Efficient Synthesis of Trimethylsilyl-Substituted Dithieno[2,3-b:3′,2′-d]thiophene, Tetra[2,3-thienylene] and Hexa[2,3-thienylene] from Substituted [3,3′]Bithiophenyl

Abstract

Efficient synthetic procedures for the preparation of b-trithiophenes (dithieno[2,3-b:3′,2′-d]thiophene) and two macrocyclic compounds, tetra[2,3-thienylene] and hexa[2,3-thienylene] bearing trimethylsilyl (TMS) groups from 2,2′-dibromo-5,5′-bistrimethylsilanyl[3,3′]bithiophenyl are reported. The UV-Vis spectra property and crystal structures of these macrocyclic oligo­thiophenes are described.

Key words

bithiophenyl - cyclization - fused-ring system - hetero­cycles - macrocylces

References and Notes

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• 21a

  Crystal Data for 10: M = 701.36, C₃₄H₅₂S₄Si₄, triclinic, space group P1, a = 12.6217(9) Å, b = 13.2892(9) Å, c = 13.3125(9) Å, a = 110.0070(10)°, b = 111.4940(10)°, g = 96.1850(10)°, V = 1881.6(2) ų, Z = 2, D_calcd = 1.238 g/cm³. A colorless crystal of dimensions 0.30 × 0.23 × 0.11 mm was used for measurement at 293 (2) K with the w scan mode on a Bruker Smart APEX diffractometer with CCD detector using Mo-K_a radiation (l = 0.71073 Å). The data were corrected for Lorentz and polarization effects and absorption corrections were performed using SADABS^21b program. The crystal structures were solved using the SHELXTL^21c program and refined using full matrix least squares. The positions of hydrogen atoms were calculated theoretically and included in the final cycles of refinement in a riding model along with attached carbons. The final cycle of full-matrix least-squares refinement was based on 7240 independent reflections [I >2s(I)] and 357 variable parameters with R1 = 0.0667, wR2 = 0.1979. The supplementary crystallographic data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.uk/data_request/cif. Please quote the reference number CCDC: 652683.

• 21b Sheldrick GM. SADABS   University of Göttingen; Germany: 1996. 
• 21c Sheldrick GM. SHELXTL Version 5.1   Bruker Analytical X-ray Systems, Inc.; Madisonv / WI: 1997. 
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15

Compounds 6 and 7 were prepared according to the method from ref. 12.

16

Preparation of 8: n-BuLi (2.5 M in hexane, 15.0 mL, 37.5 mmol, 2.2 equiv) was added dropwise to diisopropylamine (5.5 mL, 38.9 mmol, 2.3 equiv) in Et₂O (30 mL) at 0 °C. After keeping at 0 °C for 0.5 h, the prepared LDA solution was transferred by syringe into a solution of 7 (5.44 g, 16.8 mmol) with anhyd Et₂O. After keeping at 0 °C for 2 h, the reaction mixture was cooled to -78 °C, then trimethyl-chlorosilane (10.8 mL, 85.1 mmol, 5.1 equiv) was added dropwise. The reaction mixture was kept at -78 °C for 1 h and then warmed slowly to r.t. overnight. After quenching with H₂O (50 mL), the crude product was extracted with Et₂O (3 × 40 mL) and washed with H₂O (50 mL), and then dried over MgSO₄. After removing the solvent in vacuo, the residue was purified by column chromatography on silica gel with PE (60-90 °C) as eluent to yield 8 (7.00 g, 89.1%) as a white solid. From two other reactions on a 4.44-g and 5.79-g scale of 7, 5.74 g (89.5%) and 7.39 g (88.4%) of 8 were obtained, respectively; mp 79-81 °C. ¹H NMR (400 MHz, CDCl₃): d = 7.15 (s, 2 H), 0.32 (s, 18 H). ¹³C NMR (100 MHz, CDCl₃): d = 141.7, 137.0, 136.0, 115.7, 0.0 [J(²⁹Si-¹³C) = 54 Hz]. MS (EI, 70 eV): m/z = 568 (14) [M⁺], 453 (67) [M⁺ - Me]. Anal. Calcd for C₁₄H₂₀Br₂S₂Si₂ (468.42): C, 35.90; H, 4.30; S, 13.69. Found: C, 35.33; H, 4.40; S, 13.46. IR (KBr): 3095, 3078, 2927, 2857 (CH) cm^-1.

17

Preparation of 9: To a solution of 8 (1.00 g, 2.13 mmol) in anhyd Et₂O (80 mL), t-BuLi (2.5 M, 3.9 mL, 4.6 equiv) was added dropwise at -78 °C. After keeping at -78 °C for 2 h, anhyd (PhSO₂)₂S (0.67 g, 2.13 mmol, 1.0 equiv) was added, then the reaction mixture was kept at -78 °C for 2 h and warmed slowly to r.t. overnight. The reaction mixture was quenched with H₂O (50 mL), extracted with Et₂O (2 × 40 mL) and then washed with H₂O (2 × 50 mL). After drying over MgSO₄, the solvent was removed in vacuo. The residue was purified by column chromatography on silica gel with PE (60-90 °C) as eluent to yield 9 (0.47 g, 64.8%) as a white solid. From two other reactions on a 1.00-g and 3.00-g scale of 8, using n-BuLi (2.3 equiv), 0.38 g (52.4%) and 1.10 g (51.0%) of 9 were obtained, respectively; mp 49-50 °C. ¹H NMR (400 MHz, CDCl₃): d = 7.47 (s, 2 H), 0.37 (s, 18 H). ¹³C NMR (100 MHz, CDCl₃): d = 144.5, 144.1, 139.8, 125.1, -0.3. MS (EI, 70 eV): m/z = 340 (77) [M⁺], 325 (100) [M⁺ - Me]. Anal. Calcd for C₁₄H₂₀S₃Si₂ (340.67): C, 49.36; H, 5.92; S, 28.24. Found: C, 49.30; H, 5.83; S, 27.74. IR (KBr): 2951, 2889 (CH) cm^-1.

18

Preparation of 1: To a solution of 9 (2.11 g, 6.19 mmol) in CHCl₃ (30 mL), TFA (2.0 mL) was added dropwise at r.t. The reaction progress was monitored by TLC analysis. After stirring at r.t. for 1 h, the reaction mixture was quenched with H₂O (10 mL), extracted with CHCl₃ (3 × 50 mL), and then washed with sat. NaHCO₃ (40 mL) and H₂O (2 × 40 mL). After drying over MgSO₄, the solvent was removed in vacuo. A white powder of 1 (1.20 g, 98.7%) was obtained. From another reaction on a 2.09-g scale of 9, 1.17 g (97.2%) of 1 was obtained; mp 84-85 °C (lit.^10b 86-87 °C). ¹H NMR (400 MHz, CDCl₃): d = 7.40 (d, J = 5.2 Hz, 2 H), 7.38 (d, J = 5.2 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): d = 139.0, 138.3, 127.5, 118.8. MS (EI, 70 eV): m/z = 196 (100) [M⁺]. IR (KBr): 2955, 2894 (CH) cm^-1.

19

Preparation of 10 and 11: To a solution of 8 (2.00 g, 4.27 mmol) in anhyd Et₂O (60 mL), n-BuLi (2.5 M, 4.0 mL, 10.0 mmol, 2.3 equiv) was added dropwise at -78 °C. After keeping at -78 °C for 2 h, anhyd CuCl₂ (1.7 g, 12.6 mmol, 3.0 equiv) was added. The reaction mixture was kept at -78 °C for 2 h, and then slowly warmed to r.t. overnight. The reaction mixture was quenched with H₂O (50 mL), extracted with Et₂O (3 × 40 mL), washed with H₂O (50 mL), and then finally dried over MgSO₄. After removing the solvent in vacuo, the residue was purified by column chromatography on silica gel with PE (60-90 °C) as eluent to yield 10 (0.55 g, 41.5%) as a pale white crystal and 11 (0.40 g, 36.5%) as a white powder. For 10: mp 302 °C(sublimation). ¹H NMR (400 MHz, CDCl₃): d = 7.06 (s, 4 H), 0.32 (s, 36 H). ¹³C NMR (100 MHz, CDCl₃): d = 142.3, 137.7, 137.3, 136.8, 136.5, -0.2 [J(²⁹Si-¹³C) = 49 Hz]. HRMS (ESI): m/z [M + H]⁺ calcd for C₂₈H₄₁S₄Si₄: 617.1168; found: 617.1154. HRMS (ESI): m/z [M + Na]⁺ calcd for C₂₈H₄₀NaS₄Si₄: 639.0988; found: 639.0997. IR: 3160.2, 2954.9 (CH) cm^-1. For 11: mp 258-261 °C (wax), 286 °C (clear). ¹H NMR (400 MHz, CDCl₃): d = 7.17 (s, 2 H), 6.83 (s, 2 H), 6.44 (s, 2 H), 0.38 (s, 18 H), 0.28 (s, 18 H), 0.18 (s, 18 H). ¹³C NMR (100 MHz, CDCl₃): d = 140.0, 139.8, 139.5, 138.4, 138.1, 136.4, 136.0, 135.6, 134.8, 132.3, -0.1. HRMS (ESI): m/z [M + H]⁺ calcd for C₄₂H₆₁S₆Si₆: 925.1713; found: 925.1700. HRMS (ESI): m/z [M + Na]⁺ calcd for C₄₂H₆₀NaS₆Si₆: 947.1532; found: 947.1564. IR: 3160.2, 2955.5 (CH) cm^-1.

20

Compounds 2 and 3 were prepared from 10 and 11, respectively according to the method used for the preparation of 1 from 9. Compound 2: mp 252-253 °C (lit.¹³ 253-256 °C). ¹H NMR (400 MHz, CDCl₃): d = 7.40 (d, J = 5.4 Hz, 4 H), 6.96 (d, J = 5.4 Hz, 4 H). MS (EI): m/z = 328 (100) [M⁺]. HRMS (ESI): m/z [M + H]⁺ calcd for C₁₆H₉S₄: 328.9587; found: 328.9588. IR: 3101.2, 2926.0 (CH) cm^-1. Compound 3: mp 281-283 °C (sublimation). ¹H NMR (400 MHz, CDCl₃): d = 7.33 (d, J = 5.2 Hz, 2 H), 7.08 (d, J = 5.2 Hz, 2 H), 6.97 (d, J = 5.2 Hz, 2 H), 6.92 (d, J = 5.1 Hz, 2 H), 6.79 (d, J = 5.2 Hz, 2 H), 6.44 (d, J = 5.1 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): d = 135.4, 133.4, 133.3, 132.1, 131.9, 131.5, 131.0, 130.4, 130.0, 129.7, 128.8, 126.1, 125.0, 124.9. MS (EI): m/z = 492 (48) [M⁺]. HRMS (ESI): m/z [M + H]⁺ calcd for C₂₄H₁₃S₆: 492.9341; found: 492.9341. IR: 3100.5, 2924.6 (CH) cm^-1.

22

Crystal Data for 11: M = 1045.17, C₄₃H₆₁Cl₃S₆Si₆, triclinic, space group P1, a = 11.8377(12) Å, b = 14.0164(15) Å, c = 17.9101(18) Å, a = 94.620(2)°, b = 103.881(2)°, g = 94.390(2)°, V = 2861.4(5) ų, Z = 2, D_calcd = 1.213 g/cm³. A colorless crystal of dimensions 0.30 × 0.11 × 0.11 mm was used for measurement at 293 (2) K. The structure was solved by the same methods as used for 10. The final cycle of full-matrix least-squares refinement was based on 11009 observed reflections [I >2s(I)] and 541 variable parameters with R1 = 0.0731, wR2 = 0.1255. The supplementary crystallographic data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.uk/data_request/cif. Please quote the reference number CCDC: 652684.