Synlett 2007(8): 1320-1322  
DOI: 10.1055/s-2007-977453
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Bis(indolyl)methanes Catalyzed by Acidic Ionic Liquid Immobilized on Silica (ILIS)

Hisahiro Hagiwara*a, Masayoshi Sekifujia, Takashi Hoshib, Kun Qiaoc, Chiaki Yokoyamac
a Graduate School of Science and Technology, Niigata University, 8050, Ikarashi 2-nocho, Niigata 950-2181, Japan
b Faculty of Engineering, Niigata University, 8050, Ikarashi 2-nocho, Niigata 950-2181, Japan
c Institute of Multidisciplinary Research of Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
Fax: +81(25)2627368; e-Mail: hagiwara@gs.niigata-u.ac.jp;
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Publikationsverlauf

Received 19 February 2007
Publikationsdatum:
08. Mai 2007 (online)

Abstract

A new organocatalytic procedure for the synthesis of bis(indolyl)methanes with acidic ionic liquid immobilized on silica gel (ILIS-SO2Cl) has been developed. The reaction condition is ­applicable to a variety of aryl and aliphatic aldehydes and indoles. The mild nature of the reaction conditions showed that the acetoxy or TBDMS group in the aldehyde was maintained intact. The catalyst was reused four times in 93% average yield.

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Typical Experimental Procedure: A suspension of the benzaldehyde (1) (30 mL, 0.3 mmol), indole(2) (60 mg, 0.5 mmol) and ILIS-SO2Cl(4) (143 mg, loading of sulfonyl chloride: 0.35 mmol/g, 0.05 mmol) in MeCN (3 mL) was stirred gently at ambient temperature under nitrogen atmosphere for 5.5 h. The product was triturated with Et2O and the combined organic layer was evaporated to dryness. Medium pressure LC of the residue (eluent: EtOAc-
n-hexane, 3:1) afforded bis(indolyl)methane(3) (79 mg, 97% based on 2).