Recyclable polyvinyl chloride-supported pyrrolidine-thiourea as a bifunctional organocatalyst for direct asymmetric aldol reaction in aqueous medium

摘要

Novel polyvinyl chloride (PVC)-supported pyrrolidine-thiourea has been first synthesized in a simple route. The target product was used as a bifunctional organocatalyst for the direct asymmetric aldol reaction between cyclohexanone and arylaldehydes. Effects of solvent and catalyst loading on reaction have been explored. It was found that even at a small dosage of 2.5 mol %, the catalyst exhibited high catalytic activity and stereoselectivities at room temperature in aqueous medium. Additionally, the catalyst can be reused at least for three times. The PVC resin can provide hydrophobic microenvironment for the substrates and catalytic center (pyrrolidine and thiourea moiety) to contact closely. The aldol reaction may take place at the interface between the polymer and aqueous phase. And the results indicated that the thiourea moiety of catalyst had an important effect on the activity and selectivity of the aldol reaction.