Aryne‐Based Synthesis of Cyclobutadiene‐Containing Oligoacenes and Related Extended Biphenylene Derivatives

Aryne-Based Synthesis of Cyclobutadiene-Containing Oligoacenes and Related Extended Biphenylene Derivatives Berta Álvarez,a, b Jesús Janeiro,a, b Agustín Cobas,bManuel A. Ortuño,a Diego Peña,a, b Enrique Guitián,a, b and Dolores Péreza, b,* a Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), Universidade de Santiago de Compostela. 15782-Santiago de Compostela, Spain Phone: +34 881815783 E-mail: [email protected] b Departamento de Química Orgánica, Universidade de Santiago de Compostela. 15782-Santiago de Compostela, Spain Manuscript received: November 2, 2023; Revised manuscript received: January 7, 2024; Version of record online: Februar 2, 2024 Dedicated to Prof. Miquel A. Pericàs, with deep admiration for his exceptional career and outstanding contributions, including the establishment of the Institut Català d’Investigació Química (ICIQ) Supporting information for this article is available on the WWW under https://doi.org/10.1002/adsc.202301264 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution Non-Commercial NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Abstract: A previously undescribed aryne derived from a π-extended biphenylene, 2,3- didehydrobenzo[b]biphenylene, has been developed. The participation of this new aryne building block in [4+ 2] and palladium-catalyzed [2+2+2] cycloaddition reactions has been applied to the synthesis of a variety of polycyclic conjugated hydrocarbons (PCHs) with appealing structures which combine (aromatic) benzene and (antiaromatic) cyclobutadiene (CBD) rings. Among them, a family of unsubstituted (or barely substituted) CBD-oligoacenes has been accessed by iterative Diels-Alder reactions of the new aryne with furans and/or isobenzofurans, followed by deoxygenative aromatization of the resulting epoxy-derivatives. The experimental and computational studies of the newly synthesized PCHs suggest an important degree of electron delocalization along the polycyclic skeleton, more pronounced in the linearly fused derivatives. The computed ACID plots reveal clockwise current density vectors at the peripheral bonds, originating from the σ contributions of the antiaromatic cyclobutadiene rings. Keywords: Polycyclic conjugated hydrocarbons; Arynes; Cycloaddition reactions; Biphenylene; Cyclobutadienecontaining oligoacenes Introduction Polycyclic π-conjugated hydrocarbons (PCHs) have attracted wide attention from the scientific community due to their prominent role as organic semiconductors and electroactive materials for the development of organic electronics.[1] Linearly fused rigid systems, such as acenes, are considered paradigmatic organic semiconductors,[2] but their general use is hampered by the decreased chemical stability associated to the extension of the length of the acene, a feature that can be qualitatively explained on the basis of Clar’s πsextet rule.[3] Angularly fused phenes, starphenes[4] and other bent-shaped oligoacene derivatives[5] are also promising optoelectronic materials. Among the diverse families of PCHs, those containing fused four-mem- bered cyclobutadienoid rings are particularly interesting due to the properties associated with the alternation of aromatic and antiaromatic ring currents in their structures. In this context, in addition to the fascinating linear, angular and helical [N]phenylenes,[6] profusely studied by Vollhardt and co-workers[7] among others, RESEARCH ARTICLE doi.org/10.1002/adsc.202301264 Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 961 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 961/969] 1 recent interest has aroused on the study of other polycyclic systems, including linear phenylene-con- taining oligoacenes[8,9] and heteroacenes,[10] derivatives with non-linear polycyclic aromatic moieties[11] or isomeric graphene nanostructures formed by fused biphenylene units.[12] Biphenylene-containing PCHs have been recently explored for single-molecule junctions,[13] or as potential singlet fission chromophores,[14] while the effect of the cyclobutadiene rings on Baird aromaticity and its influence in the triplet state energies of the resulting π-extended derivatives[15] have also been studied. Conversion of PCHs containing cyclobutadiene (CBD) rings into contorted benzenoid conjugated hydrocarbons through metal-catalyzed CC bond activation has also been recently described.[16] Some years ago, we applied our recently discovered palladium-catalyzed [2+2+2] cycloaddition of arynes[17] to the synthesis of tris- (benzocyclobutadiene)triphenylene.[18] More recently, we used this biphenylene trimer as a probe for the siteselective covalent functionalization of a semi-conduc- tor surface.[19] Our renewed interest in PCHs containing four-membered rings led us to plan the synthesis of πextended derivatives, including CBD-containing oligoacenes, by means of cycloaddition reactions of a benzobiphenylene-based aryne building block, 2,3- didehydrobenzo[b]biphenylene (1), accessed from its Kobayashi-type aryne precursor[20] 2(Scheme 1). Here we report the results of our synthetic study, and the preliminary evaluation of the electronic properties and aromatic character of the newly synthesized CBD- containing PCHs. Results and Discussion The synthesis of 3-(trimethylsilyl)benzo[b]-bipheny- lene-2-yl triflate (2) was achieved through the two alternative routes depicted in Scheme 2, both based in the construction of the 2,3-disubstituted benzo[b]biphenylene core by means of a cobalt(I)- catalyzed [2+2+2] cycloaddition of 2,3-diethynyl- naphthalene (3) with an appropriate alkyne. Thus, reaction of 3with bis(trimethylsilyl)acetylene (BTMSA, used as co-solvent) in the presence of CpCo(CO)2, under heating and irradiation, provided 2,3-bis(trimethylsilyl)benzo[b]biphenylene (4)[21] in a satisfactory 90% yield. For the transformation of 4into triflate 2, first we attempted the protocol previously developed for the synthesis of an analogous biphenylyne precursor,[18] which allowed the isolation of 2in low yields and with scarce reproducibility. Better results were obtained when 4was subjected to a double bromodesilylation followed by nucleophilic substitution of one of the bromine atoms by methoxide to yield 5. Subsequent treatment with BBr3afforded an unstable o-bromophenol, which was directly subjected to the protocol developed in our group for the synthesis of o-(trimethylsilyl)aryl triflates[22] to give 2(route A in Scheme 2; six steps and 20.7% yield from 3). Alternatively, the Co(I)-catalyzed [2+2+2] cycloaddition of 3with the alkynylboronate 6[23] afforded 7 in 40% yield. The ipso-hydroxylation of the arylboronic ester with sodium perborate, followed by triflation of the resulting phenol, allowed the straightforward synthesis of 2in 68% yield (route B in Scheme 2; three steps and 27.2% overall yield from 3). The efficiency of 2as precursor of benzo[b]biphenylyne 1was evaluated by means of trapping experiments with typical dienes, such as furans and cyclopentadienones (Scheme 3). In particular, treatment of 2with CsF in the presence of excess furan (or 2,5-dimethylfuran) successfully afforded the corresponding [4+2] adducts 8a[24] and 8 b in 90% and 89% isolated yields, respectively. On the other hand, the reaction of 2with the polycyclic cyclopentadienone 9[25] under aryne-forming conditions followed by heating of the resulting adduct 10 in refluxing 1,1,2,2-tetrachloroethane allowed the isolation of 11 in an excellent 94% yield, as the result of a Diels-Alder reaction between aryne 1and diene 9, and subsequent cheletropic extrusion of CO. Scheme 1. 2,3-Didehydrobenzo[b]biphenylene (1) and its Kobayashi-type aryne precursor 2. Scheme 2. Synthesis of 3-(trimethylsilyl)-benzo[b]biphenylene- 2-yl triflate (2) [HMDS=hexamethyldisylazane; PBS=sodium perborate]. RESEARCH ARTICLE asc.wiley-vch.de Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 962 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 962/969] 1 16154169, 2024, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adsc.202301264 by Universidade de Santiago de Compostela, Wiley Online Library on [22/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Next, we tested the performance of 1under the conditions developed by our group for palladiumcatalyzed [2+2+2] cycloaddition reactions of arynes.[4b,17] Thus, treatment of 2with CsF in the presence of catalytic amounts of Pd(PPh3)4resulted in the formation of a yellow solid, scarcely soluble in common organic solvents, which was identified as the cyclobutadiene-containing starphene 12 on the basis of its high resolution mass spectrum (Scheme 4). When the reaction was performed in the presence of dimethyl acetylene dicarboxylate (DMAD), compound 13 was isolated in a 79% yield, as the result of a [2+2+2] cycloaddition between two molecules of aryne 1and one of the electron-deficient alkyne. In accordance to previous results with other arynes,[17b,26] the use of Pd2(dba)3as the catalyst resulted in the selective formation of dibenzobiphenylene 14 by means of the reaction of one molecule of the aryne and two of the alkyne (Scheme 4). Once proved the efficiency of triflate 2as precursor of 2,3-didehydrobenzo[b]biphenylene (1), and the utility of this novel aryne for the easy access to πextended cyclobutadiene-containing polycyclic conjugated systems, we decided to explore the use of this building block for the synthesis of oligoacene derivatives incorporating cyclobutadiene rings (CBD-oligoa- cenes). Elegant synthetic strategies recently developed by Swager,[8a,b] Xia,[8c,d] Miao[8f] or Gribble[24] have allowed the access to CBD-oligoacenes functionalized with large phenyl, alkyl and/or (trialkylsilyl)ethynyl substituents, as analogues of acenes in which the presence of four-membered rings into the linear πbackbone increases the number of Clar sextets, resulting in higher stability. The influence of the substituents in the molecular packing and electronic properties has been illustrated by some high-mobility derivatives,[8d,e] while the effect of the extension and (anti)aromaticity of the polycyclic conjugated core in charge transport has also been theoretically studied.[27] With those precedents in mind, and on the basis of our own work in the synthesis of long acenes,[28] we decided to approach the construction of unsubstituted (or barely substituted) CBD-oligoacenes from adequate endoxide-precursors, which would be accessed by iterative Diels-Alder reactions between biphenylenebased arynes and furans (or isobenzofurans). The highly reactive isobenzofurans Icould be easily generated by gentle warming of epoxyacenes II, obtained by reaction of arynes III with furans, in the presence of 3,6-bis(pyridyl)-1,2,4,5-tetrazine (BPTZ)[29] (Figure 1). This approach was used in this work for accessing isobenzofuran (15a) and derivatives 15b,15c,16,17 a and 17b. As a proof of concept of our approach we first studied the reaction of biphenylyne 18, whose gen- Scheme 3. Trapping of 2,3-didehydrobenzo[b]biphenylene (1) generated from o-silylaryl triflate 2. Scheme 4. Palladium(0)-catalyzed [2+2+2] cycloaddition reactions of 2,3-didehydrobenzo[b]biphenylene (1). RESEARCH ARTICLE asc.wiley-vch.de Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 963 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 963/969] 1 16154169, 2024, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adsc.202301264 by Universidade de Santiago de Compostela, Wiley Online Library on [22/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License eration from triflate 19 had been previously reported by our group,[18] with isobenzofuran 16 obtained from endoxyde 20. The reaction afforded the epoxy-deriva- tive 21 in a satisfactory 74% yield. Deoxygenative aromatization of 21 was successfully achieved by treatment with catalytic amounts of ammonium perrhenate in the presence of triphenylphosphite as oxygen scavenger,[30] affording 22 as a white, highly insoluble solid in 70% yield (Scheme 5). The identity of 22 was deduced on the basis of its HRMS and UV- vis spectra (see SI), being diagnostic the red shift of the lowest energy absorption band of 22 (λmax = 451 nm) with respect to that of 21 (λmax =388 nm). The low solubility of 22 precluded the analysis by 1H NMR. Next, we studied the cycloaddition of benzo[b]biphenylyne (1) generated by fluoride-induced decomposition of triflate 2, with in situ generated isobenzofurans 15,16 and 17, obtaining the expected cycloadducts 23–25 in satisfactory yields, ranging from 42% for 23b to 73% for 23a (Scheme 6), as perfectly stable and soluble products which could be fully characterized. The deoxygenative aromatization of 23–25 was successfully performed by rhenium-catalyzed procedure mentioned above or by treatment with HCl and iPrOH (effective for the dimethyl-substituted 25b), to afford the expected CBD-oligoacenes 26–28 in good yields (Scheme 6). Remarkably, the cyclopentenefused derivative 26c resulted soluble enough to successfully obtain its 1H NMR spectrum in 1,1,2,2- tetrachloroethane-d2. With regard to the other newly synthesized CBD-oligoacenes, although the lack of solubility precluded their characterization by NMR, their identity was confirmed by high resolution mass spectrometry and analysis of their UV-vis spectra. In particular, compounds such as 26a–cor 28a–b displayed similar spectra that those reported for previously described alkynyl or aryl-substituted analogues.[8] Selected experimental data provided by the UV-vis and fluorescence spectra of the newly synthesized Figure 1. Isobenzofuran building blocks used in this work. Scheme 5. Synthesis of bis(benzocyclobuta)anthracene 22 by iterative Diels-Alder reactions of biphenylyne (18) [BPTZ= 3,6-bis(pyridyl)-1,2,4,5-tetrazine]. Scheme 6. Synthesis of cyclobutadiene-containing oligoacenes 26–28 by cycloaddition reactions of 2,3- didehydrobenzo[b]biphenylene (1); see SI for details. RESEARCH ARTICLE asc.wiley-vch.de Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 964 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 964/969] 1 16154169, 2024, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adsc.202301264 by Universidade de Santiago de Compostela, Wiley Online Library on [22/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License cyclobutadiene-containing PCHs are summarized in Table 1, together with the results of the computational estimation of the energy gaps (see SI for full details). The spectra of the [2+2+2] cycloadducts 12–14 show lowest energy absorptions in the range of 421 (for 14) to 448 (for 13) nm. With regard to the linearly fused derivatives, it is worth to note that while all the epoxy-oligoacenes 23–25 exhibit almost identical lowest energy absorptions around 405–410 nm, associated to the benzo[b]biphenylene chromophore, the corresponding deoxygenated CBD-oligoacenes show larger λmax values (see Figure 2a, for 25b/28 b). The wavelength of these lowest absorptions increases with the size of the linear polycyclic system, from λmax �440 nm for 26, to 479 nm for 28 b. In all cases, the absorption is also significantly red-shifted with respect to that of anthracene (λmax =373 nm), the largest polycyclic benzenoid chromophore contained in each of the structures, demonstrating an important degree of electron delocalization along the polycyclic skeleton despite the presence of the antiaromatic cyclobutadiene moieties. Comparison of the spectra of the angularly shaped 13 with the linear analogues of similar size 28 suggests that the electron delocalization is more significant in the latter. With regard to the fluorescence, it is remarkable the very small Stokes shifts observed in the linear CBD- oligoacenes, ranging from 0 to 2 nm, which is indicative of the rigid structure of these compounds. As another interesting feature, the fluorescence spectra of solid 28a and 28b exhibit large bathochromic shifts with respect to measurements in solution (146 and 119 nm, respectively; see Figure 2b for 28 b), that are significantly larger than those observed for the same polycyclic systems provided with pendant phenyl and TIPS-ethynyl groups[8a] and may constitute a preliminary evidence of effective electronic coupling between neighbouring molecules in the solid state.[31] The structures and properties of the newly synthesized compounds were also computationally studied. Optical gaps were calculated by TDDFT using the B3LYP and O3LYP density functionals with the 6–311 + +G(d,p) basis set (see Table S1). While the B3LYP calculated gaps resulted, as expected, slightly overestimated, the use of O3LYP, which is similar to B3LYP but with a smaller percentage of exact HF, predicts smaller energy gaps that are in excellent agreement with the experimental values (within 0.2 eV for all compounds analyzed, see Tables 1 and S1). Next, we studied the local and global aromaticity/ antiaromaticity for the newly synthesized CBD-PCHs by NICS-XY scan calculations,[32] using the σ-only method[33] at the GIAO-B3LYP/6-311+G(d) level of theory (see SI for details). In all compounds, positive NICS values were observed for the four-membered rings, indicating their antiaromatic character. The para- Table 1. Spectroscopic properties[a] and Egap estimation of the new CBD-containing PCHs. Comp. λmax (nm) λonset (nm) λem (nm) Egap(opt)[c] (eV) Egap(calc)[d] (eV) 11 459 465 464 (505)b) 2.67 2.67 12 437 455 468 2.73 2.67 13 448 455 455 2.73 2.75 14 421 427 428 2.90 3.09 22 451 460 451 2.70 2.82 26a 433 441 468 2.80 2.79 26b 440 445 441 2.79 2.77 26c 436 440 441 2.81 2.75 27 458 473 459 2.62 2.73 28a 470 475 470 (599)[b] 2.60 2.67 28b 479 490 480 (616)[b] 2.53 2.54 [a] Measured in 1,2,4-trichlorobenzene, except the spectra of 11,13,14 and 26 a, measured in CHCl3. [b] Measured in the solid state by means of an integrating sphere. [c] Egap(opt) =1241/λonset. [d] Calculated at the TDDFT/O3LYP/6-311+G(d,p) level. Figure 2. a) Overlay of the absorbance spectra of precursor 25 b (in CHCl3) and CBD-oligoacene 28b (in 1,2,4-trichloroben- zene). b) Absorbance and fluorescence spectra of 28b in solution, and fluorescence in the solid state. RESEARCH ARTICLE asc.wiley-vch.de Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 965 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 965/969] 1 16154169, 2024, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adsc.202301264 by Universidade de Santiago de Compostela, Wiley Online Library on [22/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License tropicity of the cyclobutadiene rings is more pronounced for compound 22 (NICS=6 ppm), with single benzene rings fused to the CBD at the PCH termini, and for the angularly-fused systems 12 and 13 (NICS �5.5 ppm), while the bis(naphthocyclobuta)anthracene ring system 28, previously studied by Xia and coworkers,[8c] presents peak NICS values of 3.9 ppm (for 28a). On the other hand, the aromatic character of the different benzenoid rings in each PCH structure is affected by the presence of the antiaromatic cyclobutadienoids and the associated bond localization. To illustrate this feature, Figure 3 shows the NICS-XY scans of the 9-ring polycyclic systems of 12,13a and 28a, showing the terminal benzenoid rings as the less affected (more aromatic character), the rings directly attached to the CBDs as the less aromatic, and a significant difference in the aromatic character of the central ring of the polycyclic systems, being that of the linearly-fused CBD-oligoacene 28a the most aromatic. Finally, to visualize the local diatropic and paratropic ring currents induced by local aromaticity and antiaromaticity, we computed the anisotropy of the induced current density (ACID).[34] As a representative example, Figure 4a shows the ACID plot of 28a; where clockwise current density vectors indicate aromaticity (black arrows) and anti-clockwise ones describe anti-aromaticity (red arrows). As expected, benzene units show clockwise ring currents, while anti-clockwise ring currents are observed in the cyclobutadiene rings. However, taking a closer look at the latter in Figure 4b, one can see the presence of clockwise current density vectors on the peripheral bonds of the four-membered rings, suggesting a global diatropic current loop that rounds the whole system. Figure 4c shows that these clockwise vectors come Figure 3. NICS-XY scans at the B3LYP/6–311+G(d) level for 12,13a and 28 a. Figure 4. a) ACID plot of 28 a at isosurface value of 0.04. b) Zoom in on the cyclobutadiene unit. c) Contributions from π- and σtype orbitals. RESEARCH ARTICLE asc.wiley-vch.de Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 966 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 966/969] 1 16154169, 2024, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adsc.202301264 by Universidade de Santiago de Compostela, Wiley Online Library on [22/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License from the contributions of the σ system. The other studied compounds present similar features, and their ACID plots can be consulted in Figure S3 (SI). Conclusion In conclusion, we have synthesized a family of extended cyclobutadiene-containing PCHs with diverse structures, by means of efficient [4+2] or palladiumcatalyzed [2+2+2] cycloaddition reactions of a novel aryne building block derived from benzo[b]biphenylene. The set of extended phenylenes synthesized include CBD-oligoacenes (with up to nine linearly-fused rings), angularly-fused analogues and a star-shaped benzobiphenylene trimer. Our approach allowed the synthesis of stable, unsubstituted (or barely substituted) CBD-oligoacenes, which according to preliminary examination of their emission spectra might display effective electronic coupling in the solid state, as unsubstituted acenes do. Experimental and computational studies on the whole series of newly synthesized systems reveal an important degree of electron delocalization along the polycyclic skeletons despite the presence of the antiaromatic cyclobutadiene rings, with more pronounced delocalization observed in the linearly fused CBD-oligoacenes. The current density plotted onto the ACID isosurface indicates a complex pattern of currents that unveils the presence of clockwise peripherical current originating from the σ contributions of the four-membered rings, thus providing new insights into the aromatic and antiaromatic interactions within these intriguing molecular architectures. Experimental Section Selected Experimental Procedures Trimethyl[3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan- 2-yl)benzo[b]biphenylen-2-yl]silane (7) A solution of 2,3-diethynylnaphthalene (160 mg, 0.91 mmol), CpCo(CO)2(35 mL, 0.23 mmol) and trimethyl[(4,4,5,5- tetramethyl-1,3,2-dioxaborolan-2-yl)ethynyl]silane (6, 200 mg, 0.91 mmol), in a mixture of xylene (8 mL) and THF (3.5 mL), was slowly added (3 h, syringe pump) to a boiling solution of 6 (720 mg, 3,21 mmol) in xylene (12 mL). Light from a projector lamp (300 W, 50% of its power) was directed at the reaction mixture during the addition. After refluxing and irradiation of the mixture for one additional hour, the solvents were removed under vacuum. The crude residue was purified by column chromatography on silica gel (hexane/CH2Cl2, 4:2) to yield trimethyl[3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2- yl)benzo[b]biphenylen-2-yl]silane 7as orange solid (130 mg, 35%). 3-(Trimethylsilyl)benzo[b]biphenylene-2-yl Trifluoromethanesulfonate (2) A solution of trimethyl[3-(4,4,5,5-tetramethyl-1,3,2-dioxaboro- lan-2-yl)benzo[b]biphenylen-2-yl]silane (7, 20 mg, 0.05 mmol) in THF (2 mL) was added to a solution of sodium perborate (PBS, 38 mg, 0.25 mmol) in H2O (2 mL). After stirring at room temperature for 1 h, the reaction mixture was extracted with CH2Cl2(3×5 mL), the combined organic layers were dried with Na2SO4, filtered and concentrated under reduced pressure. The crude residue was used in the next step without any further purification. The residue was dissolved in dry CH2Cl2(2.3 mL) and to the resulting solution, kept at 78°C, freshly destilled i- Pr2NEt (14 mL, 0.08 mmol) and Tf2O (17 mL, 0.10 mmol) were successively added. After stirring for 1 h at 78°C, the reaction mixture was allowed to reach room temperature and stirred for 2 h. The reaction mixture was quenched with aqueous NaHCO3 (saturated solution, 2 mL), the phases were separated and the organic layer was extracted with CH2Cl2(2×10 mL). The combined organic layers were dried with Na2SO4, filtered and concentrated under reduced pressure. The crude was purified by column chromatography on silica gel (hexane/CH2Cl2, 4:2) yielding triflate 2as a pale yellow solid (15 mg, 68%). Tris(naphthocyclobuta)triphenylene (12) To a solution of 2(50 mg, 0.12 mmol) and Pd(PPh3)4(12 mg, 0.01 mmol) in dry CH3CN (3.5 mL), placed in a Schlenk flask under argon, anhydrous CsF (60 mg, 0.4 mmol) was added. The reaction mixture was stirred at room temperature for over 14 h. The resulting suspension was concentrated under reduced pressure, the solid was collected by centrifugation subjected to sonication-assisted washing with portions of CH3CN (2×2 mL), H2O (2 mL), CH3OH (2×2 mL), Et2O (2×2 mL) and CH2Cl2 (2×2 mL), and dried under vacuum to afford 12 as a yellow powder (14 mg, 58%). General Procedure for the Synthesis of Oligoacene Endoxides 21, 23–25 A solution of epoxyacene II and 3,6-bis(pyridin-2-yl)-1,2,4,5- tetrazine (BPTZ) in CH2Cl2, was stirred at 45°C until complete consumption of the starting material (TLC monitoring), generating in situ the corresponding isobenzofuran I(15–17). To this solution, kept at room temperature in a Schlenk flask, a solution of the precursor of aryne (2or 19, 1 equiv.) in CH3CN was added, followed by finely powdered, anhydrous CsF (5– 10 equiv.; addition of the solid under a positive flow of argon). The mixture was stirred at room temperature for 14 h, then the solvent was evaporated under reduced pressure and the desired endoxide was isolated either by quick chromatography in silica gel (for 21,23a,23 b and 23c) or by centrifugation and repeated washing with different solvents (for 24,25a and 25b). General Procedure for the Deoxygenative Aromatization of Endoxides 21, 23–25 Method A[39] A solution of the oligoacene endoxide in a iPrOH/CHCl3/HCl (37%) mixture was heated at 80°C for 24 h. Then, the reaction RESEARCH ARTICLE asc.wiley-vch.de Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 967 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 967/969] 1 16154169, 2024, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adsc.202301264 by Universidade de Santiago de Compostela, Wiley Online Library on [22/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License mixture was cooled to room temperature, washed with NaHCO3 saturated solution, and extracted with CHCl3. The combined organic layers were concentrated under reduced pressure, the solid was collected by centrifugation, subjected to sonicationassisted washing with CH2Cl2, CH3OH and Et2O, and dried under vacuum to afford the aromatized product. Method B A flame-dried flask is charged with NH4ReO4, P(OPh)3and dry toluene. After stirring for 20 min, the corresponding endoxide was added and the resulting mixture was stirred for 14 h. Then, the solvent was concentrated under reduced pressure, the solid was collected by centrifugation, subjected to sonication-assisted washing with portions of CH2Cl2, H2O, CH3OH, CH2Cl2, and dried under vacuum to afford the corresponding aromatic product. Acknowledgements Financial support from grants PID2019-110037GB-I00, PID2022-140845OB-C62 and PID2022-139933NB-I00, funded by MCIN/AEI/10.13039/501100011033, the European Union’s Horizon 2020 (FET-Open project SPRING, Grant No. 863098), and ERC Synergy Grant MOLDAM (951519), the Xunta de Galicia (ED431C 2020/22, ED431H 2020/21 and Centro singular de investigación de Galicia accreditation 2019–2022, ED431G 2019/03) and the European Union (European Regional Development Fund-ERDF) is gratefully acknowledged. The authors thank the Centro de Supercomputación de Galicia (CESGA) for generous allocation of computer time. BA and JJ thank the Agencia Estatal de Investigación for the award of pre-doctoral fellowships (BES-2017-079748 and PRE2020- 092897, respectively). References [1] a) X.-Y. Wang, X. Yao, K. Müllen, Sci. China Chem. 2019,62, 1099–1144; b) H. Ito, K. Ozaki, K. Itami, Angew. Chem. Int. Ed. 2017,56, 11144–11164; c) O. Ostroverkhova, Chem. Rev. 2016,116, 13279–13412; d) A. Narita, X.-Y. Wang, X. Feng, K. Müllen, Chem. Soc. Rev. 2015,44, 6616–6643; e) H. Dong, X. Fu, J. Liu, Z. Wang, W. Hu, Adv. Mater. 2013,25, 6158–6183; f) Z. Sun, Q. Yen, C. Chi, J. Wu, Chem. Soc. Rev. 2012, 41, 7857–7889. [2] a) J. E. Anthony, Chem. Rev. 2006,106, 5028–5048; b) J. E. Anthony, Angew. Chem. Int. Ed. 2008,47, 452– 483. [3] M. Solá, Front. Chem. 2013,1, 22. [4] a) E. C. Rüdiger, M. Müller, J. Freudenberg, U. H. F. Bunz, Org. Mater. 2019,1, 1–18; b) I. Pozo, E. Guitián, D. Pérez, D. Peña, Acc. Chem. Res. 2019,52, 2472– 2481. [5] T. Okamoto, C. P. Yu, C. Mitsui, M. Yamagishi, H. Ishii, J. Takera, J. Am. Chem. Soc. 2020,142, 9083–9096. [6] O. S. Miljanić, K. P. C. Vollhardt, in Carbon-Rich Compounds: From Molecules to Materials (Eds.: M. M. Haley, R. R. Tywinski), Wiley-VCH, 2006, pp. 140–197. [7] a) B. C. Berris, G. H. Hovakeemian, Y. H. Lai, H. Mestdagh, K. P. C. Vollhardt, J. Am. Chem. Soc. 1985, 107, 5670–5687; b) C. Eickmeier, D. Holmes, H. Junga, A. J. Matzger, F. Sherhag, M. Shim, K. P. C. Vollhardt, Angew. Chem. Int. Ed. 1999,38, 800–804; c) S. Han, A. D. Bond, R. L. Disch, D. Holmes, J. M. Schulman, S. J. Teat, K. P. C. Vollhardt, G. D. Whitener, Angew. Chem. Int. Ed. 2002,41, 3223–3227; d) A. Fonari, J. C. Röder, H. Shen, T. V. Timofeeva, K. P. C. Vollhardt, Synlett 2004,25, 2429–2433. [8] a) R. R. Parkhurst, T. M. Swager, J. Am. Chem. Soc. 2012,134, 15351–15356; b) S. P. Luppino, T. M. Swager, Synlett 2017,38, 323–326; c) Z. Jin, Y. C. Teo, N. G. Zulaybar, M. D. Smith, Y. Xia, J. Am. Chem. Soc. 2017, 139, 1806–1809; d) Z. Jin, Z.-F. Yao, K. P. Barker, J. Pei, Y. Xia, Angew. Chem. Int. Ed. 2019,58, 2034–2039; e) E. G. Miller, M. Singh, S. Parkin, T. Sammakia, N. H. Damrauer, J. Org. Chem. 2023,88, 12251–12256; f) J. Wang, M. Chu, J.-X. Fan, T.-K. Lau, A.-M. Ren, X. Lu, Q. Miao, J. Am. Chem. Soc. 2019,141, 3589–3596. [9] a) C. Sánchez-Sánchez, A. Nicolai, F. Rossel, J. Cai, J. Liu, X. Feng, K. Müllen, P. Ruffieux, R. Fasel, V. Meunier, J. Am. Chem. Soc. 2017,139, 17617–17623; b) C. Sánchez-Sánchez, T. Dienel, A. Nicolai, N. Kharche, L. Liang, C. Daniels, V. Meunier, J. Liu, X. Feng, K. Müllen, J. R. Sánchez-Valencia, O. Gröning, P. Ruffieux, R. Fasel, Chem. Eur. J. 2019,25, 12074– 12082; c) M. S. G. Mohammed, J. Lawrence, F. García, P. Brandimarte, A. Berdonces-Layunta, D. Pérez, D. Sánchez-Portal, D. Peña, D. G. de Oteyza, Nanoscale Adv. 2021,3, 2351–2358; d) I. Izydorczyk, O. Stoica, M. Krawiec, R. Blieck, R. Zuzak, M. Stepien, A. Echavarren, S. Godlewski, Chem. Commun. 2022,58, 4063– 4066. [10] a) P. Biegger, M. Schaffroth, C. Patze, O. Tverskoy, F. Rominger, U. H. F. Bunz, Chem. Eur. J. 2015,21, 7048– 7052; b) S. Yang, B. Shan, X. Xu, Q. Miao, Chem. Eur. J. 2016,22, 6637–6642; c) S. Yang, M. Chu, Q. Miao, J. Mater. Chem. C 2018,6, 3651–3657; d) Y. C. Teo, Z. Jin, Y. Xia, Org. Lett. 2018,20, 3300–3304. [11] a) Z. Gu, G. B. Boursalian, V. Gandon, R. Padilla, H. Shen, T. V. Timofeeva, P. Tongwa, K. P. C. Vollhardt, A. A. Yakovenko, Angew. Chem. Int. Ed. 2011,50, 9413–9417; b) Z. Jin, Y. C. Teo, S. J. Teat, Y. Xia, J. Am. Chem. Soc. 2017,139, 15933–15939; c) M. Gao, H. Chen, Q. Miao, Eur. J. Org. Chem. 2022,2022, e202101315. [12] a) F. Schlütter, T. Nishiuchi, V. Enkelmann, K. Müllen, Angew. Chem. Int. Ed. 2014,53, 1538–1542; b) Q. Fan, L. Yan, M. R. Trip, O. Krejci, S. Dimosthenous, S. R. Kachel, M. Chen, A. Foster, P. Liljeroth, J. M. Gottfriend, Science 2021,372, 852–856. [13] M. Ganterbein, X. Li, S. Sangtarash, J. Bai, G. Olsen, A. Alqorashi, W. Hong, C. J. Lambert, M. R. Bryce, Nanoscale 2019,11, 20659–20666. [14] O. E. Bakouri, J. R. Smith, H. Ottosson, J. Am. Chem. Soc. 2020,142, 5602–5617. RESEARCH ARTICLE asc.wiley-vch.de Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 968 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 968/969] 1 16154169, 2024, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adsc.202301264 by Universidade de Santiago de Compostela, Wiley Online Library on [22/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License [15] a) R. Ayub, O. E. Bakouri, K. Jorner, M. Solà, H. Ottosson, J. Org. Chem. 2017,82, 6327–6340; b) F. Plasser, Chem 2021,3, 532–549. [16] X. Yin, K. Zheng, Z. Jin, M. Horst, Y. Xia, J. Am. Chem. Soc. 2022,144, 12715–12724. [17] a) D. Peña, S. Escudero, D. Pérez, E. Guitián, L. Castedo, Angew. Chem. Int. Ed. 1998,37, 2659–2661; b) D. Peña, D. Pérez, E. Guitián, L. Castedo, J. Am. Chem. Soc. 1999,121, 5827–5828. [18] B. Iglesias, A. Cobas, D. Pérez, E. Guitián, K. P. C. Vollhardt, Org. Lett. 2004,6, 3557–3560. [19] S. Godlewski, M. Engelund, D. Peña, R. Zuzak, H. Kawai, M. Kolmer, J. Caeiro, E. Guitián, K. P. C. Vollhardt, D. Sánchez-Portal, M. Szymonski, D. Pérez, Phys. Chem. Chem. Phys. 2018,20, 11037–11046. [20] For a recent review on the use of o-(trimethylsilyl)aryl triflates as convenient aryne precursors, see: J. Shi, L. Li, Y. Li, Chem. Rev. 2021,121, 3892–4044. [21] S. Taillemite, C. Aubert, D. Fichou, M. Malacria, Tetrahedron Lett. 2005,46, 8325–8329. [22] D. Peña, A. Cobas, D. Pérez, E. Guitián, L. Castedo, Synthesis 2002, 1454–1458. [23] R. R. Harker, P. M. Delaney, M. Simms, M. J. Tozer, J. P. A. Harrity, Tetrahedron 2013,69, 1546–1552. [24] Adduct 8 a had been previously reported: E. O. Ongayo, P. Z. Mannes, A. Pletnev, D. B. Granger, Q. Ai, C. Risko, J. E. Anthony, G. W. Gribble, Tetrahedron Lett. 2020,61, 152182. [25] R. A. Pascal Jr, W. D. McMillan, D. Van Engen, R. G. Eason, J. Am. Chem. Soc. 1987,109, 4660–4665. [26] D. Peña, D. Pérez, E. Guitián, L. Castedo, J. Org. Chem. 2000,65, 6944–6950. [27] H. Yin, D. Zheng, Y. Quiao, X. Chen, J. Mater. Chem. C 2019,7, 6721–6727. [28] a) J. Krüger, F. García, F. Eisenhut, D. Skidin, J. M. Alonso, E. Guitián, D. Pérez, G. Cuniverti, F. Moresco, D. Peña, Angew. Chem. Int. Ed. 2017,56, 11945–11948; b) F. Eisenhut, T. Kühne, F. García, S. Fernández, E. Guitián, D. Pérez, G. Trinquier, G. Cunniverty, C. Joachim, D. Peña, F. Moresco, ACS Nano 2020,14, 1011–1017. [29] N. R. Warrener, J. Am. Chem. Soc. 1971,93, 2346–2348. [30] M. Murai, T. Ogita, K. Takai, Chem. Commun. 2019,55, 2332–2335. [31] S. T. Roberts, R. E. McAnally, J. N. Mastron, D. H. Webber, M. T. Whited, R. L. Brutchey, M. E. Thompson, S. E. Bradforth, J. Am. Chem. Soc. 2012,134, 6388– 6400. [32] R. Gershoni-Poranne, A. Stanger, Chem. Eur. J. 2014, 20, 5673–5688. [33] A. Stanger, J. Org. Chem. 2010,75, 2281–2288. [34] a) R. Herges, D. Geuenich, J. Phys. Chem. A 2001,105, 3214–3220; b) D. Geuenich, K. Hess, F. Köhler, R. Herges, Chem. Rev. 2005,105, 3758–3772. [35] L. S. Hegedus, in Organometallics in Synthesis: A Manual; Schlosser, M. Ed.; John Wiley & Sons: New York, 1994, pp. 1123–1217. [36] T. Kitamura, M. Yamane, K. Inoue, M. Todaka, N. Fukatsu, Z. Meng, Y. Fujiwara, J. Am. Chem. Soc. 1999, 121, 11674–11679. [37] R. Akita, K. Kawanishi, T. Hamura, Org. Lett. 2015,17, 3094–3097. [38] I. J. Anthony, D. Wege, Aust. J. Chem. 1996,49, 1263– 1272. [39] Method A was attempted for the aromatization of 23–25, but only worked satisfactorily for the dimethylated compound 25b. RESEARCH ARTICLE asc.wiley-vch.de Adv. Synth. Catal. 2024,366, 961–969 © 2024 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbH 969 Wiley VCH Montag, 26.02.2024 2404 / 336569 [S. 969/969] 1 16154169, 2024, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adsc.202301264 by Universidade de Santiago de Compostela, Wiley Online Library on [22/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License