Enantioselective synthesis of pyrazolone derivatives catalysed by a chiral squaramide catalyst

An efficient chiral squaramide-catalysed enantioselective Michael addition of pyrazolin-5-ones to beta,gamma-unsaturated alpha-ketoesters has been developed. The chiral pyrazolone derivatives were obtained in moderate to high yields (up to 99% yield) with high enantioselectivities (up to 96% ee) for most substrates. This catalytic asymmetric reaction provides valuable and easy access to chiral pyrazolone ketoester derivatives.