Recyclable palladium-catalyzed cyclocarbonylation between benzyl chlorides and salicylic aldehydes towards coumarins

A novel and practical route to coumarin derivatives has been developed via the heterogeneous Pd-catalyzed carbonylative reaction and subsequent intramolecular condensation process starting from commercially easily available benzyl chlorides and salicylic aldehydes. Reactions were performed in the existence of 2 mol% of an SBA-15-immobilized bidentate phosphine palladium complex [SBA-15-P,P-PdCl2] in dioxane at 110 °C with Et3N as base under 10 bar of CO to afford a wide range of coumarin derivatives mostly with good to high yields. Importantly, this new heterogenized palladium complex was easy to recover via filtration of the reaction mixture, and was recyclable up to 8 times without apparent drop in its catalytic performance.