Unprecedented visible light-initiated topochemical [2 + 2] cycloaddition in a functionalized bimane dye

• Metodej Dvoracek,
• Brendan Twamley,
• Mathias O. Senge and
• Mikhail A. Filatov

Beilstein J. Org. Chem. 2025, 21, 500–509, doi:10.3762/bjoc.21.37

• )bimane (DMOCDO10) and syn-(Me,Me)bimane (DXABIM10) [26], a room temperature structure of Me4B (TNZBCO10) [27], and a planar syn-(H,ethynyl)bimane (WAYHEJ) [28]. Optical properties The optical properties of the three bimanes were measured to investigate differences in their excited state properties, as

Streamlined modular synthesis of saframycin substructure via copper-catalyzed three-component assembly and gold-promoted 6-endo cyclization

• Asahi Kanno,
• Ryo Tanifuji,
• Satoshi Yoshida,
• Sota Sato,
• Saori Maki-Yonekura,
• Kiyofumi Takaba,
• Jungmin Kang,
• Kensuke Tono,
• Koji Yonekura and
• Hiroki Oguri

Beilstein J. Org. Chem. 2025, 21, 226–233, doi:10.3762/bjoc.21.14

• manipulation to install the C1 sidechain for saframycins, respectively [14][39]. The alkyne segment 8 was prepared by protecting group manipulations in three steps from the known starting material, 2-ethynyl-6-hydroxybenzaldehyde (15), which can be readily synthesized from commercially available 1-bromo-3

Synthesis of tricarbonylated propargylamine and conversion to 2,5-disubstituted oxazole-4-carboxylates

• Kento Iwai,
• Akari Hikasa,
• Kotaro Yoshioka,
• Shinki Tani,
• Kazuto Umezu and
• Nagatoshi Nishiwaki

Beilstein J. Org. Chem. 2024, 20, 2827–2833, doi:10.3762/bjoc.20.238

• reacts with butyllithium, ring closure occurs between the ethynyl and carbamoyl groups, yielding 2,5-disubstituted oxazole-4-carboxylates. This cyclization also occurs when the propargylamine is heated with ammonium acetate, resulting in double activation. Keywords: acid amide; diethyl mesoxalate; N

• results, a plausible mechanism was proposed, as shown in Scheme 3a. The 5-exo-dig ring closure is induced by O-attack of the amide moiety on the ethynyl group to form 6, during which a stoichiometric proton source (water in the solvent) is necessary. Subsequently, one of the ethoxycarbonyl groups at the 4

• mechanism, as illustrated in Scheme 3b [13][14], we cannot negate this mechanism because the reaction media and bases were different. PCPA 4a was heated in the presence of methanesulfonic acid to undergo 6-endo-dig cyclization. However, hydration predominantly occurred, converting the ethynyl group to a

Synthesis of benzo[f]quinazoline-1,3(2H,4H)-diones

• Ruben Manuel Figueira de Abreu,
• Peter Ehlers and
• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 2708–2719, doi:10.3762/bjoc.20.228

• ), 215 (17), 202 (23), 189 (13); HRESIMS-TOF (m/z): [M + H]+ calcd for C20H17N2O2, 317.1290; found, 317.1282. 5-(4-Fluorophenyl)-6-((4-fluorophenyl)ethynyl)-1,3-dimethylpyrimidine-2,4(1H,3H)-dione (4h). Compound 4h was obtained as a brown solid in 43% yield (46.2 mg, 131 µmol, Rf 0.17 (heptane/ethyl

• (PPh3)4 (10 mol %), NaOH (3 equiv), 1,4-dioxane/water 5:1, 100 °C, 1 h; iv) p-TsOH (20 equiv), toluene, 100 °C, 4 h. Synthesis and isolated yields of 1,3-dimethyl-5-aryl-6-[2-(aryl)ethynyl]uracils 4a–i. Reaction conditions: 3 (1 equiv), boronic acid (1.2 equiv), Pd(PPh3)4 (5 mol %), NaOH (3 equiv), 1,4

• of 1,3-dimethyl-5-phenyl-6-[2-(phenyl)ethynyl]uracil derivatives 5a, 5d, 5f, 5g, 5h, and 5i in dichloromethane (c = 1·10−5 M) at 20 °C. Supporting Information Supporting Information File 20: Copies of NMR spectra. Acknowledgements We are grateful for the technical and analytical support of the

Syntheses and medicinal chemistry of spiro heterocyclic steroids

• Laura L. Romero-Hernández,
• Ana Isabel Ahuja-Casarín,
• Penélope Merino-Montiel,
• Sara Montiel-Smith,
• José Luis Vega-Báez and
• Jesús Sandoval-Ramírez

Beilstein J. Org. Chem. 2024, 20, 1713–1745, doi:10.3762/bjoc.20.152

• reported a novel and straightforward method for synthesizing spiro 2,5-dihydrofuran derivatives starting from 17-ethynyl-17-hydroxysteroids such as lynestrenol (38) (Scheme 12) [25]. The 17-hydroxy group of steroids underwent allylation using allyl bromide and sodium hydride. After formation of the alkenyl

• microwaved, a Diels–Alder reaction occurred, yielding the spiro product 41. The reaction conditions were also applied to 17-ethynyl-17-hydroxysteroids derived from mestranol and desogestrel obtaining similar results. The one-pot RCEYM/Diels–Alder reaction was only applied to mestranol and lynestrenol

Synthesis and properties of 6-alkynyl-5-aryluracils

• Ruben Manuel Figueira de Abreu,
• Till Brockmann,
• Alexander Villinger,
• Peter Ehlers and
• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 898–911, doi:10.3762/bjoc.20.80

• for the 5-phenyl group, which is twisted out of the plane with a dihedral angle of φ = 70.3°. Furthermore, it could be observed that the 6-[2-(phenyl)ethynyl] group is slightly curved, due to the dihedral angle of the alkyne group (174.5 ° and 176.7 °). Analysis of the lattice structure of 5a revealed

• absorption (left) and emission (right, λex = 400 nm) spectra of 1,3-dimethyl-5-phenyl-6-[2-(phenyl)ethynyl]uracil derivatives 5d, 5f, 5k, 5l, and 5m in dichloromethane (c = 1·10−5 M). Synthesis of 1,3-dimethly-5-[2-(aryl)ethynyl]-6-[2-(aryl)ethynyl]uracils 4 and 1,3-dimethyl-5-aryl-6-[2-(aryl)ethynyl]uracils

• 5:1, 100 °C, 1 h. Synthesis of 5-bromo-1,3-dimethyl-6-[2-(aryl)ethynyl]uracils 3a–j. Reaction conditions: 2 (1.0 equiv), arylacetylene (1.2 equiv), Pd(PPh3)Cl2 (5 mol %), CuI (5 mol %), NEt3 (10 equiv), DMSO, 25 °C, 6 h. aYields of isolated products. bReaction temperature: 50 °C. Structure of the

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

• ’-dicyanoquinone diimides [82], and 6,6-dicyanopentafulvenes (DCFs) [83][84] have been employed. Notably, the [2 + 2] CA–RE reaction of DMA-ethynyl-appended porphyrin with TCNQ is observed to occur on a metal surface (specifically Au(111)) under high-vacuum conditions, with successful visualization achieved

• the DCF molecule [83][84], as shown in Scheme 3. In the reaction between 4-ethynyl-N,N-dimethylaniline (1) and triisopropylsilylethynyl-substituted DCF 2a, heating at 80 °C in acetonitrile selectively yields the corresponding adduct 3a with 64% yield. In 3a, the anilino group forms a covalent linkage

• derivative 39, wherein a DMA–ethynyl group is introduced at the 9-position, with TCNE at 40 °C in THF yielded the corresponding TCBD 40 with 91% yield. Subsequent heating of 40 in toluene at 70 °C led to an intramolecular cyano-DA (CDA) reaction, which quantitatively afforded the CDA product 41 (Scheme 15

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

• , ethynylbenzene, or 4-ethynylbenzonitrile yielded compounds 19–21, while two-fold Sonogashira coupling with ((2-ethynylphenyl)ethynyl)triisopropylsilane resulted in compound 22. Desilylation of the alkynes of compound 22 with tetrabutylammonium fluoride (TBAF) and subsequent intramolecular Glaser–Hay coupling of

• Sonogashira couplings of compound 25 with triisopropylsilylacetylene and ((2-ethynylphenyl)ethynyl)triisopropylsilane yielded compounds 26 and 27, respectively. A two-fold, intramolecular Glaser–Hay coupling of compound 27 (after desilylation) was attempted under the conditions that were successful in the

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

• condensation (Table 4, entry 7). As expected, based on the above consideration, 4-ethynyl-1,1'-biphenyl (1h) afforded both hydration and condensation products 2h and 3h in similar amounts (Table 4, entry 8), while the presence of a chlorine in the para position of the phenyl ring allowed to obtain the

Biphenylene-containing polycyclic conjugated compounds

• Cagatay Dengiz

Beilstein J. Org. Chem. 2023, 19, 1895–1911, doi:10.3762/bjoc.19.141

• % yields, respectively. When comparing compounds 25a and 25b, UV–vis and fluorescence studies (λmax = 500 nm, λem = 502 nm, Φem = 0.45 for 25a; λmax = 513 nm, λem = 517 nm, Φem = 0.26 for 25b; λmax = 442 nm, λem = 444 nm, Φem = 0.97 for 9,10-bis((triisopropylsilyl)ethynyl)anthracene – blue-colored) provide

Aromatic systems with two and three pyridine-2,6-dicarbazolyl-3,5-dicarbonitrile fragments as electron-transporting organic semiconductors exhibiting long-lived emissions

• Karolis Leitonas,
• Brigita Vigante,
• Dmytro Volyniuk,
• Audrius Bucinskas,
• Pavels Dimitrijevs,
• Sindija Lapcinska,
• Pavel Arsenyan and
• Juozas Vidas Grazulevicius

Beilstein J. Org. Chem. 2023, 19, 1867–1880, doi:10.3762/bjoc.19.139

• equiv), tetrakis(triphenylphosphine)palladium(0) (11.6 mg, 0.01 mmol, 0.05 equiv), CuI (1.2 mg, 0.006 mmol, 0.03 equiv) in 2 mL of DMF was degassed with Ar. Then, the appropriate ethynyl derivative (0.24 mmol, 1.2 equiv) and 1 mL of triethylamine were added and the resulting mixture was heated at 90 °C

• ) ethynyltrimethylsilane (2 equiv), PdCl2(PPh3)2 (0.07 equiv), CuI (0.05 equiv), diisopropylethylamine, DMF, 55 °C, 12 h; e) K2CO3 (2 equiv), MeOH/Et2O, 1 h; f) Pd(PPh3)4 (0.1 equiv), CuI (1 equiv), DMF/DIPEA, 80 °C, 48 h. Synthesis of dicyanocarbazoles 7–9. Reaction conditions: a) corresponding ethynyl arene, Pd(Ph3P)4

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

Construction of hexabenzocoronene-based chiral nanographenes

• Ranran Li,
• Di Wang,
• Shengtao Li and
• Peng An

Beilstein J. Org. Chem. 2023, 19, 736–751, doi:10.3762/bjoc.19.54

• pursuit of HBC-tetramer-based supertwistacene (compound 115 in Scheme 12), Wang and co-workers synthesized a chiral HBC-dimer 46 [46], in which two HBC units structurally shared one benzene ring (Scheme 6). 1,4-Bis((4-(tert-butyl)phenyl)ethynyl)benzene reacted with tetracyclone 2 through a two-fold Diels

• Sonogashira cross-coupling reaction of phenylacetylene 50 and 1,4-dibromotetrafluorobenzene. The resulting bis[aryl(ethynyl)]tetrafluorobenzene 59 was able to undergo a 2-fold [4 + 2] cycloaddition reaction with cyclopentadienone 2, affording polyaromatic 60 in a 70% yield. The final step was the Scholl

Synthesis, structure, and properties of switchable cross-conjugated 1,4-diaryl-1,3-butadiynes based on 1,8-bis(dimethylamino)naphthalene

• Semyon V. Tsybulin,
• Ekaterina A. Filatova,
• Alexander F. Pozharskii,
• Valery A. Ozeryanskii and
• Anna V. Gulevskaya

Beilstein J. Org. Chem. 2023, 19, 674–686, doi:10.3762/bjoc.19.49

• two 7-(arylethynyl)-1,8-bis(dimethylamino)naphthalene fragments was prepared via the Glaser–Hay oxidative dimerization of 2-ethynyl-7-(arylethynyl)-1,8-bis(dimethylamino)naphthalenes. The oligomers synthesized in this way are cross-conjugated systems, in which two conjugation pathways are possible: π

• from the donor moiety [34]. We therefore compared the UV spectra of the oligomers 5d and 5e and monomers 6d and 6e with those of model p,p'-disubstituted diphenylacetylenes having donor NMe2 and acceptor NO2 or CN termini. The reported absorption maxima of 4-((4-(dimethylamino)phenyl)ethynyl

• )benzonitrile and N,N-dimethyl-4-((4-nitrophenyl)ethynyl)aniline in chloroform solution are 373 and 416 nm, respectively [35]. In the same time, λmax for 2-((4-nitrophenyl)ethynyl)-1,8-bis(dimethylamino)naphthalene is 474 nm [36]. The red shift observed in the spectrum of this compound as well as in the spectra

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

• the coumarin moiety in the case of zinc porphyrin analogues. In 2017, Yamana et at. [35] reported the synthesis of porphyrin-DNA conjugate 50 by a solid-phase “click reaction” between azidoporphyrin 39a and oligodeoxynucleotides 49 bearing an ethynyl group in the presence of CuSO4·5H2O and sodium

1,4-Dithianes: attractive C2-building blocks for the synthesis of complex molecular architectures

• Bram Ryckaert,
• Ellen Demeyere,
• Frederick Degroote,
• Hilde Janssens and
• Johan M. Winne

Beilstein J. Org. Chem. 2023, 19, 115–132, doi:10.3762/bjoc.19.12

• use in intermolecular cycloadditions, as the putative gold(I)-coordinated intermediates like 112 are indeed quite similar to those expected to arise from dihydrodithiin alcohol 90 (see Scheme 19) [112]. However, our results with the simple 2-ethynyl-1,3-dithiolane (116) immediately showed that the

Preparation of an advanced intermediate for the synthesis of leustroducsins and phoslactomycins by heterocycloaddition

• Anaïs Rousseau,
• Guillaume Vincent and
• Cyrille Kouklovsky

Beilstein J. Org. Chem. 2022, 18, 1385–1395, doi:10.3762/bjoc.18.143

• 206.6, 154.9, 85.1, 82.3, 59.0, 45.0, 36.5, 32.2, 28.4, 18.1, 12.1 ppm; HRMS (m/z): [M + Na]+ calcd 424.2490; found, 424.2480; [α]D20 +37.4 (c 0.5, CH2Cl2). (5S,6R)-5-Ethyl-6-ethynyl-5,6-dihydro-2H-pyran-2-one (21): Caesium fluoride (290 mg, 1.91 mmol, 1.3 equiv) was added to a solution of the lactone

• ) ppm; 13C NMR (90 MHz, CDCl3) δ 162.5, 148.8, 120.3, 77.4, 76.6, 70.7, 38.7, 22.6, 10.9 ppm; HRMS (m/z): [M + Na]+ calcd 173.0573; found, 173.0572; [α]D20 +132.0 (c 1.0, CH2Cl2). (2R,3S,6RS)-3-Ethyl-2-ethynyl-6-methoxy-3,6-dihydro-2H-pyran (19): This compound was prepared according to reference [18]. A

Introducing a new 7-ring fused diindenone-dithieno[3,2-b:2',3'-d]thiophene unit as a promising component for organic semiconductor materials

• Valentin H. K. Fell,
• Joseph Cameron,
• Alexander L. Kanibolotsky,
• Eman J. Hussien and
• Peter J. Skabara

Beilstein J. Org. Chem. 2022, 18, 944–955, doi:10.3762/bjoc.18.94

• further functionalised with (triisopropylsilyl)ethynyl [24] (6) or with 1,3-dithiole units [25] (7) by other research groups. The (triisopropylsilyl)ethynyl (TIPSE) groups are introduced to improve the solubility and solid-state order, fostering intermolecular π-orbital interactions [26]. Moreover

Synthesis of novel alkynyl imidazopyridinyl selenides: copper-catalyzed tandem selenation of selenium with 2-arylimidazo[1,2-a]pyridines and terminal alkynes

• Mio Matsumura,
• Kaho Tsukada,
• Kiwa Sugimoto,
• Yuki Murata and
• Shuji Yasuike

Beilstein J. Org. Chem. 2022, 18, 863–871, doi:10.3762/bjoc.18.87

• phenyllithium in THF at −78 °C led to a nucleophilic substitution reaction with the elimination of the ethynyl group to form the desired phenylimidazopyridinyl selenide 6a in 49% yield. In the reaction with n-butyllithium, alkyl derivative 6b was isolated in the same way. The reaction of 4aa with the Ruppert

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

• with HgCl2 (0.5 equiv) in presence of N-bromosuccinimide (NBS) undergoes cyclization yielding stable bromo alkenes 87 (Scheme 28) [80][81]. Atta et al. reported the specific cyclization of ethynyl phenols 88 in presence of HgCl2 at ambient temperature yielding benzofuran derivatives 89. They had

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

• -(n-dodecyl)azulene (16) is shown in Scheme 5A. The Sonogashira cross-coupling reaction between 4,7-dibromo-6-(n-dodecyl)azulene (13) and 4,7-diethynyl-6-(n-dodecyl)azulene (16) yielded 4,7-polyazulene 17 linked through ethynyl bridges (Scheme 5B). Similarly, the Yamamoto cross-coupling reaction

• backbone, resulting in the blue shift of absorption bands (λmax around 350 nm). Interestingly, the ethynyl linker in 17 was assisting the effective delocalization despite the presence of the n-alkyl group at position 6, as evidenced by its large red-shifted absorption at 456 nm compared to 19. The

• ) complexes. Synthesis of ‘true polyazulene’ 3 or 3’ by cationic polymerization. Synthesis of 1,3-polyazulene 5 by Yamamoto protocol. Synthesis of 4,7-dibromo-6-(n-alkyl)azulenes 12–14. Synthesis of (A) 4,7-diethynyl-6-(n-dodecyl)azulene (16) and (B) 4,7-polyazulene 17 containing an ethynyl spacer. Synthesis

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• aromatic ketones (Scheme 27) [61]. The authors coupled acetophenone derivatives 116 and 1,4-benzenediboronates 117 at a 2:1 ratio, to obtain p-terphenyl derivatives 118. In the second step, the conversion of the acetyl group of compounds 118 to an ethynyl group afforded diethynylterphenyls 119. In the last

• double cyclization and concluded that the reaction strongly depended on the position of the ethynyl groups in the terphenyl compounds. Terphenyls 125 were the most appropriate to prepare dibenzo[a,h]anthracenes in good yield (49–92%). AuCl was a notable catalyst because it maintained high cyclization

2,4-Bis(arylethynyl)-9-chloro-5,6,7,8-tetrahydroacridines: synthesis and photophysical properties

• Najeh Tka,
• Mohamed Adnene Hadj Ayed,
• Mourad Ben Braiek,
• Mahjoub Jabli,
• Noureddine Chaaben,
• Kamel Alimi,
• Stefan Jopp and
• Peter Langer

Beilstein J. Org. Chem. 2021, 17, 1629–1640, doi:10.3762/bjoc.17.115

• prepared products are given in Table 4. For phenylethynyl-substituted product 4a, the blue colored surface, located mainly at the cyclohexane ring, visualizes the electron deficiency. While the red region, localized essentially at the nitrogen atom and its closer ethynyl group, show the electron abundance

• rings. For product 4f, the high electron-deficient effect of the trifluoromethyl groups induces the appearance of blue surfaces around the tetrahydroacridine core, the ethynyl groups and the external phenyl rings, indicating a significant decrease of their electronic densities. However, a yellow-red

• region is added to the electrostatic map of compound 4g, due to the positive mesomeric effect of the π-donating methoxy substituent. Accordingly, we conclude that substituents at the introduced arylethynyl groups can communicate electronically with the central tetrahydroacridine core via the ethynyl

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

• Pezhman Shiri,
• Ali Mohammad Amani and
• Thomas Mayer-Gall

Beilstein J. Org. Chem. 2021, 17, 1600–1628, doi:10.3762/bjoc.17.114

• (Scheme 38) [61]. A number of 4-ethynyl-5-iodo-1,2,3-triazoles 134 have been synthesized through the Cu-catalyzed 1,3-dipolar cycloaddition of iododiacetylenes 132 with organic azides 133 using CuI(PPh3)3 and 2,6-lutidine as a catalytic system at room temperature. Then, 4-ethynyl-5-iodo-1,2,3-triazoles

• −Miyaura cross-coupling produced a series of 5-aryl-4-ethynyl triazoles 136 in the presence of Pd(PPh3)4 as catalyst and K3PO4 as base in 1,4-dioxane as solvent at 100 °C (Scheme 39) [62]. A paper by Sekar et al. described the synthesis of polycyclic triazoles 142 through a domino alkyne insertion and C–H

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

• -workers [74][75]. The boronic esters (136a,b) were coupled with 5′-O-DMTr-2′-deoxy-5-iodouridine (135) via Suzuki coupling to give double-headed nucleosides 137 and 138 (Scheme 34) [73]. The double-headed nucleosides 5′-O-dimethoxytrityl-5-(3-(thymin-1-yl)phenyl)ethynyl-2′-deoxyuridine (140) and 5′-O

• -dimethoxytrityl-5-(4-(thymin-1-yl)phenyl)ethynyl-2′-deoxyuridine (141) were synthesized via a Sonogashira cross coupling reaction between the N1-(3/4-iodophenyl)thymine derivatives 136c and 136d and 2′-deoxy-5-ethynyluridine derivative 139 (Scheme 35) [75]. All four nucleoside monomers were converted into

• ]. Hrdlicka and co-workers [24] also synthesized 5-C-triazolyl-functionalized double-headed nucleosides 154a,b starting from 5-C-ethynyl-functionalized LNA uridine 152. The LNA uridine 152 was reacted with 1-azidopyrene (153a) and 1-azidomethylpyrene (153b) separately under copper-catalyzed alkyne azide