Ordered organo-inorganic hybrid mesoporous solid acid catalysts (Zr–TMS–TFA) for Michael addition of indoles with α,β-unsaturated carbonyl compounds under environmentally benign solvent free conditions

The trifluoromethanesulfonic (trflic) acid functionalized Zr–TMS materials were synthesized and characterized by powder XRD, N2-sorption, elemental analysis, FTIR spectroscopy, NH3–TPD, and 13C CP MAS NMR techniques. The samples with different loadings of triflic acid (TFA) over Zr–TMS (5–25 wt.%) were synthesized. The acid density of TFA functionalised Zr–TMS (Zr–TMS–TFA) materials increased with loading of TFA from 5 through 25 wt.%. The catalytic performance of Zr–TMS–TFA catalysts was evaluated in Michael addition of 3-methylindole to α,β-unsaturated ketones under liquid phase and solvent free reaction conditions. For example, the conversion of 3-methylindole increased with increasing loading of TFA from 38 through 87%. The selectivity of C2-adduct compared to that of N-adduct also increased with increasing loading of TFA. The higher conversion was observed in the case of electron-withdrawing group containing indoles with higher selectivity of C-adduct. The catalysts were found to be reusable.

The triflic functionalized over Zr–TMS mesoporous material were synthesized and thoroughly characterized by powder X-ray diffraction, N2-sorption, elemental analysis, FTIR-spectroscopy, NH3 –TPD, and 13C CP MAS NMR techniques. The different loadings of triflic acid over Zr–TMS (5–25 wt %) have been synthesized. The total acidity of Zr–TMS materials are increased as increasing loading of triflic acid from 5–25 wt %. The synthesized catalyst have been investigated for Michael-addition of 3-methylindole to α,β-unsaturated ketone under liquid phase conditions. This methodology has been applied in organic synthesis, natural product, drug molecules, etc. The conversion of 3-methylindole increased as increasing loading of triflic acid from 38–87 % under solvent free condition. The selectivity of C2-adduct increases and reduces N-adduct as increasing loading of triflic acid. The high conversion was observed in the case of electron-withdrawing group contain in indole with 100 % selectivity of C-adduct. The higher catalytic activities explained on the basis of total acidity of the material.Figure optionsDownload as PowerPoint slideHighlights
► Zr–TMS.
► Triflic acid.
► Michael-addition.
► Indole.
► α,β-Unsaturated carbonyls.