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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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Hagiwara et al. (2007) studied this question.
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