Triflic Acid Functionalized Carbon@Silica Composite: Synthesis and Applications in Organic Synthesis; DFT Studies of Indeno[1,2‐b]indole

Abstract

Triflic acid functionalized carbon@silica composite (CStar@SiO2TfOH) was synthesized by the partial carbonization of starch in the presence of silica followed by the immobilization of triflic acid and its catalytic activity was explored for the three component synthesis of hexahydroacridine‐1,8‐diones and indeno[1,2‐b]indole‐9,10‐diones. CStar@SiO2‐TfOH was characterized using different techniques, such as Fourier‐Transform Infrared Spectroscopy (FTIR), Thermogravimetricanalysis (TGA), X‐ray Powder Diffraction (XRD), Energy Dispersive X‐ray (EDX), Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HR‐TEM) and was found to be recyclable upto five runs without any noticeable change. Further, the intermediate formed during the preparation of hexahydroacridine‐1,8‐dione has been isolated and its structure was confirmed by single crystal X‐ray crystallography which confirms the proposed mechanism. Also, to confirm the structure of 4b,9b‐dihydroxy‐5‐(4‐chlorophenyl)‐7,7‐dimethyl‐4b,5,7,8‐tetrahydroindeno[1,2‐b]indole‐9,10(6H,9bH)‐dione we have performed the DFT study and found that the 1H and 13C chemical shift values and IR wavenumbers predicted by B3LYP method were very close to the experimentally determined values.