Efficient chemical fixation of CO2 promoted by a bifunctional Ag2WO4/Ph3P system†
An efficient heterogeneous silver-catalyzed reaction for construction of the α-methylene cyclic carbonate motif was developed through carboxylative assembly of propargyl alcohols and CO2. Such a CO2 fixation protocol proceeded smoothly with only 1 mol% of Ag2WO4 and 2 mol% of PPh3 as well as atmospheric CO2 at room temperature under solvent-free conditions, in an environmentally benign and low energy manner along with an easy operating procedure. Notably, up to 98% isolated yields of carbonates could be attained with exclusive chemo-selectivity. In addition, the dual activation capacity of Ag2WO4 towards both the propargylic substrate and CO2 is based on which cooperative catalytic mechanism by the silver cation and the tungstate anion is proposed. Recycling trials on carboxylative cyclization of propargyl alcohols and CO2 illustrate that the catalyst can be reused at least 4 times with retention of high catalytic activity and selectivity. Especially, it allows the direct and effective application in the one-pot synthesis of various oxazolidinones bearing exocyclic alkenes and carbamates in moderate to high yields upon the alternative introduction of primary or secondary amines.