Synthesis and catalytic activity of the thermoresponsive polymers having pyrrolidine side chains as base functionalities

摘要

Optically active polymers having chiral 2-aminomethylpyrrolidine side chains have been newly synthesized by a radical homopolymerization of the corresponding protected acrylamide monomer and copolymerization with N-isopropylacrylamide followed by deprotection. The resulting polymers were found to be thermoresponsive showing lower critical solution temperatures (LCSTs) at 27-65°C in their aqueous solutions. The pyrrolidine side chains of the resulting thermoresponsive polymer promoted aldol reaction between cyclohexanone and p-nitrobenzaldehyde in water, and the reaction proceeded most smoothly at its LCST. Moreover, the diastereomeric ratio (syn: anti) of the aldol adducts obtained at the reaction at 40°C was 22: 78, whereas the diastereomeric ratio (syn: anti) was 55: 45 at 20°C. These results indicate that the pyrrolidine side chains catalyze the aldol reactions in the relatively hydrophobic field generated by the thermoresponsive polymer at its LCST.