Controllable Preparation of Chiral Oxazoline-Cu(II) Catalyst as Nanoreactor for Highly Asymmetric Henry Reaction in Water

Abstract

A biomimetic nanoreactor of catalyst Cu(II)–PNxOy was prepared by reversible addition-fragmentation chain transfer polymerization (RAFT) starting from chiral amino acid. Characterizations of this catalyst disclosed a clear biomimetic thermoresponsive behavior in water. The biomimetic chiral oxazoline Cu single-chain nanoparticles (SCNPs) could undergo self-folding in water to form nanoreactors which were capable to catalyze the asymmetric Henry reaction. Dramatical acceleration of reaction rate by “concentrator effect” and outstanding catalytic efficiency were observed in this nanoreactor system. Almost quantitative conversion (96%) of 4-nitrobenzaldehyde with high enantioselectivity (ee value, 95%) was achieved by using only 2.0 mol% this newly developed catalyst within 18 h in water. Remarkably, this biomimetic nanoreactor could be easily recovered by regulating local temperature and reused for at least 6 times without significant decrease of reactivity. Utilizing this new catalyst, the asymmetric Henry reaction of benzaldehyde compounds with nitromethane could perform efficiently in pure water without any addition of organic solvent. This protocol offers an efficient and environmentally benign method for the asymmetric Henry reaction which exhibits high potential for industrial applications.