Silica-Immobilized CuI: An Efficient Reusable Catalyst for Three-Component Coupling Reaction of Aldehyde, Amine and Alkyne

Abstract

Silica-supported copper catalysts were effectively used in the three-component coupling of aldehydes, amines and alkynes to afford the corresponding propargylamines in moderate to ex­cellent yields. The catalyst was quantitatively recovered from the reaction by a simple filtration and reused for a number of cycles with almost consistent activity.

silica - copper - three-component coupling - propargyl­amines - reusable catalyst

References and Notes

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18

Preparation of Imine-Modified Silica-Supported Copper Catalysts:¹⁷
SiO ₂ -Py-Cu(OAc) ₂ : SiO₂-Py (1 g) was stirred with a solution of Cu(OAc)₂ (1 mmol) in acetone (25 mL) for 24 h to get SiO₂-Py-(CuOAc)₂. The copper content was measured by ICP-AES and it was found to be 0.43 mmol/g. Similarly SiO₂-Sal-Cu(OAc)₂ (Cu: 0.41 mmol/g), SiO₂-BPy-Cu(OAc)₂ (Cu: 0.39 mmol/g), and SiO₂-Thio-Cu(OAc)₂ (Cu: 0.41 mmol/g) were prepared from Cu(OAc)₂ in acetone. SiO₂-Py-CuCl₂ (Cu: 0.47 mmol/g) was prepared from an acetone solution of CuCl₂. SiO₂-Py-CuI was prepared from a MeCN solution of CuI and the copper content was 0.45 mmol/g.

19

Typical Procedure for A ^³ Coupling Reaction: A mixture of aldehyde (1 mmol), amine (1.2 mmol), alkyne (1.5 mmol) and SiO₂-Py-CuI (110 mg, 5 mol%) in MeCN (3 mL) was stirred in a round-bottomed flask at 90 °C under nitrogen. After completion of the reaction (monitored by TLC) the catalyst was filtered. After removing the solvent at reduced pressure, the crude material was purified by chromatography on silica gel using hexane-EtOAc mixture as eluent to afford the corresponding propargylamines. Spectroscopic data of the new compounds are given below:
Diallyl-[1-(4-bromophenyl)-3-phenylprop-2-ynyl]amine (Table 3, entry 12): ¹H NMR (300 MHz, CDCl₃): δ = 7.40-7.62 (m, 6 H), 7.28-7.38 (m, 3 H), 5.70-5.91 (m, 2 H), 5.24 (d, J = 17.0 Hz, 2 H), 5.12 (d, J = 9.3 Hz, 2 H), 4.99 (s, 1 H), 3.16-3.29 (m, 2 H), 2.90-3.06 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 138.5, 136.3, 131.8, 131.1, 129.8, 128.4, 122.8, 121.4, 117.4, 88.1, 84.7, 55.9, 53.5. ESI-MS: m/z = 368 [M + 1], 366 [M + 1], 271, 269, 146, 104. Anal. Calcd for C₁₉H₂₀BrN: C, 66.67; H, 5.89; N, 4.09. Found: C, 66.71; H, 5.92; N, 4.01.
4-[1-(4-Bromophenyl)-3- p -tolylprop-2-ynyl]morpholine (Table 3, entry 16): ¹H NMR (300 MHz, CDCl₃): δ = 7.45-7.61 (m, 4 H), 7.37 (d, J = 8.0 Hz, 2 H), 7.12 (d, J = 8.0 Hz, 2 H), 4.69 (s, 1 H), 3.61-3.79 (m, 4 H), 2.52-2.68 (m, 4 H), 2.38 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 138.5, 137.1, 131.8, 131.3, 130.3, 129.0, 121.7, 119.8, 89.1, 83.5, 67.2, 61.4, 49.8, 21.4. EI-MS: m/z = 371 [M⁺], 369 [M⁺], 285, 283, 214, 205, 189, 128, 86, 56. Anal. Calcd for C₂₀H₂₀BrNO: C, 64.87; H, 5.44; N, 3.78. Found: C, 64.89; H, 5.47; N, 3.75.