SiO2-KHSO4 catalyst based rapid synthesis of structurally modified bis(3-indolyl)methanes via N-substituted indole

In the present study, structurally diverse improvement was made towards bis(indolyl)methanes 5(a-e) and 5′(a-e) along with 6(a-e) and 6′(a-e) by multicomponent approach. Mono and di-N- substituted BIMs were formed by 2(a-e) and 2′(a-e), 3(a-e) and 3′(a-e). Silica-potassium hydrogen sulfate (SiO2-KHSO4) benign and efficient catalyst is used for the synthesis of new compounds where pre-modified indole unit was alkylated by substituted aromatic aldehydes. The yield was significantly affected in the presence of SiO2-KHSO4 and maximum yield (89% in 1 h reaction) of BIMs was achieved using SiO2-KHSO4 (mol 5%). The SiO2-KHSO4 also considerably reduced the reaction time for the synthesis of BIMs. This protocol was found to be beneficial with respect to catalyst, short reaction time, simple work-up and high yield. The compounds thus prepared are studied through FTIR, 1H NMR and MS spectral data.