Sulfonated carbon/silica composite functionalized Lewis acids for one-pot synthesis of 1,2,4,5-tetrasubstituted imidazoles, 3,4-dihydropyrimidin-2(1H)-ones and for Michael addition of indole to α,β-unsaturated ketones

Novel Lewis acid catalysts were prepared from sulfonated carbon/silica composites derived from starch and silica by treatment with Lewis acids AlCl3, SbCl3, Bi(NO3)3, ZnCl2 and FeCl3. The catalytic activity of the Lewis acids was evaluated for one-pot synthesis of 1,2,4,5-tetrasubstituted imidazoles, 3,4-dihydropyrimidin-2(1H)-ones and for Michael addition of indole to α,β-unsaturated ketones. Different Lewis acids were investigated with a view to select the most effective solid Lewis acid for organic synthesis. All the Lewis acid catalysts were characterized by FTIR, XRD and AAS analysis and the most active catalyst CSC-Star-SO3-AlCl2 was also characterized by TGA, SEM and TEM.

Graphical abstractNovel sulfonated carbon/silica composite functionalized Lewis acids viz. CSC-Star-SO3-AlCl2, CSC-Star-SO3-SbCl2, CSC-Star-SO3-FeCl2, CSC-Star-SO3-Bi(NO3)2 and CSC-Star-SO3-ZnCl have been prepared and their catalytic activity was evaluated for the one-pot synthesis of 1,2,4,5-tetrasubstituted imidazoles, 3,4-dihydropyrimidin-2(1H)-ones and for Michael addition of indole to α,β-unsaturated ketones. CSC-Star-SO3-AlCl2 was found to be the most active catalyst for catalyzing these reactions.Figure optionsDownload full-size imageDownload high-quality image (84 K)Download as PowerPoint slideHighlights► Sulfonated carbon/silica functionalized Lewis acids were prepared from starch. ► Different Lewis acids were tested with a view to select the most active solid acid. ► Lewis acid catalysts were characterized by FTIR, XRD and AAS analysis. ► Most active catalyst CSC-Star-SO3-AlCl2 was also characterized by TGA, SEM and TEM. ► CSC-Star-SO3-AlCl2 was found to be recyclable under the reaction conditions.