Streocontrolled Construction of Six Vicinal Stereogenic Centers on Spiropyrazolones via Organocascade Michael/Michael/1,2-Addition Reactions

A highly stereoselective one-pot procedure for the synthesis of spiropyrazolone derivatives bearing six contiguous stereogenic centers including two tetrasubstituted carbons has been developed. Under sequential catalysis by two organocatalysts, a cinchona-derived aminosquaramide and DBU, a series of diversely functionalized spiropyrazolones are obtained in good yields (47-62%) and excellent stereoselectivities (up to >25:1 dr and 98-99% ee). The opposite enantiomers of the spiropyrazolones are also accessible by employing a pseudoenantiomeric aminosquaramide catalyst.