Hydroxy-Group-Facilitated Vinylic Iodination of ortho-Vinylnaphthols Using Molecular Iodine

Abstract

An efficient and simple one-pot method for the iodination of ortho-vinylnaphthols using molecular iodine is disclosed. The reaction is believed to proceed through formation of quinone methide intermediate. The method tolerates different functional groups and provides corresponding ortho-iodovinylnaphthols in good to excellent yields.

Key words

vinylnaphthol - iodovinylnaphthols - molecular iodine - iodination

• References and Notes

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• 12 Synthesis of 2a In an oven-dried 25 mL round-bottom flask compound 1a (246 mg, 1.0 mmol), I₂ (634 mg, 2.5 mmol), and MeCN (3 mL) was added. The reaction mixture was refluxed for 4 h. After cooling the reaction mixture, the reaction was quenched with Na₂S₂O₃ solution and extracted with EtOAc (2 × 5 mL). The combined organic layer was dried over anhydrous Na₂SO₄ and then concentrated on rotatory evaporator under vacuum. The crude product was purified by column chromatography over silica gel (100–200 mesh) using hexane–EtOAc as eluent to give 2a as an off-white viscous liquid. Spectral Data for Selected Compounds 1-(2-Iodo-1-phenylvinyl)naphthalen-2-ol (2a) Yield 89%; off-white viscous liquid. ¹H NMR (300 MHz, CDCl₃): δ = 7.86 (d, J = 9.0 Hz, 1 H), 7.81 (dd, J = 8.19, 2.30 Hz, 1 H), 7.63 (s, 1 H), 7.49 (dd, J = 8.19, 2.30 Hz, 1 H), 7.40–7.21 (m, 8 H), 5.20 (s, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 149.4, 146.9, 138.7, 131.5, 130.4, 129.1, 129.0, 128.9, 128.3, 127.1, 126.5, 124.1, 123.7, 121.1, 117.7, 86.0. IR: 756, 1188, 1250, 3055, 3496 cm^–1. ESI-HRMS: m/z calcd for C₁₈H₁₄IO⁺ [M + H]⁺: 373.0084; found: 373.0087. 1-(2-Iodo-1-p-tolylvinyl)-7-methoxynaphthalen-2-ol (2f) Yield 63%; viscous liquid; ¹H NMR (400 MHz, CDCl₃): δ = 7.80 (d, J = 8.8 Hz, 1 H), 7.74 (d, J = 8.9 Hz, 1 H), 7.57 (s, 1 H), 7.25 (d, J = 8.2 Hz, 2 H), 7.14 (d, J = 8.8 Hz, 1 H), 7.11 (d, J = 8.1 Hz, 2 H), 7.03 (dd, J = 8.9, 2.5 Hz, 1 H), 6.81 (d, J = 2.4 Hz, 1 H), 5.32 (s, 1 H), 3.75 (s, 3 H), 2.33 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 158.6, 150.0, 147.0, 138.9, 136.1, 132.9, 130.0, 129.8, 129.7, 126.4, 124.5, 120.6, 115.8, 115.0, 103.2, 84.7, 55.2, 21.2. IR: 795, 825, 1242, 1621, 3063, 3441 cm^–1. ESI-HRMS: m/z calcd for C₂₀H₁₈IO₂ ⁺ [M + H]⁺: 417.0346; found: 417.0351. 6-(3,4-Dimethoxyphenyl)-1-(2-iodo-1-phenylvinyl)naphthalen-2-ol (2n) Yield 56%; pale yellow liquid. ¹H NMR (300 MHz, CDCl₃): δ = 7.97 (s, 1 H), 7.91 (d, J = 8.2 Hz, 1 H), 7.71–7.48 (m, 3 H), 7.40–7.12 (m, 8 H), 6.96 (d, J = 7.3 Hz, 1 H), 5.29 (s, 1 H), 3.95 (s, 3 H), 3.92 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 149.4, 149.2, 148.5, 146.9, 138.7, 136.4, 134.0, 130.5, 130.5, 129.4, 129.0, 128.9, 126.7, 126.5, 125.7, 124.6, 121.1, 119.5, 118.1, 111.6, 110.5, 86.0, 56.0. IR: 818, 1134, 1512, 1597, 3055, 3526 cm^–1. ESI-HRMS: m/z calcd for C₂₆H₂₂IO₃ ⁺ [M + H]⁺: 509.0608; found: 509.0611.
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