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Synlett 2009(4): 643-647  
DOI: 10.1055/s-0028-1087926
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

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

Hisahiro Hagiwara*a, Hirokazu Sasakia, Takashi Hoshib, Toshio Suzukib
a Graduate School of Science and Technology, Niigata University, 8050 2-Nocho, Ikarashi, Nishi-ku, Niigata 950-2181, Japan
Fax: +81(25)2627368; e-Mail: hagiwara@gs.niigata-u.ac.jp;
b Faculty of Engineering, Niigata University, 8050 2-Nocho, Ikarashi, Nishi-ku, Niigata 950-2181, Japan
Further Information

Publication History

Received 18 November 2008
Publication Date:
16 February 2009 (online)

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Sustainable Click Reaction Catalyzed by Supported Ionic Liquid Catalyst (Cu-SILC)Synlett 2009; 2009(19): 3224-3224
DOI: 10.1055/s-0029-1218519

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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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.

25

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.