Evaluation of the nitroaldol reaction in the presence of metal ion-crosslinked alginates

Understanding the ability of biopolymers to promote selective C-C bond formation could provide important insights into the molecular mechanisms underlying evolution, and could help in the design of safer and greener'' catalysts in the future. This work describes the preparation of metal ion-crosslinked alginate materials and the evaluation of their potential catalytic activity towards the Henry (nitroaldol) reaction between a variety of aldehydes and nitroalkanes. The results demonstrated broad substrate specificity and a remarkable influence of the solvent nature, metal ion, and physical state of the alginate-based catalysts. In this sense, Ca2+-alginate hydrogel beads in DMSO used as a heterogeneous and recyclable catalyst were found to be the most efficient system, although the reaction could also proceed in an aqueous medium. Moreover, both small and large-scale model reactions between 4-nitrobenzaldehyde and nitromethane were performed successfully at room temperature. The possibility of coupling the reaction with an enzymatic resolution of the so-obtained beta-nitroalcohol products was also assessed. All materials were characterized using different techniques including, among others, FT-IR, TGA, ICP-OES, and FE-SEM.