CHOSE AN ARTICLE TYPE Copper-Mediated Simple and Efficient Synthesis of Tribenzohexadehdro[12]annulene and its Derivatives

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CHOSE AN ARTICLE TYPE Copper-Mediated Simple and Efficient Synthesis of Tribenzohexadehdro[12]annulene and its Derivatives
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  1 CHOSE AN ARTICLE TYPE Template for SYNLETT and SYNTHESIS © Thieme Stuttgart · New York 2004-05-04 page 1 of 6 Abstract:  A simple and efficient synthesis of tribenzohexadehy-dro[12]annulene and its derivatives was carried out using coupling reaction of acetylenes with iodoarenes in the presence of catalytic amounts of CuI and PPh 3 , together with 3 equiv of K  2 CO 3  in DMF. This synthetic procedure was applied to the synthesis of a large annulenoannulene derivative. Key words:  annulenes, cross-coupling, cyclizations, macrocycles, oligomerization There has been a considerable interest in cyclic phenyl-acetylenes such as dehydroannulenes, 1  cyclynes, 2  and  phenylacetylene macrocycles, 3  because of their π -conjugation, all-carbon networks, 4,5  formation of unusual metal complexes, 2  self-association 6  and inclusion proper-ties. 7  Tribenzohexadehydro[12]annulene (tribenzocy-clyne) 1a  is a unit structure of graphyne. 4  Since 1a  is one of the most useful cyclic acetylenes, a variety of syn-thetic methods for 1a  have been developed. The an-nulene 1a  can be prepared by Stephenes-Castro coupling of copper (2-iodophenyl)acetylide, 8  palladium-catalyzed trimerization of 4-(2-bromophenyl)-2-methylbutyne-2-ol, 9  palladium-catalyzed co-cyclization of 1,2-diiodobenzene with acetylene, 10  a combination of Wittig reaction and bromination/dehydrobromination proce-dures 11  or recently reported alkyne metathesis. 12  How-ever, the synthesis of 1a  still remains troublesome, espe-cially for medium to large scale reactions. Here we re- port a practical procedure for the synthesis of 1a  and related compounds. Although the Sonogashira reaction of phenylacetylene with bromo- or iodobenzene using Pd(PPh 3 ) 2 Cl 2  and CuI in Et 3  N produces diphenylacetylene in a quantitative yield, 13  cyclotrimerization of (2-bromophenyl)acetylene under similar conditions affords 1a  in a very low yield due to homo-coupling of (2-bromophenyl)acetylene as a  prefarable reaction. 14  The cyclotrimerization of (2-iodophenyl)acetylene under similar Sonogashira condi-tions also formed only a trace amount of 1a . Thus, the homo-coupling of acetylene units takes place more eas-ily than the normal Sonogashira coupling in the case of (2-bromophenyl)- and (2-iodophenyl)acetylenes. A copper-catalyzed cross-coupling of phenylacetylene with iodobenzene in an aprotic solvent such as DMF and DMSO was reported to produce diphenylacetylene in a quantitative yield. 15  Since this reaction proceeds smoothly to produce no homo-coupling product, we tried to apply the cyclotrimerization of (2-iodophenyl)acetylene 3a  and its derivatives with catlytic amounts of CuI and PAr  3  (Ar = Ph or 2-furyl) in the  presence of K  2 CO 3  as a base in DMF. Although the reac-tion takes place at high temperatures (160-165 °C), the desired 1a  and related annulenes 1b - d  can be prepared in moderate to good yields (Figure 1). Additionally, the annulenoannulene derivative 2b  can be synthesized in a short pathway. RRRRRR 1a1b : R = Me 1c : R = Bu n 1d : R = OMe 2a:  R = H 2c: R = Bu n RRRRRRRR   Figure 1  The structures of the annulenes  1a - d  and 2a , c . For the construction of the [12]annulene framework, the cyclotrimerization of 3a-d  was first investigated under various conditions using CuI and PAr  3  (Scheme 1 and Table 1). The reaction of 3a  with CuI (30-50 mol%) and PPh 3 (30-50 mol%) in DMF proceeded smoothly at 160-165 ºC for 24 h to afford 1a  in 54-55% yields (entries 1 and 2). A similar reaction of 3a  in DMSO, however, resulted in the formation of a complex mixture of uni-dentified products (entry 3). As the ligand, tri(2- Copper-Mediated Simple and Efficient Synthesis of Tribenzohexadehdro-[12]annulene and its Derivatives Masahiko Iyoda,* Siriwan Sirinintasak, Yoshihiro Nishiyama, Anusorn Vorasingha, Fatema Sultana, Kazumi Nakao, Yoshiyuki Kuwatani, Haruo Matsuyama, Masato Yoshida, Yoshihiro Miyake Department of Chemistry, Graduate School of Science, Tokyo Metropolitan university, Hachioji, Tokyo 192-0397, Japan Fax+81(426)772525; E-mail: iyoda-masahiko@c.metro-u.ac.jp  Received   This article is dedicated to Professor Teruaki Mukaiyama for his 77th birthday.  2 CHOSE AN ARTICLE TYPE Template for SYNLETT and SYNTHESIS © Thieme Stuttgart · New York 2004-05-04 page 2 of 6 furyl)phosphine can be employed for the cyclotrimeriza-tion to give 1a  in 41% yield (entry 4). IRRRRRRRRPAr  3 CuI 1a: R = H 1b : R = Me 1c : R = Bu n 1d : R = OMe160-165 °C 3a: R = H 3b : R = Me 3c : R = Bu n 3d : R = OMe24 h   Scheme 1  Synthesis of 1 - 4 . Although the reaction of phenylacetylene with iodoben-zene in the presence of CuI (5 mol%) and PPh 3  (10 mol%) proceeded smoothly at 120 °C to produce di- phenylacetylene, 3a  was recovered unchanged under similar conditions. As the ligand, P( o -tolyl) 3 , As(PPh) 3  and Ph 2 PCH 2 CH 2 PPh 2  can be employed for the cyclotrimerization of 3a  to afford 1a  in lower yields. Additionally, the reaction of 3a  with a stoichiometric amount of CuI and PPh 3  (1 equiv) also leads to 1a  in 44% yield. Table 1  Cyclotrimerization of 3a - d  with CuI and PAr  3 . a EntryCuI(mol%)Ligand(mol%)SolventProduct(%)  b 130PPh 3  (30)DMF 1a  (55)250PPh 3  (50)DMF 1a  (54)330PPh 3  (30)DMSO 1a  (0)430P(2-furyl) 3  (30)DMF 1a  (41) a Conditions: 160-165 °C, 24 h.  b Isolated yield. 33a3a3a3a 530P(2-furyl) 3  (30)DMF 1b  (28) 3b 730PPh 3  (30)DMF 1c  (31) 3c 830P(2-furyl) 3  (30)DMF 1d  (17) 3d 630P(2-furyl) 3  (30)DMF 1c  (37) 3c  The cyclotrimerization of 3a  can be applied for the  preparation of substituted tribenzohexadehydro[12]-annulenes 1b - d . (2-Iodoaryl)acetylenes 3b - d  were pre- pared by the Sonogashira reaction of the corresponding 1,2-diiodoarenes, followed by deprotection with K  2 CO 3  in methanol. As shown in Table 1, the reactions of 3b - d  with CuI (30 mol%) and P(2-furyl) 3  (30 mol%) in DMF at 160 °C for 24 h produced 1b - d  in 28, 37 and 17% yields (entries 5, 6 and 8). In the case of 3c , the reaction with 30 mol% of CuI and PPh 3  under similar conditions afforded 1c  in 31% yield (entry 7). Although the copper-catalyzed cyclotrimerization of 3b - d  with PPh 3  yielded 1b - d , the reaction with P(2-furyl) 3  afforded 1b - d  in bet-ter yields (entries 5-8). For the construction of the [12]annulene framework, we next tried the [6+6]- or [10+2]cyclization using the cop- per-mediated cross-coupling strategy. As shown in Scheme 2, the reaction of 7a  with 1.5 equiv of 1,2-diethynylbenzene in the presence of CuI (30 mol%), PPh 3  (30 mol%) and K  2 CO 3  (3 equiv) in DMF at 160 °C for 24 h afforded 1a  in 33% yield, whereas a similar reaction of 8a  with 1 equiv of 1,2-diiodobenzene pro-duced 1a  in 51% yield. Since the annulenoannulene 2a  is an interesting target molecule, 1,16  the synthesis of 2a  was tried using our [10+2]coupling reaction. Thus, the cross-coupling of 8a  with 0.5 equiv of 1,2,4,5-tetraiodobenzene was carried out using CuI and PPh 3  in DMF. However, the reaction gave a complex mixture, and only a trace amount of 2a  was detected by MS analysis, presumably due to an extremely low solubility of 2a  and its precursors. 2a : R = H 2c : R = Bu n II 1a IBr RRBr RRRRRRXXRRRR 4c : R = Bu n 5c : R = Bu n 6c : R = Bu n , X = Br  8c : R = Bu n +1) TMSA, Pd(PPh 3 ) 2 Cl 2 PdCl 2 (PPh 3 ) 4 4c 1) TMSA[Pd] 7a PPh 3 CuI160 °C PPh 3 CuI160 °C +  8a RRRRRRRR 8 +IIIIPPh 3 CuI160 °C 2) K 2 CO 3 CuI, Et 3 NCuI, Et 3 N 8a : R = H 7a : R = H, X = I2) K 2 CO 3   Scheme 2 Synthesis of 1a , 2a  and 2c Taking into account the low solubility of 2a , the synthsis of 2c  was attempted, because eight butyl groups may increase the solubility of 2c  enough to isolate a pure compound. The precursor 8c  was prepared starting from  3 CHOSE AN ARTICLE TYPE Template for SYNLETT and SYNTHESIS © Thieme Stuttgart · New York 2004-05-04 page 3 of 6 4c . 17  The Sonogashira reaction of 4c  with trimethylsilyl-acetylene (TMSA), followed by deprotection yields 5c  (two steps, 80%). The cross-coupling of 5c  with 4c  in the  presence of PdCl 2 (PPh 3 ) 2  and CuI in Et 3  N afforded 6c  (88%). The Sonogashira reaction of 6c  with TMSA, followed by deprotection produced the diethynyl precur-sor 8c  in 58% overall yield. The reaction of 8c  with 1,2,4,5-tetraiodobenzene (0.5 equiv) in the presence of CuI (1 equiv) and PPh 3  (1 equiv) in DMF at 160-165 °C for 24 h produced the desired 2c  in 1% yield. The an-nulenoannulene 2c  is a stable yellow crystalline com- pound and has a moderate solubility in CH 2 Cl 2 , THF and CS 2 . 1.00.50200400600 (a) (b) λ /nmIntensity   Figure 2  Electronic (a) and fluorescence spectra (b) of 2c  in CH 2 Cl 2 . Interestingly, 2c  shows an intense fluorescence at 495, 535 and 555 nm (Figure 2) with a large Storks shift of 190 nm, reflecting the tribenzohexadehydro[12]annulene structure. The fluorescence quantum yield ( Φ  = 0.21) of 2c  is fairly large. Additionally, 2c  forms a 2:1 silver complex with AgBF 4  at equilibrium (Figure 3), although we assume a partial formation of the 2:1 complex after mixing 2c  and AgBF 4 . The formation of the ( 2c ) 2 -AgBF 4  complex was confirmed by TOF-MS and 1 H NMR analysis. 18 Ag + Bu n Bu n Bu n Bu n Bu n Bu n Bu n Bu n BF 4- Bu n Bu n Bu n Bu n Bu n Bu n Bu n Bu n   Figure 3  The silver complex ( 2c ) 2 -AgBF 4 . 1 H and 13 C NMR spectra were recorded on JEOL LA-500 and JEOL LA-400 instruments. Spectra are reported (in δ ) referenced to Me 4 Si. Mass spectra were recorded on JEOL JMS-AX 500 and KRATOS AXIMA-CFR instruments. Only the more intense or structurally diagnostic mass spec-tral fragment ion peaks are reported. High-Resolution MS was determined on JEOL JMS-SX102A instrument. Elec-tronic spectra were recorded on a SHIMADZU UV-VIS- NIR scanning spectrophotometer (Model UV-3101-PC). Melting points were determined with a Rigaku DSC8230L differential scanning calorimetry apparatus and a Yanaco MP-500D melting point apparatus. Elemental analyses were  performed in the microanalysis laboratory of Tokyo Metro- politan University. Column chromatography was carried out with use of EM Reagents silica gel 60, 70-230 mesh ASTM, Daiso silica gel 1001W, or neutral alumina activity II-III, 70-230 mesh ASTM. All solvents were dried by conven-tional procedures and distilled before use. 1,2-Diiodo-4,5-dimethylbenzene, 19  4,5-dibutyl-1,2-diiodo-benzene, 20  1,2-diiodo-4,5-dimethoxybenzene 21  and (2-iodophenyl)-acetylene 8b,22  were prepared according to literature proce-dures. (2-Iodoaryl)acetylenes 3: General Prucedure To a 50 ml two-necked flask equipped with an argon bal-loon, 1,2-iodoarene (10 mmol), trimethylsilylacetylene (1.17 g, 12 mol), NEt 3  20 mL, CuI (38 mg, 0.2 mmol) and PdCl 2 (PPh 3 ) 2  (70 mg, 0.1 mmol) were added. The reaction mixture was stirred for 6-15 h at room temperature. The solvent was removed under reduced pressure. The residue was passed through a short column of Al 2 O 3  and eluted with hexane/CH 2 Cl 2  to give crude product which was purified by column chromatography on silica gel using hexane/CH 2 Cl 2  as an eluent to afford 1-iodo-2- trimethylsilylethynylarene. To a solution of 1-iodo-2-trimethylsilylethynylarene (5 mmol) in methanol (20 mL) was added K  2 CO 3  (69 mg, 0.5 mmol), and the mixture was stirred for 1-5 h at room tem- perature. The mixture was poured into H 2 O and extracted with ether. The organic phase was washed with saturated aq.  NH 4 Cl solution, and dried over MgSO 4 . After removal of the drying reagent, the solvent was evaporated under re-duced pressure to give a residue which was passed through a silica gel column using hexane/CH 2 Cl 2  as an eluent to afford 3 . 2-Ethynyl-1-iodo-4,5-dimethylbenzene 3b Colorless cryst.; yield: 43%; mp 72.5-73 °C. 1 H NMR (CDCl 3 ) δ  2.18 (s, 3H), 2.21 (s, 3H), 3.31 (s, 1H), 7.27 (s, 1H), 7.60 (s, 1H). 13 C NMR (CDCl 3 ) δ  19.17, 19.31, 79.78, 85.25, 96.60, 125.83, 134.29, 136.68, 139.40, 139.65. MS (EI): m/z   (%) = 256 (100, M + ), 129 (30), 128 (53). HRMS (FAB): m/z   calcd for C 9 H 10 I: 255.9749; found 255.9750 4,5-Dibutyl-2-ethynyl-1-iodobenzene 3c Colorless oil; yield: 51%.  4 CHOSE AN ARTICLE TYPE Template for SYNLETT and SYNTHESIS © Thieme Stuttgart · New York 2004-05-04 page 4 of 6 1 H NMR (CDCl 3 ) δ  0.92-0.96 (m, 6H), 1.35-1.40 (m, 4H), 1.49-1.55 (m, 4H), 2.50-2.55 (m, 4H), 3.31 (s, 1H), 7.28 (s, 1H), 7.59 (s, 1H). 13 C NMR (CDCl 3 ) δ  13.93, 22.62, 22.68, 31.71, 31.89, 32.94, 33.02, 79.67, 85.39, 96.78, 125.75, 134.02, 139.06, 140.71, 143.73. MS (EI): m/z   (%) = 340 (81, M + ), 255 (100), 170 (20). HRMS (FAB): m/z   calcd for C 16 H 21 I: 340.0688; found 340.0688 2-Ethynyl-1-iodo-4,5-dimethoxlbenzene 3d Colorless cryst.; yield: 40%; mp 109.5-110 °C. 1 H NMR (CDCl 3 ) δ  3.31 (s, 1H), 3.86 (s, 3H), 3.88 (s, 3H), 6.99 (s, 1H), 7.21 (s, 1H). 13 C NMR (CDCl 3 ) δ  55.97, 56.16, 79.29, 85.30, 89.64, 115.41, 120.79, 120.88, 148.85, 150.01. MS (EI): m/z   (%) = 288 (100, M + ), 273 (19), 118 (49). HRMS (FAB): m/z   calcd for C 10 H 9 IO 2 : 287.9647; found 287.9646 Cyclotrimerization of 3; General Prucedure (Table 1) To a solution of (2-iodoaryl)acetylene 3  (1.5 mmol) and PPh 3  (118 mg, 0.45 mmol) or P(2-furyl) 3  (104.5 mg, 0.45 mmol) in DMF (5 mL) were added CuI (86 mg, 0.45 mmol) and K  2 CO 3  (622 mg, 4.5 mmol). The mixture was heated with stirring for 24 h in an oil bath at 160 °C under argon atmosphere. The mixture was poured into water and ex-tracted with toluene. The combined organic phases were washed with saturated aq. NH 4 Cl solution, and dried over MgSO 4 . The drying reagent was removed by filtration, and the solvent was evaporated under reduced pressure. The residue was passed through a short column on Al 2 O 3  and eluted with hexane/CH 2 Cl 2  to give crude product which was  purified by column chromatography on silica gel using hexane/CH 2 Cl 2  as an eluent to afford 1  together with a small amount of a cyclic tetramer (tetrabenzooctadehy-dro[16]annulene or its derivatives). Tribenzohexadehydro[12]annulene (1a) 8-12   Yellow plates; yield: 55%; mp 208.5-210 °C. 1 H NMR (CDCl 3 ) δ  7.19 (m, 6H), 7.39 (m, 6H). 13 C NMR (CDCl 3 ) δ  92.99, 126.35, 128.39, 132.10. Hexamethyltribenzohexadehydro[12]annulene (1b) 10,12 Yellow cryst.; yield: 29%; mp ca.  340 °C (decomp). 1 H NMR (CD 2 Cl 2 ) δ  2.21 (s, 18H), 7.10 (s, 6H). 13 C NMR (CD 2 Cl 2 ) δ  19.70, 92.42, 124.29, 133.15, 138.22. MS (EI): m/z   (%) = 384 (100, M + ), 192 (14). HRMS (EI): m/z   calcd for C 30 H 24 : 384.1878; found 384.1832 Hexabuthyltribenzohexadehydro[12]annulene (1c) Yellow cryst.; yield: 31%; mp 153-154.5 °C. 1 H NMR (CDCl 3 ) δ  0.95 (t,  J   = 7.3 Hz, 18H), 1.37-1.41 (m, 12H), 1.51-1.57 (m, 12H), 2.52 (t,  J   = 7.9 Hz, 12H), 7.11 (s, 6H). 13 C NMR (CDCl 3 ) δ  14.00, 22.74, 32.05, 32.89, 92.18, 124.08, 132.33, 141.18. MS (EI): m/z   (%) = 636 (100, M + ), 551 (17), 318 (13). HRMS (FAB): m/z   calcd for C 48 H 60 : 636.4695; found 636.4687 Hexamethoxytribenzohexadehydro[12]annulene (1d) 12   Yellow cryst.; yield: 17%; mp > 250 °C. 1 H NMR (CDCl 3 ) δ  3.87 (s, 18H), 6.74 (s, 6H). 3 C NMR (CD 2 Cl 2 ) δ  55.89, 91.91, 113.78, 119.81, 149.06. MS (EI): m/z   (%) = 480 (100, M + ), 335 (13), 281 (5). HRMS (FAB): m/z   calcd for C 30 H 24 O 6 : 480.1573; found 480.1573 Coupling of 7a with 1,2-diethynylbenzene To a mixture of CuI (63 mg, 0.33 mmol), PPh 3  (87 mg, 0.33 mmol) and K  2 CO 3  (414 mg, 3 mmol) in DMF (10 mL) was addad 7a 23  (430 mg, 1 mmol) and 1,2-diethynylbenzene (189 mg, 1.5 mmol) under argon. The mixture was stirred for 24 h at 160 °C. The mixture was poured into H 2 O and extracted with ether. The organic phase was washed with saturated aq. NH 4 Cl solution, and dried over MgSO 4 . After removal of the solvent, 1a  was isolated by silica gel column chromatography (99 mg, 33%). Coupling of 8a with 1,2-diiodobenzene In a similar manner to the reaction of 7a  with 1,2-diethynylbenzene, the reaction of 8a  (226 mg, 1 mmol), 1,2-diiodobenzene (330 mg, 1 mmol), CuI (63 mg, 0.33 mmol), PPh 3  (87 mg, 0.33 mmol) and K  2 CO 3  (414 mg, 3 mmol) in DMF (10 mL) afforded 1a  (153 mg, 51%). 1-bromo-4,5-dibutyl-2-ethylnylbenzene 5c  To a 20 mL flask, 1-bromo-2-iodo-4,5-dibutylbenzene 2.53 g (6.4 mmol), trimethylsilylacetylene 1.0 ml (7.09 mmol),  NEt 3  12 mL, CuI 121.7 mg (0.64 mmol) and PdCl 2 (PPh 3 ) 2  453.3 mg (0.64 mmol) were added. The reaction mixture was stirred overnight at room temperature under argon. The mixture was poured into saturated aq. NH 4 Cl solution (20 ml) and extracted with ether (3 x 20mL). The combined organic phases were washed with sat. aq. NaCl solution (20 ml) and dried over MgSO 4 . After filtration, solvent was removed under reduced pressure, and the residue was sepa-rated by column chromatography on silica gel using hexane as an eluent to afford 1-bromo-4,5-dibutyl-2-trimethylsilylethylnyl benzene (2.26 g, 96%).  5 CHOSE AN ARTICLE TYPE Template for SYNLETT and SYNTHESIS © Thieme Stuttgart · New York 2004-05-04 page 5 of 6 To a 20 ml flask, 1-bromo-4,5-dibutyl-2-trimethylsilyl-ethylnylbenzene 2.26 g (6.2 mmol), K  2 CO 3  857.5 mg (6.2 mmol) and MeOH 15 ml were added. The mixture was stirred for 30 minutes at room temperature. The mixture was poured into sat. aq. NaCl solution (25 mL) and ex-tracted with ether (3 x 20 ml). The combined organic phases were dried over MgSO 4 . After filtration, solvent was evaporated, and the residue was separated by column chro-matography on Al 2 O 3  using hexane as an eluent to afford 5c  (1.59 g, 88%) as a yellow oil. 1 H NMR (CDCl 3 ) δ  0.92-0.96 (m, 6H), 1.37-1.41 (m, 4H), 1.51-1.54 (m, 4H), 2.51-2.57 (m, 4H), 3.30 (s, 1H), 7.30 (s, 1H), 7.34 (s, 1H). 13 C NMR (CDCl 3 ) δ  13.94, 22.64, 22.68, 31.64, 32.09, 32.97, 32.99, 80.43, 82.27, 121.16, 122.20, 132.69, 134.58, 139.88, 143.73. Bis(2-bromo-4,5-dibutylphenyl)acetylene 6c  To a 10 ml flask were added 1-bromo-4,5-dibutyl-2-ethylnyl benzene 1.44 g (4.9 mmol), 1-bromo-2-iodo-4,5-dibutylbenzene 1.94 g (4.9 mmol), NEt 3  8.8 ml, CuI 93.4 mg (0.49 mmol) and PdCl 2 (PPh 3 ) 2  346.8 mg (0.49 mmol). The mixture was stirred overnight at room temperature. The mixture was poured into sat. aq. NH 4 Cl solution (20 mL) and extracted with ether (3 x 20 ml). The combined organic phases were washed with sat. aq. NaCl solution (20 ml) and dried over MgSO 4 . After filtration, solvent was evaporated, and the residue was passed through a short Al 2 O 3  column and eluted with hexane/benzene. The crude  product was purified by column chromatography on silica gel using hexane/benzene (9:1) as an eluent to give 6c  (2.56 g, 93%). 1 H NMR (CDCl 3 ) δ  0.95 (t x 2,  J = 7.3 Hz, 6H x 2), 1.36-1.43 (m, 8H), 1.51-1.58 (m, 8H), 2.53-2.59 (m, 8H), 7.36 (s, 2H), 7.37 (s, 2H). 13 C NMR (CDCl 3 ) δ  13.96, 22.69, 22.70, 31.75, 32.12, 33.03, 33.11, 91.44, 122.21, 122.32, 132.74, 134.00, 139.81, 143.17. MS (EI): m/z   (%) = 562 (52, M + +4), 560 (100, M + +2), 558 (51, M + ), 477 (21), 475 (40), 473 (20). HRMS (FAB): m/z   calcd for C 30 H 40 Br  2 : 558.1497; found 558.1490 Bis(2-ethynyl-4,5-butylphenyl)acetylene 8c Bis-(2-bromo-3,4-dibutylphenyl)acetylene 6c  (2.51 g, 4.48 mmol), trimethylsilylacetylene 2.5 ml (17.7 mmol), PPh 3  117.6 mg (0.49 mmol), CuI 42.7 mg (0.22 mmol) and PdCl 2 (PPh 3 ) 2  158.8 mg (0.23 mmol) and piperidine 20 ml were placed in a 50 ml flask. The mixture was evacuated with argon and stirred overnight at 80 ° C. The mixture was  poured into sat. aq. NH 4 Cl solution (25 mL) and extracted with ether (3 x 20 ml). The combined organic phases were washed with sat. aq. NaCl solution (20 ml) and dried over MgSO 4 . After filtration, solvent was evaporated, and the residue was separated by column chromatography on silica gel using hexane/benzene as an eluent to afford bis(2-trimetylsilylethynyl-4,5-dibutylphenyl)acetylene (2.07 g, 78%) as a viscous oil. To a solution of bis(2-trimetylsilylethynyl-4,5-dibutyl- phenyl)acetylene (1.47 g, 2.47.mmol) in THF (10 mL) and methanol (10 ml) was added K  2 CO 3  (341.5 mg, 2.47 mmol) under argon. The mixture was stirred for 1 h at room tem- perature. The mixture was poured into sat. aq. NaCl solu-tion (25 mL) and extracted with ether (3 x 20 ml). The combined organic phases were dried over MgSO 4 . The solvent was removed under reduced pressure, and the resi-due was separated by column chromatography on Al 2 O 3  using hexane/benzene as eluent to afford 8c  (916 mg, 82%) as a viscos oil. 1 H NMR (CDCl 3 ) δ  0.951 (t,  J = 7.3 Hz, 6H), 0.954 (t,  J = 7.3 Hz, 6H), 1.37-1.42 (m, 8H), 1.52-1.59 (m, 6H), 2.56-2.60 (m, 8H), 3.26 (s, 2H), 7.31 (s, 2H), 7.35 (s, 2H). 13 C NMR (CDCl 3 ) δ  13.98, 22.70, 22.72, 32.06, 32.12, 33.01, 33.03, 79.99, 82.64, 91.00, 121.52, 123.60, 132.84, 133.20, 141.11, 141.64. MS (EI): m/z   (%) = 450 (100, M + ), 365 (25), 293 (6). HRMS (FAB): m/z   calcd for C 34 H 42 : 450.3287; found 450.3291 Annulenoannulene 2c To a mixture of 1,2,4,5-tetraiodobenzene (227 mg, 0.39 mmol), K  2 CO 3 (324 mg, 2.34 mmol), CuI (148 mg, 0.78 mmol) and PPh 3 (614 mg, 2.34 mmol) was added a solution of 8c  (352 mg, 0.78 mmol) in DMF (2 mL) under argon. The mixture was stirred for 20 h at 160 ο C. The mixture was  poured into sat. aq. NH 4 Cl solution (25 mL) and extracted with CS 2  (3 x 30 ml). The combined organic phases were washed with sat. aq. NaCl solution (20 ml) and dried over MgSO 4 . The solvent was removed under reduced pressure, and the residue was separated by column chromatography on Al 2 O 3  using hexane/benzene as an eluent to give 2c  (3 mg, 1%) as yellow cryst.; mp >250 °C. 1 H NMR (CS 2 /CD 2 Cl 2  1:1) δ  1.02-1.05 (m, 24H), 1.44-1.51 (m, 16H), 1.58-1.64 (m, 16H), 2.60 (t,  J   = 7.6 Hz, 16H), 7.08 (s, 4H), 7.09 (s, 4H), 7.17 (s, 2H). 13 C NMR (CS 2 /CD 2 Cl 2  1:1) δ  13.97, 22.58, 22.67, 31.91, 31.97, 32.88, 32.89, 79.98, 82.53, 91.00, 121.57, 123.61, 132.70, 133.07, 140.89, 141.41. UV-VIS (CH 2 Cl 2 ) : nm (log ε ) = 252 (4.32), 310 (4.98), 345 (5.03), 399 (3.81), 440 (3.49), 454 (3.41), 486 (3.11). LDTOF-MS: m/z   970 (M + ). Acknowledgement The authors are grateful to Prof. Yoshito Tobe for fruitful discussions. This work has been supported in part by CREST of JST (Japan Science and Technology Corpora-tion).
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