Silica-Supported Acidic Ionic Liquid

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 4^th use (yields after 2.5 h; 1^st use: 82%; 2^nd use: 95%; 3^rd use: 98%; 4^th use: 78%).