Efficient chemical fixation of CO2 promoted by a bifunctional Ag2WO4/Ph3P system

Abstract

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.