Squaramide-catalysed enantioselective Michael addition of pyrazolin-5-ones to nitroalkenes

An efficient chiral squaramide-catalysed enantioselective Michael addition of pyrazolin-5-ones to nitroalkenes has been developed. This reaction afforded the chiral pyrazol-3-ol derivatives in high to excellent yields (up to >99%) with high enantioselectivities (up to 94% ee) for most substrates under very low catalyst loading (0.25 mol%). This catalytic asymmetric reaction provides valuable and easy access to chiral pyrazol-3-ol derivatives, which possess potential pharmaceutical activity.