Asymmetric Chlorination of 4-Substituted Pyrazolones Catalyzed by Chiral Copper Complexes

A fast and highly enantioselective chlorination of 4-pyrazolones catalyzed by bis(oxazoline)–Cu(ClO4)2·6H2O complexes has been developed. Under the optimized conditions, a series of pyrazolones bearing stereogenic chlorine-attached carbon centers were obtained in moderate to high yields (up to 98%) and with enantioselectivities of up to 98% ee.