Silica-immobilized piperazine: A sustainable organocatalyst for aldol and Knoevenagel reactions

Silica-supported piperazine was found to be an efficient catalyst for aldol reactions of aromatic aldehydes and ketones with straightforward product isolation and catalyst reuse. Furthermore, the catalyst is active in Knoevenagel-type reactions to afford coumarin derivatives, using 2-methyltetrahydrofuran (2-MeTHF) as a novel bio-based solvent. (C) 2010 Elsevier Ltd. All rights reserved.