Structurally Complexes Aromatic Aldehydes on Knoevenagel Condensation Catalyzed by Chitosan Hydrogel Beads

Nowadays, the synthesis of applicable products in everyday life is an increasing research topic. Knoevenagel condensation presents a broad range of applications in synthesis of multiple substances involving domino reactions to obtain five- and six-membered heterocycles such as polysubstituted pyrrolidines, dihydrothiophenes and 1,4-dihydropyridines. Chitosan has been employed as support of metallic catalysts in hydrogenation of ethyl cinnamate, Suzuki cross coupling or to transform nitriles into amides. Very recently, this polymer has been used in several reactions (e.g. aldol, Henry o Michael reactions) as heterogeneous catalyst using simple aldehydes. We report here, the synthesis of new Knoevenagel switchable products obtained from malononitrile and highly modified aldehydes owning different steric hindrance and electronic effects. The heterogeneous chitosan catalyst role has been studied to improve on conversion, time and yields compared with non-catalyzed reactions.We thank the AECID (Projects A/023577/09 and A/030422/10) and the 'Junta de Andalucía' (FQM 142 and Project P09-AGR-4597) for financial support.