Co-immobilization of Laccase and TEMPO in the Compartments of Mesoporous Silica for a Green and One-Pot Cascade Synthesis of Coumarins by Knoevenagel Condensation

Co-immobilization of bio- and chemocatalysts produces sustainable, recyclable hybrid systems that open new horizons for green cascade approaches in organic synthesis. Here, the co-immobilization of laccase and 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) in mesoporous silica was used for the one-pot aqueous synthesis of 30 coumarin-3-carboxylate derivatives under mild conditions through the condensation of insitu oxidized 2-hydroxybenzyl alcohols and malonate derivatives. A maximum yield was obtained after incubating at pH6.0 and 45 degrees C for 24h. An efficient organic synthesis was catalyzed by the hybrid catalyst in 10% organic solvent. More than 95% of the initial activity of the enzyme was preserved after 10 cycles, and no significant catalyst deactivation occurred after 10 runs. This new system efficiently catalyzed the insitu aerobic oxidation of salicyl alcohols, followed by Knoevenagel condensation, which confirmed the possibility of producing efficient hybrid catalysts by co-immobilization of catalytic species in mesoporous materials.