Synthesis and Characterization of Acetylenic Scaffolds Containing Dithiafulvenes About a Central Anthraquinodimethane Core

Abstract

A large conjugated chromophore containing four redox-active dithiafulvenes about a central anthraquinodimethane core and a new alkyne-extended tetrathiafulvalene has been synthesized by alkyne-alkyne coupling reactions. Studies of the optical and redox properties of these acetylenic scaffolds have been performed.

Key words

alkynes - chromophores - conjugation - halides - heterocycles

References and Notes

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11

Synthesis of 2b Compounds 4 (80 mg, 0.14 mmol) and 1 (2.8 g, 8.5 mmol) were dissolved in THF (40 mL) and MeOH (120 mL). Then, K₂CO₃ (1.41 g, 10.2 mmol) was added to the solution that was stirred for 45 min until TLC showed complete deprotection of both compounds. The mixture was diluted with Et₂O (100 mL) and washed with H₂O (2 × 150 mL). The organic phase was dried (MgSO₄) and concentrated in vacuo. The residue was dissolved in CH₂Cl₂ (100 mL), whereupon Hay catalyst (8 mL) was added [Hay catalyst: CuCl (0.52 g, 5.2 mmol), TMEDA (0.64 mL, 5.6 mmol), CH₂Cl₂ (9 mL)]. The mixture was vigorously stirred under open atmosphere until TLC showed no remaining starting materials. Repeated flash chromatography (SiO₂, CH₂Cl₂ → CH₂Cl₂-EtOAc, 9:1) yielded almost pure 2b (63 mg) that was recrystallized from CH₂Cl₂-MeOH to give the pure product as a dark purple solid (50 mg, 27%); mp 57 °C (decomp.). ¹H NMR (300 MHz, CDCl₃): δ = 3.85 (s, 12 H), 3.86 (s, 12 H), 5.53 (s, 4 H), 7.42 (m, 4 H), 8.25 (m, 4 H). ¹³C NMR (75 MHz, CDCl₃): δ = 53.73 (two signals over-lapping), 79.79, 81.85, 84.39, 84.84, 91.65, 99.81, 127.20, 128.55, 131.42, 131.98, 133.62, 149.55, 151.21, 159.51, 159.66. MS (MALDI-TOF): m/z = 1316.7 [M⁺]. Anal. Calcd for C₆₄H₃₆O₁₆S₈: C, 58.35; H, 2.75. Found: C, 58.17; H, 2.89.

13

Synthesis of 5 NCS (528 mg, 3.95 mmol) was dissolved in anhyd acetone (10 mL) under an argon atmosphere, whereupon a solution of NaI (600 mg, 4.00 mmol) in anhyd acetone (5 mL) was slowly added, resulting in the formation of a precipitate. After stirring for 15 min at r.t., a mixture of 1 (330 mg, 1.01 mmol) and AgNO₃ (10 mg, 0.059 mmol) in anhyd acetone (5 mL) was added. The reaction mixture was left in the dark at r.t. overnight. Then it was cooled on an ice bath, and H₂O (30 mL) was added. The resulting red precipitate was isolated and then redissolved in CH₂Cl₂ (15 mL). The solution was dried (MgSO₄), filtered, and concentrated in vacuo. Purification by flash chromatography (SiO₂, CH₂Cl₂-cyclohexane, 1:1) gave 5 as an orange solid (320 mg, 83%); mp 73 °C (decomp.). ¹H NMR (300 MHz, CDCl₃): δ = 5.29 (s, 6 H), 6.49 (s, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 53.58, 53.64, 110.79, 130.22, 132.04, 134.67, 141.98, 159.67, 159.74; one signal overlapping. HRMS (ES-TOF): m/z calcd for C₁₀H₇O₄S₂I: 381.8831; found: 381.8846 [M⁺].

15

Synthesis of 6Method 1: LiI (6.4 mg, 0.046 mmol), 1,2,2,6,6-penta-methylpiperidine (0.12 mL, 0.66 mmol), [Pd₂(dba)₃] (6.0 mg, 0.008 mmol) were dissolved in deoxygenated benzene (4 mL) under an argon atmosphere. Then, CuI (1.3 mg, 0.006 mmol) and trimethylsilylacetylene (0.02 mL, 0.15 mmol) were added. A solution of the iodide 5 (42 mg, 0.11 mmol) in benzene (4 mL) was added, and the mixture was heated at 30 °C for 24 h. The crude mixture was filtered through a short plug of silica (SiO₂, CH₂Cl₂), affording the product 6 as a yellow solid that slowly turned black upon standing (23 mg, 59%).
Method 2: Compound 1 (0.25 g, 0.76 mmol) was deprotected by K₂CO₃ in MeOH-THF as described previously (ref. 3). The resulting terminal acetylene was dissolved in CH₂Cl₂ (30 mL), whereupon trimethylsilyl-acetylene (1.0 mL, 7.0 mmol) was added followed by Hay catalyst (2 mL) [Hay catalyst: CuCl (0.13 g, 1.3 mmol), TMEDA (0.16 g, 1.4 mmol), CH₂Cl₂ (4.5 mL)]. After stirring for 1 h under open atmosphere, the mixture was concentrated in vacuo. Purification by flash chromatography (SiO₂, CH₂Cl₂-cyclohexane, 1:1) gave 6 as a yellow solid (210 mg, 81%); mp 47 °C (decomp.). ¹H NMR (300 MHz, CDCl₃): δ = 0.21 (s, 9 H), 3.83 (s, 3 H), 3.84 (s, 3 H), 5.43 (s, 1 H). ¹³C NMR (75MHz, CDCl₃): δ = -0.20, 53.70 (two signals overlapping), 73.85, 84.83, 87.88, 91.47, 95.51, 131.34, 131.69, 150.92, 159.52, 159.69. MS (MALDI-TOF): m/z = 352 [M⁺]. HRMS (ES): m/z calcd for C₁₅H₁₆NaO₄S₂Si: 375.0157; found: 375.0154 [M + Na⁺].

16

Synthesis of 7 Compound 6 (83 mg, 0.24 mmol) was dissolved in THF (3.5 mL) and MeOH (10 mL), whereupon K₂CO₃ (0.10 g, 8 mmol) was added. After stirring for 1 h, the deprotection was complete (according to TLC analysis), and Et₂O (100 mL) was added. The organic phase was extracted with H₂O (75 mL), dried (MgSO₄), and concentrated in vacuo. The residue was dissolved in CH₂Cl₂ (30 mL) and Hay catalyst (1 mL) was added [Hay catalyst: CuCl (0.13 g, 1.3 mmol), TMEDA (0.16 g, 1.4 mmol), CH₂Cl₂ (4.5 mL)]. The reaction mixture was stirred for 1 h under open atmosphere and then concentrated in vacuo. Column chromatography (SiO₂, CH₂Cl₂-cyclohexane, 1:1) followed by recrystallization from CH₂Cl₂-MeOH gave pure 7 (43 mg, 64%); mp 153 °C (decomp.). ¹H NMR (300 MHz, CDCl₃): δ = 3.85 (s, 6 H), 3.87 (s, 6 H), 5.48 (s, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 53.80 (two signals overlapping), 66.44, 72.75, 76.34, 85.57, 90.43, 131.72, 131.97, 154.15, 159.36, 159.49. MS (MALDI-TOF): m/z = 558 [M⁺]. Anal. Calcd for C₂₄H₁₄O₈S₄: C, 51.60; H, 2.53; found: C, 51.64; H, 2.53.