynes, and cross-conjugated radiaannulenes (RAs) that gain aromaticity upon reduction. In some cases, the DTF units are

• the introduction of an indeno[1,2-b]fluorene (IF) core [13], providing indenofluorene-extended TTFs (IF-TTFs) of the general structure shown in Figure 1. The π-system can be further expanded as well at the dithiole rings. For example, we have recently developed a synthetic protocol for fusing a

• smaller fluorene PAH. These compounds were prepared by a Lawesson’s reagent-promoted coupling between fluorenone 5 and the Ts-protected 1,3-dithiole-2-thione building blocks 2 and 3, respectively, shown in Scheme 3 (albeit in modest yields). Fluorene-based DTF compounds have previously been explored in

Pyridine C(sp²)–H bond functionalization under transition-metal and rare earth metal catalysis

• Haritha Sindhe,
• Malladi Mounika Reddy,
• Karthikeyan Rajkumar,
• Akshay Kamble,
• Amardeep Singh,
• Anand Kumar and
• Satyasheel Sharma

Beilstein J. Org. Chem. 2023, 19, 820–863, doi:10.3762/bjoc.19.62

• intact under the reaction conditions without any further oxidation. Different oxidants resulted in different products such as the monoarylated product 118 formed in the presence of TBHP as oxidant and the benzylated product 119 was obtained when potassium persulfate was used. Interestingly, aza-fluorene

Post-synthesis from Lewis acid–base interaction: an alternative way to generate light and harvest triplet excitons

• Hengjia Liu and
• Guohua Xie

Beilstein J. Org. Chem. 2022, 18, 825–836, doi:10.3762/bjoc.18.83

• optoelectronic properties of a fluorene-based copolymer with an sp2 nitrogen heteroatom via supramolecular coordination [33]. The PL emission in solution showed an obvious red-shifted profile. The polymer LED with different molar equivalents of Lewis acids was investigated. The EL peak wavelength was gradually

• . Regarding the materials developed by Lin et al., supramolecular coordination of PF8-co-DAF8 (13, Figure 5) with Lewis acids played an important role. They selected the more rigid 4,5-diazafluorene (DAF) with nitrogen atoms inserted at the 4 and 5-positons of the fluorene moiety [33]. The heteroatomic

• fluorene showed enhanced planarity of the molecule. The coordination tended to be more efficient if a stronger Lewis acid was employed. The bipolar host material 35DCzPPy (14, Figure 5) was initially synthesized by Kido’s group [39]. It combines two carbazole electron donors with high triplet energy and a

Thiophene/selenophene-based S-shaped double helicenes: regioselective synthesis and structures

• Mengjie Wang,
• Lanping Dang,
• Wan Xu,
• Zhiying Ma,
• Liuliu Shao,
• Guangxia Wang,
• Chunli Li and
• Hua Wang

Beilstein J. Org. Chem. 2022, 18, 809–817, doi:10.3762/bjoc.18.81

• similar method, Takimiya reported the synthesis of six-ring-fused and four-ring-fused heteroacenes containing selenopheno[3,2-b]selenophene in 2007 and 2009, respectively [23][24]. Five years later, Cheng reported the synthesis of two types of five-ring-fused isomers of diselenopheno[2,3-b:7,6-b′]fluorene

• and diselenopheno[3,2-b:6,7-b′]fluorene through the cyclization of terminal acetylene as well as six types of biselenophene-based fused tricyclic derivatives [25][26]. In 2017, we reported the first member of diselenoselenophenes (DSSs), 2,5-di(trimethylsilanyl)diseleno[2,3-b:3′,2′-d]selenophene ((TMS

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

• sensitivity could be attributed to the resonance stabilization of the positive charge on the five-membered ring of the azulene by the electron-donating groups at the 2-position. These polymers were quite robust as they underwent several cycles of electro-cycling before degradation. Azulene-fluorene copolymers

• In 2009, Xu and co-workers [40] synthesized various examples of azulene-fluorene conjugated polymers by using Suzuki cross-coupling reactions. The first set of polymers, poly[2,7-(9,9-dialkylfluorenyl)-alt-(1’,3’-azulenyl)] 106–109 was prepared by the reaction of 1,3-dibromoazulene (4) with 9,9

• )azulene (114) was required, and its synthesis was achieved from 2-bromofluorene (110) by following the protocol presented in Scheme 19B. The reaction of 114 with fluorene borates 102 and 104 under Suzuki conditions yielded polymers 115 and 116, respectively (Scheme 19C). The solubility of all polymers was

Design, synthesis and photophysical properties of novel star-shaped truxene-based heterocycles utilizing ring-closing metathesis, Clauson–Kaas, Van Leusen and Ullmann-type reactions as key tools

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2021, 17, 1374–1384, doi:10.3762/bjoc.17.96

• , superior solubility, improve morphological, optical, electrical and film-forming properties because of the involvement of extra dimensionality. Amongst them, the heptacyclic truxene scaffold possessing three overlapping fluorene units and its congeners are of archetypal interest due to their potential

• 600 to 4000 cm−1. UV–vis spectra were recorded on a UV-1800 Shimadzu spectrophotometer and the fluorescence spectra were recorded on an Agilent Carry Eclipse spectrofluorimeter. Synthesis of 10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene (7): Truxene scaffold 7 was prepared according to a literature

• followed by dichloromethane gave a white powder (4.7 g, 80%). Synthesis of 5,5,10,10,15,15-hexabutyl-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene (2): Truxene (7, 4 g, 11.68 mmol), DMSO (35 mL), and t-BuOK (11.79 g, 105.12 mmol) were mixed in a two-necked round bottom flask (100 mL) under nitrogen

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• Scheme 32 from 9,9-didecyl-9H-fluorene and monomethyl terephthalate chloride [152]. The authors of reference [153] presented a series of 2,2';6',2"-terpyridine (tpy)-substituted methanofullerenes and pyrrolidinofullerene dyads 184–186 linked through para-phenylene or para-phenyleneethynylphenylene units

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• alcohols was shown by Cohen and Kaluszyner [55][56] and by Streitwieser et al. [57]. The cyclodehydration of 9c occurs in polyphosphoric acid to afford fluorene 37 (Scheme 8) [57]. A mechanistic proposal invoking the initial generation of the α-(trifluoromethyl)carbenium ion 10c↔10c’ was mentioned by the

• authors [55][56]. Related studies on diphenyl derivative 9c in a mixture of H2SO4 and chloroform also showed the formation of fluorene derivative 37 in 25% yield [58]. Exploiting this impact of the trifluoromethyl substituent in the cationic Nazarov electrocyclization, the synthesis of CF3-substituted

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• good yield. Dehydrogenation of 7 with chloranil then provided 9-(dimethylamino)-9-(trifluoromethyl)fluorene 8. In an analogous reaction sequence, 11H-benzo[a]fluorene derivative 9 was obtained from 3-(2-naphthyl)propyn-1-iminium salt 1b and 2,3-dimethylbutadiene (Scheme 2) in a one-pot three-step

• -up were identified by their NMR and analytical data as 2-(1-phenylvinyl)indene 12a and a small amount of benzo[a]fluorene 13a (δF = −69.74 and −69.20 ppm, respectively). The results obtained with styrenes bearing a substituent at the olefinic bond provide useful information with respect to the

Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

• Dominik Göbel,
• Marius Friedrich,
• Enno Lork and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139

• cycloadditions with model alkynes. Besides two ortho- and para-bromo-substituted benzaldehydes, the azide functionalization of a fluorene-based structure will be presented. The copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) of the so-synthesized azide-functionalized bromocarbaldehydes with terminal

• -methylbenzaldehyde). Bromofluorenecarbaldehyde 5 The synthetic route to azide-functionalized 7-bromofluorene-2-carbaldehyde 5 started from unfunctionalized fluorene. Double bromination to 14, followed by double methylation of the methylene bridge to 15 and a lithiation/formylation sequence afforded 7-bromofluorene-2

• previous deprotection reactions, fluorene 21 was converted by means of a three-step sequence to the desired azide-functionalized 7-bromofluorene-2-carbaldehyde 5 in 86% yield and an overall yield of 45% (starting from fluorene). The molecular structure of 5 could be verified by X-ray diffraction (XRD, see

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• (Figure 11) [129]. Four conjugated polymers containing dibenzothiophene sulfone (FSO) monomers, linked by either biphenyl (FSO-BP), fluorene (FSO-F), 2,8-dibenzothiophene (FSO-FSz), or 3,7-dibenzothiophene (FSO-FS) monomers were synthesised and applied in the photocatalytic hydrogen evolution reaction

Synthesis and properties of quinazoline-based versatile exciplex-forming compounds

• Rasa Keruckiene,
• Simona Vekteryte,
• Ervinas Urbonas,
• Matas Guzauskas,
• Eigirdas Skuodis,
• Dmytro Volyniuk and
• Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 1142–1153, doi:10.3762/bjoc.16.101

• efficiency (EQE) of 19.2% [7]. Two blue emitters based on fluorene-bridged quinazoline and quinoxaline derivatives were used in the active layers of OLEDs with EQEs of 1.58% and 1.30%, suggesting that the self-aggregation of emitters had a considerable effect on the photoluminescent and electroluminescent

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• dendrimers functionalized with TPA fluorophores used a blue-emitting quadrupolar fluorophore based on a fluorene core [37][38][39][40][41] and functionalized by a phenol on one side. The synthesis was carried out from generation 1 (12 fluorophores) to generation 4 (96 fluorophores) (Scheme 2). The

Catalyst-free assembly of giant tris(heteroaryl)methanes: synthesis of novel pharmacophoric triads and model sterically crowded tris(heteroaryl/aryl)methyl cation salts

• Rodrigo Abonia,
• Luisa F. Gutiérrez,
• Braulio Insuasty,
• Jairo Quiroga,
• Kenneth K. Laali,
• Chunqing Zhao,
• Gabriela L. Borosky,
• Samantha M. Horwitz and
• Scott D. Bunge

Beilstein J. Org. Chem. 2019, 15, 642–654, doi:10.3762/bjoc.15.60

• aldehydes, chromone aldehydes, and fluorene aldehydes (Ar2CHO) and coumarins (Ar3) in 1:1:1 ratio to form the corresponding tris(heteroaryl)methanes (Ar1Ar2Ar3)CH along with (Ar1Ar1Ar2)CH triads. A series of new 2:1 triads were also synthesized by coupling substituted indoles with Ar2CHO. The coupling

• new structure. This concept has recently received attention by the pharmaceutical industry because it provides new options to develop more specific drugs for the treatment of persistent and challenging pathologies [27][28] (Scheme 1). The indole, coumarin, quinoline, chromone and fluorene moieties are

• ternary heteroarylmethane-inspired hybrids by coupling diversely substituted indoles (Ar1) with quinoline aldehydes, quinolone aldehydes, chromone aldehydes, and fluorene aldehydes (Ar2CHO) and coumarins (Ar3) in 1:1:1 ratio by simple reflux in ethanol solvent to form the corresponding highly crowded tris

Selective benzylic C–H monooxygenation mediated by iodine oxides

• Kelsey B. LaMartina,
• Haley K. Kuck,
• Linda S. Oglesbee,
• Asma Al-Odaini and
• Nicholas C. Boaz

Beilstein J. Org. Chem. 2019, 15, 602–609, doi:10.3762/bjoc.15.55

• , it shows incompatibility with functional groups such as alkenes, phenols, phenyl ethers, and alcohols, which are readily oxidized. The dibenzylic C–H bonds of fluorene and xanthene were also able to be functionalized. Xanthene (4a) was over-oxidized to the ketone (xanthone, 5a) in 57% yield (Figure 3

• ). Similarly, fluorene was oxidized to a mixture of 9-fluorenyl acetate (5b, 31%) and fluorenone (5c, 20%). The same mixture of acetate and ketone is observed at a higher temperature (150 °C), but the overall yield was lower. It is proposed that the stabilizing presence of two benzene rings on the monooxidized

Olefin metathesis in multiblock copolymer synthesis

• Maria L. Gringolts,
• Yulia I. Denisova,
• Eugene Sh. Finkelshtein and
• Yaroslav V. Kudryavtsev

Beilstein J. Org. Chem. 2019, 15, 218–235, doi:10.3762/bjoc.15.21

• ) polymerization. This approach was implemented for the preparation of fluorene-containing multiblock copolymers [62][63]. Poly(9,9-di-n-octylfluorene-2,7-vinylene, PFV) obtained by ADMET polymerization of 2,7-divinyl-9,9-di-n-octylfluorene in the presence of Gr2 under reduced pressure (Scheme 4), possessed

Synergistic approach to polycycles through Suzuki–Miyaura cross coupling and metathesis as key steps

• Sambasivarao Kotha,
• Milind Meshram and
• Chandravathi Chakkapalli

Beilstein J. Org. Chem. 2018, 14, 2468–2481, doi:10.3762/bjoc.14.223

• product 35 was subjected to SM coupling using phenylboronic acid (36) to afford the cross-coupling product 37 (97%, Scheme 5). In another instance, a simple synthetic approach to spiro-fluorene derivative 41 was described involving a serial usage of RCM and SM coupling [37]. To this end, bromofluorene 38

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

Fluorogenic PNA probes

• Tirayut Vilaivan

Beilstein J. Org. Chem. 2018, 14, 253–281, doi:10.3762/bjoc.14.17

• oligonucleotides or analogues. One notable example is the use of a labeled PNA probe in combination with water-soluble cationic conjugated polyelectrolytes (CCP) for the FRET-based detection of DNA [114]. The CCP is typically an extended π-conjugated system, such as oligophenylene/fluorene with appending

• DNA. In addition to TO, other environment-sensitive labels, such as fluorene [168], pyrene [167][169][170], diaminocarbazole [171] and Nile red [172], have been successfully employed in the development of single-labeled fluorogenic aegPNA, γPNA and acpcPNA probes (Figure 18). Up to a 73-fold