Chiral Squaramide Catalyzed Enantioselective 1,6-Michael Addition of Pyrazolin-5-ones to Styrylisoxazole Derivatives

The cinchonidine squaramide catalyzed enantioselective 1,6-Michael addition reaction between pyrazolin-5-ones and 3-methyl-4-nitro-5-alkenylisoxazoles has been developed. This method successfully afforded various chiral heterocyclic compounds that containing both pyrazole and isoxazole moieties in good yields (up to 91%) with high enantiomeric ratios (er up to 91:9).