Elemental Iodine-CatalyzedCoupling of Alkynylsilanes with Acid Chlorides: A Facile Synthesisof α,β-Acetylenic Ketones

Abstract

Alkynylsilanes undergo coupling smoothly with acid chloridesin the presence of molecular iodine under mild reaction conditionsto afford the corresponding α,β-acetylenic ketonesin excellent yields in a short reaction time with high selectivity.

Key words

alkynylsilanes - iodine - acid chlorides - α,β-acetylenic ketones

References

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9

General procedure:To a stirred solution of the alkynylsilane (1 mmol), and iodine(5 mol%) in dichloromethane (10 mL), acyl chloride (1.2mmol) was added slowly in a dropwise manner at 0 °C andthe mixture was allowed to stir at room temperature for the appropriatetime (Table [1] ).After complete conversion as indicated by TLC, the reaction mixturewas quenched with water (15 mL) and extracted with dichloromethane(2 × 15 mL). The combined extracts were washed with 15% solutionof sodium thiosulphate, dried over anhydrous Na₂SO₄,and concentrated in vacuo. The resulting product was purified bycolumn chromatography on silica gel (Merck, 100-200 mesh,ethyl acetate-hexane, 1:9) to afford the pure 1-alkynylketone.
Spectral data for selected products. 3k: Liquid, ¹H NMR (CDCl₃) δ:0.92 (t, 3 H, J = 6.5 Hz), 1.25(s, 3 H), 1.30 (s, 3 H), 1.49-1.70 (m, 4 H), 2.09 (dd,1 H, J = 8.0 Hz, 8.5 Hz), 2.20-2.45(m, 3 H), 6.90 (d, 1 H, J = 8.5Hz). IR (KBr): 2950, 2165, 1660, 1610, 1420 cm^-1.EIMS: m/z: 308, 306 M⁺,199, 197, 177, 43.
3i: Liquid, ¹HNMR (CDCl₃) δ: 0.30 (s, 9 H), 3.82 (s, 3 H), 7.10(dd, 1 H, J = 7.9 Hz, 2.0 Hz),7.39 (dd, 1 H, J = 7.9 Hz, 2.0Hz), 7.55 (d, 1 H, J = 2.0 Hz),7.70 (d, 1 H, J = 7.9 Hz). IR(KBr): 2160, 1680, 1610, 1255 cm^-1.EIMS: m/z: 232 M⁺, 217,135, 107.
3o: Liquid, ¹HNMR (CDCl₃) δ: 7.60 (d, 2 H, J = 8.0Hz), 8.15 (d, 2 H, J = 8.0 Hz).IR (KBr): 2170, 1670, 1659, 1610 cm^-1.EIMS: m/z: 306, 304, 302 M⁺,269, 267, 163.