Asymmetric Aldol Reaction on Water Using an Organocatalyst Tethered on a Thermoresponsive Block Copolymer

Abstract

L-Proline moieties, which serve as organocatalysts, were tethered on block copolymers that consisted of thermoresponsive poly(N-isopropylacrylamide) and PEG-grafted polyacrylate blocks. The copolymer dissolved in water at temperatures below the LCST (25 °C), whereas they formed micelles at temperatures above the LCST (50 °C). Aldol reactions between an arylaldehyde and a ketone were conducted in this aqueous solution. The aldol products were obtained in high yield with high diastereo- and enantioselectivity (96% ee). The catalyst solution could be reused up to three times.