A tandem one-pot method for the direct synthesis of polysubstituted triphenylene 2,3-dicarboxylic esters with different substitution patterns was developed by enyne metathesis of diarylacetylene, followed by Diels–Alder, aromatization and a cyclization cascade

Feng, Chun

Hu, Ping

Redshaw, Carl

Tian, X. L.

Tian, Xian-Li

Wang, Bi-Qin

Xiang, Shi-Kai

Yu, Wen-Hao

Zhao, Ke-Qing

Zhou, Jing

English

An efficient one-pot synthetic procedure was developed for the direct preparation of polysubstituted triphenylene 2,3-dicarboxylic esters via a tandem addition process from diarylacetylene.</p

Chun Feng

Xian-Li Tian

Jing Zhou

Shi-Kai Xiang

Wen-Hao Yu

Bi-Qin Wang

Ping Hu

Carl Redshaw

Ke-Qing Zhao

Crossref

Organic & Biomolecular Chemistry

A convenient tandem one-pot synthesis of donor–acceptor-type triphenylene 2,3-dicarboxylic esters from diarylacetylene

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Journal Name Cite this: DOI: 10.1039/c0xx00000x  Dynamic Article Links ► ARTICLE TYPE A convenient tandem one-pot synthesis of donor-acceptor-type triphenylene 2,3-dicarboxylic esters from diarylacetylene Chun Feng, *a Xian-Li Tian,a Jing Zhou,a Shi-Kai Xiang,a Wen-hao Yu,a Bi-Qin Wang, *a Ping Hu,a Carl Redshaw a,b  and Ke-Qing Zhao a Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX 5 DOI: 10.1039/b000000x A tandem one-pot method for the direct synthesis of polysubstituted triphenylene 2,3-dicarboxylic esters with different substitution patterns has been developed through enyne metathesis of diarylacetylene,  followed by Diels-Alder, 10 aromatization and a cyclization cascade Derivatives of triphenylene, which is comprised of a flat polyaromatic core surrounded by multiple flexible n-carbon side chains, are potential HIV inhibitors for use in AIDS therapy. 1 Furthermore, triphenylenes have been extensively explored as 15 building blocks for the preparation of functional electronic and optoelectronic devices in material chemistry owing to their remarkable self-assembling and charge transporting properties.2 There are two exceptional examples of triphenylene structure in terms of the electronic properties of the peripheral substituents. 20 Firstly, there is the most commonly studied electron-rich or donor-type hexaalkoxytriphenylene (Figure 1, A), which usually exhibit hexagonal columnar mesophases over relatively narrow temperature ranges above room temperature. 3 Secondly, the electron-deficient or acceptor-type triphenylene functionalized 25 with six polar ester groups (Figure 1, B), allows for an exceptionally wide-range of 2D lattices in its columnar assembly and it has been noted that such columns can align in homeotropic fashion on a variety of substrates.2c  Williams and co-workers have shown that the addition of electron-withdrawing substituents 30 can lead to an increase in the molecular dipole moment, which help to minimize the repulsive interactions between adjacent aromatic π-systems and promotes the formation and stabilization of columnar phases.4 Therefore studies on triphenylene derivatives possessing electron-withdrawing substituents have 35 attracted increased interest.2c,5 However, reports on monomeric triphenylenes derivatives possessing simultaneously both electron-donating and electron -withdrawing substituents are exceedingly rare, probably because of the lack of practical synthetic methods. 40 45 Figure 1 Two exceptional examples of triphenylene molecular 50 55 Scheme 1   Synthetic approach for the preparation of triphenylene dicarboxylic esters For the construction of the triphenylene framework, oxidative coupling between suitably substituted biphenyl and benzene derivatives,6 iodine promoted photocyclisation,7 Lewis acid 60 promoted cyclization of ortho-terphenyl (prepared by Ullman coupling reaction or by Suzuki-type cross coupling reactions),8 and the oxidative trimerization of arenes,9 etc.,10 have been reported. However, the scope of the above strategies was limited to the preparation of triphenylenes containing electron-donating 65 substituents (e.g., -OR, -SR etc.).2a,2g By contrast, the introduction of electron-withdrawing group is restricted to classic electrophilic aromatic substitutions, which have severe electronic and regioselective constraints,11 and the chemistry of [6]radialene,2c,5b which involves the use of the expensive 70 hexakis(bromomethyl)benzene. On the other hand, most of the syntheses of functionalized triphenylenes suffer from the lack of readily available precursors and require multiple steps with harsh conditions. Thus, the direct and convenient synthesis of triphenylene derivatives from easily available starting materials 75 remains a challenge. Recently, we developed a concise method to prepare a series of functionalized ortho-terphenyls via a CuI-promoted enyne metathesis–Diels-Alder annulation-oxidation strategy.12 As an extension of our previous work, we envisioned that two vicinal 80 aromatic rings could be fused to the central benzene ring through well-established oxidative coupling reactions to directly construct triphenylene skeletons. More importantly, electron-withdrawing substituents can be easily installed on to the skeleton via DA reactions as shown in Scheme 1. In this paper, we introduce a 85 new strategy for the direct synthesis of donor-acceptor-type triphenylene 2,3-dicarboxylic esters in a one-pot manner through a cascade reaction involving enyne metathesis of diarylacetylene, cycloaddition with dienophile, and subsequent aromatization and oxidative cyclodehydrogenation. 90 EWGEWGGDEGDEEWGEWGGDEGDEGDEGDE+EWGEWG+GDEGDEOCnH2n+1OCnH2n+1H2n+1CnOH2n+1CnOOCnH2n+1OCnH2n+1CO2RCO2RCO2RCO2RRO2CRO2CA B [journal], [year], [vol], 00–00  |  1 Considering that the final step of the synthesis involves an 5 10 Scheme 2 Two pathways for the synthesis of triphenylene 4a intramolecular oxidative aromatic coupling which works with 15 highly electron-rich precursors,13 an electron-rich diarylacetylene is necessary to make the biaryl connection more likely to occur according to our design. The triphenylenes that have been most intensively studied, due to their liquid crystal properties, are those with alkoxy substituents. Given this, we choose the tetraalkoxy-20 substituted diarylacetylene (1a) as a model substrate. Treatment of 1a with the Grubbs-II catalyst in the presence of CuI, followed by DA reaction with dimethylacetylenedicarboxylate (DMAD) and aromatization with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) gave the desired ortho-terphenyl (3a) in 48 25 % isolated yield. Subsequent oxidative cyclodehydrogenation of 3a using 2 equivalents of FeCl3 as an oxidant in a mixture of dichloromethane and nitromethane at 0 oC gave the final product 4a in 90 % isolated yield, and 43 % overall  yield (Scheme 2 path a). Since the aromatization of 2a and the oxidative 30 cyclodehydrogenation of 3a involve the use of an oxidant, we postulated that the two steps can be processed as one step if the proper amount of oxidant was used. To our delight, treatment of the reaction mixture of 2a with 4 equivalents of  FeCl3 in a mixture of dichloromethane and nitromethane at 0 oC indeed gave 35 the final product 4a in 58 % overall isolated yield (Scheme 2 path b). Notably, all steps can be carried out in a one-pot manner, and do not involve the isolation of intermediates. A previous report has indicated that certain oxygen functionalities in the substrate can strongly coordinate with the 40 ruthenium carbene complex, thereby decreasing its catalytic activity and impeding enyne metathesis.14 Thus Lewis acids were introduced into the reaction system to compete or prevent the coordination of the O-atom to the ruthenium carbene intermediate. 15The preliminary study indicates that Ti(OiPr)4 is 45 the best choice in this reaction. When the reaction was run with the addition of 5 % mol of Ti(OiPr)4 using 4 equivalents of FeCl3 as an oxidant, the reaction gave the expected product 4a in 71 % overall isolated yield (see ESI†, Table 1, entry 7). Increasing the amount of Ti(OiPr)4 did not affect the reaction. However, AlCl3 50 and TiCl4 were too strong to use in this reaction. Use of other oxidants such as MoCl5 and DDQ/H+ did not afford a better performance than FeCl3 (see ESI†, Table 1). Subsequently, we set out to test different substrates for the formation of polysubstituted triphenylene 2,3-dicarboxylic esters 55 (Table 1). Various alkoxy-substituted diarylacetylenes were tested and the desired products 4 with different substitution patterns (from tetra- to hepta-substituted) were produced in variable overall yields. The reaction takes place in moderate to good overall yield provided that at least two alkoxyl groups are 60 present in one of the rings (from 4a to 4g) or if the two alkoxyl groups are respectively located at the para position of the newly formed bond (4h). While some substrates are suitable, the efficiency is decreased for certain electronic (4j and 4k) and steric (4l) factors. However, the Br group can be incorporated 65 into the triphenylene skeleton with this strategy (4k), which offers the potential for further functionalization. Moreover, unsymmetrical peripheral substitution can easily be achieved by changing the length of some of the side chains in the substrate, which has a large effect on the thermal behaviour of liquid 70 crystalline materials.16 Further, the presence of a methoxyl group at the peripheral position can be used to produce valuable hydroxy-functionalized triphenylenes by demethylation, which  Table 1 Synthesis of polysubstituted triphenylene 2,3-dicarboxylic ester75 80  85  90 95 a All the reactions were carried out in the scale of 0.125 mmol of 1. b 6.0 100 equivalent of FeCl3 was used. c 2.5 equivalent of MoCl5 as oxidant. d 2.0 equivalent of 1,4-quinone was used instead of DMAD. can be further utilized to construct more complicated structures.17 Importantly, 1-((3,4-bis(hexyloxy)phenyl)ethynyl)naphthalene and 2-((3,4-105 bis(hexyloxy)phenyl)ethynyl)naphthalene were also suitable substrates for the synthesis of  more complicated dimethyl-12,13-bis(hexyloxy)benzo[f]chrysene-2,3-dicarboxylate (4l) and dimethyl-12,13-bis(hexyloxy)benzo[g]chrysene-2,3-dicarboxylate (4m). Notably, 1,4-quinone is also suitable as a 110 reaction partner, which lead to the formation of 2,3,6,7-tetrakis(hexyloxy)benzo[f] tetraphene-10,13-dione (4n) in 43 % isolated yield. This strategy can also be applied to the syntheses of twinned and oligomeric triphenylene discotics. Starting from 4-ethynyl-115 1) Grubbs-2   CH2=CH2 (1 atm)2)3) DDQCO2MeCO2MeCO2MeMeO2CCO2MeCO2MeCO2MeCO2MeC6H13OOC6H13C6H13OOC6H13C6H13OOC6H13C6H13OOC6H13C6H13OOC6H13C6H13OOC6H13C6H13OOC6H13C6H13OOC6H131a 2a3aPath aPath b4aFeCl3 (2 equiv.)FeCl3 (4 equiv.)(48 % over 3 steps)90 %58 % overall yieldCO2MeCO2Me(1) 10% mol Grubbs-2 , CuI (5% mol), Ti(OiPr)4 (5% mol), CH2=CH2 (1 atm),toluene(5 mL), 80 ℃ , 24 h(3) FeCl3 ( 4 equiv), CH2Cl2/CH3NO2,  0 ℃ ,  Ar, 1 hRRRR(2) DMAD ( 5 equiv), 100 ℃ , 24 hCO2MeCO2MeOC6H13C6H13OOC6H13C6H13O4aa (71 %)CO2MeCO2MeOC6H13H3COH3COOC6H134ba (62 %)CO2MeCO2MeOC6H13C6H13OH3COCO2MeCO2MeOC6H13C6H13OOCH34fa, b (57 %)CO2MeCO2MeOC6H13C6H13OPh4ea, b (50 %)4ca, b (57 %)CO2MeCO2MeOC6H13C6H13O4ja, b (26 %)H3COOCCO2MeCO2MeOC6H13OC6H13CO2MeCO2MeOC6H134ha, b (60 %)OC6H13C6H13OBrCO2MeCO2MeOC6H13C6H13OOC6H13C6H13OOO4na, d (43 %)C6H13O4ga, b (55 %)OC6H13C6H13OCO2MeCO2MeOC6H13C6H13OCO2MeCO2MeOCH3H3COH3COCO2MeCO2Me4la, b (51 %)4ma, b (26 %)OC6H13C6H13OH3COCO2MeCO2MeOCH3H3CO4da, b (65 %)4ia (41 %)1 44ka, c (27 %)2  |  Journal Name, [year], [vol], 00–00 1,2-bis(hexyloxy)benzene, which can be prepared in two steps from 1,2-bis(hexyloxy)-4-iodobenzene. A Sonogashira coupling reaction with commercial 4,4'-diiodo-1,1'-biphenyl furnished the corresponding 4,4'-bis((3,4-bis(hexyloxy)phenyl)ethynyl)-1,1'-biphenyl (5). Treatment of 5 with our developed strategy directly 5 afforded the polysubstituted symmetrical triphenylene dimer (6) in 38 % isolated yield (Scheme 3). 10 15 Scheme 3. Synthesis of triphenylene dimer 20 The thermal properties of compound 4a were examined using polarized optical microscopy and differential scanning calorimetry (DSC). This difunctionalized triphenylene was found to exhibit columnar hexagonal mesophases over a much broader temperature range of 39-170 °C versus 2,3,6,7,10,11-25 hexaalkoxytriphenylene (HAT6), which forms a columnar hexagonal phase from only 67-98 °C.3a This large difference likely reflects enhancement in the mesophase stability probably through polarisation of the ester carbonyl groups, which exert an intercolumnar dipole-dipole interaction.2c,430 Conclusions In conclusion, we have designed an efficient synthetic procedure for the preparation of polysubstituted triphenylene 2,3-dicarboxylic esters via a tandem addition process starting from the readily available diarylacetylene. It should be noted that 35 although this method proceeds in moderate overall yield, it is complementary to other traditional strategies for preparing new types of triphenylene derivatives. This can be viewed as a simple alternative that may offer access to more complicated triphenylene-based molecules with different substitution patterns 40 via a one-pot strategy by tuning the structure of the diarylacetylene and dienophile. Although these early studies have focused on derivatives that contain only two types of peripheral substitution pattern, this approach can be adapted to the assembly of analogues having more than two types of peripheral 45 substitution. Our preliminary studies indicate that the compound 4a exhibits a liquid crystal phase over a much broader temperature range compared to the hexaalkoxytriphenylene. Further investigations are under way to examine the effect of structural modifications on the self-assembly as well as the 50 mesomorphic properties of these compounds. This work was supported by the NSFC (No. 21072140, 21202109, 51273133), Special Funds for Sharing the Large Precision Equipments (Nos. DJ2013-20 and DJ2013-21) and Research Projects (Nos.xyz2013-14-39 and PY01) of Sichuan 55 Normal University is gratefully acknowledged. Notes and references a College of Chemistry and Material Sciences, Sichuan Normal University, Chengdu, 610066, P.R. China. E-mail: feng_chun@126.com; wangbiqin1964@126.com  60 b Department of Chemistry, The University of Hull, Hull, HU6 7RX, UK † Electronic Supplementary Information (ESI) available. See DOI: 10.1039/b000000x/ 1  (a) A. Ané, G. Prestat, G. T. Manh, M. Thiam, S. Josse, M. Pipelier, J. Lebreton, J. P. Pradère, D. Dubreuil, Pure Appl. Chem., 2001, 73, 65 1189; (b) M. Montembault, G. Vo-Than, A. Deyine, V. Fargeas, M. Villieras, A. Ané, D. Dubreuil, D. Esquieu, C. Grégoire, S. Opi, J.-M. Péloponése, G. Campbell, J. Watkins, J. de Mareil, A.-M. Aubertin, C. Bailly, E. Loret, J. Lebreton, Bioorg. Med. Chem. Lett., 2004, 14, 1543. 70 2    (a) S. Kumar Pala, S. Setia, B. S. Avinash, S. Kumar, Liq. Cryst., 2013, 40, 1769; (b) T. Osawa, T. 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Wendorff,  Liq Cryst., 1999, 26, 483. 17  (a) R. Abeysekera, R. J. Bushby, C. Caillet, I. W. Hamley, O. R. 120 Lozman, Z. Lu, A. W. Robards, Macromolecules, 2003, 36, 1256; (b) N. Boden, R. J. Bushby, A. N. Cammidge, J. Am. Chem. Soc., 1995, 117, 924; (c) P. Henderson, H. Ringsdorf, P. Schuhmacher, Liq Cryst., 1995, 18, 191. 125 C6H13OC6H13O OC6H13OC6H13MeO2CMeO2CC6H13O OC6H13CO2MeCO2MeC6H13O OC6H13(1) 20 % mol Grubbs-2 , CuI (10 % mol), Ti(OiPr)4 (10 % mol), CH2=CH2 (1 atm),toluene(5 mL), 80 ℃ , 24 h(3) FeCl3( 12 equiv.), CH2Cl2/CH3NO2,  0℃ , Ar, 1h(2) DMAD( 10 equiv.), 100 ℃ , 24 h56Journal Name, [year], [vol], 00–00  |  3 

A convenient tandem one-pot synthesis of donor-acceptor-type triphenylene 2,3-dicarboxylic esters from diarylacetylene

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A convenient tandem one-pot synthesis of donor-acceptor-type triphenylene 2,3-dicarboxylic esters from diarylacetylene

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