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DOI: 10.1055/s-2007-968801
Silica-Supported Acidic Ionic Liquid
Contributor(s):Yasuhiro Uozumi, Yohei OeNiigata University and Tohoku University, Sendai, Japan
Synthesis of Bis(indolyl)methanes Catalyzed by Acidic Ionic Liquid Immobilized on Silica (ILIS)
Synlett 2007, 1320-1322
Publication History
Publication Date:
24 July 2007 (online)
Key words
silica support - ionic liquids - bis(indolyl)methanes
Significance
A new protocol for the synthesis of bis(indolyl)methanes 3 catalyzed by an acidic ionic liquid immobilized on silica (ILIS) under mild reaction conditions was developed. Thus, the reactions of indole 1 with various aldehydes 2 were carried out in the presence of 10 mol% of ILIS-SO2Cl to give the corresponding bis(indolyl)methanes 3 in 65-97% yield. In the reaction of indole 1 with p-chlorobenzaldehyde, the catalyst can be recycled three times without significant loss of catalytic activity decreasing only in the 4th use (yields after 2.5 h; 1st use: 82%; 2nd use: 95%; 3rd use: 98%; 4th use: 78%).
Comment
The authors previously reported the preparation of ILIS catalysts and their applications to the esterification reaction of carboxylic acids with alcohols and the nitration of aromatic compounds (K. Qiao, H. Hagiwara, C. Yokoyama J. Mol. Catal. A: Chem. 2006, 246, 65). The combination of the silica support, the acidic sulfonyl chloride group, and the ionic liquid component realized high catalytic activity for the present reaction.