Chiral squaramide catalyzed synthesis of C4 substituted chiral pyrazol-3-ol derivatives via a facile asymmetric Michael addition of 3-methyl-2-pyrazolin-5-one to β-nitrostyrenes
Asymmetric Michaeladdition of 3-methyl-2-pyrazolin-5-one to β-nitrostyrenes, catalyzed by a series of chiral squaramide bifunctional catalysts derived from cinchona alkaloids, yielded chiral pyrazol-3-ol derivatives. These pyrazol-3-ol derivatives were obtained in moderate to high yields with good enantioselectivities under mild conditions using 1 mol % of the catalyst. This reaction affords valuable