Sustainable Click Reaction Catalyzed by Supported Ionic Liquid Catalyst (Cu-SILC)

Abstract

Cuprous bromide was immobilized as a copper-supported ionic liquid catalyst (Cu-SILC) in the pores of amorphous mercaptopropyl silica gel with the aid of an ionic liquid, [bmim]PF₆. The heterogeneous Cu-SILC effectively and regioselectively catalyzed Huisgen [3+2] cycloadditions at room temperature in aqueous ethanol, and was used up to six times after simple decantation.

Key words

heterogeneous catalysis - ionic liquids - click reaction - copper - supported catalysis

References and Notes

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• 13 Observed octanol-water partition coefficients (KOWs) are 0.0220 for [bmim]PF₆ and 0.11 for [bmim]NTf₂. See: Ropel L. Belvèze LS. Aki SNVK. Stadtherr MA. Brennecke JF. Green Chem.  2005,  7:  83 
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Preparation of Cu-SILC
Mercaptopropyl silica gel (powder for column chromatography supplied by Fuji Silysia Chemical LTD., 2.068 g) and CuBr˙Me₂S (62 mg, 0.302 mmol) were added to a solution of [bmim]PF₆ (200 mg, 10 wt%) in MeCN. Resulting slurry was stirred at r.t. for 4 h, when the brown color of MeCN solution was transparent. After evaporation of MeCN in vacuo, the powder was rinsed with anhyd Et₂O (5×). Evacuation of in vacuo provided Cu-SILC (2.301 g, 0.15 mmol/g SiO₂) as white powder.

21

Click Reaction of Benzylazide and 2-Methylbut-3-yn-2-ol A suspension of benzylazide (65 mg, 0.49 mmol), 2-methyl-but-3-yn-2-ol (51 mg, 0.61 mmol), and Cu-SILC (299 mg, 0.035 mmol CuBr) in 50% aq EtOH (2 mL) was stirred at r.t. for 2 h. The organic layer was separated by filtration and the flask was rinsed with Et₂O. The combined organic layer was evaporated to dryness in vacuo. The residue was purified by column chromatography (eluent: n-hexane-EtOAc = 3:1 to 1:5) to afford 2-[1-benzyl-1,2,3-triazol-4-yl]propan-2-ol (3a, 96 mg, 91%). Recovered Cu-SILC was used intact for further recycle experiments.

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Compound 3d: ^¹H NMR (270 MHz, CDCl₃): δ = 2.11-2.22 (m, 2 H), 2.38 (br s, 1 H), 2.67-2.88 (m, 2 H), 4.88 (br s, 1 H), 5.51 (s, 2 H), 7.14-7.40 (m, 11 H). ^¹³C NMR (67.5 MHz, CDCl₃): δ = 151.5, 141.4, 134.4, 129.0, 128.7, 128.4, 128.3, 128.0, 125.8, 120.1, 66.4, 54.2, 38.9, 31.7. IR: 3409, 3011, 1496, 1456, 1224, 1049 cm^-¹. HRMS: m/z [M]⁺ calcd for C₁₈H₁₉N₃O: 293.1528; found: 293.1524.

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Compound 3h: ^¹H NMR (270 MHz, CDCl₃): δ = 1.64 (s, 6 H), 1.79 (s, 6 H), 2.24 (s, 10 H), 7.50 (s, 1 H). ^¹³C NMR (67.5 MHz, CDCl₃): δ = 154.2, 115.2, 68.6, 59.5, 43.0, 36.0, 30.6, 30.5, 29.5. IR: 3398, 2981, 2857, 1454, 1360, 1310, 1167, 1057, 1026, 954, 854 cm^-¹. HRMS: m/z [M]⁺ calcd for C₁₅H₂₃N₃O: 261.1841; found: 261.1838.

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Compound 3j: ^¹H NMR (270 MHz, CDCl₃): δ = 0.03 (s, 6 H), 0.85 (s, 9 H), 1.23 (s, 3 H), 1.31 (s, 3 H), 1.57 (s, 3 H), 1.59 (s, 3 H), 3.61-3.79 (m, 3 H), 4.17-4.23 (m, 1 H), 4.41 (dd, J = 14.3, 5.9 Hz, 1 H), 4.63 (dd, J = 14.3, 3.2 Hz, 1 H), 7.57 (s, 1 H). ^¹³C NMR (67.5 MHz, CDCl₃): δ = 155.3, 120.6, 109.7, 77.3, 77.1, 68.2, 62.9, 51.6, 30.4, 30.3, 26.9, 26.9, 25.9, 18.3, -5.4, -5.5. IR: 3450, 2988, 2956, 2931, 2110, 1463, 1383, 1255, 1089, 838 cm^-¹. HRMS: m/z [M]⁺ calcd for C₁₈H₃₅N₃O₄Si: 385.2397; found: 385.2392.

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Compound 3k: ^¹H NMR (270 MHz, CDCl₃): δ = 1.30 (s, 3 H), 1.41 (s, 3 H), 1.64 (s, 3 H), 1.65 (s, 3 H), 2.12 (s, 3 H), 2.53 (br s, 1 H), 3.88-3.94 (m, 1 H), 4.12-4.25 (m, 3 H), 4.54 (dd, J = 14.4, 5.1 Hz, 1 H), 4.63 (dd, J = 14.4, 3.6 Hz, 1 H), 7.61 (s, 1 H). ^¹³C NMR (67.5 MHz, CDCl₃): δ = 170.4, 155.6, 120.8, 110.3, 76.1, 75.5, 68.2, 63.2, 50.9, 30.4, 30.3, 26.9, 26.8, 20.7. IR: 3470, 2989, 1742, 1374, 1226, 1167, 1046 cm^-¹. HRMS: m/z [M]⁺ calcd for C₁₄H₂₃N₃O₅: 313.1637; found: 313.1638.

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Compound 3l: ^¹H NMR (270 MHz, CDCl₃): δ = 0.97 (d, J = 6.6 Hz, 3 H), 1.19-1.52 (m, 3 H), 1.59 (s, 3 H), 1.64 (s, 6 H), 1.68 (s, 3 H), 1.73-1.78 (m, 1 H), 1.88-2.00 (m, 3 H), 2.52 (br s, 1 H), 4.32-4.38 (m, 2 H), 5.04-5.09 (m, 1 H), 7.42 (s, 1 H). ^¹³C NMR (67.5 MHz, CDCl₃): δ = 155.4, 131.2, 123.9, 118.8, 68.1, 48.2, 37.1, 36.5, 30.3, 29.8, 25.5, 25.1, 19.0, 17.5. IR: 3408, 2976, 2929, 1460, 1380, 1168, 1052, 955, 853 cm^-¹. HRMS: m/z [M]⁺ calcd for C₁₅H₂₇N₃O: 265.2154; found: 265.2158.