Studies toward the Synthesis of Hepta-peri-heptabenzo-[7]circulene

Abstract

In this letter we report the synthesis and characterization of two new heptagon-embedded nonplanar π-conjugated molecules, which can be regarded as synthetic precursors of hepta-peri-heptabenzo-[7]circulene, an interesting but unknown polycyclic arene with negative curvature.

Key words

polycyclic arenes - negatively curved π molecules - oxidative cyclodehydrogenation

• References and Notes

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• 17 Synthesis of 6b A mixture of compound 5b (0.25 g, 0.50 mmol) and diphenylcyclopropenone (4, 0.21 g, 1.0 mmol) in toluene (12 mL) was heated under an atmosphere of N₂ at reflux for about 4 d. The solution was concentrated under a reduced pressure, and the crude product was purified by silica gel column chromatography using hexane–EtOAc (4:1) as eluent yielding 0.22 g (0.32 mmol, 64%) of 6b as a white solid; mp 267.6–269.7 °C. ¹H NMR (400 MHz, CD₂Cl₂): δ = 8.67 (d, ³ J = 8.1 Hz, 2 H), 8.06 (dd, ³ J = 8.4 Hz, ⁴ J = 0.8 Hz, 2 H), 7.57 (t, ³ J = 7.0, ⁴ J = 1.2 Hz, 2 H), 7.33 (t, ³ J = 7.3 Hz, ⁴ J = 1.1 Hz, 2 H), 7.18–7.20 (m, 4 H), 7.06–7.12 (m, 6 H), 6.22–6.25 (m, 6 H), 3.48 (s, 12 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.4, 160.5, 146.5, 142.3, 135.30, 135.27, 133.9, 130.9, 130.2, 129.9, 129.6, 128.1, 127.8, 126.9, 126.2, 122.5, 108.6, 99.9, 55.2. HRMS (ESI⁺): m/z calcd for C₄₇H₃₆O₅ [M + Na]⁺: 703.2455; found: 703.2468. Synthesis of 10 A solution of 6b (34.0 mg, 0.0499 mmol) in anhydrous CH₂Cl₂ (50 mL) was bubbled with N₂ for 10 min. Then a solution of FeCl₃ (243 mg, 1.50 mmol, 30 equiv) in MeNO₂ (1.3 mL), which was also bubbled with N₂ for 10 min, was added to the above solution at 0 °C dropwise. The resulting black solution was stirred at 0 °C with a stream of N₂ bubbled through it for about 15 min. The reaction was quenched by addition of 1 mL of MeOH, and the mixture was treated with water. The aqueous phase was extracted with CH₂Cl₂, and the combined organic layers were washed with a sat. NaHCO₃ aqueous solution, brine, dried over anhydrous Na₂SO₄ and then concentrated under reduced pressure. The dark red crude product was purified by column chromatography on silica gel using CH₂Cl₂–hexane (1:1, v/v) as eluent. Compound 10 (25.6 mg, 0.0381 mmol) was obtained as orange red powder in a yield of 75%; mp >350 °C. ¹H NMR (400 MHz, CDCl₃): δ = 9.51–9.54 (m, 2 H), 8.78–8.81 (m, 2 H), 8.68 (d, ³ J = 7.6 Hz, 2 H), 8.64 (d, ³J = 8.0 Hz, 2 H), 7.81 (t, ³ J = 7.8 Hz, 2 H), 7.63–7.66 (m, 4 H), 7.04 (s, 2 H), 4.15 (s, 6 H), 4.03 (s, 6 H). ¹³C NMR (100 MHz, C₂D₂Cl₄): δ = 198.0, 158.2, 156.1, 136.6, 130.1, 129.3, 128.4, 128.2, 128.0, 127.7, 127.2, 126.9, 125.7, 125.3, 125.14, 125.05, 124.9, 122.7, 119.1, 113.1, 111.3, 97.1, 56.2, 56.1. HRMS (ESI⁺): m/z calcd for C₄₇H₂₈O₅ [M + H]⁺: 673.2010; found: 673.2012.
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