A novel calix[4]arene-based bifunctional squaramide organocatalyst for enantioselective Michael addition of acetylacetone to nitroolefins

A new chiral calix[4]arene-based organocatalyst 3 bearing bis-squaramide moieties was designed and synthesized from p-tert-butylcalix[4] arene. This bifunctional squaramide organocatalyst was used in the enantioselective conjugate addition of acetylacetone to beta-nitrostyrenes. The corresponding adducts were obtained in good to excellent yields with high enantioselectivities (up to 94% ee).