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 alpha,beta-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. (C) 2011 Elsevier B.V. All rights reserved.