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DOI: 10.1055/s-2008-1032082
Sustainable Conjugate Addition of Indoles Catalyzed by Acidic Ionic Liquid Immobilized on Silica
Publication History
Publication Date:
12 February 2008 (online)
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Abstract
A new protocol for 1,4-conjugate addition of indoles to vinyl ketones has been developed, employing Lewis acidic ionic liquid immobilized on silica, ILIS-SO2Cl, as a catalyst, which exhibited an efficient, mild and recyclable nature. The reaction condition is applicable to various vinyl ketones and indoles. The mild nature of the reaction condition showed that the acetoxy or TBDMS group in indoles was maintained intact. The catalyst was used six times resulting in 86% average yield.
Key words
catalysis - Michael additions - indoles - ionic liquids - supported catalysis
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References and Notes
Typical Experimental Procedure: A suspension of but-3-en-2-one (50 µL, 0.6 mmol), indole (35.3 mg, 0.3 mmol) and ILIS-SO2Cl (4; 171 mg; loading of sulfonyl chloride: 0.35 mmol/g, 0.06 mmol) in Et2O (0.2 mL) was stirred gently at ambient temperature for 4 h in open air, resulting in evaporation of Et2O. The catalyst was washed with Et2O and separated by centrifugation. After decantation of the Et2O layer, the catalyst was washed again with EtOAc and then with CH2Cl2 in a similar manner. The combined organic layer was evaporated to dryness. Medium pressure LC of the residue (eluent: EtOAc-n-hexane, 1:1) afforded the conjugated addition product 3 (51.9 mg, 92% based on indole 2).