Synthesis of New Tetrathiafulvalene Modules for Acetylenic Scaffolding

Abstract

Benzene-extended derivatives of tetrathiafulvalene (TTF) containing silyl-protected acetylene groups at the exo-cyclic fulvene carbons were prepared by a double Wittig olefination of a diacetylenic derivative of terephthalaldehyde. Acetylenic coupling reactions at the lateral acetylene appendages with phenylacetylene and 4-iodonitrobenzene afforded large π-conjugated chromophores.

Key words

alkynes - arenes - conjugation - cross-coupling - Wittig reactions

References

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11

All new compounds were fully characterized by ¹H- and ¹³C NMR spectroscopy, elemental analysis and/or HR-MS. Selected experimental procedures: Compound 6: To a solution of the phosphonium salt 5 (1.23 g, 2.42 mmol) in dry THF (40 mL) at -78 ºC was slowly added n-BuLi (1.6 m in hexane, 1.5 mL, 2.4 mmol), resulting in a red solution. Then 4 (0.543 g, 1.10 mmol) in dry THF (15 mL) was slowly added. The resulting orange solution was stirred at -78 ºC for 2 h, whereupon sat aq NH₄Cl (200 mL) was added. Then Et₂O (300 mL) was added, the organic phase was separated, dried (MgSO₄), and concentrated in vacuo. Column chromatography (SiO₂, CH₂Cl₂) afforded 6 (0.652 g, 66%) as an orange solid. Mp 155-156 °C. ¹H NMR (300 MHz, CDCl₃): δ = 1.14 (s, 42 H), 3.84 (s, 6 H), 3.89 (s, 6 H), 7.55 (s, 4 H). ¹³C NMR (75 MHz, CDCl₃): δ = 11.3, 18.7, 53.3, 53.5, 101.6, 104.8, 107.7, 126.5, 129.6, 133.0, 135.4, 141.2, 159.4, 160.2. MALDI-TOF-MS [matrix: 2,5-dihydroxybenzoic acid (DHB)]: m/z = 898 (M⁺). Elemental analysis: Calcd for C₄₄H₅₈O₈S₄Si₂ (899.35): C, 58.76; H, 6.50; S, 14.26; Found: C, 58.94; H, 6.38; S, 14.38. Compound 9 : To a solution of 8 (126 mg, 0.12 mmol) in CH₂Cl₂ (10 mL) was added phenylacetylene (1 mL) and thereafter Hay catalyst (1 mL) [Hay catalyst: CuCl (0.13 g, 1.3 mmol) and TMEDA (0.16 g, 1.4 mmol) in CH₂Cl₂ (4.5 mL)]. The mixture was stirred for 20 min and then concentrated in vacuo without heating. Column chromatography (SiO₂, CH₂Cl₂/cyclohexane, 1:1) afforded 9 (89 mg, 60%) as an orange oily solid. ¹H NMR (300 MHz, CDCl₃): δ = 0.88 (t, 6.6 Hz, 12 H), 1.27 (br s, 56 H), 1.66-1.74 (m, 8 H), 4.22 (t, 7.0 Hz, 4 H), 4.27 (t, 6.5 Hz, 4 H), 7.34-7.36 (m, 6 H), 7.53 (dd, 2.1/7.2 Hz, 4 H), 7.56 (s, 4 H). ¹³C NMR (75 MHz, CDCl₃): δ = 14.1, 22.7, 25.7, 25.8, 28.3, 29.1, 29.2, 29.3, 29.5 (× 2), 31.9, 67.0, 67.2, 73.8, 79.9, 83.6, 86.2, 105.4, 121.8, 126.9, 128.4, 129.2, 130.4, 132.3, 132.7, 135.4, 145.5, 158.9, 159.5. MALDI-TOF-MS (DHB): m/z = 1291 (M⁺). HR-FT-MALDI-MS (DHB): Calcd for C₇₈H₉₈O₈S₄ (M⁺): 1290.6145; Found: 1290.6161. Compound 10: 8 (209 mg, 0.19 mmol) and 4-iodonitro-benzene (490 mg, 1.97 mmol) were dissolved in dry THF (10 mL), and the mixture was thoroughly Ar-degassed. Then [PdCl₂(PPh₃)₂] (10 mg, 0.014 mmol) and diisopropylamine (1.5 mL) were added under Ar-degassing. Finally, CuI (3 mg, 0.016 mmol) was added, and the mixture was stirred for 3 h. Then Et₂O (300 mL) was added, and the organic phase was washed with H₂O (250 mL) and saturated aqueous NH₄Cl (250 mL), dried (MgSO₄), and concentrated in vacuo. Column chromatography (SiO₂, CH₂Cl₂/cyclohexane, 2:1) afforded 10 (74 mg, 29%) as an orange oily solid. ¹H NMR (300 MHz, CDCl₃): δ = 0.88 (m, 12 H), 1.27 (br s, 56 H), 1.70-1.76 (m, 8 H), 4.24 (t, 6.8 Hz, 4 H), 4.29 (t, 6.5 Hz, 4 H), 7.62 (s, 4 H), 7.63 (d, 8.8 Hz, 4 H), 8.21 (d, 8.8 Hz, 4 H). ¹³C NMR (75 MHz, CDCl₃): δ = 14.1, 22.7, 25.7, 25.8, 28.3, 29.2 (× 2), 29.3, 29.5 (× 3), 31.9, 67.1, 67.3, 93.4, 97.3, 105.8, 123.7, 126.9, 129.8, 130.6, 131.6, 132.7, 135.5, 144.3, 146.9, 158.9, 159.5. HR-FT-MALDI-MS (DHB): Calcd for C₇₄H₉₆N₂O₁₂S₄: 1332.5846 (M⁺); Found: 1332.5833. Elemental analysis: Calcd for C₇₄H₉₆N₂O₁₂S₄ (1333.82): C, 66.64; H, 7.25; N, 2.10; S, 9.61; Found: C, 66.84; H, 7.33; N, 2.15; S 9.55.