Oxidative Dehydrogenation and the Aromatization of Polycycles Using o-Iodoxybenzoic Acid (IBX)

Abstract

An efficient and convenient method for the dehydro­genation and aromatization of various polycycles using o-iodoxybenzoic acid (IBX) is described.

dehydrogenation - Diels-Alder reaction - IBX - quinones - aromatization

References

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11

Typical Experimental Procedure: To a solution of IBX (0.2-0.4 mmol) in DMSO (10 mL) was added Diels-Alder adduct (0.1 mmol) and the mixture was stirred at 80-85 °C for 10-24 h, until the starting material disappeared. At the conclusion of the reaction (TLC monitoring), the reaction mixture was quenched with H₂O. The insoluble iodosobenzoic acid (IBA) was filtered off with the aid of a Celite^® pad. The filtrate was extracted with Et₂O (3 × 30 mL) and the combined organic layers were washed with sat. NaHCO₃ solution and finally with brine. The organic layer was dried over anhyd MgSO₄ and removal of solvent gave the crude compound which was purified by the column chromatography (silica gel) using petroleum ether and EtOAc to afford the pure dehydrogenated compound. Selected spectral data: Compound 7: ¹H NMR (300 MHz, CDCl₃): δ = 2.31-2.34 (m, 2 H), 4.09-4.12 (m, 2 H), 6.57 (s, 2 H), 6.86 (dd, J ₁ = J ₂ = 1.8 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 48.5, 73.9, 135.8, 142.6, 160.8, 184.1. MS: m/z = 172 [M⁺]. Compound 8: ¹H NMR (300 MHz, CDCl₃): δ = 2.30-2.40 (m, 2 H), 4.24-4.27 (m, 2 H), 6.90 (dd, J ₁ = J ₂ = 1.8 Hz, 2 H), 7.69 (dd, J ₁ = 5.5 Hz, J ₂ = 3.3 Hz, 2 H), 8.07 (dd, J ₁ = 5.6 Hz, J ₂ = 3.3 Hz, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 48.8, 73.4, 126.3, 132.9, 133.4, 142.6, 163.2, 181.8. MS: m/z = 223 [M + H⁺]. Compound 9: ¹H NMR (400 MHz, CDCl₃): δ = 2.36-2.42 (m, 2 H), 4.30-4.32 (m, 2 H), 6.94 (dd, J ₁ = J ₂ = 1.8 Hz, 2 H), 7.64-7.67 (m, 2 H), 8.02-8.05 (m, 2 H), 8.59 (s, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 48.8, 73.2, 128.4, 129.2, 129.8, 130.1, 134.6, 142.5, 164.6, 181.3. Compound 10: ¹H NMR (300 MHz, CDCl₃): δ = 1.98 (s, 6 H), 2.20-2.30 (m, 2 H), 4.08-4.09 (m, 2 H), 6.83 (dd, J ₁ = J ₂ = 1.8 Hz, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 12.3, 48.6, 73.5, 139.6, 142.6, 160.2, 184.3. MS: m/z = 201 [M + H⁺]. Compound 11: ¹H NMR (400 MHz, CDCl₃): δ = 2.17 (s, 3 H), 2.33-2.38 (m, 2 H), 4.14-4.16 (m, 2 H), 6.49 (s, 1 H), 6.91 (dd, J ₁ = J ₂ = 2.0 Hz, 2 H), 7.06-7.09 (m, 1 H), 7.20-7.33 (m, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 20.4, 48.4, 48.7, 73.8, 125.6, 129.1, 129.4, 130.3, 133.5, 133.8, 136.2, 142.5, 142.7, 147.7, 160.6, 160.8, 182.9, 184.3. MS: m/z = 263 [M + H⁺]. Compound 12: ¹H NMR (300 MHz, CDCl₃): δ = 2.29-2.39 (m, 8 H), 4.21-4.23 (m, 2 H), 6.89 (dd, J ₁ = J ₂ = 1.8 Hz, 2 H), 7.79 (s, 2 H).¹³C NMR (75 MHz, CDCl₃): δ = 182.0, 162.8, 142.8, 142.6, 130.8, 127.4, 73.3, 48.7, 20.1. Compound 17: mp 117 °C. Lit mp 117-119 °C. [13] Compound 18: ¹H NMR (300 MHz, CDCl₃): δ = 2.15 (s, 6 H), 2.38 (s, 6 H), 7.81 (s, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 183.5, 143.2, 143.1, 130.2, 127.4, 20.2, 12.9. Compound 19: mp 209 °C. Lit mp 209-210 °C. [14] Compound 20: ¹H NMR (400 MHz, CDCl₃): δ = 2.44 (s, 6 H), 4.65 (dt, J ₁ = 5.2 Hz, J ₂ = 1.6 Hz, 4 H), 5.30 (d, J = 10.4 Hz, 2 H), 5.52 (d, J = 17.2 Hz, 2 H), 6.13-6.23 (m, 2 H), 6.61 (s, 2 H), 7.99 (s, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 148.2, 135.6, 133.9, 125.4, 121.6, 117.2, 103.9, 69.4, 20.4.

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