Enantioselective reaction using polymer-supported catalyst in water

The use of water as a media in organic reaction has attracted much attention since many chemists have recognized the several advantages in terms of cost, safety, and environmental impact.(1) A number of reagents and catalysts have been developed for the organic reaction in water. For example, water-soluble catalysts by virtue of water-soluble ligands have been developed in organometallic chemistry. Carbon-carbon bond forming reaction, one of the most important reactions of organic synthesis, could be carried out by using such kind of water-soluble catalysts. Sulfonated triphenylphosphine ligand (TPPTS) has been successfully used as a water-soluble ligand of Pd catalyst in the carbon-carbon bond forming reactions.(2) On the other hand, crosslinked polymer-supported reagents and catalysts have been widely used in organic reaction mainly due to their easy separation from the reaction mixture. Combination of these two important methodologies, aqueous-phase organic reaction and polymer-supported catalysts, would provide a strong tool for efficient organic synthesis. In order to find a suitable system we have surveyed the polymer structure, which could be utilized in water. First, we have tested borohydride reduction in water in the presence of polystyrene having hydorophilic pendant groups. We also applied this type of polymers to the preparation of polymeric chiral catalyst for the asymmetric reduction of prochiral ketones in water.